135 research outputs found
The Survival Rate of Ejected Terrestrial Planets with Moons
During planet formation, a gas giant will interact with smaller protoplanets
that stray within its sphere of gravitational influence. We investigate the
outcome of interactions between gas giants and terrestrial-sized protoplanets
with lunar-sized companions. An interaction between a giant planet and a
protoplanet binary may have one of several consequences, including the delivery
of volatiles to the inner system, the capture of retrograde moons by the giant
planet, and the ejection of one or both of the protoplanets. We show that an
interesting fraction of terrestrial-sized planets with lunar sized companions
will likely be ejected into interstellar space with the companion bound to the
planet. The companion provides an additional source of heating for the planet
from tidal dissipation of orbital and spin angular momentum. This heat flux
typically is larger than the current radiogenic heating of the Earth for up to
the first few hundred million years of evolution. In combination with an
atmosphere of sufficient thickness and composition, the heating can provide the
conditions necesary for liquid water to persist on the surface of the
terrestrial mass planet, making it a potential site for life. We also determine
the possibility for directly detecting such systems through all-sky infrared
surveys or microlensing surveys. Microlensing surveys in particular will
directly measure the frequency of this phenomenon.Comment: 4 pages, 2 figures, Accepted to ApJ
Cool Customers in the Stellar Graveyard IV: Spitzer Search for Mid-IR excesses Around Five DAs
Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs, require
external accretion of material to explain the presence of weak metal line
absorption in their photospheres. The source of this material is currently
unknown, but could come from the interstellar medium, unseen companions, or
relic planetesimals from asteroid belt or Kuiper belt analogues. Accurate
mid-infrared photometry of these white dwarfs provide additional information to
solve the mystery of this accretion and to look for evidence of planetary
systems that have survived post main sequence evolution. We present {\em
Spitzer} IRAC photometry accurate to 3% for four DAZs and one DA with
circumstellar absorption lines in the UV. We search for excesses due to unseen
companions or circumstellar dust disks. We use {\em Hubble Space Telescope}
NICMOS imaging of these white dwarfs to gauge the level of background
contamination to our targets as well as rule out common proper motion
companions to WD 1620-391. All of our targets show no excesses due to
companions 20 M, ruling out all but very low mass companions to these
white dwarfs at all separations. No excesses due to circumstellar disks are
observed, and we place limits on what types of disks may still be present.Comment: 18 pages, 8 figures, Accepted to A
The WIRED Survey. IV. New Dust Disks from the McCook & Sion White Dwarf Catalog
We have compiled photometric data from the Wide-field Infrared Survey
Explorer All Sky Survey and other archival sources for the more than 2200
objects in the original McCook & Sion Catalog of Spectroscopically Identified
White Dwarfs. We applied color-selection criteria to identify 28 targets whose
infrared spectral energy distributions depart from the expectation for the
white dwarf photosphere alone. Seven of these are previously known white dwarfs
with circumstellar dust disks, five are known central stars of planetary
nebulae, and six were excluded for being known binaries or having possible
contamination of their infrared photometry. We fit white dwarf models to the
spectral energy distributions of the remaining ten targets, and find seven new
candidates with infrared excess suggesting the presence of a circumstellar dust
disk. We compare the model dust disk properties for these new candidates with a
comprehensive compilation of previously published parameters for known white
dwarfs with dust disks. It is possible that the current census of white dwarfs
with dust disks that produce an excess detectable at K-band and shorter
wavelengths is close to complete for the entire sample of known WDs to the
detection limits of existing near-IR all-sky surveys. The white dwarf dust disk
candidates now being found using longer wavelength infrared data are drawn from
a previously underrepresented region of parameter space, in which the dust
disks are overall cooler, narrower in radial extent, and/or contain fewer
emitting grains.Comment: accepted for publication in The Astrophysical Journal; 34 pages, 5
figures, 5 tables; added missing reference in Section 2 (p. 7
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
Optical Coronagraphic Spectroscopy of AU Mic: Evidence of Time Variable Colors?
