Radiation Pressure-Driven Magnetic Disk Winds in Broad Absorption Line Quasi-Stellar Objects

We explore a model in which QSO broad absorption lines (BALS) are formed in a radiation pressure-driven wind emerging from a magnetized accretion disk. The magnetic field threading the disk material is dragged by the flow and is compressed by the radiation pressure until it is dynamically important and strong enough to contribute to the confinement of the BAL clouds. We construct a simple self-similar model for such radiatively driven magnetized disk winds, in order to explore their properties. It is found that solutions exist for which the entire magnetized flow is confined to a thin wedge over the surface of the disk. For reasonable values of the mass-loss rate, a typical magnetic field strength such that the magnetic pressure is comparable to the inferred gas pressure in BAL clouds, and a moderate amount of internal soft X-ray absorption, we find that the opening angle of the flow is approximately 0.1 rad, in good agreement with the observed covering factor of the broad absorption line region

Spectroscopy of SN 1987A at 0.9-2.4 microns: Days 1348-3158

We present near-infrared spectroscopic observations of SN 1987A covering the period 1358 to 3158 days post-explosion. This is the first time that IR spectra of a supernova have been obtained to such late epochs. The spectra comprise emission from both the ejecta and the bright, ring-shaped circumstellar medium (CSM). The most prominent CSM emission lines are recombination lines of H I and He I, and forbidden lines of [S III] and [Fe II]. The ejecta spectra include allowed lines of H I, He I and Na I and forbidden lines of [Si I], [Fe I], [Fe II], and possibly [S I]. The intensity ratios and widths of the H I ejecta lines are consistent with a low-temperature Case B recombination spectrum arising from non-thermal ionisation/excitation in an extended, adiabatically cooled H-envelope, as predicted by several authors. The slow decline of the ejecta forbidden lines, especially those of [Si I], indicates that pure non-thermal excitation was taking place, driven increasingly by the decay of 44Ti. The ejecta iron exhibits particularly high velocities (4000-4500 km/s), supporting scenarios where fast radioactive nickel is created and ejected just after the core-bounce. In addition, the ejecta lines continue to exhibit blueshifts with values about -200 km/s to -800 km/s to at least day 2000. These blueshifts, which first appeared around day 600, probably indicate that very dense concentrations of dust persist in the ejecta, although an alternative explanation of asymmetry in the excitation conditions is not ruled out.Comment: 18 pages, 8 figures, uses mn.sty, MNRAS, in pres

Matter Outflows from AGN: A Unifying Model

We discuss a self-consistent unified model of the matter outflows from AGNs based on a theoretical approach and involving data on AGN evolution and structure. The model includes a unified geometry, two-phase gas dynamics, radiation transfer, and absorption spectrum calculations in the UV and X-ray bands. We briefly discuss several questions about the mass sources of the flows, the covering factors, and the stability of the narrow absorption details.Comment: 6 figures, accepted for publication in Astrophysics and Space Scienc

A Comparative Study of the Mass Distribution of Extreme-Ultraviolet selected White Dwarfs

Original article can be found at: http://www.journals.uchicago.edu/ApJ/--Copyright American Astronomical SocietyWe present new determinations of e ective temperature, surface gravity, and masses for a sample of 46 hot DA white dwarfs selected from the Extreme Ultraviolet Explorer (EUV E) and ROSAT Wide Field Camera bright source lists in the course of a near-infrared survey for low-mass companions. Our analysis, based on hydrogen non-LTE model atmospheres, provides a map of LTE correction vectors, which allow a thorough comparison with previous LTE studies. We Ðnd that previous studies underestimate both the systematic errors and the observational scatter in the determination of white dwarf parameters obtained via Ðts to model atmospheres. The structure of very hot or low-mass white dwarfs depends sensitively on their history. To compute white dwarf masses, we thus use theoretical mass-radius relations that take into account the complete evolution from the main sequence. We Ðnd a peak mass of our white dwarf sample of 0.59 M in agreement with the results of previous analyses. However, we do _, not conÐrm a trend of peak mass with temperature reported in two previous analyses. Analogous to other EUV-selected samples, we note a lack of low-mass white dwarfs and a large fraction of massive white dwarfs. Only one white dwarf is likely to have a helium core. While the lack of helium white dwarfs in our sample can be easily understood from their high cooling rate, and therefore low detection probability in our temperature range, this is not enough to explain the large fraction of massive white dwarfs. This feature very likely results from a decreased relative sample volume for low-mass white dwarfs caused by interstellar absorption in EUV-selected samples.Peer reviewe

Cool companions to hot white dwarfs

Original article can be found at: http://www.journals.uchicago.edu/ApJ/--Copyright American Astronomical SocietyLow-mass companions to high-mass stars are difficult to detect, which is partly why the binary fraction for high-mass stars is still poorly constrained. Low-mass companions can be detected more easily however, once high-mass stars turn into white dwarfs. These systems are also interesting as the progenitors of a variety of intensely studied interacting binary systems, like novae, CVs, symbiotics, Ba and CH giants, Feige 24-type systems, and dwarf carbon stars. We describe a near-IR photometric search for cool red dwarf companions to hot white dwarfs (WDs). IR photometry o ers a sensitive test for low-mass main-sequence (MS) companions. Our sample of EUV-detected WDs o ers several advantages over previous (largely proper motionÈselected) WD samples: (1) the high WD temperatures (24,000\Teff\ 70,000 K) insure excellent IR Ñux contrast with cool dwarfs; (2) the range of evolutionary parameter space occupied by the WDs is considerably narrowed; and (3) the random e ects of the intervening ISM provide a complete but reasonably sized sample. While some composite systems have been found optically among WDs detected in recent EUV All-Sky Surveys, we develop an IR technique that probes farther down the main sequence, detecting yet more companions. We use detailed DA model atmosphere Ðts to optical spectra to predict K magnitudes and distances, against which we contrast our near-IR observations. Our photometric survey reveals 10 DAs with a signiÐcant excess in both J and K. Half are newly discovered and are most likely previously unrecognized binary systems. Neither the frequency of infrared excess nor the mass estimate of the red dwarf companion correlate with white dwarf mass, as might be expected if either the EUV detectability or mass of the white dwarfs were signiÐcantly a ected by a companion. Infrared spectra of these systems should help to determine the mass and spectral type of the cool companions presumably causing the IR excess, leading to better estimates of the mass ratio distribution in binaries. Counting previously known binaries, and resolved pairs, we Ðnd the total binary fraction of the sample is at least a third. Since most WD progenitors had initial masses º2 M we thus _, provide a photometric measure of the binary fraction of high-mass stars that would be difficult to perform in high-mass main-sequence stars. We estimate that 90% of the companions are of type K or later.Peer reviewe