Dynamics of Line-Driven Winds from Disks in Cataclysmic Variables. I. Solution Topology and Wind Geometry

We analyze the dynamics of 2-D stationary, line-driven winds from accretion disks in cataclysmic variable stars. The driving force is that of line radiation pressure, in the formalism developed by Castor, Abbott & Klein for O stars. Our main assumption is that wind helical streamlines lie on straight cones. We find that the Euler equation for the disk wind has two eigenvalues, the mass loss rate and the flow tilt angle with the disk. Both are calculated self-consistently. The wind is characterized by two distinct regions, an outer wind launched beyond four white dwarf radii from the rotation axis, and an inner wind launched within this radius. The inner wind is very steep, up to 80 degrees with the disk plane, while the outer wind has a typical tilt of 60 degrees. In both cases the ray dispersion is small. We, therefore, confirm the bi-conical geometry of disk winds as suggested by observations and kinematical modeling. The wind collimation angle appears to be robust and depends only on the disk temperature stratification. The flow critical points lie high above the disk for the inner wind, but close to the disk photosphere for the outer wind. Comparison with existing kinematical and dynamical models is provided. Mass loss rates from the disk as well as wind velocity laws are discussed in a subsequent paper.Comment: 21 pages, 10 Postscript figures; available also from http://www.pa.uky.edu/~shlosman/publ.html. Astrophysical Journal, submitte

Analysis of the Flux and Polarization Spectra of the Type Ia Supernova SN 2001el: Exploring the Geometry of the High-velocity Ejecta

SN 2001el is the first normal Type Ia supernova to show a strong, intrinsic polarization signal. In addition, during the epochs prior to maximum light, the CaII IR triplet absorption is seen distinctly and separately at both normal photospheric velocities and at very high velocities. The high-velocity triplet absorption is highly polarized, with a different polarization angle than the rest of the spectrum. The unique observation allows us to construct a relatively detailed picture of the layered geometrical structure of the supernova ejecta: in our interpretation, the ejecta layers near the photosphere (v \approx 10,000 km/s) obey a near axial symmetry, while a detached, high-velocity structure (v \approx 18,000-25,000 km/s) with high CaII line opacity deviates from the photospheric axisymmetry. By partially obscuring the underlying photosphere, the high-velocity structure causes a more incomplete cancellation of the polarization of the photospheric light, and so gives rise to the polarization peak and rotated polarization angle of the high-velocity IR triplet feature. In an effort to constrain the ejecta geometry, we develop a technique for calculating 3-D synthetic polarization spectra and use it to generate polarization profiles for several parameterized configurations. In particular, we examine the case where the inner ejecta layers are ellipsoidal and the outer, high-velocity structure is one of four possibilities: a spherical shell, an ellipsoidal shell, a clumped shell, or a toroid. The synthetic spectra rule out the spherical shell model, disfavor a toroid, and find a best fit with the clumped shell. We show further that different geometries can be more clearly discriminated if observations are obtained from several different lines of sight.Comment: 14 pages (emulateapj5) plus 18 figures, accepted by The Astrophysical Journa

On the Mass of Population III Stars

Performing 1D hydrodynamical calculations coupled with non-equilibrium processes for H2 formation, we pursue the thermal and dynamical evolution of filamentary primordial clouds and attempt to make an estimate on the mass of population III stars. It is found that, almost independent of initial conditions, a filamentary cloud continues to collapse nearly isothermally due to H_2 cooling until the cloud becomes optically thick against the H_2 lines. During the collapse the cloud structure separates into two parts, i.e., a denser spindle and a diffuse envelope. The spindle contracts quasi-statically, and thus the line mass of the spindle keeps a characteristic value determined solely by the temperature ($\sim 800$ K). Applying a linear theory, we find that the spindle is unstable against fragmentation during the collapse. The wavelength of the fastest growing perturbation lessens as the collapse proceeds. Consequently, successive fragmentation could occur. When the central density exceeds $n_c \sim 10^{10-11} cm^{-3}$, the successive fragmentation may cease since the cloud becomes opaque against the H_2 lines and the collapse decelerates appreciably. The mass of the first star is then expected to be typically $\sim 3 M_\odot$, which may grow up to $\sim 16 M_\odot$ by accreting the diffuse envelope. Thus, the first-generation stars are anticipated to be massive but not supermassive.Comment: 23 pages, 6 figures, accepted by ApJ (April 10

2D non-LTE Modeling for Axi-symmetric Winds. II. A Short Characteristic Solution for Radiative Transfer in Rotating Winds

We present a new radiative transfer code for axi-symmetric stellar atmospheres and compare test results against 1D and 2D models with and without velocity fields. The code uses the short characteristic method with modifications to handle axi-symmetric and non-monotonic 3D wind velocities, and allows for distributed calculations. The formal solution along a characteristic is evaluated with a resolution that is proportional to the velocity gradient along the characteristic. This allows us to accurately map the variation of the opacities and emissivities as a function of frequency and spatial coordinates, but avoids unnecessary work in low velocity regions. We represent a characteristic with an impact-parameter vector p (a vector that is normal to the plane containing the characteristic and the origin) rather than the traditional unit vector in the direction of the ray. The code calculates the incoming intensities for the characteristics by a single latitudinal interpolation without any further interpolation in the radiation angles. Using this representation also provides a venue for distributed calculations since the radiative transfer can be done independently for each p.Comment: 18 pages, 12 figures, accepted for publication in A&

