伊藤 洋一

Abstract In this study, we revisit 32 planetary systems around evolved stars observed within the framework of the Okayama Planet Search Program (OPSP) and its collaborative framework of the East Asian Planet Search Network to search for additional companions and investigate the properties of stars and giant planets in multiple-planet systems. With our latest radial velocities obtained from Okayama Astrophysical Observatory, we confirm an additional giant planet in the wide orbit of the 75 Cet system ($P_{\rm {c } } = 2051.62_{-40.47}^{+45.98}\ \rm {d}$, $M_{\rm {c } }\sin i=0.912_{-0.090}^{+0.088}\,\,M_{\rm {J } }$, and $a_{\rm {c } }=3.929_{-0.058}^{+0.052}\ \rm {au}$), along with five stars exhibiting long-term radial velocity accelerations, which indicates massive companions in the wide orbits. We also find that the radial velocity variations of several planet-harboring stars may indicate additional planet candidates, stellar activities, or other understudied sources. These stars include ϵ Tau, 11 Com, 24 Boo, 41 Lyn, 14 And, HD 32518, and ω Ser. We further constrain the orbital configuration of the HD 5608, HD 14067, HD 120084, and HD 175679 systems by combining radial velocities with astrometry, as their host central stars exhibit significant astrometric accelerations. For other systems, we simply refine their orbital parameters. Moreover, our study indicates that the OPSP planet-harboring stars are more metal poor compared to the currently known planet-harboring stars, and this is likely due to the B − V color upper limit at 1.0 for star selection in the beginning of the survey. Finally, by investigating the less massive giant planets (<5 MJ) around currently known planet-harboring evolved stars, we find that metallicity positively correlates with the multiplicity and total planet mass of the system, which can be evidence for the core-accretion planet formation model.

We report the detection of a giant planet orbiting the G-type giant star HD 167768 from radial velocity measurements using the High Dispersion Echelle Spectrograph (HIDES) at Okayama Astrophysical Observatory (OAO). HD 167768 has a mass of 1.08(-0.12) (+0.14) M-?, a radius of 9.70 R-+0.25 (-0.25)?, a metallicity of [Fe/H] = -0.67+0.09 -0.08 , and a surface gravity of log g = 2.50(-0.06.)(+0.06) .The planet orbiting the star is a warm Jupiter, having a period of 20.6532(-0.0032)( +0.0032) d, a minimum mass of 0.85(-0.11)(+0.12) MJ , and an orbital semimajor axis of 0.1512 ( +0.0058)(-0.0063)au. The planet has one of the shortest orbital periods among those ever found around deeply evolved stars (log g < 3.5) using radial velocity methods. The equilibrium temperature of the planet is 1874 K, as high as a hot Jupiter. The radial velocities show two additional regular variations at 41 d and 95 d, suggesting the possibility of outer companions in the system. Follow-up monitoring will enable validation of the periodicity. We also calculated the orbital evolution of HD 167768 b and found that the planet will be engulfed within0.15 Gyr.

Abstract “Changing-look active galactic nuclei” (CLAGNs) are known to change their apparent types between types 1 and 2, usually accompanied by a drastic change in their luminosity on timescales of years. However, it is still unclear whether materials in broad-line regions (BLRs) in CLAGNs appear and disappear during the type-transition or remain at the same location while the line production is simply activated or deactivated. Here we present our X-ray–optical monitoring results of a CLAGN, NGC 3516, by Suzaku, Swift, and ground telescopes, with our primary focus on the narrow Fe–Kα emission line, which is an effective probe of the BLR materials. We detected significant variations of the narrow Fe–Kα line on a timescale of tens of days during the type-2 (faint) phase in 2013–2014, and conducted “narrow Fe–Kα reverberation mapping,” comparing its flux variation with those of the X-ray continuum from a corona and B-band continuum from an accretion disk. We derived, as a result, a time lag of ${10.1}_{-5.6}^{+5.8}$ days (1σ errors) for the Fe–Kα line behind the continuum, which is consistent with the location of the BLR determined in optical spectroscopic reverberation mapping during the type-1 (bright) phase. This finding shows that the BLR materials remained at the same location without emitting optical broad lines during the type-2 phase. Considering the drastic decrease of the radiation during the type-transition, our result is possibly inconsistent with the hotly discussed formation models of the BLR, which propose that the radiative pressure from an accretion disk should be the main driving force.

