10,347 research outputs found
Resolving the terrestrial planet forming regions of HD113766 and HD172555 with MIDI
We present new MIDI interferometric and VISIR spectroscopic observations of
HD113766 and HD172555. Additionally we present VISIR 11um and 18um imaging
observations of HD113766. These sources represent the youngest (16Myr and 12Myr
old respectively) debris disc hosts with emission on <<10AU scales. We find
that the disc of HD113766 is partially resolved on baselines of 42-102m, with
variations in resolution with baseline length consistent with a Gaussian model
for the disc with FWHM of 1.2-1.6AU (9-12mas). This is consistent with the
VISIR observations which place an upper limit of 0."14 (17AU) on the emission,
with no evidence for extended emission at larger distances. For HD172555 the
MIDI observations are consistent with complete resolution of the disc emission
on all baselines of lengths 56-93m, putting the dust at a distance of >1AU
(>35mas). When combined with limits from TReCS imaging the dust at ~10um is
constrained to lie somewhere in the region 1-8AU. Observations at ~18um reveal
extended disc emission which could originate from the outer edge of a broad
disc, the inner parts of which are also detected but not resolved at 10um, or
from a spatially distinct component. These observations provide the most
accurate direct measurements of the location of dust at 1-8AU that might
originate from the collisions expected during terrestrial planet formation.
These observations provide valuable constraints for models of the composition
of discs at this epoch and provide a foundation for future studies to examine
in more detail the morphology of debris discs.Comment: 22 pages, 19 figures, accepted for publication in MNRA
Predicting the frequencies of diverse exo-planetary systems
Extrasolar planetary systems range from hot Jupiters out to icy comet belts
more distant than Pluto. We explain this diversity in a model where the mass of
solids in the primordial circumstellar disk dictates the outcome. The star
retains measures of the initial heavy-element (metal) abundance that can be
used to map solid masses onto outcomes, and the frequencies of all classes are
correctly predicted. The differing dependences on metallicity for forming
massive planets and low-mass cometary bodies are also explained. By
extrapolation, around two-thirds of stars have enough solids to form Earth-like
planets, and a high rate is supported by the first detections of low-mass
exo-planets.Comment: 5 pages, 2 figures; accepted by MNRA
Steady-state evolution of debris disks around A stars
In this paper a simple analytical model for the steady-state evolution of
debris disks due to collisions is confronted with Spitzer observations of main
sequence A stars. All stars are assumed to have planetesimal belts with a
distribution of initial masses and radii. In the model disk mass is constant
until the largest planetesimals reach collisional equilibrium whereupon the
mass falls off oc 1/t. We find that the detection statistics and trends seen at
both 24 and 70um can be fitted well by the model. While there is no need to
invoke stochastic evolution or delayed stirring to explain the statistics, a
moderate rate of stochastic events is not ruled out. Potentially anomalous
systems are identified by a high dust luminosity compared with the maximum
permissible in the model (HD3003, HD38678, HD115892, HD172555). Their
planetesimals may have unusual properties (high strength or low eccentricity)
or this dust could be transient. While transient phenomena are also favored for
a few systems in the literature, the overall success of our model, which
assumes planetesimals in all belts have the same strength, eccentricity and
maximum size, suggests a large degree of uniformity in the outcome of planet
formation. The distribution of planetesimal belt radii, once corrected for
detection bias, follows N(r) oc r^{-0.8+-0.3} for 3-120AU. Since the inner edge
is often attributed to an unseen planet, this provides a unique constraint on
the planetary systems of A stars. It is also shown that P-R drag may sculpt the
inner edges of A star disks close to the Spitzer detection threshold (HD2262,
HD19356, HD106591, HD115892). This model can be readily applied to the
interpretation of future surveys, and predictions are made for the upcoming
SCUBA-2 survey, including that >17% of A stars should be detectable at 850um.Comment: Accepted by Ap
Multi-Epoch Observations of HD69830: High Resolution Spectroscopy and Limits to Variability
The main-sequence solar-type star HD69830 has an unusually large amount of
dusty debris orbiting close to three planets found via the radial velocity
technique. In order to explore the dynamical interaction between the dust and
planets, we have performed multi-epoch photometry and spectroscopy of the
system over several orbits of the outer dust. We find no evidence for changes
in either the dust amount or its composition, with upper limits of 5-7% (1
per spectral element) on the variability of the {\it dust spectrum}
over 1 year, 3.3% (1 ) on the broad-band disk emission over 4 years,
and 33% (1 ) on the broad-band disk emission over 24 years. Detailed
modeling of the spectrum of the emitting dust indicates that the dust is
located outside of the orbits of the three planets and has a composition
similar to main-belt, C-type asteroids asteroids in our solar system.