Instabilities in the Envelopes and Winds of Very Massive Stars

The high luminosity of Very Massive Stars (VMS) means that radiative forces play an important, dynamical role both in the structure and stability of their stellar envelope, and in driving strong stellar-wind mass loss. Focusing on the interplay of radiative flux and opacity, with emphasis on key distinctions between continuum vs. line opacity, this chapter reviews instabilities in the envelopes and winds of VMS. Specifically, we discuss how: 1) the iron opacity bump can induce an extensive inflation of the stellar envelope; 2) the density dependence of mean opacity leads to strange mode instabilities in the outer envelope; 3) desaturation of line-opacity by acceleration of near-surface layers initiates and sustains a line-driven stellar wind outflow; 4) an associated line-deshadowing instability leads to extensive small-scale structure in the outer regions of such line-driven winds; 5) a star with super-Eddington luminosity can develop extensive atmospheric structure from photon bubble instabilities, or from stagnation of flow that exceeds the "photon tiring" limit; 6) the associated porosity leads to a reduction in opacity that can regulate the extreme mass loss of such continuum-driven winds. Two overall themes are the potential links of such instabilities to Luminous Blue Variable (LBV) stars, and the potential role of radiation forces in establishing the upper mass limit of VMS.Comment: 44 pages, 13 figures. Chapter to appear in the book "Very Massive Stars in the Local Universe", Springer, J.S. Vink, e

A Region of Violent Star Formation in the Irr Galaxy IC 10: Structure and Kinematics of Ionized and Neutral Gas

We have used observations of the galaxy IC 10 at the 6-m telescope of the Special Astrophysical Observatory with the SCORPIO focal reducer in the Fabry-Perot interferometer mode and with the MPFS spectrograph to study the structure and kinematics of ionized gas in the central region of current intense star formation. Archive VLA 21-cm observations are used to analyze the structure and kinematics of neutral gas in this region. High-velocity wings of the H-alpha and [SII] emission lines were revealed in the inner cavity of the nebula HL 111 and in other parts of the complex of violent star formation. We have discovered local expanding neutral-gas shells around the nebulae HL 111 and HL 106.Comment: 22 pages, 10 figures; accepted in Astronomy Report

Sub-millimeter Observations of Giant Molecular Clouds in the Large Magellanic Cloud: Temperature and Density as Determined from J=3-2 and J=1-0 transitions of CO

We have carried out sub-mm 12CO(J=3-2) observations of 6 giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC) with the ASTE 10m sub-mm telescope at a spatial resolution of 5 pc and very high sensitivity. We have identified 32 molecular clumps in the GMCs and revealed significant details of the warm and dense molecular gas with n(H2) $\sim$ 10$^{3-5}$ cm$^{-3}$ and Tkin $\sim$ 60 K. These data are combined with 12CO(J=1-0) and 13CO(J=1-0) results and compared with LVG calculations. We found that the ratio of 12CO(J=3-2) to 12CO(J=1-0) emission is sensitive to and is well correlated with the local Halpha flux. We interpret that differences of clump propeties represent an evolutionary sequence of GMCs in terms of density increase leading to star formation.Type I and II GMCs (starless GMCs and GMCs with HII regions only, respectively) are at the young phase of star formation where density does not yet become high enough to show active star formation and Type III GMCs (GMCs with HII regions and young star clusters) represents the later phase where the average density is increased and the GMCs are forming massive stars. The high kinetic temperature correlated with \Halpha flux suggests that FUV heating is dominant in the molecular gas of the LMC.Comment: 74 pages, including 41 figures, accepted for publication in ApJ

Mass-loss rates of Very Massive Stars

We discuss the basic physics of hot-star winds and we provide mass-loss rates for (very) massive stars. Whilst the emphasis is on theoretical concepts and line-force modelling, we also discuss the current state of observations and empirical modelling, and address the issue of wind clumping.Comment: 36 pages, 15 figures, Book Chapter in "Very Massive Stars in the Local Universe", Springer, Ed. Jorick S. Vin

First results from the NA60 experiment at CERN

Since 1986, several heavy ion experiments have studied some signatures of the formation of the quark-gluon plasma and a few exciting results have been found. However, some important questions are still unanswered and require new measurements. The NA60 experiment, with a new detector concept that vastly improves dimuon detection in proton-nucleus and heavy-ion collisions, studies several of those open questions, including the production of open charm. This paper presents the experiment and some first results from data collected in 2002.Comment: Paper presented at the XXXVIII Rencontres de Moriond, QCD and High Energy Hadronic Interactions, Les Arcs, March 22-29, 2003. 4 pages, 6 figure

Study of dimuon production in Indium-Indium collisions with the NA60 experiment

The NA60 experiment at the CERN-SPS is devoted to the study of dimuon production in heavy-ion and proton-nucleus collisions. We present preliminary results from the analysis of Indium-Indium collisions at 158 GeV per nucleon. The topics covered are low mass vector meson production, J/psi production and suppression, and the feasibility of the open charm measurement from the dimuon continuum in the mass range below the J/psi peak.Comment: Contribution at XXXXth Rencontres de Moriond, "QCD and High Energy Hadronic Interactions