We report the discovery of a triple-giant-planet system around an evolved star HD 184010 (HR 7421, HIP 96016). This discovery is based on observations from Okayama Planet Search Program, a precise radial velocity survey, undertaken at Okayama Astrophysical Observatory between 2004 April and 2021 June. The star is K0 type and located at the beginning of the red giant branch. It has a mass of 1.35(-0.21)(+0.19) M-circle dot, a radius of 4.86(-0.49)(+0.55) R-circle dot, and a surface gravity log g of 3.18(-0.07)(+0.08). The planetary system is composed of three giant planets in a compact configuration: the planets have minimum masses of M-b sin i = 0.31(-0.04)(+0.03) M-J, M-c sin i = 0.30(-0.05)(+0.04) M-J, and M-d sin i = 0.45(-0.06)(+0.04) M-J, and orbital periods of P-b = 286.6(-0.7)(+2.4) d, P-c = 484.3(-3.5)(+5.5) d, and P-d = 836.4(-8.4)(+8.4) d, respectively, which are derived from a triple Keplerian orbital fit to three sets of radial velocity data. The ratio of orbital periods are close to P-d : P-c : P-b similar to 21 : 12 : 7, which means the period ratios between neighboring planets are both lower than 2 : 1. The dynamical stability analysis reveals that the planets should have near-circular orbits. The system could remain stable over 1Gyr, initialized from co-planar orbits, low eccentricities (e = 0.05), and planet masses equal to the minimum mass derived from the best-fitting circular orbit fitting. Besides, the planets are not likely in mean motion resonance. The HD 184010 system is unique: it is the first system discovered to have a highly evolved star (log g < 3.5 cgs) and more than two giant planets all with intermediate orbital periods (10(2) < P < 10(3) d).

Zero-age main-sequence (ZAMS) stars are considered to have enormous starspots and show strong chromospheric emission lines because of their strong surface magnetic field. We discuss the dynamo activities of ZAMS stars with respect to their periodic light variation caused by a starspot and with respect to the strength of the chromospheric emission lines. The light curves of 33 ZAMS stars in IC 2391 and IC 2602 were obtained from TESS (Transiting Exoplanet Survey Satellite) photometric data. The light curves can be grouped into the following four categories: single frequency, possible shape changer, beater, and complex variability. The amplitudes of the light curves are 0.001-0.145 mag, similar to those of ZAMS stars in Pleiades. The starspot coverages are 0.1%-21%. We found that the light variations and Ca II emission line strength of ZAMS stars in IC 2391, IC 2602, and the Pleiades cluster are as large as those of the most active superflare stars and two orders larger than those of the Sun, and are located on the extensions of the superflare stars. These results suggest that superflare stars link the properties of the Sun to those of the ZAMS stars of ages between 30 and 120 Myr. ZAMS stars with a single frequency or possible shape change in the light curve tend to have both large light variation, indicating large spot coverage, and saturated Ca II emission line strength. ZAMS stars with beat or complex variability have small spot coverage and a faint Ca II emission line. We also detected 21 flares in the TESS light curves of 12 ZAMS stars in IC 2391 and IC 2602, where most of these stars have saturated chromospheric Ca II emission lines. The energies of the flares are estimated to be similar to 10(33)-10(35) erg, which is comparable with the energy of a superflare.

