137 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
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
Infrared Spectroscopy of CO Ro-vibrational Absorption Lines toward the Obscured AGN IRAS 08572+3915
We present high-resolution spectroscopy of gaseous CO absorption in the
fundamental ro-vibrational band toward the heavily obscured active galactic
nucleus (AGN) IRAS 08572+3915. We have detected absorption lines up to highly
excited rotational levels (J<=17). The velocity profiles reveal three distinct
components, the strongest and broadest (delta_v > 200 km s-1) of which is due
to blueshifted (-160 km s-1) gas at a temperature of ~ 270 K absorbing at
velocities as high as -400 km s-1. A much weaker but even warmer (~ 700 K)
component, which is highly redshifted (+100 km s-1), is also detected, in
addition to a cold (~ 20 K) component centered at the systemic velocity of the
galaxy. On the assumption of local thermodynamic equilibrium, the column
density of CO in the 270 K component is NCO ~ 4.5 x 10^18 cm-2, which in fully
molecular gas corresponds to a H2 column density of NH2 ~ 2.5 x 10^22 cm-2. The
thermal excitation of CO up to the observed high rotational levels requires a
density greater than nc(H2) > 2 x 10^7 cm-3, implying that the thickness of the
warm absorbing layer is extremely small (delta_d < 4 x 10-2 pc) even if it is
highly clumped. The large column densities and high radial velocities
associated with these warm components, as well as their temperatures, indicate
that they originate in molecular clouds near the central engine of the AGN.Comment: 13 pages, 7 figures, accepted for publication in PASJ (Vol.65 No.1
2013/02/25
Homogeneous comparison of planet candidates imaged directly until 2008
We present a compilation of the planet candidates currently known from direct
imaging. We have gathered available data from the literature and derive the
luminosity of all candidates in a homogeneous way using a bolometric
correction, the distances and the K band magnitudes of the objects. In a final
step we find the masses of the candidates from a comparison of the luminosity
or, if not available, an absolute brightness and several well known hot-start
evolutionary models.Comment: 4 pages, 1 figure, Proceedings of the 2nd Subaru International
Conference on Exoplanets and Disks: Their Formation and Diversity, Keauhou -
Hawaii - USA, 9-12 March 2009; 2nd version: Several typos correcte
A Short Guide to Debris Disk Spectroscopy
Multi-wavelength spectroscopy can be used to constrain the dust and gas
properties in debris disks. Circumstellar dust absorbs and scatters incident
stellar light. The scattered light is sometimes resolved spatially at visual
and near-infrared wavelengths using high contrast imaging techniques that
suppress light from the central star. The thermal emission is inferred from
infrared through submillimeter excess emission that may be 1-2 orders of
magnitude brighter than the stellar photosphere alone. If the disk is not
spatially resolved, then the radial distribution of the dust can be inferred
from Spectral Energy Distribution (SED) modeling. If the grains are
sufficiently small and warm, then their composition can be determined from
mid-infrared spectroscopy. Otherwise, their composition may be determined from
reflectance and/or far-infrared spectroscopy. Atomic and molecular gas absorb
and resonantly scatter stellar light. Since the gas is believed to be
secondary, detailed analysis analysis of the gas distribution, kinematics, and
composition may also shed light on the dust composition and processing history.Comment: 6 pages, 2nd Subaru International Conference on Exoplanets and Disks:
Their Formation and Diversity, Keauhou - Hawaii, 9-12 March 200
Search for H₃⁺ isotopologues toward CRL 2136 IRS 1
Context. Deuterated interstellar molecules frequently have abundances relative to their main isotopologues much higher than the overall elemental D-to-H ratio in the cold dense interstellar medium. H₃⁺ and its isotopologues play a key role in the deuterium fractionation; however, the abundances of these isotopologues have not been measured empirically with respect to H₃⁺ to date.
Aims. Our aim was to constrain the relative abundances of H₂D⁺ and D₃⁺ in the cold outer envelope of the hot core CRL 2136 IRS 1.
