伊藤 洋一

We present the results of an age determination study of pre-main sequence stars in the Taurus star-forming region. The ages of 10 single stars with masses of 0.5-1.1 M&lt inf&gt ⊙&lt /inf&gt were derived from the surface gravities, estimated from high-resolution optical and nearinfrared spectroscopy. The equivalent width ratios of nearby absorption line pairs were employed for the surface gravity diagnostic, which directly reflects the parameters of the stellar atmosphere without any veiling correction. From a comparison of determined ages and near-infrared color excesses such as J - H, J - K, and J - L, the inner disk lifetime of the young stars with 0.5-1.1 M&lt inf&gt ⊙&lt /inf&gt in Taurus is estimated to be 3-4 Myr.

We report on the detection of a substellar companion orbiting an evolved intermediate-mass (M?∈=∈2.4∈M) star HD∈14067 (G9∈III) using a precise Doppler technique. Either a periodic Keplerian variation with a decreasing linear velocity trend (P∈=∈1455∈d, K1∈=∈92.2∈m∈s-1, e∈=∈0.533, and $\\dot {\\gamma } = -22.4\\:$m∈s-1∈yr-1) or a single Keplerian orbit without linear trend (P∈=∈2850∈d, K1∈=∈100.1∈m∈s-1, and e∈=∈0.697) can be well fitted to the radial velocities of this star. The minimum mass (m2∈sin∈i∈=∈7.8∈MJ for the model with a linear trend, or m2∈sin∈i∈=∈9.0∈MJ for the model without a linear trend) suggests a long-period giant planet orbiting an evolved intermediate-mass star. The eccentricity of the orbit is among the highest ones ever detected for planets moving around evolved stars.

Main-belt asteroids have been continuously colliding with one another since they were formed. Their size distribution is primarily determined by the size dependence of asteroid strength against catastrophic impacts. The strength scaling law as a function of body size could depend on collision velocity, but the relationship remains unknown, especially under hypervelocity collisions comparable to 10 km s-1. We present a wide-field imaging survey at an ecliptic latitude of about 25° for investigating the size distribution of small main-belt asteroids that have highly inclined orbits. The analysis technique allowing for efficient asteroid detections and high-accuracy photometric measurements provides sufficient sample data to estimate the size distribution of sub-kilometer asteroids with inclinations larger than 14°. The best-fit power-law slopes of the cumulative size distribution are 1.25 ± 0.03 in the diameter range of 0.6-1.0 km and 1.84 ± 0.27 in 1.0-3.0 km. We provide a simple size distribution model that takes into consideration the oscillations of the power-law slope due to the transition from the gravity-scaled regime to the strength-scaled regime. We find that the high-inclination population has a shallow slope of the primary components of the size distribution compared to the low-inclination populations. The asteroid population exposed to hypervelocity impacts undergoes collisional processes where large bodies have a higher disruptive strength and longer lifespan relative to tiny bodies than the ecliptic asteroids. © 2013. The American Astronomical Society. All rights reserved.

Equivalent widths and line widths of Ca II infrared triplet emission lines were measured in the high-resolution optical spectra of 39 young stellar objects. We found that the equivalent widths of the emission lines decrease with stellar evolution. It has often been claimed that strong chromospheric activity is generated by a dynamo process caused by fast rotation of the photosphere. However, we found no clear correlation between the strength of the Ca II lines and the stellar rotation velocity. Instead, we found that the objects with high mass accretion rates had stronger Ca II emission lines. This correlation supports the turbulent chromosphere model or the magnetic accretion theory for classical T Tauri stars. We also noticed that the equivalent widths of Ca II lines in transitional disk objects are one-tenth of those in classical T Tauri stars, even if the masses of the circumstellar disks are comparable. © 2013 National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing Ltd.

We report on the detections of planetary companions orbiting around three evolved intermediate-mass stars based on precise radial velocity measurements at Okayama Astrophysical Observatory. HD2952 (K0III, 2.5M) and ω Ser (G8III, 2.2M) host a relatively low-mass planet with minimum masses of m 2sini = 1.6MJ and 1.7MJ in nearly circular orbits with periods of P = 312 and 277 d, respectively. HD120084 (G7 III, 2.4M) hosts an eccentric planet with m2sini = 4.5MJ in an orbit with P = 2082 d and an eccentricity of e = 0.66. The planet has one of the largest eccentricities among those ever discovered around evolved intermediate-mass stars, almost all of which have an eccentricity smaller than 0.4. We also show that the radial-velocity variations of stellar oscillations for G giants can be averaged out below a level of a few ms -1, at least on a timescale of a week by high-cadence observations. This enables us to detect a super-Earth and a Neptune-mass planet in short-period orbits even around such giant stars. © 2013. Astronomical Society of Japan.

Debris disks around young main-sequence stars often have gaps and cavities which for a long time have been interpreted as possibly being caused by planets. In recent years, several giant planet discoveries have been made in systems hosting disks of precisely this nature, further implying that interactions with planets could be a common cause of such disk structures. As part of the SEEDS high-contrast imaging survey, we are surveying a population of debris-disk-hosting stars with gaps and cavities implied by their spectral energy distributions, in order to attempt to spatially resolve the disk as well as to detect any planets that may be responsible for the disk structure. Here, we report on intermediate results from this survey. Five debris disks have been spatially resolved, and a number of faint point sources have been discovered, most of which have been tested for common proper motion, which in each case has excluded physical companionship with the target stars. From the detection limits of the 50 targets that have been observed, we find that beta Pic b-like planets (similar to 10 M-jup planets around G-A-type stars) near the gap edges are less frequent than 15%-30%, implying that if giant planets are the dominant cause of these wide (27 AU on average) gaps, they are generally less massive than beta Pic b.

We carried out an imaging survey for extrasolar planets around stars in the Pleiades (125 Myr, 135 pc) in the H and K-S bands using HiCIAO combined with adaptive optics, AO188, on the Subaru telescope. We found 13 companion candidates fainter than 14.5 mag in the H band around 9 stars. Five of these 13 were confirmed to be background stars by measurement of their proper motion. One was not found in the second epoch observation, and thus was not a background or companion object. One had multi-epoch images, but the precision of its proper motion was not sufficient to conclude whether it was a background object. Four other candidates are waiting for second-epoch observations to determine their proper motion. Finally, the remaining two were confirmed to be 60 M-J brown dwarf companions orbiting around HD 23514 (G0) and HII 1348 (K5), respectively, as had been reported in previous studies. In our observations, the average detection limit for a point source was 20.3 mag in the H band beyond 1.'' 5 from the central star. On the basis of this detection limit, we calculated the detection efficiency to be 90% for a planet with 6 to 12 Jovian masses and a semi-major axis of 50-1000 AU. For this reason we extrapolated the distribution of the planet mass and the semi-major axis derived from radial velocity observations, and adopted the planet evolution model Baraffe et al. (2003, A&A, 402, 701). Since there was no detection of a planet, we estimated the frequency of such planets to be less than 17.9% (2 sigma) around one star of the Pleiades cluster.