The chromosphere is the active atmosphere in which energetic eruption events, such as flares, occur. Chromospheric activity is driven by the magnetic field generated by stellar rotation and convection. The relationship between chromospheric activity and the Rossby number, the ratio of the rotational period to the convective turnover time, has been extensively examined for many types of stars, by using narrow chromospheric emission lines, such as the Ca ii lines and the Mg ii H and K lines. However, the stars with small Rossby numbers, i.e., stars with rapid rotations and/or long convective turnover times, show constant strengths of such lines against the Rossby number. In this study, we investigate the infrared Mg i emission lines at 8807 angstrom of 47 zero-age main-sequence (ZAMS) stars in IC 2391 and IC 2602 using the archive data of the Anglo-Australian Telescope at the University College London Echelle Spectrograph. After subtracting the photospheric absorption component, the Mg i line is detected as an emission line for 45 ZAMS stars, the equivalent widths of which are between 0.02 angstrom and 0.52 angstrom. A total of 42 ZAMS stars show the narrower Mg i emission lines instead of the Ca ii infrared triplet emission lines, suggesting that they are formed at different depths. The ZAMS stars with smaller Rossby numbers show stronger Mg i emission lines. The Mg i emission line is not saturated even in the saturated regime of the Ca ii emission lines, i.e., Rossby number i emission line is considered to be a good indicator of chromospheric activity, particularly for active objects.

We report the detection of radial velocity (RV) variations in nine evolved G- and K-type giant stars. The observations were conducted at Okayama Astrophysical Observatory. Planets or planet candidates can best explain these regular variations. However, a coincidence of near 280d variability among five of them prevents us from fully ruling out stellar origins for some of the variations, since all nine stars behave similarly in stellar properties. In the planet hypotheses for the RV variations, the planets (including one candidate) may survive close to the boundary of the so-called "planet desert" around evolved stars, having orbital periods between 255 and 555 d. Besides, they are the least-massive giant planets detected around G- and K-type giant stars, with minimum masses between 0.45 M-J and 1.34 M-J. We further investigated other hypotheses for our detection, yet none of them can better explain regular RV variation. With our detection, we can be convinced that year-long regular variation with amplitude down to 15 m s(-1) for G- and K-type giant stars is detectable. Moreover, we performed simulations to further confirm the detectability of planets around these stars. Finally, we explored giant planets around intermediate-mass stars, and likewise found a four-Jupiter-mass gap (e.g., Santos et al. 2017, A&A, 603, A30), which is probably a boundary of the giant planet population.

<title>Abstract</title> The detections of gravitational waves (GW) by LIGO/Virgo collaborations provide various possibilities to physics and astronomy. We are quite sure that GW observations will develop a lot both in precision and in number owing to the continuous works for the improvement of detectors, including the expectation to the newly joined detector, KAGRA, and the planned detector, LIGO-India. In this occasion, we review the fundamental outcomes and prospects of gravitational wave physics and astronomy. We survey the development focusing on representative sources of gravitational waves: binary black holes, binary neutron stars, and supernovae. We also summarize the role of gravitational wave observations as a probe of new physics.

We present the results of the high-resolution spectroscopy of the FU Orionis-type star V960 Mon. The brightness of V960 Mon decreased continuously after the outburst was detected in 2014 November. During this dimming event, we carried out medium-resolution spectroscopic monitoring observations and found that the equivalent width of the absorption features showed variations. To further investigate the spectroscopic variations, we conducted a high-resolution spectroscopic observation of V960 Mon with the Subaru Telescope and the High Dispersion Spectrograph on 2018 January 8 and 2020 February 1. By comparing this spectrum with the archival data of the Keck Observatory and the High Resolution Echelle Spectrometer taken between 2014 and 2017, we found that the absorption profiles changed as V960 Mon faded. The line profile of absorption lines such as Fe i and Ca i can be explained by a sum of the spectra of the disk atmosphere and the central star. The model spectrum created to explain the variations of the line profiles suggests that the effective temperature of the central star is similar to 5500 K, which is comparable to that of the pre-outburst phase with a distance of 1.6 kpc with Gaia. The spectrum also shows that the effective temperature of the disk atmosphere decreased as V960 Mon faded. The variations of the H alpha and Ca ii lines (8498.0, 8542.1 A) also show that the V960 Mon spectrum became central-star dominant.