We present coronagraphic long slit spectra of AU Mic's debris disk taken with
the STIS instrument aboard the Hubble Space Telescope (HST). Our spectra are
the first spatially resolved, scattered light spectra of the system's disk,
which we detect at projected distances between approximately 10 and 45 AU. Our
spectra cover a wavelength range between 5200 and 10200 angstroms. We find that
the color of AU Mic's debris disk is bluest at small (12-35 AU) projected
separations. These results both confirm and quantify the findings qualitatively
noted by Krist et al. (2005), and are different than IR observations that
suggested a uniform blue or gray color as a function of projected separation in
this region of the disk. Unlike previous literature that reported the color of
AU Mic's disk became increasingly more blue as a function of projected
separation beyond approximately 30 AU, we find the disk's optical color between
35-45 AU to be uniformly blue on the southeast side of the disk and
decreasingly blue on the northwest side. We note that this apparent change in
disk color at larger projected separations coincides with several fast, outward
moving "features" that are passing through this region of the southeast side of
the disk. We speculate that these phenomenon might be related, and that the
fast moving features could be changing the localized distribution of sub-micron
sized grains as they pass by, thereby reducing the blue color of the disk in
the process. We encourage follow-up optical spectroscopic observations of the
AU Mic to both confirm this result, and search for further modifications of the
disk color caused by additional fast moving features propagating through the
disk.Comment: Accepted by AJ, 13 pages, 8 figures, 1 tabl
Cool Customers in the Stellar Graveyard I: Limits to Extrasolar Planets Around the White Dwarf G29-38
We present high contrast images of the hydrogen white dwarf G 29-38 taken in
the near infrared with the Hubble Space Telescope and the Gemini North
Telescope as part of a high contrast imaging search for substellar objects in
orbit around nearby white dwarfs.
We review the current limits on planetary companions for G29-38, the only
nearby white dwarf with an infrared excess due to a dust disk. We add our
recent observations to these limits to produce extremely tight constraints on
the types of possible companions that could be present. No objects 6
M are detected in our data at projected separations 12 AU, and no
objects 16 M are detected for separations from 3 to 12 AU, assuming
a total system age of 1 Gyr. Limits for companions at separations 3 AU come
from a combination of 2MASS photometry and previous studies of G29-38's
pulsations. Our imaging with Gemini cannot confirm a tentative claim for the
presence of a low mass brown dwarf. These observations demonstrate that a
careful combination of several techniques can probe nearby white dwarfs for
large planets and low mass brown dwarfs.Comment: 20 pages, 4 figures, Accepted to Ap
A SUBTLE INFRARED EXCESS ASSOCIATED WITH A YOUNG WHITE DWARF IN THE EDINBURGH-CAPE BLUE OBJECT SURVEY
We report the discovery of a subtle infrared excess associated with the young white dwarf EC 05365–4749 at 3.35 and 4.6 μ m. Follow-up spectroscopic observations are consistent with a hydrogen atmosphere white dwarf of effective temperature 22,800 K and log [ g (cm s{sup −2})] = 8.19. High-resolution spectroscopy reveals atmospheric metal pollution with logarithmic abundances of [Mg/H] = −5.36 and [Ca/H] = −5.75, confirming the white dwarf is actively accreting from a metal-rich source with an intriguing abundance pattern. We find that the infrared excess is well modeled by a flat, opaque debris disk, though disk parameters are not well constrained by the small number of infrared excess points. We further demonstrate that relaxing the assumption of a circular dusty debris disk to include elliptical disks expands the widths of acceptable disks, adding an alternative interpretation to the subtle infrared excesses commonly observed around young white dwarfs
The HR 4796A Debris System: Discovery of Extensive Exo-Ring Dust Material
The optically and IR bright, and starlight-scattering, HR 4796A ring-like
debris disk is one of the most (and best) studied exoplanetary debris systems.
The presence of a yet-undetected planet has been inferred (or suggested) from
the narrow width and inner/outer truncation radii of its r = 1.05" (77 au)
debris ring. We present new, highly sensitive, Hubble Space Telescope (HST)
visible-light images of the HR 4796A circumstellar debris system and its
environment over a very wide range of stellocentric angles from 0.32" (23 au)
to ~ 15" (1100 au). These very high contrast images were obtained with the
Space Telescope Imaging Spectrograph (STIS) using 6-roll PSF-template
subtracted coronagraphy suppressing the primary light of HR 4796A and using
three image plane occulters and simultaneously subtracting the background light
from its close angular proximity M2.5V companion. The resulting images
unambiguously reveal the debris ring embedded within a much larger,
morphologically complex, and bi-axially asymmetric exoring scattering
structure. These images at visible wavelengths are sensitive to, and map, the
spatial distribution, brightness, and radial surface density of micron size
particles over 5 dex in surface brightness. These particles in the exo-ring
environment may be unbound from the system and interacting with the local ISM.
Herein we present a new morphological and photometric view of the larger than
prior seen HR 4796A exoplanetary debris system with sensitivity to small
particles at stellocentric distances an order of magnitude greater than has
previously been observed.Comment: 28 pages, 17 figures, accepted for publication in the Astronomical
Journal 21 December 201
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