Methods. We carried out three observations targeting H₃⁺ and its isotopologues using the spectrographs CRIRES at the VLT, iSHELL at IRTF, and EXES on board SOFIA. In addition, the CO overtone band at 2.3 μm was observed by iSHELL to characterize the gas on the line of sight.
Results. The H₃⁺ ion was detected toward CRL 2136 IRS 1 as in previous observations. Spectroscopy of lines of H₂D⁺ and D₃⁺ resulted in non-detections. The 3σ upper limits of N(H₂D⁺)/N(H₃⁺) and N(D₃⁺)/N(H₃⁺) are 0.24 and 0.13, respectively. The population diagram for CO is reproduced by two components of warm gas with the temperatures 58 and 530 K, assuming a local thermodynamic equilibrium (LTE) distribution of the rotational levels. Cold gas (<20 K) makes only a minor contribution to the CO molecular column toward CRL 2136 IRS 1.
Conclusions. The critical conditions for deuterium fractionation in a dense cloud are low temperature and CO depletion. Given the revised cloud properties, it is no surprise that H₃⁺ isotopologues are not detected toward CRL 2136 IRS 1. The result is consistent with our current understanding of how deuterium fractionation proceeds
The Subaru Coronagraphic Extreme AO project
High contrast coronagraphic imaging is a challenging task for telescopes with
central obscurations and thick spider vanes, such as the Subaru Telescope. Our
group is currently assembling an extreme AO bench designed as an upgrade for
the newly commissionned coronagraphic imager instrument HiCIAO, that addresses
these difficulties. The so-called SCExAO system combines a high performance
PIAA coronagraph to a MEMS-based wavefront control system that will be used in
complement of the Subaru AO188 system. We present and demonstrate good
performance of two key optical components that suppress the spider vanes, the
central obscuration and apodize the beam for high contrast coronagraphy, while
preserving the throughput and the angular resolution.Comment: 4 pages, 2nd Subaru International Conference on Exoplanets and Disks:
Their Formation and Diversity, Keauhou - Hawaii, 9-12 March 200
Integral field spectroscopy of supernova explosion sites: constraining mass and metallicity of the progenitors -- II. Type II-P and II-L supernovae
Thirteen explosion sites of type II-P and II-L supernovae in nearby galaxies
have been observed using integral field spectroscopy, enabling both spatial and
spectral study of the explosion sites. We used the properties of the parent
stellar population of the coeval supernova progenitor star to derive its
metallicity and initial mass (c.f. Paper I). The spectrum of the parent stellar
population yields the estimates of metallicity via strong-line method, and age
via comparison with simple stellar population (SSP) models. These metallicity
and age parameters are adopted for the progenitor star. Age, or lifetime of the
star, was used to derive initial (ZAMS) mass of the star by comparing with
stellar evolution models. With this technique, we were able to determine
metallicity and initial mass of the SN progenitors in our sample. Our result
indicates that some type-II supernova progenitors may have been stars with mass
comparable to SN Ib/c progenitors.Comment: Accepted to the Astronomical Journa
The effect of our local motion on the Sandage-Loeb test of the cosmic expansion
Redshifts of an astronomical body measured at multiple epochs (e.g.,
separated by 10 years) are different due to the cosmic expansion. This
so-called Sandage-Loeb test offers a direct measurement of the expansion rate
of the Universe. However, acceleration in the motion of Solar System with
respect to the cosmic microwave background also changes redshifts measured at
multiple epochs. If not accounted for, it yields a biased cosmological
inference. To address this, we calculate the acceleration of Solar System with
respect to the Local Group of galaxies to quantify the change in the measured
redshift due to local motion. Our study is motivated by the recent
determination of the mass of Large Magellanic Cloud (LMC), which indicates a
significant fraction of the Milky Way mass. We find that the acceleration
towards the Galactic Center dominates, which gives a redshift change of 7 cm/s
in 10 years, while the accelerations due to LMC and M31 cannot be ignored
depending on lines of sight. We create all-sky maps of the expected change in
redshift and the corresponding uncertainty, which can be used to correct for
this effect.Comment: 6 pages, 3 figures. Accepted for publication in PAS
- …