We present near-infrared coronagraphic imaging polarimetry of RY Tau. The scattered light in the circumstellar environment was imaged at the H band at a high resolution (similar to 0 ''.05) for the first time, using Subaru/HiCIAO. The observed polarized intensity (PI) distribution shows a butterfly-like distribution of bright emission with an angular scale similar to the disk observed at millimeter wavelengths. This distribution is offset toward the blueshifted jet, indicating the presence of a geometrically thick disk or a remnant envelope, and therefore the earliest stage of the Class II evolutionary phase. We perform comparisons between the observed PI distribution and disk models with (1) full radiative transfer code, using the spectral energy distribution (SED) to constrain the disk parameters; and (2) monochromatic simulations of scattered light which explore a wide range of parameters space to constrain the disk and dust parameters. We show that these models cannot consistently explain the observed PI distribution, SED, and the viewing angle inferred by millimeter interferometry. We suggest that the scattered light in the near-infrared is associated with an optically thin and geometrically thick layer above the disk surface, with the surface responsible for the infrared SED. Half of the scattered light and thermal radiation in this layer illuminates the disk surface, and this process may significantly affect the thermal structure of the disk.

Nereid, the outer satellite of Neptune, has a highly eccentric prograde orbit with a semimajor axis of larger than 200 in units of Neptune's radius, and is classified as an irregular satellite. Although the capture origin of irregular satellites has been widely accepted, several previous studies suggest that Nereid was formed in the circumplanetary disk of Neptune and ejected outward to the present location by Triton. A series of our photometric observations confirm that Nereid's rotation period, 11.5 hr, is stable and nonchaotic, as indicated by Grav, Holman, and Kavelaars (2003, ApJ, 591, L71). The optical colors of Nereid are indistinguishable from those of trans-Neptunian objects and Centaurs, especially from these objects with neutral colors. We also found the consistency of Nereid's rotation period based on the size-rotation distribution of small outer bodies. It is likely that Nereid originated as an immigrant body captured from the heliocentric orbit that was 4-5AU away from Neptune's orbit. © 2013 Astronomical Society of Japan.

We present the results of the optical spectropolarimetry of Earthshine on the Moon for Earth phase angles ranging from 49° to 96°. The observations were conducted on 2011 March 9-13 (UT) using the spectropolarimeter HBS installed on the 1.88m telescope at Okayama Astrophysical Observatory. The wavelength coverage was 450-850 nm with a resolution of 6 nm. The observed Earthshine polarization degree spectra exhibit decreasing polarization degree with increasing wavelength at any phase. The overall degree of polarization increases as the Earth approaches a quadrature phase. The phase dependence differs with the wavelengths the maximum polarization for the V band occurs at a phase angle of ∼90°, whereas that for longer wavelengths is reached at larger phase angles. This is interpreted as indicating that Earthshine polarization at shorter wavelengths is dominated by atmospheric Rayleigh scattering, whereas that at longer wavelengths has an increasingly effective contribution from the Earth surface reflection. The wavelength dependence of the phase angle of the maximum polarization appears to be unique among the terrestrial planetary bodies in the Solar System. Therefore, this might constitute important evidence pointing toward a distinctive characteristic of Earth: the planet has a scattering but transparent atmosphere above its surface. © 2013 Astronomical Society of Japan.

Orbital elements of 37 single-lined spectroscopic binary systems (SB1s) and 5 double-lined spectroscopic binary systems (SB2s) were determined using high-dispersion spectroscopy. To determine the orbital elements accurately, we carried out precise Doppler shift measurements using the HIgh Dispersion Echelle Spectrograph mounted on the Okayama Astrophysical Observatory 1.88 m telescope. We achieved a radial-velocity precision of ∼10 m s-1 over seven years of observations. The targeted binaries have spectral types between F5 and K3, and are brighter than the 7th magnitude in the V band. The orbital elements of 28 SB1s and 5 SB2s were determined at least 10 times more precisely than previous measurements. Among the remaining nine SB1s, five objects were found to be single stars, and the orbital elements of four objects were not determined because our observations did not cover the entire orbital period. We checked the absorption lines from the secondary star for 28 SB1s and found that three objects were in fact SB2s. © 2013. The American Astronomical Society. All rights reserved.

We report the detection of a double planetary system orbiting around the evolved intermediate-mass star HD 4732 from precise Doppler measurements at Okayama Astrophysical Observatory and Australian Astronomical Observatory. The star is a K0 subgiant with a mass of 1.7 M⊙ and solar metallicity. The planetary system is composed of two giant planets with minimum mass of msin i = 2.4 M⊙J, orbital period of 360.2 days and 2732 days, and eccentricity of 0.13 and 0.23, respectively. Based on dynamical stability analysis for the system, we set the upper limit on the mass of the planets to be about 28 M⊙J (i &gt 5°) in the case of coplanar prograde configuration. © 2013. The American Astronomical Society. All rights reserved.

We report on the detections of substellar companions orbiting around seven evolved intermediate-mass stars from precise Doppler measurements at Okayama Astrophysical Observatory. oUMa (G4 II-III) is a giant with a mass of 3.1M, and hosts a planet with a minimum mass of m2sin i = 4.1MJ in an orbit with a period P = 1630 d and an eccentricity e = 0.13. This is the first planet candidate (&lt 13MJ) ever discovered around a star more massive than 3M. o CrB (K0 III) is a 2.1M giant, and has a planet of m2sin i = 1.5MJ in a 187.8 d orbit with e = 0.19. This is one of the least-massive planets ever discovered around an ̃2M star. HD5608 (K0 IV) is an 1.6M subgiant hosting a planet of m2sin i = 1.4MJ in a 793 d orbit with e = 0.19. The star also exhibits a linear velocity trend, suggesting the existence of an outer, more massive companion. 75 Cet (G3 III:) is a 2.5M giant hosting a planet of m2sin i = 3.0MJ in a 692 d orbit with e = 0.12. The star also shows a possible additional periodicity of about 200 d and 1880 d with a velocity amplitude of ̃7-10ms-1, although these are not significant at this stage. Oph (K0 III) is a 3.0M giant, and has two brown-dwarf companions of m2sin i = 24MJ and 27MJ, in orbits with P = 530.3 d and 3190 d, and e = 0.126 and 0.17, respectively, which were independently announced by Quirrenbach, Reffert, and Bergmann (2011, AIP Conf. Proc. 1331, 102). The ratio of the periods is close to 1:6, suggesting that the companions are in mean motion resonance. We also independently confirmed planets around CrB (K0 III-IV) and HD210702 (K1 IV), which were announced by Johnson et al. (2008, ApJ, 675, 784) and Johnson et al. (2007a, ApJ, 665, 785), respectively. All of the orbital parameters we obtained are consistent with the previous results. © 2012. Astronomical Society of Japan.

