Posters

To be displayed during the whole Meeting

Session: Basic Plasma Processes and Numerical Methods

N^o	1^st Author	Title
01	M.C. DE JULI	Electrostatic waves in dusty plasmas with variable charge on dust particles
02	A. ESQUIVEL	MHD turbulent mixing layers
03	H. PEREZ ROJAS	Pressures and energies of vacuum in a magnetic field. Analogies an differences with Casimir effect
04	A. SERBETO	Excitation of strong wakefields by intense neutrino bursts in a magnetized electron-positron plasma
05	R. SILVA JR.	Relativistic H-theorem and nonextensive kinetic theory
06	I. SPASSOVSKA	Soliton and Double Layer Solutions for four component dusty plasmas

Session: Space and Solar Plasmas

N^o	1^st Author	Title
07	M.A. CORSINI	Hydrodynamic 2-D model of coronal mass ejections
08	J. COSTA	Inference of magnetic fields from solar flares
09	G. CRISTIANI	Magnetic reconnection at the origin of submillimeter radiation
10	D. FALCETA-GONÇALVES	The Origin of the magnetic fields divergence in coronal holes
11	N. FARBIASH	How is the diamagnetic effect relevant to stellar surface phenomena?
12	J.L. FERREIRA	Plasma sources for laboratory simulation of space and astrophysical plasma interaction with magnetic fields
13	G. GUERRERO	Exploring solar dynamo models with a bipolytropic density profile and a deep meridional flow
14	R.R. ROSA	Characterization of solar multi-scaling magnetic loop interactions
15	C. SELHORST	Study of active regions temporal evolution at 17 GHz
16	Y. SHIRATORI	Possibilities on radio bursts from extrasolar planets
17	P.J.A. SIMÕES	Microwave solar flare spectra of complex magnetic ambient
18	A. VASQUEZ	Solar Corona Magnetic Structure and Stagnated Wind Outflow

Session: Magnetic Fields in Star Formation and Evolution

N^o	1^st Author	Title
19	S. ALENCAR	Comparing MHD diskwind models and observations of the classical T Tauri star RW Aur
20	S. ALENCAR	Non-stationary magnetospheric accretion in the classical T Tauri star AA Tau
21	N. DRAKE	Magnetic fields and surface chemical abundances in the Ap stars
22	N.R. LANDIN	Theoretical values of the Rossby number for low-mass, rotating pre-main sequence stars
23	G. PINZÓN	Star-disk interaction in classical T Tauri stars
24	G. ROJAS	Magnetic fields in weak and post T Tauri stars
25	A.A. VIDOTTO	Alfvén waves in dusty winds of cool supergiant stars

Session: Compact Objects, Accretion Disks and Outflows

N^o	1^st Author	Title
26	M.P. ALLEN	Accretion Induced Collapses may give origin to magnetars
27	T. ANDREOLLA	Core magnetic fields in ultracompact radio sources
28	C. ARAÚJO	A simple magnetohydrodynamical model for formation of supermassive black holes in QSOs
29	S. BASTRUKOV	Electrodynamics of paramagnetic neutron star
30	C.G. BERNAL	Analytical production and collimation of astrophysical jets
31	B. BORGES	Cyclical period changes in cataclysmic variables: evidence of magnetic activity cycles in the mass-donor star
32	L.C.L. BOTTI	Modeling the radio flaring behavior of 3C273
33	L. BURDERI	Accretion and magneto-dipole emission in fast rotating neutron stars: new spin equilibrium lines
34	S. CABRIT	The importance of magnetic fields in protostellar jet-driven shocks
35	A. CAPRONI	Spin-induced and magnetically driven precession in active galactic nuclei
36	A.H. CERQUEIRA	Three-dimensional numerical simulations of rotating jets
37	G.H.R. DE ARAÚJO LIMA	A MHD model for the stellar disk wind of DR Tau
38	F. DE COLLE	The effect on no-axisymmetrical perturbations on the generation of jets from magnetized accretion disks
39	E.M. DE GOUVEIA DAL PINO	A mechanism for the superluminal ejections in microquasars: a jet/accretion disk symbiosis
40	M. DIAZ	Observations of the emission-line stochastic variability in accretion disks
41	T. DI SALVO	Constraints on the neutron star magnetic field of transient LMXBs from their luminosity in quiescence
42	P.-K. FUNG	Free-electron laser in pulsar magnetosphere
43	R.F. GONZÁLEZ	Numerical simulations of Eta Carina bipolar outflows
44	E LÓPEZ	Pulsar radio emission cutoffs
45	E. LÜDKE	Magnetic fields in the hotspotless jet of 3C200
46	M. MALHEIRO	General relativistic effects of strong magnetic fields on the gravitational force: a driving engine for bursts of gamma-rays in SGRs?
47	H. MOSQUERA CUESTA	Strongest gravitational waves from neutrino oscillations at supernova core bounce
48	A. PEREZ MARTINEZ	Quark matter in stars and quantum-magnetic collapse
49	R. PICANÇO	Charged stars and the anysotropic structure
50	N.R. ROBBA	Simultaneous study of 4U 1728-34 with Chandra and Rossi XTE
51	R. SAITO	Spectral mapping of intermediate polar DQ Herculis
52	R. SAITO	Probing physical conditions in accretion discs with eclipse mapping techniques
53	M.J. VASCONCELOS	Alfvénic heating of vertically isothermal accretion disks
54	C. ZHANG	On the bottom magnetic field and magnetosphere of the accreting neutron star

Session: Magnetized ISM

N^o	1^st Author	Title
55	J. ARANEDA	Parametric instabilities of Alfvén waves in interstellar clouds
56	S. BOLDYREV	Radio wave propagation in the non-Gaussian interstellar medium
57	G. HICKEL	The environment and magnetic field of cometary globule CG30
58	P. HILY-BLANT	Coherence and magnetic fields at the parsec scales of diffuse molecular clouds
59	T. KUDOH	Magnetic turbulence in a self-gravitationally stratified cloud
60	F. OLIVEIRA ALVES	A polarimetric study in the region containing the molecular cloud Lupus 1
61	A. PEREYRA	Magnetic fields and dispersion of polarization angles: IRAS Vela Shell
62	J.W. VILAS-BOAS	Polarization properties of condensations in Musca and their relation to star formation

Session: Magnetic Fields in Galaxies, the IGM, and the Early Universe

N^o	1^st Author	Title
63	R. BOHRER-ADORNES	Synchrotron ages in hotspots of CSS quasars and radiogalaxies
64	V. BUENROSTRO-LEITER	The Parker instability in a realistic galactic model
65	M.S. DOS SANTOS	Modeling the spectrum of gravitational waves in the primordial universe
66	E. FLORIDO	Magnetic fields and the dynamics of the outer disk of spiral galaxies
67	B. GAENSLER	Probing cosmic magnetism with the square kilometre array
68	B. GAENSLER	The magnetic field of the magellanic clouds
69	R.F. GONZÁLEZ	An anisotropic thermal conduction model for Dem L316 in the magellanic cloud
70	H. MAKI	Dissipation of magnetic flux in primordial gas clouds
71	H. NISHIKORI	Global three-dimensional MHD simulations of galactic gaseous disks
72	A.L. OLIVEIRA	The "geometric amplification" of the cosmic magnetic induction
73	M. TANAKA	Magnetohydrodynamic simulations of the Wiggle instability in spiral galaxies
74	E. TELLES	The [L-sigma] relation for HII galaxies

Poster Abstracts

Session: Basic Plasma Processes and Numerical Methods

Poster 01

ELECTROSTATIC WAVES IN DUSTY PLASMAS WITH VARIABLE

CHARGE ON DUST PARTICLES

Marcelo C. de Juli (1), Ruth S. Schneider (2), Luiz F. Ziebell (2), Vera Jatenco-Pereira (1)

(1) Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo

(2) Universidade Federal do Rio Grande do Sul-UFRGS

In this work, we present results obtained, using a kinetic approach, for parallel propagation of waves in a magnetized dusty plasma. In this magnetized plasma we consider embedded spherical dust grains with constant radius and variable charge. We consider that the principal process of dust charging is the capture of electrons and ions of the plasma and use a cross-section derived from the orbital motion limited theory to describe this process. We concentrate in electrostatic waves in a homogeneous magnetized dusty plasma. The dispersion relation and damping rates are obtained. We show that the usual resonant denominator, which occurs in plasmas without dust, is modified by the addition of a purely imaginary term which contains the collision frequency of electrons and ions with dust particles. We analyse the different mechanisms of damping, like Landau damping and damping that results from the electric charge variation of the dust particles, and study the competition between them.

Poster 02

MHD TURBULENT MIXING LAYERS

Alejandro Esquivel (1), Robert A. Benjamin (1-2), Jungyeon Cho (1-3),

Alex Lazarian (1), Samuel N. Leitner (4)

(1) University of Wisconsin-Madison

(2) University of Wisconsin-Whitewater

(3) Canadian Institute for Theoretical Astrophysics

(4) Wesleyan University

Observations of the interstellar medium (ISM) reveal a very complex picture: a highly turbulent medium, very rich in structure, all embedded in a magnetic field. To a large degree the structure of the ISM is controlled by the balance of mechanical heating and radiative cooling. At the interfaces between hot (~ 10⁶ K) and cooler (10²-10⁴) gas, turbulence is believed to play a crucial role by producing exchange of material. Within this so called "turbulent mixing layers" we expect gas at intermediate temperatures, thus facilitating radiative cooling. At the same time, magnetic fields are important because they can help to control or suppress instabilities that result in turbulent mixing. Previous models to diagnose physical parameters in turbulent mixing layers are based on steady-state, one dimensional, unmagnetized models. We present numerical simulations of turbulent mixing layers, obtained with a fully 3D magnetohydrodynamical (MHD) code, including radiative transfer. With our results is possible to predict various column density ratios (C IV/N V, Si IV/C IV, O VI/C IV) that will help interpretation of UV spectra.

Poster 03

PRESSURES AND ENERGIES OF VACUUM IN A MAGNETIC FIELD. ANALOGIES AN DIFFERENCES WITH CASIMIR EFFECT

Hugo Perez Rojas, Elizabeth Rodriguez Querts

Instituto de Cibernetica, Matematica y Fisica (ICIMAF)

We study vacuum pressures and energies for electron-positron vacuum zero point energy in a strong magnetic field B and for photon vacuum in comparison with Casimir effect, by following a common method. Vacuum becomes magnetized, and due to it, the pressure transversal to B is negative, whereas along B an usual positive pressure arises. Similarly, in addition to the usual negative Casimir pressure perpendicular to the plates, the existence of a positive pressure along the plates is predicted. Both vacua bear the property of leading to a negative energy-momentum tensor trace T ¹¹ < 0, which may lead to a repulsive gravity typical of dark energy. By assuming a space distribution of magnetic and/or Casimir domains, some consequences for astrophysics and cosmology are briefly discussed.

Poster 04

EXCITATION OF STRONG WAKEFIELDS BY INTENSE NEUTRINO BURSTS IN A MAGNETIZED ELECTRON-POSITRON PLASMA

A. Serbeto(1), L.A. Rios(1), J.T. Mendonça(2), P.K. Shukla(3), R. Bingham(4)

(1)IF/UFF - Brasil,

(2)GoLP/Instituto Superior Técnico, Portugal,

(3)Institut für Theoretical Physik IV, Ruhr-Universität Bochum, Germany,

(4)Rutherford Appleton Laboratory, England

It is well established that processes involving electron-positron plasmas are of significant importance in a variety of astrophysical environments, , like active galactic nuclei (AGN) and pulsar magnetospheres. Another very important material elements in the astrophysical settings are the neutrinos. The latter are produced by the core of stars and in very high explosive astrophysical situations such as those in supernova explosions and in ultra- relativistic pair plasma jets producing g-ray bursts (GRBs). Here, we are interested in nonlinear interactions of intense neutrino bursts with a relativistic magnetized pair-plasma. A classical fluid description is used to investigate these interactions between an electron-type neutrino burst and a collisionless magnetized electron-positron plasma. It is found that the symmetry between the electron and positron dynamics is broken due to the presence of intense neutrino bursts. The latter can excite strong upper- hybrid wakefields, which can produce unlimited acceleration of pairs across the external magnetic field direction via a surfatron mechanism. Implications of our results to the production of high-energy electrons and positrons in astrophysical environments are discussed.

