946 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
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
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 heavily polluted atmosphere of the DAZ white dwarf GALEX J193156.8+011745
We report on the discovery of a new heavily polluted white dwarf. The DAZ
white dwarf GALEX J193156.8+011745 was identified in a joint GALEX/GSC survey
of ultraviolet-excess objects. Optical spectra obtained at ESO NTT show strong
absorption lines of magnesium and silicon and a detailed abundance analysis
based on VLT-Kueyen UVES spectra reveal super-solar abundances of silicon and
magnesium, and near-solar abundances of oxygen, calcium, and iron. The overall
abundance pattern bears the signature of ongoing accretion onto the white dwarf
atmosphere. The infrared spectral energy distribution shows an excess in the H
and K bands likely associated with the accretion source.Comment: Accepted for publication in MNRAS Letter
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