We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk object, with a gap structure separating its inner and outer disks. Our imagery taken with the 0 ''.15 (21 AU) radius coronagraphic mask has revealed a strongly polarized circumstellar disk surrounding UX Tau A, which extends to 120 AU, at a spatial resolution of 0 ''.1 (14 AU). It is inclined by 46 degrees +/- 2 degrees, since the west side is nearest. Although SED modeling and sub-millimeter imagery have suggested the presence of a gap in the disk, with the inner edge of the outer disk estimated to be located at 25-30 AU, we detect no evidence of a gap at the limit of our inner working angle (23 AU) at the near-infrared wavelength. We attribute the observed strong polarization (up to 66%) to light scattering by dust grains in the disk. However, neither polarization models of the circumstellar disk based on Rayleigh-scattering nor Mie-scattering approximations were consistent with the observed azimuthal profile of the polarization degrees of the disk. Instead, a geometric optics model of the disk with nonspherical grains with radii of 30 mu m is consistent with the observed profile. We suggest that the dust grains have experienced frequent collisional coagulations, and have grown in the circumstellar disk of UX Tau A.

We present Subaru/IRCS J-band data for Fomalhaut and a (re)reduction of archival 2004-2006 HST/ACS data first presented by Kalas et al. We confirm the existence of a candidate exoplanet, Fomalhaut b, in both the 2004 and 2006 F606W data sets at a high signal-to-noise ratio. Additionally, we confirm the detection at F814W and present a new detection in F435W. Fomalhaut b's space motion may be consistent with it being in an apsidally aligned, non-debris ring-crossing orbit, although new astrometry is required for firmer conclusions. We cannot confirm that Fomalhaut b exhibits 0.7-0.8 mag variability cited as evidence for planet accretion or a semi-transient dust cloud. The new, combined optical spectral energy distribution and IR upper limits confirm that emission identifying Fomalhaut b originates from starlight scattered by small dust, but this dust is most likely associated with a massive body. The Subaru and IRAC/4.5 μm upper limits imply M &lt 2 MJ, still consistent with the range of Fomalhaut b masses needed to sculpt the disk. Fomalhaut b is very plausibly "a planet identified from direct imaging" even if current images of it do not, strictly speaking, show thermal emission from a directly imaged planet. © 2012. The American Astronomical Society. All rights reserved.

We conducted wide-field near-infrared imaging observations of 32 bright rimmed clouds (BRCs). Given a detection limit of 17.7 mag at the K-band, we identified 2099 objects as young stellar object (YSO) candidates that displayed near-infrared excesses. Their masses, estimated from luminosities, range from 0.006 Mocir to 2.7 Mocir. The candidates are not uniformly distributed. For 21 BRCs, more than half of the associated YSO candidates are located inside the cloud. We found clear evidence of triggered star formation. The number of YSO candidates is not correlated with the core mass of the molecular clouds. Instead, the YSO number increases with increasing UV photon flux from the exciting star illuminating the cloud surface. UV radiation activates star formation in the BRCs. © 2012. Astronomical Society of Japan.

Transitional circumstellar disks around young stellar objects have a distinctive infrared deficit around 10 μm in their spectral energy distributions, recently measured by the Spitzer Infrared Spectrograph (IRS), suggesting dust depletion in the inner regions. These disks have been confirmed to have giant central cavities by imaging of the submillimeter continuum emission using the Submillimeter Array (SMA). However, the polarized near-infrared scattered light images for most objects in a systematic IRS/SMA cross sample, obtained by HiCIAO on the Subaru telescope, show no evidence for the cavity, in clear contrast with SMA and Spitzer observations. Radiative transfer modeling indicates that many of these scattered light images are consistent with a smooth spatial distribution for μm-sized grains, with little discontinuity in the surface density of the μm-sized grains at the cavity edge. Here we present a generic disk model that can simultaneously account for the general features in IRS, SMA, and Subaru observations. Particularly, the scattered light images for this model are computed, which agree with the general trend seen in Subaru data. Decoupling between the spatial distributions of the μm-sized dust and mm-sized dust inside the cavity is suggested by the model, which, if confirmed, necessitates a mechanism, such as dust filtration, for differentiating the small and big dust in the cavity clearing process. Our model also suggests an inwardly increasing gas-to-dust ratio in the inner disk, and different spatial distributions for the small dust inside and outside the cavity, echoing the predictions in grain coagulation and growth models. © © 2012. The American Astronomical Society. All rights reserved..

Context. Circumstellar disks and envelopes of low-mass young stellar objects (YSOs) contain significant amounts of ice. Such icy material will evolve to become volatile components of planetary systems, such as comets in our solar system. Aims. To investigate the composition and evolution of circumstellar ice around low-mass young stellar objects (YSOs), we observed ice absorption bands in the near infrared (NIR) towards eight YSOs ranging from class 0 to class II, among which seven are associated with edge-on disks. Methods. We performed slit-less spectroscopic observations using the grism mode of the InfraRed Camera (IRC) on board AKARI, which enables us to obtain full NIR spectra from 2.5 μm to 5 μm, including the CO 2 band and the blue wing of the H 2O band, which are inaccessible from the ground. We developed procedures to carefully process the spectra of targets with nebulosity. The spectra were fitted with polynomial baselines to derive the absorption spectra. The molecular absorption bands were then fitted with the laboratory database of ice absorption bands, considering the instrumental line profile and the spectral resolution of the grism dispersion element. Results. Towards the class 0-I sources (L1527, IRC-L1041-2, and IRAS 04302), absorption bands of H 2O, CO 2, CO, and XCN are clearly detected. Column density ratios of CO 2 ice and CO ice relative to H 2O ice are 21-28% and 13-46%, respectively. If XCN is OCN -, its column density is as high as 2-6% relative to H 2O ice. The HDO ice feature at 4.1 μm is tentatively detected towards the class 0-I sources and HV Tau. Non-detections of the CH-stretching mode features around 3.5 μm provide upper limits to the CH 3OH abundance of 26% (L1527) and 42% (IRAS 04302) relative to H 2O. We tentatively detect OCS ice absorption towards IRC-L1041-2. Towards class 0-I sources, the detected features should mostly originate in the cold envelope, while CO gas and OCN - could originate in the region close to the protostar, where there are warm temperatures and UV radiation. We detect H 2O ice band towards ASR41 and 2MASSJ 1628137-243139, which are edge-on class II disks. We also detect H 2O ice and CO 2 ice towards HV Tau, HK Tau, and UY Aur, and tentatively detect CO gas features towards HK Tau and UY Aur. © 2012 ESO.

