90 research outputs found
From mean-motion resonances to scattered planets: Producing the Solar System, eccentric exoplanets and Late Heavy Bombardments
We show that interaction with a gas disk may produce young planetary systems
with closely-spaced orbits, stabilized by mean-motion resonances between
neighbors. On longer timescales, after the gas is gone, interaction with a
remnant planetesimal disk tends to pull these configurations apart, eventually
inducing dynamical instability. We show that this can lead to a variety of
outcomes; some cases resemble the Solar System, while others end up with
high-eccentricity orbits reminiscent of the observed exoplanets. A similar
mechanism has been previously suggested as the cause of the lunar Late Heavy
Bombardment. Thus, it may be that a large-scale dynamical instability, with
more or less cataclysmic results, is an evolutionary step common to many
planetary systems, including our own.Comment: 12 pages, 7 figures, submitted to Ap
A New Offset Debris Ring around a Nearby Star Observed with the HST/STIS
We are conducting an HST/STIS coronagraphic imaging study of nearby stars that have Spitzer-measured infrared excesses indicating that they are surrounded by debris disks. Around one of the stars we have imaged a debris ring with a sharp inner edge and extending from about 165 AU to 250 AU. The ring center is offset from the star by -8 AU with a visually estimated intrinsic ellipticity of e-0.1 , suggestive of gravitational perturbation of the disk by a planet, like the Fomalhaut disk. Assuming a neutral disk color, the mean surface brightness of V=22.3 mag/square arcsec makes this the second faintest disk yet imaged in scattered light, second to HD 207129
Herschel/PACS photometry of transiting-planet host stars with candidate warm debris disks
Dust in debris disks is produced by colliding or evaporating planetesimals,
remnants of the planet formation process. Warm dust disks, known by their
emission at < 24 micron, are rare (4% of FGK main sequence stars) and
especially interesting because they trace material in the region likely to host
terrestrial planets, where the dust has a very short dynamical lifetime.
Statistical analyses of the source counts of excesses as found with the mid-IR
Wide Field Infrared Survey Explorer (WISE) suggest that warm-dust candidates
found for the Kepler transiting-planet host-star candidates can be explained by
extragalactic or galactic background emission aligned by chance with the target
stars. These statistical analyses do not exclude the possibility that a given
WISE excess could be due to a transient dust population associated with the
target. Here we report Herschel/PACS 100 and 160 micron follow-up observations
of a sample of Kepler and non-Kepler transiting-planet candidates' host stars,
with candidate WISE warm debris disks, aimed at detecting a possible cold
debris disk in any of them. No clear detections were found in any one of the
objects at either wavelength. Our upper limits confirm that most objects in the
sample do not have a massive debris disk like that in beta Pic. We also show
that the planet-hosting star WASP-33 does not have a debris disk comparable to
the one around eta Crv. Although the data cannot be used to rule out rare warm
disks around the Kepler planet-hosting candidates, the lack of detections and
the characteristics of neighboring emission found at far-IR wavelengths support
an earlier result suggesting that most of the WISE-selected IR excesses around
Kepler candidate host stars are likely due to either chance alignment with
background IR-bright galaxies and/or to interstellar emission.Comment: 8 pages, 3 figures, accepted for publication at Astronomy &
Astrophysics on 4 August 201
Hubble Space Telescope Observations of the HD 202628 Debris Disk
A ring-shaped debris disk around the G2V star HD 202628 (d = 24.4 pc) was imaged in scattered light at visible wavelengths using the coronagraphic mode of the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. The ring is inclined by approx.64deg from face-on, based on the apparent major/minor axis ratio, with the major axis aligned along PA = 130deg. It has inner and outer radii (> 50% maximum surface brightness) of 139 AU and 193 AU in the northwest ansae and 161 AU and 223 AU in the southeast ((Delta)r/r approx. = 0.4). The maximum visible radial extent is approx. 254 AU. With a mean surface brightnesses of V approx. = 24 mag arcsec.(sup -2), this is the faintest debris disk observed to date in reflected light. The center of the ring appears offset from the star by approx.28 AU (deprojected). An ellipse fit to the inner edge has an eccentricity of 0.18 and a = 158 AU. This offset, along with the relatively sharp inner edge of the ring, suggests the influence of a planetary-mass companion. There is a strong similarity with the debris ring around Fomalhaut, though HD 202628 is a more mature star with an estimated age of about 2 Gyr. We also provide surface brightness limits for nine other stars in our study with strong Spitzer excesses around which no debris disks were detected in scattered light (HD 377, HD 7590, HD 38858, HD 45184, HD 73350, HD 135599, HD 145229, HD 187897, and HD 201219)