We investigated the chromospheric activity of 60 pre-main-sequence (PMS) stars in four molecular clouds and five moving groups. It is considered that strong chromospheric activity is driven by the dynamo processes generated by stellar rotation. In contrast, several researchers have pointed out that the chromospheres of PMS stars are activated by mass accretion from their protoplanetary disks. In this study, the Ca II infrared triplet (IRT) emission lines were investigated utilizing medium- and high-resolution spectroscopy. The observations were conducted with Nayuta/MALLS and Subaru/HDS. Additionally, archive data obtained by Keck/HIRES, VLT/UVES, and VLT/X-Shooter were used. The small ratios of the equivalent widths indicate that Ca II IRT emission lines arise primarily in dense chromospheric regions. Seven PMS stars show broad emission lines. Among them, four PMS stars have more than one order of magnitude brighter emission line fluxes compared to the low-mass stars in young open clusters. The four PMS stars have a high mass accretion rate, which indicates that the broad and strong emission results from a large mass accretion. However, most PMS stars exhibit narrow emission lines. No significant correlation was found between the accretion rate and flux of the emission line. The ratios of the surface flux of the Ca II IRT lines to the stellar bolometric luminosity, R-IRT', of the PMS stars with narrow emission lines are as large as the largest R-IRT' of the low-mass stars in the young open clusters. This result indicates that most PMS stars, even in the classical T Tauri star stage, have chromospheric activity similar to zero-age main-sequence stars.

We report observations of a stellar occultation by the classical Kuiper Belt object (50000) Quaoar that occurred on 2019 June 28. A single-chord high-cadence (2 Hz) photometry data set was obtained with the Tomo-e Gozen CMOS camera mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The obtained ingress and egress data do not show any indication of atmospheric refraction and allow new 1? and 3? upper limits of 6 and 16 nbar, respectively, to be set for the surface pressure of a pure methane atmosphere. These upper limits are lower than the saturation vapor pressure of methane at Quaoar?s expected mean surface temperature (T?44 K) and imply the absence of a ?10 nbar-level global atmosphere formed by methane ice on Quaoar?s surface.

We present the results of imaging polarimetry of the eclipsed Moon on 2014 October 8. The observed polarization degree was less than 1% in both the V and R bands, which contrasts with the reported 2%-3% polarization during the eclipse of 2015 April 4. We examined the Earth's atmospheric data on the two dates and found that the high (>= 7 km) cloud distribution was more inhomogeneous for the 2015 eclipse than it was for the 2014 eclipse. The polarization position angle observed during the 2015 eclipse can be explained if the major polarizing source was high clouds with an intermediate horizontal optical thickness. We suggest a possible dependence of the lunar eclipse polarization on the Earth's high cloud distribution.

We present the results of the spectroscopic monitoring of the FU Orionis type star V960 Mon. Spectroscopic variations of an FU Orionis type star will provide valuable information of its physical nature and the mechanism of the outburst. We conducted medium-resolution (R ∼ 10000) spectroscopic observations of V960 Mon with the 2 m Nayuta telescope at the Nishi-Harima Astronomical Observatory, from 2015 January to 2017 January, for 53 nights in total. We focused on Hα line and nearby atomic lines, and we detected the strength variations in both absorption and emission lines. The observed variation in the equivalent width of the absorption lines corresponds to a decrease in effective temperature and increase in surface gravity. These variations were likely to originate from the luminosity fading of the accretion disk due to the decrease in mass accretion rate.

西はりま天文台では教育普及活動の一つとして、高校生・大学生を対象にした天文実習を行ってきた。この実習内容について 2015 年 7 月より、利用者からの満足度の調査と質の向上を目指してアンケート調査を実施してきた。本稿では 2015 年 7 月から 2018 年 10 月までのアンケートを集計し、どの程度利用者が満足しているか調査した。アンケートは延べ 140 の学校、団体に対して実施し、89 件の回答を得た。回収率は 64% であった。その結果、大多数の利用者が実習内容に満足と回答していることが明らかになった。また「昼間の星と太陽の観察会」「天文講義」「夜間の観測実習」と実習全体に対する満足度が近年増加傾向にあることがわかった。一方「なゆた観測見学」は満足度が下降傾向にあり、改善の余地があることがわかった。また各実習メニューの難易度についての調査も行った。その結果「適切」を選択している回答は総回答数の 86% に上ることがわかった。満足度の傾向と難易度についての回答から、西はりま天文台での天文実習は概ね利用者の期待通りであると言える結論が得られた。