We conducted an infrared search for faint companions around 351 young stellar objects in the ρ Ophiuchi molecular cloud and the Serpens molecular cloud. Nine objects in the Spitzer/IRAC archival images were identified as being young stellar companion candidates. They showed an intrinsic infrared excess one object was extremely red both in the [3.6] - [4.5] color and in the [4.5] - [5.8] color, and two objects were red in the [4.5] - [5.8] color. They were as faint as 15mag in the [3.6] band. Follow-up K-band spectroscopy revealed that the three objects had deep water absorption bands, indicative of low effective temperatures. By comparing their spectra and infrared spectral energy distributions with synthesized spectra of low-temperature objects, we derived the effective temperatures and continuum excesses for these objects. It is very likely that one is a low-mass stellar companion, and two others are young brown dwarf companions associated with young stellar objects. © 2011. Astronomical Society of Japan.

We present the SPICA Coronagraphic Instrument (SCI), which has been designed for a concentrated study of extra-solar planets (exoplanets). SPICA mission provides us with a unique opportunity to make high contrast observations because of its large telescope aperture, the simple pupil shape, and the capability for making infrared observations from space. The primary objectives for the SCI are the direct coronagraphic detection and spectroscopy of Jovian exoplanets in infrared, while the monitoring of transiting planets is another important target. The specification and an overview of the design of the instrument are shown. In the SCI, coronagraphic and non-coronagraphic modes are aplicable for both an imaging and a spectroscopy. The core wavelength range and the goal contrast of the coronagraphic mode are 3.5-27 μm, and 10 -6, respectively. Two complemental designs of binary shaped pupil mask coronagraph are presented. The SCI has capability of simultaneous observations of one target using two channels, a short channel with an InSb detector and a long wavelength channel with a Si:As detector. We also give a report on the current progress in the development of key technologies for the SCI. © 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. 31.

We present a method for determining the age of early-M type pre-main sequence (PMS) stars based on estimations of the surface gravity. The surface gravity was measured using high-resolution near-infrared K-band spectroscopy. The age of the PMS stars can be determined from the surface gravity, which correlates with the photospheric contraction. To estimate the surface gravity while avoiding veiling contamination, we developed a surface gravity indicator using equivalentwidth ratios (EWRs) of nearby absorption lines. We derived a relationship between the ratios of the Sc (22057.8 Å and 22071.3 Å) and Na (22062.4 Å and 22089.7 å ) absorption lines and the surface gravity by observing giants and main-sequence stars. The surface gravities of early-M type stars were determined with an accuracy of 0.1 in logg. The ages of target PMS stars were estimated within a factor of 1.5 by comparing the surface gravity with the evolution model of Baraffe et al. (1998, A&amp A, 337, 403). The ages of 4 PMS stars were estimated to be older than indicated by previous age determinations made using the photometric method. The EWR method allows estimating the age of PMS stars without contaminating the uncertainty of the distance, extinction, and veiling. © 2011. Astronomical Society of Japan.

We present an H-band image of FS Tauri, a 0.″2-separated classical T Tauri binary system, taken with the Coronagraphic Imager with Adaptive Optics (CIAO) on the Subaru Telescope. This new image, combined with Hubble Space Telescope/Advanced Camera for Surveys (HST/ACS) F606W-band polarimetric images, shows that the binary has complicated circumbinary features, including a circumbinary disk, western and eastern arm-like structures, and two cavities at the northeast and southwest. The circumbinary disk is 630AU in radius and the southeast side of the disk is bright in the H-band. The brightness ratio (southeast/northwest) is 1.6±0.4. A single Rayleigh-like scattering model indicates that the disk is inclined by 30° to 40° and that the southeast side corresponds to the near side along our line of sight. The H-band surface brightness of the southeast side decreases as r-1.9±0. 1 from 15.2 mag arcsec-2 to 16.8 mag arcsec-2. The outer portion of the disk is possibly more flared than its inner portion. The weak centro-symmetric polarization pattern and redder F606W - H color (4.2±0.2mag) of the southeast side are probably caused by multiple-scattering events from dust grains associated with the binary. The F606W-band image shows the bright northwest side of the disk in contrast with theH-band image. The F606W - H color of the northwest side is between 1.7mag and 3.0 mag. We consider that Haro 6-5 B (FS Tauri B), 20″ away, produces neutral scattered light from the northwest side. This idea is supported by the polarization pattern of the northwest side, which is centro-symmetric with respect to Haro 6-5 B. The arms appear to encompass the western and eastern cavities, suggesting that the arms + cavity systems are created by a bipolar outflow from the binary. However, the direction of this outflow is inconsistent with that of outflows inferred from the circumbinary disk model. These differencesmay arise from a misalignment between the circumbinary disk and the circumstellar disks. Another mechanism forming the arms + cavity systems is considered to be the inhomogeneous density distribution of materials in the circumbinary disk. © 2011. Astronomical Society of Japan.

