13 research outputs found
Pumping of a Planetesimal Disc by a Rapidly Migrating Planet
We examine the effect of a rapidly migrating protoplanet on a ring of
planetesimals. The eccentricities of the planetesimals are usually increased by
, with the exact increase being proportional to the
protoplanet's mass, and inversely proportional to its migration rate. The
eccentricity distribution is also substantially changed from a Rayleigh
distribution. We discuss the possible implications for further planet
formation, and suggest that the rapid passage of a protoplanet may not prevent
the planetesimal disc from forming further planets.Comment: Five pages, two figures, accepted by MNRA
Dust Migration and Morphology in Optically Thin Circumstellar Gas Disks
We analyze the dynamics of gas-dust coupling in the presence of stellar
radiation pressure in circumstellar gas disks, which are in a transitional
stage between the gas-dominated, optically thick, primordial nebulae, and the
dust-dominated, optically thin Vega-type disks. Dust undergo radial migration,
seeking a stable equilibrium orbit in corotation with gas. The migration of
dust gives rise to radial fractionation of dust and creates a variety of
possible observed disk morphologies, which we compute by considering the
equilibrium between the dust production and the dust-dust collisions removing
particles from their equilibrium orbits. Sand-sized and larger grains are
distributed throughout most of the gas disk, with concentration near the gas
pressure maximum in the inner disk. Smaller grains (typically in the range of
10 to 200 micron) concentrate in a prominent ring structure in the outer region
of the gas disk (presumably at radius 100 AU), where gas density is rapidly
declining with radius. The width and density, as well as density contrast of
the dust ring with respect to the inner dust disk depend on the distribution of
gas. Our results open the prospect for deducing the distribution of gas in
circumstellar disks by observing their dust. We have qualitatively compared our
models with two observed transitional disks around HR 4796A and HD 141569A.
Dust migration can result in observation of a ring or a bimodal radial dust
distribution, possibly very similar to the ones produced by gap-opening
planet(s) embedded in the disk, or shepherding it from inside or outside. We
conclude that a convincing planet detection via dust imaging should include
specific non-axisymmetric structure following from the dynamical simulations of
perturbed disks.Comment: 27 pages, 16 figures, submitted to Ap
Discovery of a New Companion and Evidence of a Circumprimary Disk: Adaptive Optics Imaging of the Young Multiple System VW Cha
Since a majority of young low-mass stars are members of multiple systems, the
study of their stellar and disk configurations is crucial to our understanding
of both star and planet formation processes. Here we present near-infrared
adaptive optics observations of the young multiple star system VW Cha. The
previously known 0.7 arcsec binary is clearly resolved already in our raw J and
K band images. We report the discovery of a new, faint companion to the
secondary, at an apparent separation of only 0.1 arcsec or 16 AU. Our
high-resolution photometric observations also make it possible to measure the
J-K colors of each of the three components individually. We detect an infrared
excess in the primary, consistent with theoretical models of a circumprimary
disk. Analytical and numerical calculations of orbital stability show that VW
Cha may be a stable triple system. Using models for the age and total mass of
the secondary pair, we estimate the orbital period to be 74 years. Thus,
follow-up astrometric observations might yield direct dynamical masses within a
few years, and constrain evolutionary models of low-mass stars. Our results
demonstrate that adaptive optics imaging in conjunction with deconvolution
techniques is a powerful tool for probing close multiple systems.Comment: 13 pages including 2 figures. To appear in Astrophysical Journal
Letter
The Gemini NICI Planet-Finding Campaign
Our team is carrying out a multi-year observing program to directly image and
characterize young extrasolar planets using the Near-Infrared Coronagraphic
Imager (NICI) on the Gemini-South 8.1-meter telescope. NICI is the first
instrument on a large telescope designed from the outset for high-contrast
imaging, comprising a high-performance curvature adaptive optics system with a
simultaneous dual-channel coronagraphic imager. Combined with state-of-the-art
observing methods and data processing, NICI typically achieves ~2 magnitudes
better contrast compared to previous ground-based or space-based programs, at
separations inside of ~2 arcsec. In preparation for the Campaign, we carried
out efforts to identify previously unrecognized young stars, to rigorously
construct our observing strategy, and to optimize the combination of angular
and spectral differential imaging. The Planet-Finding Campaign is in its second
year, with first-epoch imaging of 174 stars already obtained out of a total
sample of 300 stars. We describe the Campaign's goals, design, implementation,
performance, and preliminary results. The NICI Campaign represents the largest
and most sensitive imaging survey to date for massive (~1 Mjup) planets around
other stars. Upon completion, the Campaign will establish the best measurements
to date on the properties of young gas-giant planets at ~5-10 AU separations.
Finally, Campaign discoveries will be well-suited to long-term orbital
monitoring and detailed spectrophotometric followup with next-generation
planet-finding instruments.Comment: Proceedings of the SPIE, vol 7736 (Advances in Adaptive Optics, San
Diego, CA, June 2010 meeting), in pres
Populations of planets in multiple star systems
Astronomers have discovered that both planets and binaries are abundant
throughout the Galaxy. In combination, we know of over 100 planets in binary
and higher-order multi-star systems, in both circumbinary and circumstellar
configurations. In this chapter we review these findings and some of their
implications for the formation of both stars and planets. Most of the planets
found have been circumstellar, where there is seemingly a ruinous influence of
the second star if sufficiently close (<50 AU). Hosts of hot Jupiters have been
a particularly popular target for binary star studies, showing an enhanced rate
of stellar multiplicity for moderately wide binaries (>100 AU). This was
thought to be a sign of Kozai-Lidov migration, however recent studies have
shown this mechanism to be too inefficient to account for the majority of hot
Jupiters. A couple of dozen circumbinary planets have been proposed around both
main sequence and evolved binaries. Around main sequence binaries there are
preliminary indications that the frequency of gas giants is as high as those
around single stars. There is however a conspicuous absence of circumbinary
planets around the tightest main sequence binaries with periods of just a few
days, suggesting a unique, more disruptive formation history of such close
stellar pairs.Comment: Invited review chapter, accepted for publication in "Handbook of
Exoplanets", ed. H. Deeg & J. A. Belmont
On the Formation of Eccentric Superplanets
. Among several emerging classes of the extrasolar planets there is a puzzling class of three `planets' on highly eccentric orbits around: 70 Vir, HD114762, and 16 cyg B. At least the first two of them appear to have been born this way. They have significantly super-Jovian minimum masses close to 10 Jupiter masses, and can thus be called "superplanets". They may represent either planets or brown dwarfs. I briefly discuss some recent theories of the origin of such bodies, grouped in the following categories: (A) direct molecular cloud fragmentation, (B) protostellar disk fragmentation theories, (C) companion star-planet interaction (if the host star is double, like 16 Cyg AB), (D) classical giant planet formation followed by planet-planet interaction, and (E) resonant disk-planet interaction, predicting low orbital eccentricity for planets and high eccentricities for superplanets and stars. Theories (C)--(E) seem to best explain the bulk of observations to date. 1. The diversity of pla..