957 research outputs found
Near-Infrared Constraints on the Presence of Warm Dust at Metal-Rich, Helium Atmosphere White Dwarfs
Here, we present near-infrared spectroscopic observations of 15 helium
atmosphere, metal-rich white dwarfs obtained at the NASA Infrared Telescope
Facility. While a connection has been demonstrated between the most highly
polluted, hydrogen atmosphere white dwarfs and the presence of warm
circumstellar dust and gas, their frequency at the helium atmosphere variety is
poorly constrained. None of our targets show excess near-infrared radiation
consistent with warm orbiting material. Adding these near-infrared constraints
to previous near- and mid-infrared observations, the frequency of warm
circumstellar material at metal-bearing white dwarfs is at least 20% for
hydrogen-dominated photospheres, but could be less than 5% for those
effectively composed of helium alone. The lower occurrence of dust disks around
helium atmosphere white dwarfs is consistent with Myr timescales for
photospheric metals in massive convection zones. Analyzing the mass
distribution of 10 white dwarfs with warm circumstellar material, we search for
similar trends between the frequency of disks and the predicted frequency of
massive planets around intermediate mass stars, but find the probability that
disk-bearing white dwarfs are more massive than average is not significant.Comment: AJ, in pres
Color Gradients Detected in the HD 15115 Circumstellar Disk
We report HST/NICMOS coronagraphic images of the HD 15115 circumstellar disk
at 1.1\micron. We find a similar morphology to that seen in the visible and at
H band--an edge-on disk that is asymmetric in surface brightness. Several
aspects of the 1.1\micron data are different, highlighting the need for
multi-wavelength images of each circumstellar disk. We find a flattening to the
western surface brightness profile at 1.1\micron interior to 2\arcsec (90 AU)
and a warp in the western half of the disk. We measure the surface brightness
profiles of the two disk lobes and create a measure of the dust scattering
efficiency between 0.55-1.65\micron at 1\arcsec, 2\arcsec, and 3\arcsec. At
2\arcsec the western lobe has a neutral spectrum up to 1.1\micron and a strong
absorption or blue spectrum 1.1\micron, while a blue trend is seen in the
eastern lobe. At 1\arcsec the disk has a red F110W-H color in both lobes.Comment: 4 pages, 4 figures, emulateapj; accepted to ApJ
The WISE InfraRed Excesses around Degenerates (WIRED) Survey
The Wide-field Infrared Survey Explorer (WISE) is a NASA medium class Explorer
mission that performed an all sky survey in four infrared bands. We present an overview of the WISE
InfraRed Excesses around Degenerates (WIRED) Survey, which has the goals of characterizing
white dwarf stars in the WISE bands, confirming objects known to have infrared excess from past
observations, and revealing new examples of white dwarfs with infrared excess that can be attributed
to unresolved companions or debris disks. We obtained preliminary WISE detections (S/N > 2) in
at least one band of 405 white dwarfs from the 9316 unique possible targets in the Sloan Digital
Sky Survey Data Release 4 Catalog of Spectroscopically Identified White Dwarfs (not all potential
targets were available in the sky coverage used here). A companion paper in this volume discusses
specific results from our target detections
Detection of Weak Circumstellar Gas around the DAZ White Dwarf WD 1124-293: Evidence for the Accretion of Multiple Asteroids
Single metal polluted white dwarfs with no dusty disks are believed to be
actively accreting metals from a circumstellar disk of gas caused by the
destruction of asteroids perturbed by planetary systems. We report, for the
first time, the detection of circumstellar Ca~II gas in absorption around the
DAZ WD~1124-293, which lacks an infrared excess. We constrain the gas to 7
and 32000~AU, and estimate it to be at 54~R,
well within WD~1124-293's tidal disruption radius. This detection is based on
several epochs of spectroscopy around the Ca~II H and K lines
(=3968\AA, 3933\AA) with the MIKE spectrograph on the Magellan/Clay
Telescope at Las Campanas Observatory. We confirm the circumstellar nature of
the gas by observing nearby sightlines and finding no evidence for gas from the
local interstellar medium. Through archival data we have measured the
equivalent width of the two photospheric Ca lines over a period of 11 years. We
see 5-7\% epoch-to-epoch variation in equivalent widths over this time
period, and no evidence for long term trends. The presence of a circumstellar
gas implies a near edge-on inclination to the system, thus we place limits to
short period transiting planetary companions with R R using
the WASP survey. The presence of gas in orbit around WD~1124-293 implies that
most DAZs could harbor planetary systems. Since 25-30\% of white dwarfs show
metal line absorption, the dynamical process for perturbing small bodies must
be robust.Comment: 31 pages with 9 figures; accepted to Ap
The Link Between Planetary Systems, Dusty White Dwarfs, and Metal Polluted White Dwarfs
It has long been suspected that metal polluted white dwarfs (types DAZ, DBZ,
and DZ) and white dwarfs with dusty disks possess planetary systems, but a
specific physical mechanism by which planetesimals are perturbed close to a
white dwarf has not yet been fully posited. In this paper we demonstrate that
mass loss from a central star during post main sequence evolution can sweep
planetesimals into interior mean motion resonances with a single giant planet.
These planetesimals are slowly removed through chaotic excursions of
eccentricity that in time create radial orbits capable of tidally disrupting
the planetesimal. Numerical N-body simulations of the Solar System show that a
sufficient number of planetesimals are perturbed to explain white dwarfs with
both dust and metal pollution, provided other white dwarfs have more massive
relic asteroid belts. Our scenario requires only one Jupiter-sized planet and a
sufficient number of asteroids near its 2:1 interior mean motion resonance.
Finally, we show that once a planetesimal is perturbed into a tidal crossing
orbit, it will become disrupted after the first pass of the white dwarf, where
a highly eccentric stream of debris forms the main reservoir for dust producing
collisions. These simulations, in concert with observations of white dwarfs,
place interesting limits on the frequency of planetary systems around main
sequence stars, the frequency of planetesimal belts, and the probability that
dust may obscure future terrestrial planet finding missions.Comment: 26 pages, 8 figures, accepted to Ap
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