We present mid-infrared (8-13 μm) spectra of 11 main-belt asteroids: 1 Ceres, 3 Juno, 7 Iris, 11 Parthenope, 20 Massalia, 24 Themis, 41 Daphne, 42 Isis, 44 Nysa, 67 Asia, and 88 Thisbe. This paper makes the first report on the mid-infrared spectrum for 5 asteroids. Our observation was conducted with Michelle on UKIRT. The modified Standard Thermal Model (STM) has provided a slightly better fit to the observed spectra than the model without any modification. For 1 Ceres, we detected an emission feature that surpasses the thermal continuum by 6.2±1.1%. For the other 10 asteroids, no feature has been detected above their observational errors. However, their S/N ratios are sufficient to only detect 6% emission excess. As the causes of the observed spectral distinction, we examine possible (1) chemical and (2) physical differences on the surfaces of the asteroids: (1) 1 Ceres has silicates with a lower degree of polymerization than do the other asteroids (2a) the dominant grain size on 1 Ceres is nearer to 200 μm, and probably smaller than that on the other asteroids (2b) In addition, 1 Ceres has very small (&lt 5 μm) grains on its surface, while the other asteroids have grains that are moderately small, but larger than on 1 Ceres. In either case, the observed spectral distinctiveness of 1 Ceres, the largest asteroid, suggests that the properties of an asteroid surface may be correlated with the asteroid size. © 2011. Astronomical Society of Japan.

The SPICA coronagraph instrument (SCI) provides high-contrast imaging and moderate resolution (R<200) spectroscopy at the wavelength range from 3.5 to 27 mu m. Based on the planet evolutional model calculated by Burrows et al. (2003), SCI will search for gas giant planets down to one Jupiter mass around nearby young (1 Gyr) stars and two Jupiter masses around nearby old (5 Gyr) stars. SCI also allows to characterizing those planets of less than I Gyr by spectroscopic observations to reveal the nature of planetary formation and evolution.Focusing on the high sensitivity and high contrast at wavelengths longer than 10 pm, we show that SCI also allows us to directly image icy giant planets like Uranus and Neptune as well as gas giant planets around nearby early-type stars. In this paper, we compare the capabilities of SCI and the JWST coronagraphs and also discuss a new approach to answering questions concerning the formation and evolution of planetary systems through planet detection with SCI. (C) 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.

We investigated the size distribution of high-inclination main-belt asteroids (MBAs) so as to explore asteroid collisional evolution under hypervelocity collisions of around 10km s-1. We performed a wide-field survey for highinclination sub-km MBAs using the 8.2-m Subaru Telescope with the Subaru Prime Focus Camera (Suprime-Cam). Suprime-Cam archival data were also used. A total of 616 MBA candidates were detected in an area of 9.0 deg2 with a limiting magnitude of 24.0mag in the SDSS r filter. Most of the candidate diameters were estimated to be smaller than 1 km. We found a scarcity of sub-km MBAs with high inclination. Cumulative size distributions (CSDs) were constructed using Subaru data and published asteroid catalogs. The power-law indexes of the CSDs were 2.17±0.02 for low-inclination (&lt 15°) MBAs and 2.02±0.03 for high-inclination (&gt 15°) MBAs in the 0.7-50km diameter range. The high-inclinationMBAs had a shallower CSD. We also found that the CSD of S-like MBAs had a small slope with high inclination, whereas the slope did not vary with the inclination in the C-like group. The most probable cause of the shallow CSD of the high-inclination S-like MBAs is the large power-law index in the diameter-impact strength curve in hypervelocity collisions. The collisional evolution of MBAs may have advanced with oligopolistic survival during the dynamical excitation phase in the final stage of planet formation. © 2011. Astronomical Society of Japan.

We present new 1-1.25 μm (z and J band) Subaru/IRCS and 2 μm (K band) VLT/NaCo data for HR 8799 and a re-reduction of the 3-5 μm MMT/Clio data first presented by Hinz etal. Our VLT/NaCo data yield a detection of a fourth planet at a projected separation of 15AU - "HR 8799e." We also report new, albeit weak detections of HR 8799b at 1.03 μm and 3.3 μm. Empirical comparisons to field brown dwarfs show that at least HR 8799b and HR 8799c, and possibly HR 8799d, have near-to-mid-IR colors/magnitudes significantly discrepant from the L/T dwarf sequence. Standard cloud deck atmosphere models appropriate for brown dwarfs provide only (marginally) statistically meaningful fits to HR 8799b and c for physically implausible small radii. Models with thicker cloud layers not present in brown dwarfs reproduce the planets' spectral energy distributions far more accurately and without the need for rescaling the planets' radii. Our preliminary modeling suggests that HR 8799b has log(g) = 4-4.5, T eff = 900 K, while HR 8799c, d, and (by inference) e have log(g) = 4-4.5, T eff = 1000-1200 K. Combining results from planet evolution models and new dynamical stability limits implies that the masses of HR 8799b, c, d, and e are 6-7 MJ , 7-10 MJ , 7-10 M J , and 7-10 MJ . "Patchy" cloud prescriptions may provide even better fits to the data and may lower the estimated surface gravities and masses. Finally, contrary to some recent claims, forming the HR 8799 planets by core accretion is still plausible, although such systems are likely rare. © 2011. The American Astronomical Society. All rights reserved.

We conducted a near-infrared imaging survey of 11 young dwarfs in the Pleiades cluster using the Subaru Telescope and the near-infrared coronagraph imager. We found ten faint point sources, with magnitudes as faint as 20 mag in the K-band, with around seven dwarfs. Comparison with the Spitzer archive images revealed that a pair of the faint sources around V 1171 Tau is very red in infrared wavelengths, which indicates very low-mass young stellar objects. However, the results of our follow-up proper motion measurements implied that the central star and the faint sources do not share common proper motions, suggesting that they are not physically associated. © 2011 National Astronomical Observatories of Chinese Academy of Sciences and IOP Publishing Ltd.

We carried out low-resolution optical spectroscopy of 14 low-luminosity young stellar object (YSO) candidates in the NGC 1333 cluster. These objects were previously identified by a near-infrared imaging survey. Eleven objects were confirmed to be YSOs by the H? line emission. The strengths of the H? emission are correlated with the near-infrared excesses of the objects. The spectral types of all YSOs are estimated to be M-type, indicative of low mass. Comparisons of the results of our spectroscopic observations and previous photometric observations with evolutionary tracks on the HR diagram suggest two objects to be young brown dwarfs. © 2010. Astronomical Society of Japan.

We report on the detection of two substellar companions orbiting around evolved intermediate-mass stars by precise Doppler measurements at Subaru Telescope and Okayama Astrophysical Observatory. HD 145457 is a KO giant with a mass of 1.9 M⊙, and has a planet of minimum mass, m2 sin i = 2.9 Mj, orbiting with a period of P = 176 d and eccentricity of e = 0.11. HD 180314 is also a KO giant with 2.6M⊙, and hosts a substellar companion of m2 sin i = 22MJ, which falls in the brown-dwarf mass regime, in an orbit with P = 396d and e = 0.26. HD 145457b is one of the innermost planets and HD 180314 b is the seventh candidate of a brown-dwarf-mass companion found around evolved intermediate-mass stars. © 2010. Astronomical Society of Japan.