We report the detection of planets around two evolved giant stars from radial velocity measurements at Okayama Astrophysical observatory. 24 Boo (G3 IV) has a mass of 0.99 M-circle dot, a radius of 10.64 R-circle dot, and a metallicity of [Fe/H] = -0.77. The star hosts one planet with a minimum mass of 0.91 M-Jup and an orbital period of 30.35 d. The planet has one of the shortest orbital periods among those ever found around evolved stars using radial-velocity methods. The stellar radial velocities show additional periodicity with 150 d, which can probably be attributed to stellar activity. The star is one of the lowest-metallicity stars orbited by planets currently known. gamma Lib (K0 III) is also a metal-poor giant with a mass of 1.47 M-circle dot, a radius of 11.1 R-circle dot, and [Fe/H] = -0.30. The star hosts two planets with minimum masses of 1.02 M-Jup and 4.58 M-Jup, and periods of 415 d and 964 d, respectively. The star has the second-lowest metallicity among the giant stars hosting more than two planets. Dynamical stability analysis for the gamma Lib system sets the minimum orbital inclination angle to be about 70 degrees and suggests that the planets are in 7:3 mean-motion resonance, though the current best-fitting orbits for the radial-velocity data are not totally regular.

Polarization during a lunar eclipse is a forgotten mystery. Coyne &amp Pellicori reported the detection of significant polarization during the lunar eclipse on 1968 April 13. Multiple scattering during the first transmission through Earth's atmosphere was suggested as a possible cause of the polarization, but no conclusive determination was made. No further investigations on polarization during a lunar eclipse are known. We revisit this mystery with an interest in possible application to extrasolar planets if planetary transmitted light is indeed polarized, it may be possible to investigate an exoplanet atmosphere using "transit polarimetry." Here we report results of the first spectropolarimetry for the Moon during a lunar eclipse on 2015 April 4. We observed polarization degrees of 2%-3% at wavelengths of 500-600 nm in addition, an enhanced feature was detected at the O2 A band near 760 nm. The observed time variation and wavelength dependence are consistent with an explanation of polarization caused by double scattering during the first transmission through Earth's atmosphere, accompanied by latitudinal atmospheric inhomogeneity. Transit polarimetry for exoplanets may be useful to detect O2 gas and to probe the latitudinal atmospheric inhomogeneity, and it is thus worthy of serious consideration.

GW170817 is the first detected gravitational wave source from a neutron star merger. We present the Japanese collaboration for gravitational-wave electro-magnetic (J-GEM) follow-up observations of SSS17a, an electromagnetic counterpart of GW170817. SSS17a shows a 2.5mag decline in the z band during the period between 1.7 and 7.7 d after the merger. Such a rapid decline is not comparable with supernovae light curves at any epoch. The color of SSS17a also evolves rapidly and becomes redder during later epochs: the z - H color has changed by approximately 2.5mag during the period between 0.7 and 7.7 d. The rapid evolutions of both the color and the optical brightness are consistent with the expected properties of a kilonova that is powered by the radioactive decay of newly synthesized r-process nuclei. Kilonova models with Lanthanide elements can reproduce the aforementioned observed properties well, which suggests that r-process nucleosynthesis beyond the second peak takes place in SSS17a. However, the absolute magnitude of SSS17a is brighter than the expected brightness of the kilonova models with an ejectamass of 0.01M(circle dot), which suggests a more intensemass ejection (similar to 0.03M(circle dot)) or possibly an additional energy source.