Poster 05

RELATIVISTIC H-THEOREM AND NONEXTENSIVE KINETIC THEORY

Raimundo Silva (1), José Ademir Sales de Lima (2)

(1) Universidade do Estado do Rio Grande do Norte - UERN

(2) Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo

A proof of the relativistic H-theorem by including non-extensive effects is given. As it happens in the nonrelativistic limit, the molecular chaos hypothesis first considered by Boltzmann does not remain valid, and the second law of thermodynamics combined with a duality transformation implies that the q-parameter lies on the interval 0<q<2. It is also proved that the collisional equilibrium states (null entropy source term) are described by the relativistic q-power law extension of the exponential Juttner distribution, and as should be expected, in the limit v << c the Tsallis power law function is also recovered. As an illustration, we deduce the relativistic nonextensive equilibrium distribution for a dilute charged gas under the action of an electromagnetic field F^mn. All these results reduce to the standard ones in the extensive limit q ®1.

Poster 06

SOLITON AND DOUBLE LAYER SOLUTIONS FOR FOUR COMPONENT

DUSTY PLASMAS

Iglika Spassovska(1), Paulo Sakanaka(1), Padma Shukla(2)

(1) Instituto de Física "Gleb Wataghin", UNICAMP, Campinas, SP, Brazil.

(2) Institute für Theoretische Physik IV, Ruhr-Universität Bochum, D-44780 Bochum, Germany

In dusty plasmas with warm electrons, warm positive ions, and negative and positively charged cold dust grains which are simultaneously present, it is shown that stationary solutions of the fluid equations combined with Poisson's equation can be expressed in terms of the energy integral of a classical particle with a modified Sagdeev potential.We found that in four component dusty plasma there are changes in the nonlinear properties of the DAW. Compressive dust-acoustic solitons exist only when there is at least a trace of positively charged dust grains. The four fluid dusty plasma system, with both the negatively and positively charged dust grains, provides the ambient to excite double layers, Sakanaka et al. [1]. The latter is analyzed both analytically and numerically. The parametric regions of solitons, cavitons and double layers are given, and their profiles are displayed graphically. In particular, we have applied the theory in the laboratory plasma reported by Oohara et al. [2], and we can predict that a double layer might be possible to be launched if small quantity of ions was introduced in their experiment.

[1] P.H. Sakanaka and P.K. Shukla, Phys. Scripta, Vol T84, p.181 (2000). [2] W. Oohara, N. Tomioka, T. Hirata, R. Hatakeyama, and N. Sato, Proceedings of the 2000 International Congress on Plasma Physics, Quebec. Vol 1, p.116 (2000).

Session: Space and Solar Plasmas

Poster 07

HYDRODYNAMIC 2-D MODEL OF CORONAL MASS EJECTIONS

Marco A. Corsini (1,2), Adriana V.R. Silva (2)

(1) INPE - Instituto Nacional de Pesquisas Espaciais (2) CRAAM/Mackenzie - Centro de Radio Astronomia e Astrofísica Mackenzie

Coronal Mass Ejections (CME) are a large amounts of plasma expelled from the solar atmosphere. CMEs are threaded by magnetic fields and travel through the interplanetary space at supersonic velocities. As the ejection reaches Earth, it may interact with our magnetosphere and cause many undesired effects, such as damage to power transformers, satellites, navigation instruments, interference with long distance communications, lethal radiation to unprotected astronauts, among other problems. Since the physics of CMEs are yet not well understood, numerical models are used to study this phenomenon. Some numerical models of CMEs simulate the evolution of these structures in the interplanetary medium in order to predict their physical characteristics close to the Earth's magnetosphere. A hydrodynamic (HD) two-dimensional code, based on a method of finite differences called Modified Lax-Wendroff, was build to simulate CMEs in the interplanetary medium. This method solves the set of hydrodynamic differential equations in time and space; to increase numerical precision, it creates a new grid in an intermediate time calculating the new data in two steps. The initial condition is taken from the solution of the stationary radial HD equations using the Runge-Kutta method, which is the solar wind. The CME is then simulated as a pulse in the interplanetary medium in the initial condition. The boundary conditions are free, except for the first line (that contains the Sun) where the variables are kept constant and equal the initial solar wind values. The numerical results show the temporal and spatial evolution of a CME by the variation of its density, pressure, velocity. Comparison with observations from the LASCO experiment shows a good agreement with our numerical results.

Poster 08

INFERENCE OF MAGNETIC FIELDS FROM SOLAR FLARES

Joaquim Costa, (1) Antonio Rosal (2)

(1) INPE

(2) CRAAM-Mackenzie

The magnetic field induction present in the flare region can be inferred from the observed spectrum peak by the gyro synchrotron theory. For homogeneous magnetic field the spectrum peak is well defined and may be used for the inference of the field induction whenever we know the other important source parameters. However, the magnetic induction is the strongest dependence of the peak frequency and has been widely inferred from these spectra peak in solar flare analysis. The non homogeneous magnetic field may modify the spectrum width and peak mainly due to changes in the optically thick spectral index. Thus, for non homogeneous magnetic field the inferred induction may be interpreted as an effective value when the observation is fit, for example, by the four parameter fit-function given by most of solar flare analysis in the literature. Simple formulas are given for the gyro-synchrotron spectra peak in the literature where the peak is derived for the opacity equal one. This simplification causes the peak to be uncertain mostly for the cases where the optically thin spectral index is low. Besides, these simple equations are not applicable for spectra peak occurring below the tenth harmonic number of the electron gyro-frequency which excludes most of the observed flares. We present a simple expression for the magnetic induction in a self-absorbed gyro-synchrotron emission to infer it from the spectrum peak frequency as given by the spectrum least square fit instead of opacity equal one. Our equation is valid for a large range of parameters generally accepted for solar flare conditions including peak frequency below the tenth harmonic of the gyro-frequency.

Poster 09

MAGNETIC RECONNECTION AT THE ORIGIN OF SUBMILLIMETER RADIATION

G. Cristiani¹, G. Martínez¹, C.H. Mandrini¹, C.G. Giménez de Castro², A.V.R. Silva², E. Correia⁵, P. Kaufmann^2,3, M. Rovira¹, H. Levato⁴

1: Instituto de Astronomía y Física del Espacio, Buenos Aires, Argentina

2: Centro de Radio Astronomia e Astrofísica Mackenzie, Univ. Presbiteriana Mackenzie, Brazil.

3: Part time at CCS, Universidade Estadual de Campinas, Campinas, Brazil

4: Complejo Astronómico El Leoncito, San Juan, Argentina.

5: Centro de Radio Astronomia e Astrofísica Mackenzie, Instituto Nacional de Pesquisas Espaciais

During the 1B/M6.9 burst ocurred on November 28, 2001 at 1634 UT in NOAA AR 9715, radio radiation was observed up to 212 GHz almost simultaneously with a chromospheric mass ejection (surge) observed at Ha wavelength. Using MDI magnetograms we could derive the magnetic field under the linear force-free field assumption. A detailed analysis of the time evolution conectivity of the magnetic field gave us clues over the energy release and thus, the origin of the impulsive phenomena observed at submillimeter and optical wavelengths. We conclude that energy has been released at very low atmospheric heights, where densities are higher. We relate these reconnections with the impulsive radio burst, and also, with the fast pulses observed at submillimeter wavelengths. A Halo CME observed in LASCO images could be a byproduct of the surge.

Poster 10

THE ORIGIN OF THE MAGNETIC FIELDS DIVERGENCE IN CORONAL HOLES

Diego Falceta-Gonçalves & Vera Jatenco-Pereira

Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo

The solar atmosphere presents complexes magnetic structures, like loops and coronal holes, which are intrinsically bounded to the solar wind acceleration and driven mechanism. UVCS/SOHO and ground observations gave a new insight on the problem. Using H I Lyman alpha and O VI line intensity distributions it is possible to identify the coronal holes boundaries, showing a super-radial geometry with diverging factor f_max ranging from 6.0 to 7.5. It is not clear yet if other stars present such structures. However, the diverging magnetic fields play an important role in the stellar winds. In this work we develop a method for determining the magnetic divergence based on its tension generated by an increase in gas pressure at the wind basis.

Poster 11

HOW IS THE DIAMAGNETIC EFFECT RELEVANT TO STELLAR SURFACE PHENOMENA?

Netzach Farbiash, Raphael Steinitz

Ben-Gurion University, Beer-Sheva, Israel 84105

Charged particles at the surface of stars interact with diverging magnetic field structures. Together with gravity, a host of phenomena can occur. Closed magnetic structures can be the source of thermal as well as chemical abundance spots. High temperature coronal structures can also be present, even in stars without surface convection. Diverging open magnetic fields can result in stellar winds. Separation of charged and neutral particles in combination with dielectronic recombination can simulate chemically peculiar abundance effects. Further subtle effects such as T\_bot>T_| are observed in the fast solar wind close to the sun. Our sun, as the closest star, exhibits many of these effects and can thus be examined in detail.

Poster 12

PLASMA SOURCES FOR LABORATORY SIMULATION OF SPACE AND ASTROPHYSICAL PLASMA INTERACTION WITH MAGNETIC FIELDS

Jose Leonardo Ferreira, Israel da Silveira Rego, Guilherme Morais de Carvalho

Instituto de Física Universidade de Brasília

In this work we describe experiments that are been carried out at the Plasma Laboratory of UNB. The aim of these experiments is to investigate several plasma phenomena with relevance to space and astrpphysical plasmas using laboratory sources of low density and low temperature plasmas. In order to perform these studies we have constructed many types of gas ionization chambers to simulate on laboratory scales of ionospheric and magnetospheric plasmas. Density and temperature conditions of D , E and F layers are produced by cold electron plasmas. These plasmas are generated in a thermionic discharge inside a magnetic cage. The quiescent warm plasma drifts to a vacuum chamber where the cold plasma is formed. In order to simulate stellar winds we are developing Kaufmann type ion souce that can generate electrons and ions in the KeV range and a Hall plasma source that can generate low density and fast flowing plasma with ion energy of 500 eV. We are also performing studies to determine the importance of the Hall effect on the coronal mass ejection. These studies are relevant to space weather forecast. We also use a magnetized plasma source, where the plasma is produced by electron cyclotron ressonance in magnetic mirror throats. By using this experimental arragement it is possible to investigate plasma diffusion in magnetic fields geometries relevant to auroral arc formation and star accreation disks. The basic plasma diagnostic is made with probes and grid energy analysers and non pertubative mesurements of the ion dynamics in the mirror throat was carried out with spectroscopy technics. We are also using data processing techniques with computers that can be relevant for on board instrumentation control of satellites. In conclusion we have developed plasma devices that can be possibly used in laboratory simulation studies of space and astrophysical plasma phenomena and/or on the calibration plasma diagnostics for the next generation of scientific satellites of INPE (Brazillian Institute for Space Research).