We present a new method for determining the age of late-K type pre-main sequence (PMS) stars by deriving their surface gravity from high-resolution I-band spectroscopy. Since PMS stars contract as they evolve, their age can be estimated by the surface gravity. We used the equivalent width ratio (EWR) of nearby absorption lines that are free of uncertainties due to veiling, to make a surface-gravity diagnostic of PMS stars. The ratios of Fe (8186.7 Å and 8204.9 Å) and Na (8183.3 Å and 8194.8 Å) absorption lines were calculated for giants, main-sequence stars, and weak-line T Tauri stars. The samples were nearly equal in effective temperature. The EWR of Fe and Na, Fe/Na, decreases significantly with increasing surface gravity, indicating that Fe/Na is a desirable diagnostic tool for deriving the surface gravity of PMS stars. The surface gravity of PMS stars with 0.8 M⊙ can be determined with accuracies of 0.1-0.2, which estimates the age of PMS stars within a factor of 1.5, on average. © 2010. Astronomical Society of Japan.

We report results of H-band (λ = 1.65 μm) imaging observations of young intermediate-mass stars using the Subaru 8.2-m Telescope with the adaptive optics AO36 and the infrared coronagraph CIAO. The targets consist of 16 Herbig Ae/Be stars (15 Herbig Ae stars and one Herbig Be star) and four additional main-sequence stars with infrared excesses. Five protoplanetary disks have been spatially resolved around the Herbig Ae stars with ages of 2-8 Myr. The resolved disks have outer radii of several 100 AU, and their surface brightnesses range from 10 mag arcsec-2 to 18 mag arcsec -2. The images reveal various morphologies in optically thick disks: spiral arms around AB Aur, a banana-split structure with an outer arm for HD 142527, a compact circumprimary disk of HD 150193, a faint discontinuous ring around HD 163296, and an unstructured face-on disk of HD 169142. The detection of an optically thick disk in scattered light implies that it is vertically flared, and intercepts stellar light at least in the outer region where those images were obtained. However, the surface brightness distribution, the resolved structure, and other observational characteristics suggest that the disks are unlikely to be continuously flared young disks with small grains well mixed with gas. The detection rate and the disk brightness do not correlate with the stellar age and the disk mass, but there is a tendency that the brightest disks are still surrounded by long-lived envelopes (AB Aur, HD 100546, HD 142527). The significant diversity of the disk structure can be attributed to the multiplicity and the initial condition of the local star-forming environments. The detections of companion candidates around our targeted stars are also reported. © 2010. Astronomical Society of Japan.

Aims. We examined the physical properties of molecular clouds (morphology, column density, number density, mass) to investigate the mechanism of triggered star formation by UV radiation from a massive star.Methods. We made extensive, high-resolution maps of molecular clouds associated and interacting with the W5-East H ii region using the 45-m telescope at the Nobeyama Radio Observatory (HPBW = 15.6) in 13 CO (J = 1-0) and C18O (J = 1-0) to reveal details in the high-density regions of the molecular clouds. In addition, to investigate the spatial distributions of young stellar objects (YSOs) in the W5-East H ii region, we mapped the spatial distributions of Class I and II candidates.Results. We identified eight 13 CO molecular clouds (three of them are known bright-rimmed clouds) and nine C18O clumps. The masses of the clouds and clumps range from 460 to 36 000 M⊙ and from 55 to 740 M⊙ respectively. The peak 13 CO column densities of the clouds facing the H ii region are twice as large as the others. They have steep density gradients toward the H ii region, indicating interactions with the H ii region. We selected 55 Class I candidates and 778 Class II candidates associated with the W5-East H ii region from the previous Spitzer IRAC/MIPS survey. Most Class I candidates are located around integrated intensity peaks of 13CO, whereas most Class II candidates are distributed along the front sides of the BRC arcs close to the exciting star.Conclusions. The alignments of the YSO candidates and the molecular clouds in order of age indicate that triggered star formation occurs in the W5-East H ii region as a result of gas compression by strong UV radiation. Based on the column densities of 13 CO and the spatial distribution of YSO candidates, we identified a new bright-rimmed cloud candidate on the west side of the W5-East H ii region. © 2009 ESO.

We have conducted high-resolution spectroscopic observations of a sample of both classical and weak-line T Tauri stars embedded in the Taurus-Auriga molecular cloud using the Okayama Astrophysical Observatory's 188 cm telescope equipped with HIDES (High Dispersion Echelle Spectrograph). Utilizing the ratios of equivalent widths of specific lines, we efficiently eliminated the effects of "veiling" and determined the atmospheric parameters individually for each object. Eight pairs of temperature-sensitive line-ratios were selected to derive the effective temperature with high precision and reliability. As for the surface gravity, we have developed a new method to determine the value. The method was first tested on observed spectral standards, and the derived surface gravities had a less than 5% deviation from the values in the literature. The derived surface gravities are well within the range of the assumed values for T Tauri stars. © 2009 Astronomical Society of Japan.

We are currently developing a polarimeter to study surface physical properties of asteroids. To enhance polarimetric accuracy and observational efficiency, we newly devised the polarimeter whose measurements can provide the two Stokes parameters Q and U, simultaneously. The test-observations of the prototype polarimeter have been carried out in December 2003 and January 2004, mounted on the 101 cm telescope at Bisei Astronomical Observatory, Okayama, Japan. In the observations, unpolarized and polarized standard stars were observed to measure an instrumental polarization and its uncertainty. As a result, an instrumental polarization of 5.06 ± 0.18% has been measured. © 2008 COSPAR.

We selected the target stars for the Subaru Strategic Exploration of Exoplanets and Disks (SEEDS) with the High-contrast Coronagraphic Imager for Adaptive Optics (HiCIAO/AO188) observations from the members of open clusters and moving groups. For this selection, we defined the criteria for open clusters and moving groups. Using those selection criteria, we made a target list for open clusters and moving groups. The number of target stars selected is 50 from each category. As a result, the target stars for the open cluster category were selected only from the Pleiades, and those for the moving groups were from six different moving groups. We calculated the expected number of exoplanet detections by HiCIAO and AO188 (to be used on Subaru) by assuming the exoplanet formation probability. The expected number of the direct exoplanet detection is 28 in this category.

