604 research outputs found
Gifts from Exoplanetary Transits
The discovery of transiting extrasolar planets has enabled us a number of
interesting stduies. Transit photometry reveals the radius and the orbital
inclination of transiting planets, and thereby we can learn the true mass and
the density of respective planets by the combined information of radial
velocity measurements. In addition, follow-up observations of transiting
planets such as secondary eclipse, transit timing variations, transmission
spectroscopy, and the Rossiter-McLaughlin effect provide us information of
their dayside temperature, unseen bodies in systems, planetary atmospheres, and
obliquity of planetary orbits. Such observational information, which will
provide us a greater understanding of extrasolar planets, is available only for
transiting planets. Here I briefly summarize what we can learn from transiting
planets and introduce previous studies.Comment: 6 pages, 2 figures, Proceedings of the 2nd Subaru International
Conference "Exoplanets and Disks: Their Formation and Diversity" Keauhou -
Hawaii - USA, 9-12 March 200
First Evidence of a Retrograde Orbit of Transiting Exoplanet HAT-P-7b
We present the first evidence of a retrograde orbit of the transiting
exoplanet HAT-P-7b. The discovery is based on a measurement of the
Rossiter-McLaughlin effect with the Subaru HDS during a transit of HAT-P-7b,
which occurred on UT 2008 May 30. Our best-fit model shows that the spin-orbit
alignment angle of this planet is \lambda = -132.6 (+10.5, -16.3) degrees. The
existence of such a retrograde planet have been predicted by recent planetary
migration models considering planet-planet scattering processes or the Kozai
migration. Our finding provides an important milestone that supports such
dynamic migration theories.Comment: PASJ Letters, in press [13 pages
Luminosity functions of YSO clusters in Sh-2 255, W3 main and NGC 7538 star forming regions
We have conducted deep near-infrared surveys of the Sh-2 255, W3 Main and NGC 7538 massive star forming regions using simultaneous observations of the J H Ks-band with the near-infrared camera SIRIUS on the UH 88-inch telescope. The near-infrared surveys cover a total area of ∼ 72 square
arcmin of three regions with 10-σ limiting magnitudes of ∼ 19.5, 18.4 and 17.3 in J, H and Ks-band, respectively. Based on the colour-colour and colourmagnitude diagrams and their clustering properties, the candidate young stellar objects are identified and their luminosity functions are constructed in Sh-2 255, W3 Main and NGC 7538. A large number of previously unreported red sources (H − K > 2) have also been detected around these regions. We argue that these red stars are most probably pre-main sequence stars with intrinsic colour excesses. The detected young stellar objects show a clear clustering pattern in each region: the Class I-like sources are mostly clustered in molecular cloud region, while the Class II-like sources in or around more evolved optical H II regions. We find that the slopes of the Ks-band luminosity functions of Sh-2 255, W3 Main and NGC 7538 are lower than the typical values reported for the young embedded clusters and their stellar populations are primarily composed of low mass pre-main sequence stars. From the slopes of the Ks-band luminosity functions, we infer that Sh-2 255, W3 Main and NGC 7538 star forming regions are rather young (age ≤ 1 Myr)
Initial Conditions of Planet Formation: Lifetimes of Primordial Disks
The statistical properties of circumstellar disks around young stars are
important for constraining theoretical models for the formation and early
evolution of planetary systems. In this brief review, I survey the literature
related to ground-based and Spitzer-based infrared (IR) studies of young
stellar clusters, with particular emphasis on tracing the evolution of
primordial (``protoplanetary'') disks through spectroscopic and photometric
diagnostics. The available data demonstrate that the fraction of young stars
with optically thick primordial disks and/or those which show spectroscopic
evidence for accretion appears to approximately follow an exponential decay
with characteristic time ~2.5 Myr (half-life = 1.7 Myr). Large IR surveys of
~2-5 Myr-old stellar samples show that there is real cluster-by-cluster scatter
in the observed disk fractions as a function of age. Recent Spitzer surveys
have found convincing evidence that disk evolution varies by stellar mass and
environment (binarity, proximity to massive stars, and cluster density).
Perhaps most significantly for understanding the planeticity of stars, the disk
fraction decay timescale appears to vary by stellar mass, ranging from ~1 Myr
for >1.3 Msun stars to ~3 Myr for <0.08 Msun brown dwarfs. The exponential
decay function may provide a useful empirical formalism for estimating very
rough ages for YSO populations and for modeling the effects of disk-locking on
the angular momentum of young stars.Comment: 8 pages, 1 figure, invited review, Proceedings of the 2nd Subaru
International Conference "Exoplanets and Disks: Their Formation and
Diversity", Keauhou - Hawaii - USA, 9-12 March 200
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