Poster 13

EXPLORING SOLAR DYNAMO MODELS WITH A BIPOLYTROPIC DENSITY PROFILE FOR A DEEP MERIDIONAL FLOW

Gustavo Guerrero(1), Jose D. Munoz(2), Elisabete M. De Gouveia Dal Pino (1)

(1) Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo

(2) Depto. de fisica, Universidad Nacional de Colombia

Circulation-dominated solar dynamo models, which employ an helioseismically rotation profile and a fixed meridional flow, give a good approximation to the large scale solar magnetic phenomena: the 11-year cycle or the so called Hale`s law of polarities. Neverthless, the larger amplitude of the radial shear ¶W/¶r at the high latitudes makes the dynamo to produce a strong toroidal magnetic field at high latitudes, in contradiction with the observations of the sunspots (Sporer`s Law). A possivel solution was proposed by Nandy and Choudhuri (2002), i.e., a deep meridional flow can conduct the magnetic field inside of a stable layer (the radiative core) and then allow it to erupt just in lower latitudes. Although they obtain good results, this hypothesis generates new problems like mixture of elements in the radiative core (that alters the abundance of the elements), and transfer of angular moment. We have recently explored this hypothesis in a different approximation, using the magnetic bouyancy mechanism proposed by Dikpati and Charbonneau (1999) and found that a deep meridional flow pushes the maximum of the toroidal magnetic field towards the solar equator but, in contrast to Nandy & Choudhuri (2002), a second zone of maximal fields remains at the poles (Guerrero & Munoz 2004). In this work, the effects of using a bipolytropic density profile in order to better reproduce the stratification in the radiative core will be presented, and finally, a possible scenario where the radiative core has a prolate shape, following early helioseismology observations of Charbonneau et al. (1999), will be also discussed.

References:

(1) Nandy, D. & Choudhuri , A. R., Science, 296, 1671, (2002)

(2) Dikpati, M. & Charbonneau, P., Ap.J., 518, 508, (1999)

(3) Guerrero, G. & Munos, J. D., MNRAS, 350,317, (2004).

(4) Charbonneau, P., Christensen-Dalsgaard, J., Henning, R., Larsen, R. M., Schou, J.,

Thompson, M. J., Tomczyk, S., ApJ, 527, 445 (1999).

Poster 14

CHARACTERIZATION OF SOLAR MULTI-SCALING MAGNETIC LOOP INTERACTIONS

Reinaldo R. Rosa (1), Marian Karlick (2), Fernando M. Ramos (1), Alan Wilter (1)

(1) Lab for Computing and Applied Math - INPE - Brazil

(2) Ondrejov Radio-Observatory - Czech Republic

Solar magnetic loop structures can exist in a broad range of spatio-temporal scales and their mutual interactions is described by nonlinear processes of magnetic reconnection triggered as a secondary regime by a primary MHD instability. From the application of gradient pattern analysis on decimetric time series as a counterpart of SOHO and TRACE flare loop observations we derive, using Tajima's model for quasi-periodic MHD coalescence, possible ranges of minimum Sagdeev potential. From this parameter we obtain a range of nonlinear oscillation period for a typical mutual solar loop interaction.

Poster 15

STUDY OF ACTIVE REGIONS TEMPORAL EVOLUTION AT 17 GHz

Caius L. Selhorst (1,2)

Adriana V. R. Silva (1,3)

Joaquim E. R. Costa (1,2)

(1) Centro de Rádio-Astronomia e Astrofísica Mackenzie - CRAAM

(2) Instituto Nacional de Pesquisas Espaciais - INPE

(3) Universidade Presbiteriana Mackenzie - UPM

We present a statistical study of the evolution of active regions observed at microwave wavelengths during the 23rd solar cycle (1992-2004). Active regions are sites of increased magnetic fields, thus the radio emission at microwave wavelengths is mostly due to gyro-resonance of thermal electrons around relatively strong magnetic fields. We analyze active regions observed in full Sun images obtained daily by the Nobeyama Solar Heliograph at 17 and 34 GHz. Additional information is obtained from photospheric magnetograms of the same day. Also a multiwavelength study provides a global view of the solar atmosphere above active regions, the radio images will further be compared to ultraviolet (SOHO) and H-alpha images. The active regions are characterized by: position, area, maximum and mean brightness temperatures, and magnetic field. The inferred magnetic fields are used to estimate the contribution to the emission at 17 GHz. We discuss the results from the correlation among these physical parameters, and their evolution throughout the solar activity cycle.

Poster 16

POSSIBILITIES ON RADIO BURSTS FROM EXTRASOLAR PLANETS

Yutaka Shiratori, Osamu Kameya, Takeo Yokoo

Dept. of Space & Earth Information Technology, Kyushu Tokai University

National Astronomical Obs. , Kyorin Univ.

We discuss on the possibilities of radio bursts from extrasolar planets. Our model is based on the model used to explain solar radio bursts. If extrasolar planets have strong magnetic fields, their magnetic fields will influence on the magnetic fields of their stars and induce frequently radio bursts.

Poster 17

MICROWAVE SOLAR FLARE SPECTRA OF COMPLEX MAGNETIC AMBIENT

Paulo José de Aguiar Simões (1,2), Joaquim Eduardo Rezende Costa (1,2)

(1) Instituto Nacional de Pesquisas Espaciais - INPE

(2) Centro de Rádio Astronomia e Astrofísica Mackenzie - CRAAM

The magnetic field lines were never so depicted as in the recent results about active regions on the sun from the EUV experiments on board of SOHO and TRACE satellites. The main result is a clear complexity of the, as called, magnetic arcs on top of the sunspots with arc second spatial resolution of the field lines connecting different magnetic polarities. The microwave solar bursts occurring in this magnetic ambient has been treated, in most of analysis, as homogeneous source of gyrosynchrotron emission. We developed a numerical code for the emission, self-absorption and transfer equation of the ordinary and extraordinary modes for this complex ambient to calculate the flux density map and spectrum of the emitting region. We applied our code for a non-thermal distribution of electrons, with number density typical for solar flares, with anisotropic pitch angle distribution, a hydrostatic ambient density and analyzed the spectrum for many viewing angles. For the magnetic field configuration we idealized a complex array of magnetic arcs simulating one of these observed scenarios for our first result presented here. The code is also prepared to use a non-linear extrapolation of photospheric magnetic field. Our main concern in this analysis was to show some of the geometric dependence of the spectrum shape as an alternative for the general interpretation based on a composition of many isotropic sources with distinct magnetic field or bremsstrahlung competition to broad and/or reinforce the emission in specific frequency bands.

Poster 18

SOLAR CORONA MAGNETIC STRUCTURE AND STAGNATED WIND OUTFLOW

Alberto M. Vasquez

Instituto de Astronomia y Fisica del Espacio

Solar observations made with the Ultraviolet Coronagraph Spectrometer (UVCS) aboard the Solar and Heliospheric Observatory (SoHO) spacecraft, have revealed that coronal protons and heavier ions have anisotropic temperature distributions (Cranmer et al., ApJ 1999). We develop semi-empirical models for the solar minimum coronal magnetic field structure (Vasquez, van Ballegooijen and Raymond, ApJ 2003) to investigate the effect of the observed proton anisotropy on the coronal magnetic structure and the bi-modal solar wind. We also explore the effect that the particular geometry of the magnetic field around the streamer belt has on the solar wind. In the present work we highlight our findings on this issue. We find that the streamer belt open magnetic field-lines (streamer legs) have non-monotonic expansion factors. This has in turn a strong impact on the solar wind speed height profiles, producing a stagnated outflow around the streamer magnetic cusp, located at the top of the streamer belt closed magnetic field-lines (streamer core). We find that this magnetic effect extends over quite important distances (of order 1 solar radii) from the magnetic cusp location. To achieve mass flux conservation along field-line tubes, density enhancements are then predicted in the region surrounding the magnetic helmet structure cusp. Our studies (see also Vasquez and Raymond, ApJ 2004) are relevant for both a better determination of the coronal streamer belt magnetic structure, and the identification of the slow wind source.

Session: Magnetic Fields in Star Formation

and Evolution

Poster 19

COMPARING MHD DISKWIND MODELS AND OBSERVATIONS OF THE CLASSICAL T TAURI STAR RW AUR

Silvia Alencar (1), Nuria Calvet (2), Lee Hartmann (2)

(1) DF-UFMG, (2) CfA

It is a consensus nowadays that both wind and magnetospheric accretion are important processes acting in the young star-disk systems and contributing in the emission line formation. Muzerolle et al. (2001) recently suggested that some Classical T Tauri stars (CTTSs) with high mass accretion rates may power powerful outflows and, in this case, most of the Ha line may indeed be due to winds. Therefore the study of the wind in young stellar objects is necessary to complement the magnetospheric accretion scenario. We are currently doing a complete study of the diskwind parameter space, varying the diskwind geometry, density, heating function and mass accretion rate together with the star/disk system inclination, in order to better understand the wind contribution to the observed line profiles of a sample of CTTSs. We use the Blandford & Payne (1982) representation for the wind, which assumes ideal, axisymmetric MHD and steady flow from a Keplerian accretion disk. We assume the problem is self-similar, so the solution for one field line can be scaled for other field lines. Once we have a diskwind model set, we solve the radiative transfer equations using the Sobolev method, following the procedure outlined in Hartmann, Hewett & Calvet (1994). We will present diskwind Ha, Hb and NaD line profile calculations for RW Aur, a high mass accretion rate young system. We will compare the model results with high-resolution observed line profiles and show that the wind contribution to the line profile is very important and should be taken into account. Our results so far indicate that the Ha, Hb and NaD observed line profiles of RW Aur are better reproduced by collimated diskwinds starting from a small region near the disk inner radius. Extended winds are not able to reproduce all the three lines simultaneously and open-angled winds generate profiles that do not look like the observed ones.

Poster 20

NON-STATIONARY MAGNETOSPHERIC ACCRETION IN THE CLASSICAL T TAURI STAR AA TAU

Silvia Alencar (1), Jerome Bouvier (2), Catherine Dougados (2)

(1) Departamento de Fisica, ICEx-UFMG, Brazil

(2) Observatoire de Grenoble, France

Many key properties of classical T Tauri stars are well accounted for by assuming that the stellar magnetic field governs the accretion flow close to the star. We report the results of a synoptic study of the photometric and spectroscopic variability of the classical T Tauri star AA Tau on timescales ranging from a few hours to several weeks. We have indications of a time delay between the main emission lines (Ha, Hb and He I) and veiling, which is consistent with accreted material propagating downwards the accretion columns at free fall velocity from a distance of about 8 R_*. During a few days, the eclipses, which are periodically observed in the light curve, disappeared, the variability of the system was strongly reduced and the line fluxes and veiling severely depressed. We argue that this episode of quiescence corresponds to the temporary disruption of the magnetic configuration at the disk inner edge. The smooth radial velocity variations of inflow and outflow diagnostics in the Ha profile yield further evidence for large scale variations of the magnetic configuration on a timescale of a month. These results may provide the first clear evidence for large scale instabilities developping in T Tauri magnetospheres as the magnetic field lines are twisted by differential rotation between the star and the inner disk. The interaction between the inner accretion disk and the stellar magnetosphere thus appears to be a highly dynamical and time dependent process.