SKARPS: The Search for Kuiper Belts around Radial-Velocity Planet Stars
The Search for Kuiper belts Around Radial-velocity Planet Stars - SKARPS -is a Herschel survey of solar-type stars known to have orbiting planets. When complete, the 100-star SKARPS sample will be large enough for a meaningful statistical comparison against stars not known to have planets. (This control sample has already been observed by Herschel's DUst around NEarby Stars - DUNES - key program). Initial results include previously known disks that are resolved for the first time and newly discovered disks that are fainter and colder than those typically detected by Spitzer. So far, with only half of the sample in hand, there is no measured correlation between inner RV planets and cold outer debris. While this is consistent with the results from Spitzer, it is in contrast with the relationship suggested by the prominent debris disks in imaged-planet systems
Disk Radii and Grain Sizes in Herschel-Resolved Debris Disks
(Abridged) The radii of debris disks and the sizes of their dust grains are
tracers of the formation mechanisms and physical processes operating in these
systems. We use a sample of 34 debris disks spatially resolved in various
Herschel programs to constrain them. While we modeled disks with both warm and
cold components, we focus our analysis only on the cold outer disks, i.e.
Kuiper-belt analogs. The disk radii derived from the resolved images reveal a
large dispersion, but no significant trend with the stellar luminosity, which
argues against ice lines as a dominant player in setting the debris disk sizes.
Fixing the disk radii to those inferred from the resolved images, we model the
spectral energy distributions to determine the dust temperatures and the grain
size distributions. While the dust temperature systematically increases towards
earlier spectral types, its ratio to the blackbody temperature at the disk
radius decreases with the stellar luminosity. This is explained by an increase
of typical grain sizes towards more luminous stars. The sizes are compared to
the radiation pressure blowout limit that is proportional to
the stellar luminosity-to-mass ratio and thus also increases towards earlier
spectral classes. The grain sizes in the disks of G- to A-stars are inferred to
be several times at all stellar luminosities, in agreement with
collisional models of debris disks. The sizes, measured in the units of
, appear to decrease with the luminosity, which may be
suggestive of the disk's stirring level increasing towards earlier-type stars.Comment: accepted for publication in ApJ, 22 pages, 7 figure
A Spitzer IRS Study of Debris Disks Around Planet-Host Stars
Since giant planets scatter planetesimals within a few tidal radii of their
orbits, the locations of existing planetesimal belts indicate regions where
giant planet formation failed in bygone protostellar disks. Infrared
observations of circumstellar dust produced by colliding planetesimals are
therefore powerful probes of the formation histories of known planets. Here we
present new Spitzer IRS spectrophotometry of 111 Solar-type stars, including
105 planet hosts. Our observations reveal 11 debris disks, including two
previously undetected debris disks orbiting HD 108874 and HD 130322. Combining
our 32 micron spectrophotometry with previously published MIPS photometry, we
find that the majority of debris disks around planet hosts have temperatures in
the range 60 < T < 100 K. Assuming a dust temperature T = 70 K, which is
representative of the nine debris disks detected by both IRS and MIPS, we find
that debris rings surrounding Sunlike stars orbit between 15 and 240 AU,
depending on the mean particle size. Our observations imply that the planets
detected by radial-velocity searches formed within 240 AU of their parent
stars. If any of the debris disks studied here have mostly large, blackbody
emitting grains, their companion giant planets must have formed in a narrow
region between the ice line and 15 AU.Comment: Accepted for publication in the Astronomical Journal. 14 pages,
including five figures and two table
Locating Planetesimal Belts in the Multiple-planet Systems HD 128311, HD 202206, HD 82943, and HR 8799
In addition to the Sun, six other stars are known to harbor multiple planets and debris disks: HD 69830, HD 38529, HD 128311, HD 202206, HD 82943, and HR 8799. In this paper, we set constraints on the location of the dust-producing planetesimals around the latter four systems. We use a radiative transfer model to analyze the spectral energy distributions of the dust disks (including two new Spitzer IRS spectra presented in this paper), and a dynamical model to assess the long-term stability of the planetesimals' orbits. As members of a small group of stars that show evidence of harboring a multiple planets and planetesimals, their study can help us learn about the diversity of planetary systems
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