The Subaru High-contrast Coronagraphic Imager for Adaptive Optics (HiCIAO) instrument is participating in the planet hunt with its direct imaging survey, the Subaru Strategic Exploration of Exoplanets and Disks (SEEDS), from which binary stars are excluded. However, these systems are expected to harbor a population of planets comparable in number to that of single stars, but differing in many aspects, such as the distribution of planet mass, orbital separation, and eccentricity. Measuring these deviations would unlock a wealth of information on the processes by which planets form and evolve, providing much-needed constraints to theory. The logical next step is therefore to complement SEEDS with a sister project focusing on binary stars: SPOTS, a "Search for Planets Of Two Stars". We propose a direct imaging survey for circumbinary planets of very tight binaries and circumstellar planets of wide binaries.

In this chapter, various observational methods of searching for extrasolar planets and circumstellar disks are reviewed. These include Doppler-shift measurements, transit detection, astrometry, gravitational lensing, spectral energy distribution, direct detection, and coronagraphy. © 2008 Springer-Verlag Berlin Heidelberg.

The discovery of three planetary companions around HR 8799 marked a significant epoch in direct imaging of extrasolar planets. Given the importance of this system, we re-analyzed H-band images of HR 8799 obtained with the Subaru 36-elements adaptive optics (AO) in 2002 July. The low-order AO imaging combined with the classical point-spread function (PSF) subtractions even revealed the extrasolar planet, HR 8799b. Our observations in 2002 confirmed that it has been orbiting HR 8799 in a counterclockwise direction. The flux of HR 8799b was consistent with those in the later epochs within the uncertainty of 0.25 mag, further supporting the planetary mass estimate by Marois et al. © 2009. The American Astronomical Society. All rights reserved.

Coronagraphic imaging for the Herbig Ae star, HD 142527, was performed using the Coronagraphic Imager with Adaptive Optics (CIAO) on the 8.2 m Subaru Telescope. The images were obtained in the H2O ice filter (λ=3.08 μm) using adaptive optics (AO), and in the L' band without AO. Combining these data with previous observational results in the H and K bands, we derived the spectra of the scattered light from the circumstellar disk around HD 142527 and detected an H2O ice absorption feature in the spectra. This result can be explained by the presence of silicate and H2O ice grains of-1 μm in size, according to the prediction model by Inoue et al. This grain size is consistent with previous observational study by Fukagawa et al. and Fujiwara et al. The present result demonstrates that high-resolution imaging of disk-scattered light in the ice band is useful for detecting H 2O ice grain distributions in circumstellar disks. © 2009. The American Astronomical Society.

We present a high-resolution (∼0."1 = 14 AU) H-band image of XZ Tau, a 0."3-separated classical T Tauri binary system, taken with the Coronagraphic Imager with Adaptive Optics (CIAO) on the Subaru Telescope. We found a scattered light nebula extending to ∼2."4 from the secondary, XZ Tau S, in the northeast region of the binary. Its surface brightness is ∼ 16.2 mag arcsec-2 in the H-band, and decreases as r -1.6±0.1. Combined with the HST/ACS Polarimetric images and the [Fe II] λ1.644μm spectra taken with the Infrared Camera and Spectrograph (IRCS) on the Subaru Telescope, the elongated structure is identified as a wall of a cavity blown by the previously known blueshifted outflow. By a comparison with previous measurements, we estimated that the orbital period is 1010±260yr and the total mass of the binary is 0.62 ±0.36 M⊙. The observed H-band magnitudes of both the primary and the secondary varied by as much as 1 mag over this decade. These H-band inconstancies may arise from a variable accretion rate and changing extinction toward each component. © 2009. Astronomical Society of Japan.

We searched for extrasolar planets in visual binary systems using precise Doppler-shift measurements taken over a period of 4 yr. Using the High Dispersion Echelle Spectrograph (HIDES) equipped on the Okayama Astrophysical Observatory (OAO) 188 cm reflector, we achieved a radial-velocity precision of about 10 m s-1. We monitored both primary and secondary stars of six visual binary systems, and primary stars of three visual binaries. Among them, three objects show large radial-velocity variations. ADS 7311 A exhibits a decreasing trend in radial velocity with a best-fit slope of-30 m s-1 yr-1, while 31 Dra A shows an increasing trend with a best-fit slope of +220 m s-1 yr-1. These long-term trends in radial velocity may be attributable to unseen companions. BDS 10966 A shows a periodic variation in radial velocity with a period of 840 d and a semiamplitude of about 120 m s-1, implying an association of a planetary-mass companion, rotational modulation, or nonradial oscillation of the photosphere. In any case, we should mention the nonassociation between BDS 10966 A and B, suggested by the different proper motions, radial velocities, and Hipparcos parallaxes. © 2009. Astronomical Society of Japan.

We present metallicity analyses of A, F, and G stars in the Pleiades cluster. High-resolution spectroscopic observations of 25 stars were made with the HIDES spectrograph on the Okayama 1.88-m telescope and the GAOES spectrograph on the Gunma 1.5-m telescope. The resultant optical spectra had an S/N of 70-220. We measured the equivalent widths of ∼60 neutral iron and ∼ 15 single-ionized iron absorption lines to determine stellar parameters and metallicities. We derived me metallicities of 22 stars by adapting the method of equivalent-width measurements. The average metallicity was +0.03 ± 0.05 dex. The dispersion was comparable to the statistical uncertainties of the metallicity measurements in addition, the metallicities of all 22 stars fell within the dispersion range, indicating their uniform metallicities. A comparison of our results with previous studies confirmed a high probability of metallicity homogeneity in Pleiades. © 2009. Astronomical Society of Japan.

We have been carrying out precise Doppler surveys of G, K giants to search for planets around intermediate-mass (1.5-5M(circle dot)) stars within the framework of international collaboration between China, Korea, and Japan. The number of targets at these sites is now about 1000 in total. We here describe the current status of our project and discuss the properties of planets around evolved stars, especially around clump giants. All of the substellar companions ever discovered around possible intermediate-mass clump giants have semimajor axes larger than 0.7 AU. When we assume that most of the clump giants are post-RGB stars, short-period planets around them might have been engulfed by the central stars at the tip of RGB due to tidal force.