Poster 21

MAGNETIC FIELDS AND SURFACE CHEMICAL ABUNDANCES IN THE AP STARS

Natalia Drake (1), Oleg Kochukhov (2), Ramiro de la Reza (1), Nina Polosukhina (3)

(1) Observatorio Nacional/MCT, Rio de Janeiro, Brazil

(2) Department of Astronomy, Vienna University, Austria (3) Crimean Astrophysical Observatory, Nauchny, Ukraine

We present the results of the high-resolution spectral monitoring of the cool magnetic chemically peculiar A-type stars HD 83368 and HD 3980. Both stars show strong spectral variations with the rotating phase, especially in the profile of the Li i 6707.8 Å line. Doppler imaging analysis of the star HD 83368 allowed to reconstruct the maps of the surface distribution of several light, iron-peak and rare-earth elements and correlate these surface distributions with phase variations of the magnetic field. We found that lithium is strongly concentrated at the magnetic poles with R _spot=15-20^o, whereas oxygen shows ring-like overabundance structure encircling the star at about the magnetic equator. Variation of the longitudinal magnetic field of HD 83368 and the magnetic intensification of F I lines in the spectrum of this star are consistent with the dipolar magnetic topology with a magnetic obliquity b=87^o and a polar strength B_p = 2.5 kG. Fundamental stellar parameters, such as the effective temperature, surface gravity, mass, luminosity, radius, and the inclination angle of the rotational axis were estimated.

Poster 22

THEORETICAL VALUES OF THE ROSSBY NUMBER FOR LOW-MASS, ROTATING PRE-MAIN SEQUENCE STARS

Natalia R. Landin (1), Luiz T. S. Mendes (1,2), Luiz P. R. Vaz (1)

(1) Departamento de Física, ICEx, UFMG

(2) Departamento de Engenharia Eletrônica, Escola de Engenharia, UFMG

Magnetic fields are at the heart of the observed stellar activity in late type stars, and they are presumably generated by a dynamo mechanism at the interface layer (tachocline) between the radiative core and the base of the convective envelope. Since dynamo models are based on the interaction between differential rotation and convective motions, the introduction of rotation in the ATON 2.3 stellar evolutionary code give us the opportunity to begin explorations regarding a physically consistent treatment of magnetic effects in stellar structure and evolution, in spite of the formidable mathematical and numerical challenges involved. As an example of such explorations, we present theoretical estimates of the convective turnover time t_c for rotating pre-main sequence solar- type stars, based on up-to-date input physics for stellar models. Those estimates, as opposed to the use of empirically derived values of t_c for such matters, can be used to calculate the Rossby number Ro, which is related to the magnetic activity strength in dynamo theories and, at least for main-sequence stars, shows an observational correlation with stellar activity. More important, they can also contribute for testing stellar models against observations.

Poster 23

STAR-DISK INTERACTION IN CLASSICAL T TAURI STARS

Giovanni Pinzón (1), Ramiro de la Reza (2)

(1,2) Observatório Nacional/MCT

We study the interaction between a dipolar magnetic field rooted in the central star and the circumstellar accretion disk in a classical T Tauri system. The computations cover the disk in a radial interval from 1 to 6 stellar radii. The model is based on a pionner work developed by Cameron & Campbell (1993) that incorporate the changes in the star moment of inertia, magnetic field strength and an exponential decrease in the accretion rate. We find solutions of this model for a few initial conditions and at low magnetic field regime. We have also find solutions using two polytropic indexes, in order to describe each region of protostellar interior, n=3 for a radiative core and n=1.5 for the convective envelope. A new internal energy distribution appears and produce a linear decreasing of the moment of inertia, maintain always the global virial equilibrium. We find a slightly increment of rotation rates due to this effect. Future studies will take in consideration the death of the disc.

Poster 24

MAGNETIC FIELDS IN WEAK AND POST T TAURI STARS

Gustavo Rojas, Jane Gregorio-Hetem

Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo

T Tauri stars are young, low mass pre-main sequence objects often surrounded by accretion disks. In magnetospheric accretion models, the strong stellar magnetic fields are thought to play a crucial role on the accretion processes, transferring the material from the circumstellar disk to the surface of the star via accretion columns. The stellar magnetic fields can be directly measured by the Zeeman broadening of photospheric lines; but most of the accreting T Tauri stars present a strong veiling, a non-photospheric emission which fills in the photospheric absorption lines, making line measurements unreliable. The weak- line T Tauri stars, on the other hand, do not present veiling, therefore being well suited for Zeeman broadening measurements of the photospheric lines. We present the results of magnetic field measurements in a sample of Weak and Post T Tauri Stars, using the Zeeman broadening of the Fe I line at l=850 nm. We find stellar magnetic fields in the range of 1 kilogauss, consistent with other works (e. g. Johns-Krull et al. 1999 ApJ 516, 900).

Poster 25

ALFVÉN WAVES IN DUSTY WINDS OF COOL SUPERGIANT STARS

Aline de Almeida Vidotto, Vera Jatenco-Pereira

Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo

One of the most promising mechanisms that drives the winds of cool supergiant/giant stars involves an outward-directed flux of Alfvén waves. This mechanism can explain both the mass-loss rates (between 10^-8 and 10^-6 M_¤ yr^-1), and the terminal velocities (between 20 and 80 km s^-1) of these winds. Alfvén waves have been observed and included in various solar wind models. From that, we learned that unless Alfvén waves are damped, the terminal velocities can be too high. Meanwhile, the damping mechanism is still uncertain. Many models were proposed using damping mechanisms such as surface resonant, non-linear, turbulent, or assuming a constant damping length. However, it's observed that late-type stars present great quantities of dust particles in their winds. It's known that the dispersion properties of Alfvén waves are modified in a dusty plasma, since charged grains in a magnetized plasma are highly coupled to the waves due to cyclotron resonances. We assume that particles are distributed over a range of sizes, implying a broad band of resonance frequencies. Here, we study the consequences of Alfvén waves damped due to its interaction with dust grains in the winds of cool supergiant stars. A preliminary result shows that only this damping mechanism is insufficient to accelerate the wind.

Session: Compact Objects, Accretion Disks and Outflows

Poster 26

ACCRETION INDUCED COLAPSES MAY GIVE ORIGIN TO MAGNETARS

Marcelo P. Allen, Jorge E. Horvath

Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo

The merging of two massive white dwarfs (that is also referred as AIC, somewhat improperly) may give origin to a Supernova Ia and a neutron star. We investigate how this model would be affected if the neutron star has a super-strong magnetic field (the definition of magnetar). Particularly, the injection of energy by the magnetar into the Supernova Remnant (SNR) makes it expands faster. We compare the observed sample of associations between magnetar candidates and SNR to test the model.

Poster 27

CORE MAGNETIC FIELDS IN ULTRACOMPACT RADIO SOURCES

Tina Andreolla, Everton Lüdke

Universidade Federal de Santa Maria, CCNE, Dep. de Física, 97150-900, Santa Maria, RS, Brazil

The Very Long Baseline Array (VLBA) has been used to obtain radio images of the compact steep-spectrum quasars 3C119, 3C216, 3C147 and 3C454 at 1.4, 2.7 and 5 GHz. The Faraday rotation is determined along the jets and appear to be of external origin according to models of depolarization of the radio radiation and range from 400 to 1600 rad m^-2. We discuss the morphological aspects of individual sources and conclude that these sources show evidence for strong deceleration for the radio compontentes. We overrrule the hypothesis that free adiabatic expansion is responsible for the deceleration, which can be explained by strong jet-environmental interactions. The frustration scenario for growth of compact sources receive support from the present observations as the compact sources appear to be thriving in a denser medium than regular FRII radio sources with a single visible jet seen in nearby quasars and radio galaxies.

Poster 28

A SIMPLE MAGNETOHYDRODYNAMICAL MODEL FOR FORMATION OF SUPERMASSIVE BLACK HOLES IN QSOs

Carlos H. C. Araújo (1), Herman J. Mosquera Cuesta (2,3,4)

(1) Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo,

São Paulo, Brazil, (2) ICPT, Trieste, Italy

(3) CBPF, Rio de Janeiro, Brazil, (4) CLAF, Rio de Janeiro, Brazil

We present a simple magnetohydrodynamical (MHD) model to describe the formation, out of the primordial gas, of spheroidal figures of equilibrium that upon the appearance of instabilities may lead to the formation of a supermassive black hole in its central region. The process could develop in a universe with redshift z > 6. A general relativistic (semi)analytical MHD model is worked out to follow the gravitational collapse inside such structure, for the simple case of the formation of a supermassive (Schwarzschildlike) black hole. The resulting complex object seems to be related to the observed radio- quiet QSOs. It is presented results and tests for the model: mass accretion disc, jets formation, configuration of the magnetic field in the structure, and eletromagnetic emission. A discussion on observational constraints for this model is also given. As a future perspective, we evaluate the possibility of reinforcing the model through inclusion of a code which traces the chemical evolution of the structure as a whole, what we call a magnetochemodynamical code.

Poster 29

ELECTRODYNAMICS OF PARAMAGNETIC NEUTRON STAR

Sergey Bastrukov

Joint Institute for Nuclear Research 141980 Dubna, Russia

The key idea underlying the paramagnetic neutron star model is that ultrastrong and highly stable magnetic fields of isolated pulsars owe its origin to permanent magnetization of stellar matter promoted by Pauli's paramagnetism: spin polarization of neutron magnetic moments brought about by frozen in the star core fossil magnetic field whose amplification in the process of gravitational collapse is motivated by conservation of magnetic flux density. In this communication the expected effects of global seismic vibtations (driven by self-gravity and magneto-elasticity of neutron star matter) and magnetoplasma oscillations in the crust (namely: Alfven, helicoidal and gyromagnetic modes) on electromagnetic emisson of paramagnetic neutron star are discussed. Emphasis is placed on theoretical treatment of observable electromagnetic activity of pulsars from standpoint of the paramagnetic neutron star model.

Poster 30

ANALYTICAL PRODUCTION AND COLLIMATION OF ASTROPHYSICAL JETS

Cristian Giovanny Bernal, William Lee Alardin

Instituto de Astronomia - UNAM

At the present time, a great amount of astronomical systems has been discovered that generate collimated flows of plasma which travel at great speeds. In the great majority of the cases, the central source is a compact object as a Neutron Star or Black Hole stellar or supermassive, on which is accreting material itself of continuous form. The structure and evolution of jet-like structures under a variety of physical conditions is a problem that generally requires numerical modeling. However, in certain cases valuable insight can be gained from purely analytical hydrodynamical solutions, which exhibit outflows of varying characteristics. We show here several solutions of this type, applicable to various accretion scenarios.

Poster 31

CYCLICAL PERIOD CHANGES IN CATACLYSMIC VARIABLES: EVIDENCE OF MAGNETIC ACTIVITY CYCLES IN THE MASS-DONOR STAR

Bernardo Borges, Raymundo Baptista

UFSC, Florianópolis/SC, Brazil

Cataclymic variables (CVs) are semi-detached binary systems in which a main sequence late-type star (the secondary) fills its Roche lobe and transfers matter to a white dwarf (the primary) through the inner Lagragian point L₁. Evolutive models of CVs predicts that the orbital periods P_orb of these systems would decrease on time scales of 10⁸-10⁹ years due to angular momentum losses either by magnetic braking via the secondary star's wind (P_orb > 3 hr) or by emission of gravitational radiation (P_orb > 3 hr). These models try to explain the observed gap of systems with P_orb in the range of ~ 2 to 3 hr as the consequence of a sharp reduction of magnetic field open lines when the secondary star become fully convective (at P_orb ~ 3 hr). However, up to now no well-studied CVs shows evidence of period decrease. Instead, most well-observed eclipsing CVs show cyclical period changes probably associated to solar-type (quasi-periodic and/or multiperiodic) magnetic activity cycles in the secondary star. The fast spinning secondaries of CVs, covering a range of masses and rotation periods, are an important laboratory to understanding magnetic activities cycles in late type stars. In the present work, we report the investigation of cyclical period changes in UU Aqr and IP Peg, CVs with orbital periods of 3.92 and 3.8 hr, respectively. The inclusion of two new points in the modulation period (P_mod) versus modulation amplitude diagram, allow a comparison with well-know cyclical period changes systems. A discussion of the distinct magnetic activity properties of short and long orbital period (P_orb < 3 hr e P _orb > 3 hr, respectively) systems in the framework of the CV evolution scenario is presented.

