136 research outputs found
9286 Stars: An Agglomeration of Stellar Polarization Catalogs
This is a revision. The revisions are minor. The new version of the catalog
should be used in preference to the old. The most serious error in the older
version was that was incorrect, being sometimes far too large,
for Reiz and Franco entries; the correct values are all zero for that
reference.
We present an agglomeration of stellar polarization catalogs with results for
9286 stars. We have endeavored to eliminate errors, provide accurate
(arcsecond) positions, sensibly weight multiple observations of the same star,
and provide reasonable distances. This catalog is included as an ASCII file
(catalog.txt) in the source of this submission.Comment: The most serious error in the older version was that
was incorrect, being sometimes far too large, for Reiz and Franco entries;
the correct values are all zero for that reference. 11 pages, no figures.
Accepted for Astronomical Journal. Catalog also available as an ASCII file by
anonymous FTP from ftp://vermi.berkeley.edu/pub/polcat/p14.ou
Statistical Properties of Galactic Starlight Polarization
We present a statistical analysis of Galactic interstellar polarization from
the largest compilation available of starlight data. The data comprises ~ 9300
stars of which we have selected ~ 5500 for our analysis. We find a nearly
linear growth of mean polarization degree with extinction. The amplitude of
this correlation shows that interstellar grains are not fully aligned with the
Galactic magnetic field, which can be interpreted as the effect of a large
random component of the field. In agreement with earlier studies of more
limited scope, we estimate the ratio of the uniform to the random
plane-of-the-sky components of the magnetic field to be B_u/B_r = 0.8.
Moreover, a clear correlation exists between polarization degree and
polarization angle what provides evidence that the magnetic field geometry
follows Galactic structures on large-scales. The angular power spectrum C_l of
the starlight polarization degree for Galactic plane data (|b| < 10 deg) is
consistent with a power-law, C_l ~ l^{-1.5} (where l ~ 180 deg/\theta is the
multipole order), for all angular scales \theta > 10 arcmin. An investigation
of sparse and inhomogeneous sampling of the data shows that the starlight data
analyzed traces an underlying polarized continuum that has the same power
spectrum slope, C_l ~ l^{-1.5}. Our findings suggest that starlight data can be
safely used for the modeling of Galactic polarized continuum emission at other
wavelengths.Comment: 31 pages, 11 figures. Minor corrections and some clarifications
included. Matches version accepted for publication by the Astrophysical
Journa
Solid-phase C60 in the peculiar binary XX Oph?
We present infrared spectra of the binary XX Oph obtained with the Infrared Spectrograph on the Spitzer Space Telescope. The data show some evidence for the presence of solid C60â the first detection of C60 in the solid phase â together with the well-known âunidentified infraredâ emission features. We suggest that, in the case of XX Oph, the C60 is located close to the hot component, and that in general it is preferentially excited by stars having effective temperatures in the range 15 000â30 000 K. C60 may be common in circumstellar environments, but unnoticed in the absence of a suitable exciting source
Swift Observations of Shock Evolution in RS Ophiuchi
Our \textit{Swift} observations of RS Oph form an unprecedented X-ray dataset
to undertake investigations of both the central source and the interaction of
the outburst ejecta with the circumstellar environment. Over the first month,
the XRT data are dominated by emission from rapidly evolving shocks. We discuss
the differences in derived parameters from those found for \textit{RXTE} at
early times and the evolution of the X-ray emission to much later times. It is
apparent that at late times several emission components are present. We find no
strong evidence of the proposed shock break-out in our data.Comment: 5 pages, 3 figures, to appear in ASP conference proceedings Volume
401 "RS Ophiuchi (2006) and the recurrent nova phenomenon
Resonance line-profile calculations based on hydrodynamical models of cataclysmic variable winds
We present synthetic line profiles as predicted by the models of 2-D line-
driven disk winds due to Proga, Stone & Drew. We compare the model line
profiles with HST observations of the cataclysmic variable IX Vel. The model
wind consists of a slow outflow that is bounded on the polar side by a fast
stream. We find that these two components of the wind produce distinct spectral
features. The fast stream produces profiles which show features consistent with
observations. These include the appearance of the P-Cygni shape for a range of
inclinations, the location of the maximum depth of the absorption component at
velocities less than the terminal velocity, and the transition from absorption
to emission with increasing inclination. However the model profiles have too
little absorption or emission equivalent width. This quantitative difference
between our models and observations is not a surprise because the line-driven
wind models predict a mass loss rate that is lower than the rate required by
the observations. We note that the model profiles exhibit a double-humped
structure near the line center which is not echoed in observations. We identify
this structure with a non-negligible redshifted absorption which is formed in
the slow component of the wind where the rotational velocity dominates over
expansion velocity. We conclude that the next generation of disk wind models,
developed for application to CVs, needs to yield stronger wind driving out to
larger disk radii than do the present models.Comment: LaTeX, 19 pages, to appear in Ap
The X-ray emission from Nova V382 Velorum: I. The hard component observed with BeppoSAX
We present BeppoSAX observations of Nova Velorum 1999 (V382 Vel), done in a
broad X-ray band covering 0.1-300 keV only 15 days after the discovery and
again after 6 months. The nova was detected at day 15 with the BeppoSAX
instruments in the energy range 1.8-10 keV and we attribute the emission to
shocks in the ejecta. The plasma temperature was kT~6 keV and the unabsorbed
flux was F(x)~4.3 x 10(-11) erg/cm**2/s. The nebular material was affected by
high intrinsic absorption of the ejecta. 6 months after after the outburst, the
intrinsic absorption did not play a role, the nova had turned into a bright
supersoft source, and the hot nebular component previously detected had cooled
to a plasma temperature kT<=1 keV. No emission was detected in either
observation above 20 keV.Comment: 1 tex file, 2 figures as .ps, and 1 .sty file of MNRA
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
Spitzer and ground-based infrared observations of the 2006 eruption of RS Ophiuchi
We present Spitzer Space Telescope and complementary ground-based infrared
observations of the recurrent nova RS Ophiuchi, obtained over the period 64-111
days after the 2006 eruption. The Spitzer IRS data show a rich emission line
spectrum superimposed on a free-free continuum. The presence of fine structure
and coronal infrared lines lead us to deduce that there are at least two
temperatures (1.5e5K and 9e5K) in the ejecta/wind environment, and that the
electron density in the `cooler' region is 2.2e5 cm-3. The determination of
elemental abundances is not straightforward but on the assumption that the Ne
and O fine structure lines arise in the same volume of the ejecta, the O/Ne
ratio is >~0.6 by number.Comment: 13 pages, 4 figures, accepted for publication in ApJ Letter
A 3-mode, Variable Velocity Jet Model for HH 34
Variable ejection velocity jet models can qualitatively explain the
appearance of successive working surfaces in Herbig-Haro (HH) jets. This paper
presents an attempt to explore which features of the HH-34 jet can indeed be
reproduced by such a model. From previously published data on this object, we
find evidence for the existence of a 3-mode ejection velocity variability, and
then explore the implications of such a variability. From simple, analytic
considerations it is possible to show that the longer period modes produce a
modulation on the shorter period modes, resulting in the formation of
``trains'' of multiple knots. The knots observed close to the source of HH-34
could correspond to such a structure. Finally, a numerical simulation with the
ejection velocity variability deduced from the HH-34 data is computed. This
numerical simulation shows a quite remarkable resemblance with the observed
properties of the HH-34 jet.Comment: 28 pages LaTex, 10 postscript figure
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