702 research outputs found
The Massive Disk Around OH 231.8+4.2
We have obtained 11.7 micron and 17.9 micron images at the Keck I telescope
of the circumstellar dust emission from OH 231.8+4.2, an evolved mass-losing
red giant with a well studied bipolar outflow. We detect both a central
unresolved point source and extended emission which is aligned with the bipolar
outflow seen on larger scales. We find that the unresolved central source can
be explained by an opaque, flared disk with an outer radius near 300 AU and an
outer temperature of about 130 K. One possible model to explain this flaring is
that the material in the disk is orbiting the central star and not simply
undergoing a radial expansion.Comment: ApJ, in pres
Ancient planetary systems are orbiting a large fraction of white dwarf stars
Infrared studies have revealed debris likely related to planet formation in
orbit around ~30% of youthful, intermediate mass, main sequence stars. We
present evidence, based on atmospheric pollution by various elements heavier
than helium, that a comparable fraction of the white dwarf descendants of such
main sequence stars are orbited by planetary systems. These systems have
survived, at least in part, through all stages of stellar evolution that
precede the white dwarf. During the time interval (~200 million years) that a
typical polluted white dwarf in our sample has been cooling it has accreted
from its planetary system the mass of one of the largest asteroids in our solar
system (e.g., Vesta or Ceres). Usually, this accreted mass will be only a
fraction of the total mass of rocky material that orbits these white dwarfs;
for plausible planetary system configurations we estimate that this total mass
is likely to be at least equal to that of the Sun's asteroid belt, and perhaps
much larger. We report abundances of a suite of 8 elements detected in the
little studied star G241-6 that we find to be among the most heavily polluted
of all moderately bright white dwarfs.Comment: 31 pages, 4 figures, 5 tables. Accepted for the Astrophysical
Detailed compositional analysis of the heavily polluted DBZ white dwarf SDSS J073842.56+183509.06: A window on planet formation?
We present a new model atmosphere analysis of the most metal contaminated
white dwarf known, the DBZ SDSS J073842.56+183509.06. Using new high resolution
spectroscopic observations taken with Keck and Magellan, we determine precise
atmospheric parameters and measure abundances of 14 elements heavier than
helium. We also report new Spitzer mid-infrared photometric data that are used
to better constrain the properties of the debris disk orbiting this star. Our
detailed analysis, which combines data taken from 7 different observational
facilities (GALEX, Gemini, Keck, Magellan, MMT, SDSS and Spitzer) clearly
demonstrate that J0738+1835 is accreting large amounts of rocky
terrestrial-like material that has been tidally disrupted into a debris disk.
We estimate that the body responsible for the photospheric metal contamination
was at least as large Ceres, but was much drier, with less than 1% of the mass
contained in the form of water ice, indicating that it formed interior to the
snow line around its parent star. We also find a correlation between the
abundances (relative to Mg and bulk Earth) and the condensation temperature;
refractory species are clearly depleted while the more volatile elements are
possibly enhanced. This could be the signature of a body that formed in a lower
temperature environment than where Earth formed. Alternatively, we could be
witnessing the remains of a differentiated body that lost a large part of its
outer layers.Comment: 16 pages, 17 figures, accepted for publication in The Astrophysical
Journa
Echoes of a decaying planetary system: the gaseous and dusty disks surrounding three white dwarfs
We have performed a comprehensive ground-based observational program aimed at
characterizing the circumstellar material orbiting three single white dwarf
stars previously known to possess gaseous disks. Near-infrared imaging
unambiguously detects excess infrared emission towards Ton 345 and allows us to
refine models for the circumstellar dust around all three white dwarf stars. We
find that each white dwarf hosts gaseous and dusty disks that are roughly
spatially coincident, a result that is consistent with a scenario in which
dusty and gaseous material has its origin in remnant parent bodies of the white
dwarfs' planetary systems. We briefly describe a new model for the gas disk
heating mechanism in which the gaseous material behaves like a "Z II" region.
In this Z II region, gas primarily composed of metals is photoionized by
ultraviolet light and cools through optically thick allowed Ca II-line
emission.Comment: 43 pages, 9 tables, 9 figures. Accepted to Ap
Near-Infrared Variability in the 2MASS Calibration Fields: A Search for Planetary Transit Candidates
The 2MASS photometric calibration observations cover ~6 square degrees on the
sky in 35 "calibration fields" each sampled in nominal photometric conditions
between 562 and 3692 times during the four years of the 2MASS mission. We
compile a catalog of variables from the calibration observations to search for
M dwarfs transited by extra-solar planets. We present our methods for measuring
periodic and non-periodic flux variability. From 7554 sources with apparent Ks
magnitudes between 5.6 and 16.1, we identify 247 variables, including
extragalactic variables and 23 periodic variables. We have discovered three M
dwarf eclipsing systems, including two candidates for transiting extrasolar
planets.Comment: The Astrophysical Journal Supplement, in press; figures compresse
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