Poster 32

MODELLING THE RADIO FLARING BEHAVIOUR OF 3C273

Luiz Claudio Lima Botti

CRAAM/INPE

Models for the emitting region should yield predictions for the evolution of the spectrum of newly created components. Light curves of blazars show evidence of outbursts propagating from high to low frequencies. An important step in the understanding of theses flares was done by Marsher and Gear in 1985 (Marsher and Gear,1985), when they studied the strong 1983 outburst of 3C273. They identified three stages of the evolution of the shock wave propagating down a relativistic jet, according to the dominant cooling process of the electrons: the Compton scattering loss phase; the synchrotron radiation loss phase and the adiabatic expansion loss phase. Another shock model was developed by Valtaoja et al. in 1992. They also identified three stages of the evolution of the shock without going into the details of the physics of the shock. Their model, based on observations, describes qualitatively theses three stages. To constrain shock models we need to extract the properties of the outbursts from the observations. This is very difficult because of the brevity of the outbursts at high frequencies (a few days to months at submillimetre spectral range) and at radio frequencies, because they often overlap due to their longer duration. All these studies are based on isolated outbursts. The method used consists in constructing simultaneous multi-frequencies spectra for as many epochs as possible after the subtraction of a quiescent spectrum, assumed to be constant with time. A different approach was developed by Turler et al. (1999). The idea was to decompose a set of light curves covering a large time span into a series of flares. The fit was made simultaneously to the same outbursts to several light curves, covering more than two decades of frequency, from the radio to submillimetre frequencies. The aim was to obtain both the spectral and temporal properties of a typical flare. We use in this work light curves of 3C273 at 4.8 GHz, 8.0 GHz, 14.5 GHz, 22 GHz and 43 GHz ( Itapetinga and Michigan radiotelescopes data). We fit these light curves simultaneously to the same outbursts. The light curve of each outburst at a given frequency is described by a simple analytical function in the Turler model. We have also used a new analytical function (more simple than Turler's function) to obtain a fast convergence of the fit. This model has therefore many free parameters to a wide range of different situations. A total of 33 physical parameters (from the shock wave model) were obtained in this work.

Turler,M., Courvoisier, T.J.-L, Paltani, S. Astron.Astrophys. 349. 45-54 (1999). Marsher, A.P., Gear, W.K ApJ. 298, 114 (1985).

Poster 33

ACCRETION AND MAGNETO-DIPOLE EMISSION IN FAST ROTATING NEUTRON STARS: NEW SPIN EQUILIBRIUM LINES

L. Burderi (1), T. Di Salvo (2), F. D'Antona (1)

(1) Osservatorio di Roma

(2) Universita' di Palermo

We consider the effects of magneto-dipole emission in accreting, low-magnetized and fast-rotating neutron stars. Despite common wisdom, these effects are relevant in determining the spin-equilibrium period of these objects. This new ingredient naturally accounts for the lack of submillisecond pulsars, the absence of millisecond pulsations in most bright low mass X-ray binaries, and the elusivity of the propeller phases in this class of objects. This model also provides an explanation for the general spin-down trend found in millisecond X-ray pulsars and, in particular, for the constant spin-down observed in SAX J1808-3658 despite a decrease in luminosity of a factor of 50.

Poster 34

THE IMPORTANCE OF MAGNETIC FIELDS IN PROTOSTELLAR

JET-DRIVEN SHOCKS

Sylvie Cabrit (1), Guillaume Pineau des Forets (2,1), Jacques Le Bourlot (1), David Flower (3),

Pierre Lesaffre (4)

(1) Observatoire de Paris, France, (2) IAS, Orsay, France

(3) University of Durham, UK, (4) CfA, Cambridge, UK

The impact of supersonic protostellar jets against the dense molecular cloud is known to create strong shocks, which may be of two types: (1) hydrodynamical "jump'' (J-type) shocks where kinetic energy is dissipated by molecular viscosity alone, or (2) magneto-hydrodynamical "continuous'' (C-type) shocks, where energy is dissipated by frictional drift between the decoupled charged and neutral fluids. Using detailed models of stationary C- and J-type planar shocks including non-equilibrium ionisation, dissociation, and chemistry, we show that the rotational H2 emission from shocked gas is a very powerful diagnostic tool to constrain the magnetic field in the preshock medium. Comparison of our model predictions with observations of protostellar flows in rotational H2 lines indicate a magnetic field parameter b = B / between 0.1 and 10, comparable to the values found by Zeeman splitting measurements (cf. invited talk by D. Crutcher). A trend for higher b near more massive protostars is also observed. The presence of C-shocks in jet-driven flows has important consequences on the fraction of the outflow momentum observable in molecular lines. Several time-dependent effects on the shock structure and molecular content will also be discussed, based on new 1D MHD simulations with an implicit algorithm and a moving mesh providing very high resolution (down to the mean free-path).

Poster 35

SPIN-INDUCED AND MAGNETICALLY DRIVEN PRECESSION IN

ACTIVE GALACTIC NUCLEI

Anderson Caproni (1), Zulema Abraham (1), Herman J. Mosquera Cuesta (2,3)

(1) Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo

(2) Centro Brasileiro de Pesquisas Fisicas

(3) Abdus Salam International Centre for Theoretical Physics

We proposed in previous papers that variations in the kinematics of the parsec- scale jet of some active galactic nuclei, as well as their long-term periodic variability at optical wavelengths, are possibly related to the precession of their jet inlets. In this work, we study the feasibility of explaining its physical origin through rigid-body precession of the accretion disk due to the misalignment between the angular momenta of the accretion disc and the Kerr black hole, as well as magnetic torques generated from the interaction between a large-scale magnetic field and the induced electric currents in the disc.

Poster 36

THREE-DIMENSIONAL NUMERICAL SIMULATIONS OF ROTATING JETS

Adriano H. Cerqueira (1), Elisabete M. de Gouveia Dal Pino (2)

(1) LATO-DCET-UESC, Brasil

(2) Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo, Brasil

Recent high resolution observations of microjets associated with T-Tauri stars have revealed important trends in the jet radial velocity field that are consistent with a rotation pattern inside the jet beam. In the context of magneto-centrifugal models for jet production, the presence of rotation could be interpreted as due to jet launching from a Keplerian accretion disk along with the magnetic field lines which are anchored into the disk-star system and provide the collimation of the beam. Motivated by these observations, we have used a three-dimensional SPH code to simulate rotating, intermitent, precessing jets. Employing initial conditions and parameters which are particularly suitable for the casee of the DG Tau microjet, we have obtained radial velocity maps that are in good agreement with the observed ones, thus indicating that the interpretation that the DG Tau microjet is rotating must be correct. Finally, we have found that a magnetic field of the order of ~ 0.5 mG is sufficient to collimate the jet against the lateral expansion caused by the centrifugal forces.

Poster 37

A MHD MODEL FOR THE STELLAR DISK WIND OF DR TAU

Gustavo H. R. de Araújo Lima (1), Silvia H. P. Alencar (1), Nuria Calvet (2) ,Lee Hartmann (2)

(1) ICEx/UFMG, (2) CfA - Harvard

Magnetospheric accretion and stellar winds are very important contributing processes in the emission line formation of young star-disk systems. It was recently suggested that some Classical T Tauri stars (CTTSs) with high mass accretion rates may trigger powerful outflows and, in this case, most of the Halpha lines may be due to winds. So, the study of winds in young stellar objects is extremelly important to complement the magnetospheric accretion scenario and to correctly predict the observed line profile behavior in these young systems. We are currently studying the diskwind parameter space (diskwind geometry, density and heating functions, mass accretion rate and star-disk system inclination), in order to calculate Halpha, Hbeta and NaD line profiles for DR Tau, and also to better understand the wind contribution to the observed line profiles of a sample of CTTSs. Then we will compare the model results for DR Tau with observed line profiles to verify if in this case the wind contribution plus magnetospheric accretion can fairly model the emission line formation. We use the Blandford & Payne (1982) representation for the wind, which assumes ideal, axisymetric MHD and steady flow from a Keplerian accretion disk. Then, once we have the diskwind model set, we solve the radiative transfer equations using the Sobolev method, following the procedure outlined in Hartmann, Hewett & Calvet (1994) for the magnetospheric accretion case.

Poster 38

THE EFFECT ON NO-AXYSIMMETRICAL PERTURBATIONS ON THE GENERATION OF JETS FROM MAGNETIZED ACCRETION DISKS

Fabio De Colle (1), Alejandro Raga (2)

(1) Instituto de Astronomia, UNAM (Mexico)

(2) Instituto de Ciencia Nucleares, UNAM (Mexico)

The generation of jets from accretion disks is a very difficult and interesting topic, not completely solved yet. We present preliminary results of three-dimensional MHD simulations, performed to study the effect of no-axisymmetrical perturbations on the generation of jets from magnetized accretion disks. Our simulations try to reproduce the effect a binary companion star (with or without accretion disk) on the stability and the dynamics of the disk, and on the stability of the ejected jet.

Poster 39

A MECHANISM FOR THE SUPERLUMINAL EJECTIONS IN MICROQUASARS: A JET/ACCRETION DISK SYMBIOSIS

E. M. de Gouveia Dal Pino (1), A. Lazarian (2)

(1) Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo

(2) University of Wisconsin, Astronomy Department

Double star systems containing stellar mass black holes and normal stars as companions have been identified in our galaxy during the last decade. Ejecting collimated bipolar radio jets with apparent superluminal velocities, these objects have been named microquasars thanks to their similarity with the distant quasars. We here propose that the large scale superluminal ejections observed in these microquasars (e.g., GRS 1915+105 source) during radio flare events are produced by violent magnetic reconnection episodes in the corona just above the inner regions of the magnetized accretion disk (with B ⋍ 10⁷ G) that surrounds the central 10-solar mass black hole. The process occurs during disk mass accretion near but below the supercritical regime (~ 10¹⁹ g s^-1), and part of the magnetic energy released by reconnection heats the coronal gas (T_c ~ 10⁷ K) that produces a steep, soft X-ray spectrum with luminosity L_X ⋍ 10³⁹ erg s^-1, in agreement with observations. The remaining magnetic energy released goes to accelerate the particles to relativistic velocities (v ~ v_A ~ c}, where v_A is the Alfvén speed) in the reconnection site through a first-order Fermi process. This produces a steep power-law electron distribution N(E) µ E^-5/2 and a corresponding synchrotron radio power-law spectrum (S_n µ n^-0.75) with spectral index comparable to the one observed during the flares.

Poster 40

OBSERVATIONS OF THE EMISSION-LINE STOCHASTIC VARIABILITY IN ACCRETION DISKS

Marcos Diaz, Fabiola Ribeiro

Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo

The presence of intrinsic stochastic brightness variability in the light curves of cataclysmic variables (CVs) is one of the observational properties that defines this class of objects. From the theoretical point of view, the physical origin of flickering in CVs is still controversial. Some descriptions for the flickering in accretion disks like the &#65533;celular-automaton&#65533; model by Yonehara, Mineshige and Welsh (1997) predict that the power spectrum density slopes should be wavelength independent. Other models propose that a radial viscosity variability (Lyubarskii 1997) is responsible for changing the mass accretion rate. From the observational point of view, defining the regions in the accretion flow that are producing flickering will certainly constrain the possible physical forming scenarios. Possibly due to the intrinsic observational difficulties, the issue of flickering in the emission lines of CVs is an almost unexplored subject. In this contribution we discuss a method for locating the emission-line flickering regions using Doppler tomography techniques. Simulations and the aplication of this method to steady accretion disks are presented.