Recent detection of gravitational waves from a neutron star (NS) merger event GW170817 and identification of an electromagnetic counterpart provide a unique opportunity to study the physical processes in NS mergers. To derive properties of ejected material from the NS merger, we perform radiative transfer simulations of kilonova, optical and near-infrared emissions powered by radioactive decays of r-process nuclei synthesized in the merger. We find that the observed near-infrared emission lasting for >10 d is explained by 0.03 M-circle dot of ejecta containing lanthanide elements. However, the blue optical component observed at the initial phases requires an ejecta component with a relatively high electron fraction (Y-e). We show that both optical and near-infrared emissions are simultaneously reproduced by the ejecta with a medium Y-e of similar to 0.25. We suggest that a dominant component powering the emission is post-merger ejecta, which exhibits that the mass ejection after the first dynamical ejection is quite efficient. Our results indicate that NS mergers synthesize a wide range of r-process elements and strengthen the hypothesis that NS mergers are the origin of r-process elements in the Universe.

Context. Spectro-polarimetry of reflected light from exoplanets is anticipated to be a powerful method for probing atmospheric composition and structure. Aims. We aim to evaluate the feasibility of the search for a spectro-polarimetric feature of water vapor using a high-contrast polarimetric instrument on a 30-40 m-class ground-based telescope. Methods. Three types of errors are considered: (a) errors from the difference between efficiencies for two orthogonally polarized states (b) errors caused by speckle noises and (c) errors caused by photon noise from scattered starlight. Using the analytically derived error formulas, we estimate the number of planets for which feasible spectro-polarimetric detection of water vapor is possible. Results. Our calculations show that effective spectro-polarimetric searches for water vapor are possible for 5 to 14 known planets. Spectro-polarimetric characterization of exoplanetary atmospheres is feasible with an extremely large telescope and a direct observing spectro-polarimeter.

We carried out low-resolution optical spectroscopy of 51 main-belt asteroids, most of which have highly-inclined orbits. They are selected from D-type candidates in the SDSS-MOC 4 catalog. Using the University of Hawaii 2.2m telescope and the Inter-University Centre for Astronomy and Astrophysics 2m telescope in India, we determined the spectral types of 38 asteroids. Among them, eight asteroids were classified as D-type asteroids. Fractions of D-type asteroids are 3.0±1.1% for low orbital inclination main-belt asteroids and 7.3 ±2.0% for high orbital inclination main-belt asteroids. The results of our study indicate that some D-type asteroids were formed within the ecliptic region between the main belt and Jupiter, and were then perturbed by Jupiter.

We report the results of optical-infrared follow-up observations of the gravitational wave (GW) event GW151226 detected by the Advanced LIGO in the framework of J-GEM (Japanese collaboration for Gravitational wave ElectroMagnetic follow-up). We performed wide-field optical imaging surveys with the Kiso Wide Field Camera (KWFC), Hyper Suprime-Cam (HSC), and MOA-cam3. The KWFC survey started at 2.26 d after the GW event and covered 778 deg2 centered at the high Galactic region of the skymap of GW151226. We started the HSC follow-up observations from ∼12 d after the event and covered an area of 63.5 deg2 of the highest probability region of the northern sky with limiting magnitudes of 24.6 and 23.8 for the i and z bands, respectively. MOA-cam3 covered 145 deg2 of the skymap with the MOA-red filter ∼2.5mon after the GW alert. The total area covered by the wide-field surveys was 986.5 deg2. The integrated detection probability for the observed area was ∼29%. We also performed galaxy-targeted observations with six optical and near-infrared telescopes from 1.61 d after the event. A total of 238 nearby (≥100Mpc) galaxies were observed with a typical I band limiting magnitude of ∼19.5. We detected 13 supernova candidates with the KWFC survey, and 60 extragalactic transients with the HSC survey. Two thirds of the HSC transients were likely supernovae and the remaining one third were possible active galactic nuclei. With our observational campaign, we found no transients that are likely to be associated with GW151226.