The SPace Infrared telescope for Cosmology and Astrophysics (SPICA) is a infrared space-borne telescope mission of the next generation following AKARI. SPICA will carry a telescope with a 3.5 m diameter monolithic primary mirror and the whole telescope will be cooled to 5 K. SPICA is planned to be launched in 2017, into the sun-earth L2 libration halo orbit by an H II-A rocket and execute infrared observations at wavelengths mainly between 5 and 200 micron. The large telescope aperture, the simple pupil shape, the capability of infrared observations from space, and the early launch gives us with the SPICA mission a unique opportunity for coronagraphic observation. We have started development of a coronagraphic instrument for SPICA. The primary target of the SPICA coronagraph is direct observation of extra-solar Jovian planets. The main wavelengths of observation, the required contrast and the inner working angle (IWA) of the SPICA coronagraph are set to be 5-27 micron (3.5-5 micron is optional), 10 , and a few λ/D (and as small as possible), respectively, in which λ is the observation wavelength and D is the diameter of the telescope aperture (3.5m). For our laboratory demonstration, we focused first on a coronagraph with a binary shaped pupil mask as the primary candidate for SPICA because of its feasibility. In an experiment with a binary shaped pupil coronagraph with a He-Ne laser (λ=632.8nm), the achieved raw contrast was 6.7×10 , derived from the average measured in the dark region without active wavefront control. On the other hand, a study of Phase Induced Amplitude Apodization (PIAA) was initiated in an attempt to achieve better performance, i.e., smaller IWA and higher throughput. A laboratory experiment was performed using a He-Ne laser with active wavefront control, and a raw contrast of 6.5×10 was achieved. We also present recent progress made in the cryogenic active optics for SPICA. Prototypes of cryogenic deformable by Micro Electro Mechanical Systems (MEMS) techniques were developed and a first demonstration of the deformation of their surfaces was performed with liquid nitrogen cooling. Experiments with piezo-actuators for a cryogenic tip-tilt mirror are also ongoing. -6 -8 -7

We have started a search for extrasolar planets in visual binary systems from 2003. We monitor them by precise radial velocity measurements, using HIgh Dispersion Echelle Spectrograph(HIDES) equipped on the Okayama Astrophysical Observatory's(OAO) 188 cm telescope. Radial velocity precision of better than 10 m/s has achieved with an iodine absorption cell during our observational span. We here report the current status of the survey. © 2008 Springer-Verlag Berlin Heidelberg.

We report the detection of a substellar companion orbiting the intermediate-mass giant star 11 Com (G8 III). Precise Doppler measurements of the star from Xinglong Station and Okayama Astrophysical Observatory (OAO) reveal Keplerian velocity variations with an orbital period of 326.03 ±0.32days, a semiamplitude of 302.8 ±2.6 ms-1, and an eccentricity of 0.231 ±0.005. Adopting a stellar mass of 2.7 ±0.3 M⊙, the minimum mass of the companion is 19.4 ±1.5 M J, well above the deuterium-burning limit, and the semimajor axis is 1.29 ±0.05 AU. This is the first result from a joint planet-search program between China and Japan aimed at revealing the statistics of substellar companions around intermediate-mass giants. 11 Com b emerged from 300 targets of the planet-search program at OAO. The program's current detection rate of brown dwarf candidates seems to be comparable to the rate of such detections around solar-type stars with orbital separations of ≲3 AU. © 2008. The American Astronomical Society. All rights reserved.

We have discovered an optically thick, nearly face-on circumstellar disk around a single M5 classical T Tauri star, FN Tau, using the coronagraphic imager CIAO on the Subaru telescope. This is the least massive T Tauri star whose circumstellar structure has been directly imaged as a scattering disk. The surface brightness in the H band declines as a power law of r -25±0.1 (110.1 ≤ r ≤ 260 AU), suggesting that the disk is flared. The disk morphology appears to be relatively featureless except for an azimuthal asymmetry in the surface brightness, indicating that the disk is not perfectly face-on but is slightly tilted. The disk mass, derived from a simple disk emission model with previous photometry at optical to millimeter wavelengths, is ∼0.007 M⊙, 6% of the mass of the central star. The disk around FN Tau is one of the best targets for disk and planet formation studies around M stars. © 2008. The American Astronomical Society. All rights reserved.

The goal of our study is to discuss how planet-hosting stars (PHSs) are born by analyzing the chemical homogeneity in open clusters. We obtained the spectra of 18 A,F,G stars in the Pleiades by the high-resolution spectroscopic observations in last January. Out of the 18 stars, the metallcities of 10 stars were derived, and their mean metallicity was obtained to be [Fe/H]mean = +0.02±0.14dex. This high dispersion may imply the chemical diversity in Pleiades. We report the results of our analysis. © 2008 Springer-Verlag Berlin Heidelberg.

We report on the detection of 3 new extrasolar planets from a precise Doppler survey of G and K giants at Okayama Astrophysical Observatory. The host stars, 18 Del (G6 III), ξ Aql (K0 III) and HD 81688 (K0 III-IV), are located in the clump region on the HR diagram with estimated masses of 2.1-2.3M⊙. 18 Del b has a minimum mass of 10.3MJ and resides in a nearly circular orbit with period of 993 d, which is the longest one around evolved stars. ξ Aql b and HD 81688 b have minimum masses of 2.8 and 2.7M J, and reside in nearly circular orbits with periods of 137 and 184d, respectively, which are the shortest ones around evolved stars. All of the substellar companions ever discovered around intermediate-mass (1.7-3.9M⊙) clump giants have semimajor axes larger than 0.68 AU, suggesting a lack of short-period planets. Our numerical calculations suggest that Jupiter-mass planets within about 0.5 AU (even up to 1 AU, depending on the metallicity and adopted models) around 2-3M⊙ stars could be engulfed by the central stars at the tip of RGB due to tidal torque from the central stars. Assuming that most of the clump giants are post-RGB stars, we can not distinguish whether the lack of short-period planets is primordial, or due to engulfment by central stars. © 2008. Astronomical Society of Japan.

We have conducted near-infrared spectroscopy of 26 faint objects around young stellar objects in the Taurus molecular cloud. These objects were detected during a course of near-infrared coronagraphic searches for companions around 72 young stellar objects with the Subaru Telescope and the near-infrared coronagraph CIAO (coronagraphic imager with adaptive optics). A comparison of the Subaru and HST archive images revealed that three central stars and faint companions share common proper motions, suggesting that they are physically associated with each other. None of the 26 sources show deep water absorption bands at near-infrared, except for DH Tau B. This result indicates that all of them, but DH Tau B, have a high photospheric temperature or a large amount of excess from circumstellar materials © 2008. Astronomical Society of Japan.