Poster 41

CONSTRAINTS ON THE NEUTRON STAR MAGNETIC FIELD OF TRANSIENT LMXBS FROM THEIR LUMINOSITY IN QUIESCENCE

T. Di Salvo(1), L. Burderi(2), N. Robba(1), R. Iaria(1)

(1) Universita' di Palermo

(2) Osservatorio Astronomico di Roma

The recently discovered coherent X-ray pulsations at a frequency of ~ 400 Hz in SAX J1808.4-3658, together with a measure of the source luminosity in quiescence, allow us to put an upper limit on the neutron star magnetic field, that is B £ 5 ´ 10⁸ Gauss, using simple considerations on the position of the magnetospheric radius during quiescent periods. Combined with the lower limit inferred from the presence of X-ray pulsations, this constrains the SAX J1808.4-3658 neutron star magnetic field in the quite narrow range (1-5) ´ 10⁸ Gauss. Similar considerations can be applied to the case of other transient LMXBs for which the spin period is known. In general we find neutron star magnetic fields lower than ~ 10⁹ Gauss.

Poster 42

FREE-ELECTRON LASER IN PULSAR MAGNETOSPHERE

Pui-Kei Fung(1), Jan Kuijpers (1,2)

(1) Astronomical Institute Utrecht, The Netherlands

(2) Dep. of Astronomy, Nijmegen, The Netherlands

Production of high brightness radio pulses using a free-electron laser is discussed in the context of pulsar radio emission. In a free-electron laser, the interaction of a beam of relativistic and mono- energetic electrons (or positrons) with electromagnetic disturbances (also called wiggler) leads to coherent radiation. The frequency of this emission depends only on the beam particles' energy and wiggler's parameters, and therefore, it is tunable. At the polar cap of the pulsar, a beam of relativistic electrons is pulled out from the surface due to large parallel electric field. Furthermore, in the magnetosphere different kinds of waves, like Langmuir waves and Alfvén waves, exist and can act as a wiggler. To apply this mechanism in the pulsar magnetosphere, numerical simulations are done by tracking charged particles in a background magnetic field and a wiggler. In the talk, the results of the numerical simulations will be presented.

Poster 43

NUMERICAL SIMULATIONS OF ETA CARINA BIPOLAR OUTFLOWS

R.F. González (1), E.M. de Gouveia Dal Pino (2), A.C. Raga (1) and P.F. Velazquez (2)

(1) Instituto de Ciencias Nucleares (UNAM) (2) Instituto de Astronomia e Geofisica (USP)

We present two-dimensional gas dynamic simulations of the formation and evolution of the Eta-Car bipolar outflows. Adopting the interacting nonspherical winds model, we have carried out high-resolution numerical simulations, which include explicitly computed time-dependent radiative cooling, for different possible scenarios of the colliding winds. From these models, we obtain important differences in the shape and kinematical properties of the Homunculus structure. In particular, we find an appropriate combination of the wind parameters (that control the degree of non-spherical symmetry) and obtain numerical experiments that best match both the observed morphology and the expansion velocity of the Eta-Car bipolar shell. Additionally, our numerical simulations show the formation of a bipolar nebula embedded within the Homunculus (the little Homunculus) developed from a secondary eruptive event suffered by the star in the 1890s, and also the development of tenuous, high velocity ejections in the equatorial region that could explain some of the high speed features observed in the equatorial ejecta.

Poster 44

PULSAR RADIO EMISSION CUTOFFS

Ericson López

Observatorio Astronómico de Quito

The propagation of radio emission in pulsar magnetospheres is discussed. The dispersive properties of waves in a pulsar plasma are considered in detail. In our calculations, we have included relativistic effects on the dispersion properties of the electromagnetic waves. The formulation that we have employed gives us natural transverse electromagnetic modes and longitudinal solutions which are interpreted as pressure modes and cyclotron absorption. The occurrence of plasma instabilities is analyzed beside the conditions which should be fulfilled in order to permit the wave propagation and conversion for frequencies close the cutoffs of the system.

Poster 45

MAGNETIC FIELDS IN THE HOTSPOTLESS JET OF 3C200

Everton Lüdke

Universidade Federal de Santa Maria, CCNE - Departamento de Fisica - LARIE,

97150-900 Santa Maria, RS, Brazil

3C200 is a remarkable radio galaxy at redshift 0.458. It exhibits a luminous, hotspotless jet which is visible both in optical HST NICMOS images and the Chandra X-ray images as well as an extended radio halo around the counter-jet side. In this paper, I present the results of a high-resolution MERLIN and VLA observations where magnetic fields along the jet is studied in detail through minimum energy conditions and polarization-sensitive measurements. Faraday rotation models to the jet and counter-jet sides have been fitted in order to obtain the intrinsic magnetic field distribution. Various radio source kinematical parameters have been obtained from dynamical analysis and are further discussed.

Poster 46

General relativistic effects of strong magnetic fields on the gravitational force: a driving engine for bursts of

gamma-rays in SGRs?

Manuel Malheiro, Subharthi Ray, Herman J. Mosquera Cuesta and Jishnu Dey

CBPF-Brazil

In general relativity all forms of energy contribute to gravity and not only just ordinary matter as in Newtonian Physics. This fact can be seen in the modified hydrostatic equilibrium equation for relativistic stars pervaded by magnetic (B) fields. It has an additional term coupled to the matter part as well as an anisotropic term which is purely of magnetic origin. That additional term coming from the pressure changed by the radial component of the diagonal electromagnetic field tensor, weakens the gravitational force when B is strong enough and can even produce an unexpected change in the attractive nature of the force by reversing its sign. In an extreme case, this new general relativistic (GR) effect can even trigger an instability in the star as a consequence of the sudden reversal of the hydrostatic pressure gradient. We suggest here that this GR effect may be the possible central engine driving the transient giant outburst observed in Soft Gamma-ray Repeaters (SGRs). In small regions of the neutron star (NS), strong magnetic condensation can take place. Beyond a critical limit, these highly magnetized bubbles may explode releasing the trapped energy as a burst of gamma rays of ~10^36-40 erg.

Poster 47

STRONGEST GRAVITATIONAL WAVES FROM NEUTRINO OSCILLATIONS AT SUPERNOVA CORE BOUNCE

Herman Mosquera Cuesta (1) and Karen Fiuza (2)

(1)CBPF-ICRA-BR

(2)IF-UFRGS

Resonant active-to-active (n_a ® n_a), as well as active-to-sterile (n_a ® n_s neutrino (n) oscillations can take place during the core bounce of a supernova collapse. Besides, over this phase, weak magnetism increases antineutrino () mean free paths, and thus its luminosity. Because the oscillation feeds mass-energy into the target n species, the large mass-squared difference between species (n_a ® n_s) implies a huge amount of energy to be given off as gravitational waves (L_GWs ~ 10⁴⁹ erg s^-1), due to anisotropic but coherent n flow over the oscillation length. This asymmetric n-flux is driven by both the spin-magnetic and the universal spin-rotation coupling. The novel contribution of this paper stems from 1) the new computation of the anisotropy parameter a ~ 0.1-0.01, and 2) the use of the tight constraints from neutrino experiments as SNO and KamLAND, and the cosmic probe WMAP, to compute the gravitational-wave emission during neutrino oscillations in supernovae core collapse and bounce. We show that the mass of the sterile neutrino n_s that can be resonantly produced during the flavor conversions makes it a good candidate for dark matter as suggested by Fuller et al. (2003). The new spacetime strain thus estimated is still several orders of magnitude larger than those from n difussion (convection and cooling) or quadrupole moments of neutron star matter. This new feature turns these bursts the more promissing supernova gravitational-wave signal that may be detected by observatories as LIGO, VIRGO, etc., for distances far out to the VIRGO cluster of galaxies.

Poster 48

QUARK MATTER IN STARS AND QUANTUM-MAGNETIC COLLAPSE

Perez Martinez, Aurora (1) Perez Rojas, Hugo (1) Mosquera Cuesta, Herman (2)

(1) ICIMAF, (2) CBPF

Quark matter is expected to exists in the interior of compact stellar objects as neutron stars or even the more exotic strange stars, based on the Bodmer-Witten conjecture. Bare strange quark stars and (normal) strange quark-matter stars, those possessing a baryon (electron) crust, are hypothesized as good candidates to explain the properties of a set of peculiar stellar sources as the enigmatic X-ray source RX J1856.5-3754, some pulsars as PSR B1828-11 and PSR B1642-03 (Xu 2003), and the anomalous X-ray pulsars and soft gamma-ray repeaters (Zhang et al. 2000). In the MIT bag model, quarks are treated as a degenerate Fermi gas confined in a region of space having a vacuum energy density B_bag (the bag constant). In this note, the equations of state of degenerate quarks gases are studied in the presence of ultra strong magnetic fields. The behavior of a system made-up of quarks having (or not) an anomalous magnetic moment is reviewed. A structural instability is found, which is related to the anisotropic nature of the pressures in this highly magnetized matter. The conditions for the collapse of this system are obtained and compared to a previous model of neutron stars build-up on a neutron gas having anomalous magnetic moment.

Poster 49

Charged Stars and the Anysotropic Structure

Rodrigo Picanço and Manuel Malheiro

CBPF-Brazil

In this work we will review the structure of a charged polytropic star with polytropic equation of state. We will assume that these stars are spherically symmetric and have only a radial electric field. It will be showed that these assumptions generate an anisotropy in the structure of the star: the radial component of the Energy-Momentum tensor is different from angular components. Recently in the literature it was showed that one can write a new hydrostatic equilibrium equation (TOV equation) using only the radial component of the stress tensor (P_r), instead the usual thermodynamic pressure. Usually we define the edge of a star being the place where the pressure goes to zero (P(R)=0), but with this new equation we can define the edge by being the place where the P_r vanishes. We will solve both cases for a charge distribution that goes with the matter-energy density. With that we will compare both cases and see which one is more stable and realistic. We will also study the effects that the anisotropy causes in the structure of the star.

Poster 50

SIMULTANEUOS STUDY OF 4U 1728-34 WITH CHANDRA AND ROSSI XTE

N. R. Robba, A. D'Ai', R. Iaria, T. Di Salvo

DSFA-Univ. di Palermo

We report the simultaneous study of the Atoll-source 4U 1728-34 using two simultaneous RXTE and Chandra Observations. The source is positioned on its Color-Color Diagram between the island state and the banana state. The High Energy Trasmission Grating on board Chandra indicates that an iron emission line between 6 and 7 keV is not present contrarily until now supposed. The high temporal resolution of RXTE allows a systematic study of the Power spectra of the source giving results in agreement with the previous RXTE results.

Poster 51

SPECTRAL MAPPING OF INTERMEDIATE POLAR DQ HERCULIS

Roberto K. Saito, Raymundo Baptista

Universidade Federal de Santa Catarina

DQ Her is an eclipsing intermediate polar, the which serves as the prototype of a class of cataclysmic variables that show pulsations at periods less than the system orbit period. We report an eclipse mapping study of the spectra and structure of the accretion disc of DQ Her. The analysis is based on 3272 spectra obtained at the Hale 5m telescope, using the 2D Frutti detector on July 1987. The integration time for each spectrum was 10s, and the usable spectral coverage is ~ 3800-5000 Å. We removed the orbital velocity of the primary star K₁=140 km s^-1 from the spectra and the corrected spectra were binned to a dispersion of 2 Å pixel^-1. The spectra were sliced into narrow passbands in the continuum and in velocity-resolved passbands for the lines, and light curves were extracted for each band. The light curves were analyzed with maximum-entropy eclipse mapping techniques producing a set of monochromatic maps of the disc brightness distribution and the spectrum of an additional, uneclipsed component. We obtained spatially resolved spectra of the accretion disc as a function of distance from the disc centre, for the regions around the magnetic white dwarf at disc centre, and for the gas stream. This analysis allow us to study the structure and the behavior of the disc inner regions in the presence of an magnetic field, to compare the results with the previous works about the DQ Her and to test the current models proposed to explain the accretion physics in intermediate polar systems.