Additionally, we find no evidence for a wide variety of gas species associated
with the dust. Our new higher SNR spectra do not confirm our previously claimed
detection of HO ice leading to a firm conclusion that the debris can be
associated with the break-up of one or more C-type asteroids formed in the dry,
inner regions of the protoplanetary disk of the HD69830 system. The modeling of
the spectral energy distribution and high spatial resolution observations in
the mid-infrared are consistent with a 1 AU location for the emitting
material
Herschel Observations of Debris Discs Orbiting Planet-hosting Subgiants
Debris discs are commonly detected orbiting main-sequence stars, yet little
is known regarding their fate as the star evolves to become a giant. Recent
observations of radial velocity detected planets orbiting giant stars highlight
this population and its importance for probing, for example, the population of
planetary systems orbiting intermediate mass stars. Our Herschel survey
observed a subset of the Johnson et al program subgiants, finding that 4/36
exhibit excess emission thought to indicate debris, of which 3/19 are
planet-hosting stars and 1/17 are stars with no current planet detections.
Given the small numbers involved, there is no evidence that the disc detection
rate around stars with planets is different to that around stars without
planets. Our detections provide a clear indication that large quantities of
dusty material can survive the stars' main-sequence lifetime and be detected on
the subgiant branch, with important implications for the evolution of planetary
systems and observations of polluted or dusty white dwarfs. Our detection rates
also provide an important constraint that can be included in models of debris
disc evolution.Comment: 12 pages, MNRAS, accepte
Transience of hot dust around sun-like stars
There is currently debate over whether the dust content of planetary systems
is stochastically regenerated or originates in planetesimal belts evolving in
steady state. In this paper a simple model for the steady state evolution of
debris disks due to collisions is developed and confronted with the properties
of the emerging population of 7 sun-like stars that have hot dust <10AU. The
model shows there is a maximum possible disk mass at a given age, since more
massive primordial disks process their mass faster. The corresponding maximum
dust luminosity is f_max=0.00016r^(7/3)/t_age. The majority (4/7) of the hot
disks exceed this limit by >1000 and so cannot be the products of massive
asteroid belts, rather the following systems must be undergoing transient
events characterized by an unusually high dust content near the star: eta
Corvi, HD69830, HD72905 and BD+20307. It is also shown that the hot dust cannot
originate in a recent collision in an asteroid belt, since there is also a
maximum rate at which collisions of sufficient magnitude to reproduce a given
dust luminosity can occur. Further it is shown that the planetesimal belt
feeding the dust in these systems must be located further from the star than
the dust, typically at >2AU. Other notable properties of the 4 hot dust systems
are: two also have a planetesimal belt at >10AU (eta Corvi and HD72905); one
has 3 Neptune mass planets at <1AU (HD69830); all exhibit strong silicate
features in the mid-IR. We consider the most likely origin for the dust in
these systems to be a dynamical instability which scattered planetesimals
inwards from a more distant planetesimal belt in an event akin to the Late
Heavy Bombardment in our own system, the dust being released from such
planetesimals in collisions and possibly also sublimation.Comment: 16 pages, accepted by ApJ, removed HD128400 as hot dust candidat
Search for long lived charged massive particles in pp collisions at s-hat = 1.8TeV
We report a search for the production of long-lived charged massive particles in a data sample of 90 pb-1 of √s=1.8 TeV pp̅ collisions recorded by the Collider Detector at Fermilab. The search uses the muonlike penetration and anomalously high ionization energy loss signature expected for such a particle to discriminate it from backgrounds. The data are found to agree with background expectations, and cross section limits of O(1) pb are derived using two reference models, a stable quark and a stable scalar lepton
ALMA and Herschel Observations of the Prototype Dusty and Polluted White Dwarf G29-38
ALMA Cycle 0 and Herschel PACS observations are reported for the prototype,
nearest, and brightest example of a dusty and polluted white dwarf, G29-38.
These long wavelength programs attempted to detect an outlying, parent
population of bodies at 1-100 AU, from which originates the disrupted
planetesimal debris that is observed within 0.01 AU and which exhibits L_IR/L =
0.039. No associated emission sources were detected in any of the data down to
L_IR/L ~ 1e-4, generally ruling out cold dust masses greater than 1e24 - 1e25 g
for reasonable grain sizes and properties in orbital regions corresponding to
evolved versions of both asteroid and Kuiper belt analogs. Overall, these null
detections are consistent with models of long-term collisional evolution in
planetesimal disks, and the source regions for the disrupted parent bodies at
stars like G29-38 may only be salient in exceptional circumstances, such as a
recent instability. A larger sample of polluted white dwarfs, targeted with the
full ALMA array, has the potential to unambiguously identify the parent
source(s) of their planetary debris.Comment: 8 pages, 5 figures and 1 table. Accepted to MNRA
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