Poster 52

PROBING PHYSICAL CONDITIONS IN ACCRETION DISCS WITH ECLIPSE

MAPPING TECHNIQUES

Roberto Saito, Alexandre Zabot, Raymundo Baptista

UFSC

Spectral eclipse mapping of cataclysmic variables is a powerful probe of physical conditions in their accretion discs. The spatially-resolved spectra can be fitted with disc atmosphere models to infer the spatial dependency of relevant disc physical parameters. Here we report the results of a spectral mapping experiment based on Hubble Space Telescope time-resolved spectroscopy of the dwarf nova V2051 Ophiuchi while the star was in an unusual, faint brightness state during 1996. Two consecutive eclipses of the star were observed, the first in the optical (l3200-4800 Å) and the second in the ultraviolet range (l1200-2500 Å). The spectra were sliced into narrow passbands in the continuum and in the lines, and light curves were extracted for each band. The light curves were analyzed with eclipse mapping techniques producing a set of monochromatic maps of the disc brightness distribution and the spectrum of an additional, uneclipsed component. We present combined UV-optical spatially resolved spectra of the accretion disc as a function of distance from the disc centre, of the white dwarf at disc centre and of the bright spot at the disc rim, as well as the spectrum of the uneclipsed light. We construct a grid of disc atmosphere models assuming an isothermal slab of gas in LTE and fit synthetic spectroscopy to the observed spectra in order to derive the effective temperature, surface density, turbulent Mach number and disc scale height in each case. We compare the derived run of the temperature with radius with the T µ R^-3/4 law expected for a steady-state optically thick disc model. The results are discussed in the framework of the current models proposed to explain the outburst behaviour of dwarf novae.

Poster 53

ALFVÉNIC HEATING OF VERTICALLY ISOTHERMAL ACCRETION DISKS

Maria Jaqueline Vasconcelos

Laboratório de Astrofísica Teórica e Observacional - LATO/UESC

Protostellar accretion disks are structures that are formed around young stars. Despite the many advances in the understanding of these objects, their temperature structure is not yet known. In this work we continue the investigation of heating caused by damping of Alfvén waves. It was considered, in a self consistent way, collisional and viscous-resistive damping. The heating generated by these mechanisms was compared with traditional heating sources such as viscous dissipation and reprocessing of star's radiation within the disk. The frequency and the amplitude of the waves was constrained. The results show that there is an increase of the effective temperature of the outer regions of the disk, consistent with recent H₂ observations. The ionization degree increases and has a value above 10^-12 for R \la 4 UA.

Poster 54

ON THE BOTTOM MAGNETIC FIELD AND MAGNETOSPHERE OF THE

ACCRETING NEUTRON STAR

Chengmin Zhang

National Astronomical Observatories, Chinese Academy of Sceinces, 100012, Beijing, P.R. China

The magnetic fields of neutron stars decay in the binary phase, mainly because the fields are buried by accreted matter. We obtain the minimum magnetic field after the accretion, about 3*10^7 Gauss, which we define as the bottom magnetic field. The magnetic fields of neutron stars approach to the bottom value after accreting matter of half solar mass, and it is also obtained that the bottom magnetic field is proportionally related to the luminosity of binary X-ray neutron star.

Session: Magnetized ISM

Poster 55

PARAMETRIC INSTABILITIES OF ALFVÉN WAVES IN INTERSTELLAR CLOUDS

Jaime A. Araneda (1), Sergio Dasso (2), Felix A. Borotto (1)

(1) Departamento de Física, Universidad de Concepción, Chile.

(2) Instituto de Astronomía y Física del Espacio IAFE, Buenos Aires, Argentina.

Kinetic dispersion relation of parametrically unstable Alfvén waves propagating in a gravitating interstellar cloud is obtained. We examine the effects of Landau damping and Jeans instability on the mode structure and growth rates caused by the coupling of the large amplitude Alfvén wave to compressive fluctuations. We show that unstable regions can be substantially different from a fluid theory.

Poster 56

RADIO WAVE PROPAGATION IN THE NON-GAUSSIAN INTERSTELLAR MEDIUM

Stanislav Boldyrev (1), Carl Gwinn (2), Arieh Konigl(1)

(1) University of Chicago

(2) University of California, Santa Barbara

Radio waves propagating from distant pulsars in the magnetized interstellar medium, are refracted by electron density inhomogeneities, so that the intensity of observed pulses fluctuates with time. The theory relating the observed pulse time-shapes to the electron-density correlation function has developed for 30 years, however, several puzzles have remained. First, observational scaling of pulse broadening with the pulsar distance is anomalously strong; it is consistent with the standard model only when non-uniform statistics of electron fluctuations along the line of sight are assumed. Second, the observed pulse shapes are consistent with the standard model only when the scattering material is concentrated in a thin slab between the pulsar and the Earth. Third, observations require the presence of electron-density fluctuations at very small scales, 10⁷-10⁸ cm., much smaller than the Coulomb mean free path in ionized (HII) regions. We propose that these paradoxes are resolved at once if one assumes stationary and uniform, but non-Gaussian statistics of the electron-density distribution. Such statistics must be of Levy type, and the propagating ray should exhibit a Levy flight. We propose that a natural realization of such statistics is provided by the interstellar medium with random electron-density discontinuities. We develop a theory of wave propagation in such a non-Gaussian random medium, and demonstrate its good agreement with observations.

Ref.: S. Boldyrev & C. R. Gwinn, Phys. Rev. Lett. 91, 131101 (2003); ApJ 584, 791 (2003)

Poster 57

THE ENVIRONMENT AND MAGNETIC FIELD OF COMETARY GLOBULE CG30

Gabriel Hickel (1,2), José W.S. Vilas-Boas (2)

(1) UNIVAP, (2) INPE

We present a multiwavelenght/multitechnique analysis of cometary globule CG30. This globule shows herbig-haro objects associated with a young low-mass binary star (IRAS 08076-3556) that is deeply embedded into the globule. We used IRAS images to derivated the dust properties; molecular transitions (CO, ¹³CO, C¹⁸O, HCN and HCO⁺) to calculated the mass, density, temperature, ion fraction and outflow properties; and linear polarization in R optical and to studyed the magnetic field around the globule. CG30 presents a quadripolar outflow that modify the density and temperature of gas, and disturb the polarization degree of dust grains. The magnetic field around the globule shows signals of compression and torsion and has importance to support the globule morphology. We briefly discuss the relations between the young low-mass binary and its bithplace. This work is supported by FAPESP.

Poster 58

COHERENCE AND MAGNETIC FIELDS AT THE PARSEC SCALES OF DIFFUSE MOLECULAR CLOUDS

Hily-Blant P.⁽¹⁾ and Falgarone E.⁽²⁾

(1) Institut de Radio Astronomie Millimétrique, St-Martin-d'Hères, France

(2) LERMA/LRA, Ecole Normale Supérieure/Observatoire de Paris, France

In the "turbulence--dominated star formation mechanism'', magnetic fields are thought to play a minor role in the structuration of diffuse molecular clouds, being overwhelmed by largely supersonic and superAlfvénic shocks. While this might be the case at the large scales of Giant Molecular Clouds (GMCs), we show here that magnetic fields are possibly the dominant process structuring the diffuse molecular gas at scales of 1 parsec and below. This work relies on large millimeter datasets (» 10⁴ emission spectra in the first two rotational transitions of CO and ¹³CO) observed at high angular resolution (0.015 pc). The data are compared with published GMCs properties (Heyer et al. 1996) and with radiative transfer calculations in numerical simulations of 3-dimensional MHD flow (Padoan et al. 1998). Results are as follows. First, maps are highly anisotropic with elongated structures often aligned with the magnetic fields projection on the sky. Second, unlike what is found at the GMCs scales and in numerical simulations, the dependence of the velocity dispersion with column density supports the idea of dynamically important magnetic fields. Third, the observed surface filling factor is at odds with that predicted by superAlfvénic simulations.

Poster 59

MAGNETIC TURBULENCE IN A SELF-GRAVITATIONALLY STRATIFIED CLOUD

Takahiro Kudoh, Shantanu Basu

University of Western Ontario

We perform numerical simulations of nonlinear MHD waves in a self-gravitationally stratified molecular cloud that is bounded by a hot and tenuous external medium, within a 1.5-dimensional approximation. Under the influence of a sinusoidal or random driving source of Alfvenic disturbances, the cloud is lifted up by the pressure of MHD waves and reaches a steady state characterized by oscillations about a new time-averaged equilibrium state. For various strengths and frequencies of the input energy or the strength of the magnetic field, models of an ensemble of clouds show that the velocity dispersion in the cloud s µ Z^0.5, where Z is a characteristic size of the cloud. This is consistent with observational results. Due to the stratification, lower frequency modes than the input frequency are produced when Alfven waves propagate to the upper low-density atmosphere. The power spectrum shows that the most of the energy per mass of the turbulence in the stratified cloud is contained in the lowest frequency modes, even though the driving may occur partly or entirely at higher frequencies. This result of stratification is distinct from that of a uniform medium.

Poster 60

A POLARIMETRIC STUDY IN THE REGION CONTAINING THE

MOLECULAR CLOUD LUPUS 1

Felipe Oliveira Alves, Gabriel Armando Pellegatti Franco

Universidade Federal de Minas Gerais

We have carried out polarimetric observations to investigate the geometry of the magnetic field in the region of the star forming cloud Lupus 1. This study is based upon deep R-band CCD polarimetry, covering Lupus 1 as well as the surrounding area containing the IRAS 100 micron cavity. The observational data were collected with the IAG 60 cm telescope at Observatório do Pico dos Dias (LNA/MCT - Brasópolis - Brazil). Our first analysis shows that a variation of the magnetic field orientation through the region can produce complex polarization patterns from which the field geometry cannot easily be determined. The polarization patterns are inconsistent with strictly uniform or unidirectional magnetic fields on extended spatial scales. A comparison with the 100 micron emission shows that locally the polarization vectors exhibit strong alignment with the orientation of the observed infrared patches. But, for Lupus 1, these vectors are perpendicular the its filamentar strucure. Parallel to this job, measurements of interstellar polarization from Hipparcos stars have been done to estimate the distance to this cloud and to the Pipe Nebula. For Lupus, our results converged to a value of 130-150 pc and, for the Pipe Nebula, the preliminary results suggest a lower limit of ~ 140 pc.

Poster 61

MAGNETIC FIELDS AND DISPERSION OF POLARIZATION ANGLES: IRAS VELA SHELL

Antonio Pereyra, Antonio Mario Magalhães

Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo

The dispersion of polarization position angles can provide an estimate of the ratio of kinetic energy density to magnetic energy density (r_kin/ r_mag) and the local magnetic field intensity in the interstellar medium, as first suggested by Chandrasekhar and Fermi. Nevertheless, a relatively large number of data points is necessary in order to obtain a reasonable estimate. We use a recently published catalog of several hundred objects toward the western side of IRAS Vela Shell in order to investigate the distribution of the local magnetic field in small (~pc) scales across an ionization front (I-front). We find variations of r_kin/r_mag of one order magnitude along the I-front, with the magnetic pressure generally dominating over the turbulent motions. In a few of cases the polarization angle appears to change randomly, suggesting that the kinetic energy may dominate. These findings suggests that the magnetic component has a significant contribution to the dynamical balance of this region. This work is supported by FAPESP. AMM is partly supported by CNPq.

Poster 62

POLARIZATION PROPERTIES OF CONDENSATIONS IN MUSCA AND THEIR RELATION TO STAR FORMATION

José Williams Vilas-Boas(1), Roberto P. Kahn (1), Gabriel Hickel (2)

(1)Instituto Nacional de Pesquisas Espaciais-INPE

(2) Universidade do Vale do Paraíba-UNIVAP

Observations of the J=1-0 ¹³CO carbon monoxide line with space resolution of 48 arc seconds are combined with polarimetry of background stars, in the center of Musca dark cloud, in order to explore the influence of early stages of star formation on the polarization due to the neighbour dust and gas. Condensations with and without star formation activity are analyzed.

Session: Magnetic Fields in Galaxies, the IGM,

and the Early Universe

Poster 63

SYNCHROTRON AGES IN HOTSPOTS OF CSS QUASARS AND RADIOGALAXIES

Rosane Bohrer-Adornes (1), Everton Lüdke(1), Debora M. Katz-Stone (2)

(1) Universidade Federal de Santa Maria, CCNE, Dep. de Física, 97150-900, Santa Maria, RS, Brazil

(2) United States Naval Academy Annapolis, MA, USA

In this paper we discuss estimatives of synchrotron ages of quasars and radiogalaxies belonging to the Compact Steep-Spectrum radio sources (CSS) classification of extragalactic radio sources. We have observed selected CSSs from the Fanti et al. original sample with the Very Large Array between 5 and 44 GHz and the MERLIN network at 1.6 GHz. Hotspots radio fluxes have been computed at similar angular resolutions. We attempted to fit standard Kardashev- Pacholczyk and continuum injection models with inverse compton losses to the hotspot spectra. Ages range from 0.06 to 0.15 Myears and agree with a Scheuer growth model if the environmental densities are higher by at least ~ 200 times those found in giant radio galaxies, if equipartition fields are assumed. Further observational properties of the sample are discussed.

Poster 64

THE PARKER INSTABILITY IN A REALISTIC GALACTIC MODEL

Valeria Buenrostro-Leiter

Instituto de Astronomía, UNAM

The Parker Instability is here studied in a full Galactic Potential that includes a 3-D modeling of the bar and spiral pattern components. These mass distributions satisfy the dynamical self consistency.

Poster 65

MODELING THE SPECTRUM OF GRAVITATIONAL WAVES IN THE

PRIMORDIAL UNIVERSE

Marcelle S. dos Santos, J. C. Fabris, S. V. B. Gonçalves, and Elisabete M. De Gouveia Dal Pino

Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo

Recent observations from type Ia Supernovae and from cosmic microwave background (CMB) anisotropies have revealed that most of the matter of the Universe interacts in a repulsive manner composing the so called dark energy constituent of the Universe. The analysis of cosmic gravitational waves (GW) represents, besides the CMB temperature and polarization anisotropies, an additional approach in the determination of parameters that may constrain the dark energy models and their consistence. In recent work (Fabris, Gonçalves, and Santos 2004), a generalized Chaplygin gas model was considered in a flat universe and the corresponding spectrum of gravitational waves was obtained. The present work adds a massless gas component to that model and the new spectrum is compared to the previous one. The Chaplygin gas is also used to simulate a L-CDM model by means of a particular combination of parameters so that the Chaplygin gas and the L-CDM models can be easily distinguished in the theoretical scenarios here established. The lack of direct observational data is partialy solved when the signature of the GW on the CMB spectra is determined.

Reference:

Fabris, J. C., Gonçalves, S. V. B., and Santos, M. S., 2004 to appear in General Relativity and Gravitation, gr-qc\0404053

Poster 66

MAGNETIC FIELDS AND THE DYNAMICS OF THE OUTER DISK OF SPIRAL GALAXIES

Estrella Florido, Eduardo Battaner

University of Granada

Recent observations may support the hypothesis of magnetically driven rotation curves in spiral galaxies. Following this model three dynamical regions should be expected: 1) An inner region where magnetic fields are ignorable, 2) A region in which the magnetic strength decreases slower than 1/R, and 3) an outermost region where the strength reaches a slope proportional to 1/R. This radial variation is observed in N6946 and in the Milky Way.

Poster 67

PROBING COSMIC MAGNETISM WITH THE SQUARE KILOMETRE ARRAY

Bryan M. Gaensler (1), Rainer Beck (2)

(1) Harvard University

(2) Max-Planck-Institut fuer Radioastronomie

Understanding the Universe is impossible without understanding magnetic fields. But in spite of their importance, the evolution, structure and origin of magnetic fields are all still open problems in fundamental physics and astrophysics. When and how were the first fields generated? Are present-day magnetic fields a result of dynamo action, or do they represent persistent primordial magnetism? What role do magnetic fields play in turbulence, cosmic ray acceleration and galaxy formation? We explain how the Square Kilometer Array (SKA) can deliver new data which will directly address these currently unanswered issues. Much of what we plan for the SKA is based on an all-sky survey of rotation measures, in which Faraday rotation towards >10⁷ background sources will provide a dense grid for probing magnetism in the Milky Way, nearby galaxies, and in distant galaxies, clusters and protogalaxies. Using these data, we can map out the evolution of magnetized structures from redshifts z>3 to the present, can distinguish between different origins for seed magnetic fields in galaxies, and can develop a detailed model of the magnetic field geometry of the intergalactic medium and of the overall Universe. With the unprecedented capabilities of the SKA, the window to the Magnetic Universe can finally be opened.

Poster 68

THE MAGNETIC FIELD OF THE MAGELLANIC CLOUDS

Bryan M. Gaensler (1), Marijke Haverkorn (1), Lister Staveley-Smith (2), John Dickey (3), Snezana Stanimirovic (4), Joseph Gelfand (1), Naomi McClure-Griffiths (2)

(1) Harvard University

(2) CSIRO Australia Telescope National Facility

(3) University of Tasmania

(4) University of California, Berkeley

The Magellanic Clouds provide a key testbed for understanding galactic magnetism. These two galaxies are very different from the Milky Way and from each other; any commonalities in their magnetic properties can thus point toward fundamental underlying mechanisms which generate a galaxy's magnetic field. I will present new radio polarization surveys of the Large and Small Magellanic Clouds and of the Magellanic Bridge, using the unique spectropolarimetric capabilities of the Australia Telescope Compact Array. The resulting data on Faraday rotation and linear polarization provide a study of magnetic fields in unprecedented detail for any external galaxy.

Poster 69

AN ANISOTROPIC THERMAL CONDUCTION MODEL FOR DEM L316 IN THE MAGELLANIC CLOUD

Ricardo González & Pablo Velázquez

(1) Instituto de Ciencias Nucleares (UNAM)

We present axisymmetric numerical simulations of the Large Magellanic Cloud SNRs system DEM L316. Using a 2D version of the Yguazú-a adaptative grid code (developed by Raga et al. 2000), we have generated soft and hard X-ray emission maps of DEM L316 which include anisotropic thermal conduction effects. The observed morphology of this system suggests that the two supernova remmants maybe spatially connected. However, our simulations probably show that DEM L316 is not an interacting system.

Poster 70

DISSIPATION OF MAGNETIC FLUX IN PRIMORDIAL GAS CLOUDS

Hideki Maki, Hajime Susa

Department of Physics, Rikkyo University

We report on the strength of the seed magnetic flux of the accretion disk surrounding Pop III stars. The magnetic field in accretion disks might play an important role in the transport of angular momentum because of the turbulence induced by MRI. On the other hand, since the primordial star-forming clouds contain no heavy elements or grains, they experience a very different thermal history and magnetic-field-dissipation history in the course of their gravitational contraction from those in the present-day star-forming molecular clouds. In order to assess the magnetic field strength in the accretion disk of Pop III stars, we calculate the thermal and chemical history of the primordial collapsing clouds and investigate the coupling of the magnetic field with the primordial gas. As a result, we find that the magnetic field strongly couples with the primordial gas cloud throughout the collapse, i.e., the magnetic field is frozen to the gas, as long as the initial field strength satisfies B ≲ 10^-5(n_H/10³ cm^-3)^0.55 G. And furthermore, we find that if the initial field strength in the prestellar core is

Poster 71

GLOBAL THREE-DIMENSIONAL MHD SIMULATIONS OF GALACTIC GASEOUS DISKS

Hiromitsu Nishikori (1), Mami Machida (2), Ryoji Matsumoto (3)

(1) Graduate School of Science and Technology, Chiba University

(2) National Astronomical Observatory of Japan

(3) Department of Physics, Faculty of Science, Chiba University

We present the results of global three dimensional magnetohydrodynamic simulations of galactic gaseous disks. As the gravitational potential we adopt a model of our galaxy including dark matter given by Miyamoto et al. (1980). The initial gas distribution is that of an equilibrium torus in the gravitational potential. We assume initially weak troidal magnetic field. As the magnetorotational instability develops the torus becomes turbulent. Due to the magnetic stress exerted by the turbulent magnetic field angular momentum is distributed in the torus. The torus changes itself into a disk. Magnetic energy increases exponentially and saturates when B~1mG. The magnetic field is maintained for more than 5.0 ´ 10⁹ yrs. The ratio of the flactuation magnetic field to the mean magnetic field is ïd B / B ï ~ 1. The mean magnetic field obtained from numerical simulations shows bisymmetric spiral structure. We also present the results of global MHD simulations of bar galaxies. Spiral structure of mean magnetic field is more prominent in bar galaxies than in spiral galaxies.

Poster 72

THE "GEOMETRIC AMPLIFICATION" OF THE COSMIC MAGNETIC INDUCTION

Alexandre L. Oliveira, Carlos R. Rabaça

Universidade Federal do Rio de Janeiro - UFRJ

We search for an amplification mechanism of the seed cosmic magnetic induction by studying a new version of the Dirac's \AE ther in a curved cosmological background. We find that the variation of the scale factor R(t) with cosmic time brings to the magnetic field the desired effect of amplification, that we call geometric amplification.

Poster 73

MAGNETOHYDRODYNAMIC SIMULATIONS OF THE WIGGLE INSTABILITY IN SPIRAL GALAXIES

Minoru Tanaka (1), Keiichi Wada (2), Ryoji Matsumoto (2)

(1) Graduate School of Science and Technology, Chiba University

(2) National Astronomical Observatory of Japan

(3) Department of Physics, Faculty of Science, Chiba University

We studied the stability of galactic spiral shocks by two dimensional global magnetohydrodynamic simulations. Recently, Wada & Koda (2003) showed by global hydrodynamic simulations that galactic gas flows behind the spiral shock become unstable against the perturbation parallel to the shock and form spur-like density structures. They attributed the origin of this wiggle instability to the Kelvin-Helmholtz (K-H) instability triggered by the acceleration of the gas behind the shock. In their simulations, however, the effects of galactic magnetic fields were ignored. We carried out global simulations including galactic magnetic fields. The initial magnetic field is assumed to be either uniform or purely toroidal. We found that although magnetic field reduces the growth rate of the K-H instability, wiggle instability develops even in galaxies with mG magnetic fields. We also present the results of local simulations to demonstrate the dependence of the growthrate of the instability on wavelength. When magnetic field exists, the interval of spurs is determined by the most instable wavelength of the wiggle instability.

Poster 74

THE [L-SIGMA] RELATION FOR HII GALAXIES

Eduardo Telles, Vinicius Bordalo

Observatório Nacional

Local HII galaxies present a Fundamental Plane of [L-s] where either the equivalent width of Hb or the oxygen abundance O/H act as a second parameter. These relations are powerful cosmological distance indicators since emission line galaxies may be found to high redshifts, though some caution must be taken till systematic effects are better understood.