We find a new substellar companion to the Pleiades member star, Pleiades HII 3441, using the Subaru telescope with adaptive optics. The discovery is made as part of the high-contrast imaging survey to search for planetary-mass and substellar companions in the Pleiades and young moving groups. The companion has a projected separation of 0.'' 49 +/- 0.'' 02 (66 +/- 2 au) and a mass of 68 +/- 5 M-J based on three observations in the J-, H-, and K-s-bands. The spectral type is estimated to be M7 (similar to 2700 K), and thus no methane absorption is detected in the H band. Our Pleiades observations result in the detection of two substellar companions including one previously reported among 20 observed Pleiades stars, and indicate that the fraction of substellar companions in the Pleiades is about 10.0(-8.8)(+26.1)%. This is consistent with multiplicity studies of both the Pleiades stars and other open clusters.

From 2013 April to 2014 April, we performed X-ray and optical simultaneous monitoring of the type 1.5 Seyfert galaxy NGC. 3516. We employed Suzaku and five Japanese ground-based telescopes-the Pirka, Kiso Schmidt, Nayuta, MITSuME, and the Kanata telescopes. The Suzaku observations were conducted seven times with various intervals ranging from days or weeks to months, with an exposure of similar to 50 ks each. The optical B-band observations not only covered those of Suzaku almost simultaneously, but also followed the source as frequently as possible. As a result, NGC. 3516 was found in its faint phase with a 2-10 keV flux of 0.21-2.70. x 10(-1)1 erg s(-1) cm(-2). The 2-45 keV X-ray spectra were composed of a dominant variable hard power-law (PL) continuum with a photon index of similar to 1.7 and a nonrelativistic reflection component with a prominent Fe-Ka emission line. Producing the B-band light curve by differential image photometry, we found that the B-band flux changed by similar to 2.7 x 10(-1)1 erg s(-1) cm(-2), which is comparable to the X-ray variation, and we detected a significant flux correlation between the hard PL component in X-rays and the B-band radiation, for the first time in NGC. 3516. By examining their correlation, we found that the X-ray flux preceded that in the B band by 2.0(-0.6)(+0.7) days (1 sigma error). Although this result supports the X-ray reprocessing model, the derived lag is too large to be explained by the standard view, which assumes a "lamppost"-type X-ray illuminator located near a standard accretion disk. Our results are better explained by assuming a hot accretion flow and a truncated disk.

We present a measurement of H2O ice crystallinity on the surface of trans-neptunian objects with near-infrared narrow-band imaging. The newly developed photometric technique allows us to efficiently determine the strength of a 1.65 μm absorption feature in crystalline H2O ice. Our data for three large objects - Haumea, Quaoar, and Orcus - which are known to contain crystalline H2O ice on the surfaces, show a reasonable result with high fractions of the crystalline phase. It can also be pointed out that if the grain size of H2O ice is larger than ∼20 μm, the crystallinities of these objects are obviously below 1.0, which suggests the presence of the amorphous phase. In particular, Orcus exhibits a high abundance of amorphous H2O ice compared to Haumea and Quaoar, possibly indicating a correlation between the bulk density of the bodies and the degree of surface crystallization. We also found the presence of crystalline H2O ice on Typhon and 2008 AP129, both of which are smaller than the minimum size limit for inducing cryovolcanism as well as a transition from amorphous to crystalline phase through thermal evolution due to the decay of long-lived isotopes.

A radial velocity (RV) survey for intermediate-mass giants has been in operation for over a decade at Okayama Astrophysical Observatory (OAO). The OAO survey has revealed that some giants show long-term linear RV accelerations (RV trends), indicating the presence of outer companions. Direct-imaging observations can help clarify what objects generate these RV trends. We present the results of high-contrast imaging observations of six intermediate-mass giants with long-term RV trends using the Subaru Telescope and HiCIAO camera. We detected co-moving companions to gamma Hya B (0.61(-0.14)(+0.12)M(circle dot)), HD 5608 B (0.10 +/- 0.01M(circle dot)), and HD 109272 B (0.28 +/- 0.06M(circle dot)). For the remaining targets (iota Dra, 18 Del, and HD 14067), we exclude companions more massive than 30-60 M-Jup at projected separations of 1 ''-7 ''. We examine whether these directly imaged companions or unidentified long-period companions can account for the RV trends observed around the six giants. We find that the Kozai mechanism can explain the high eccentricity of the inner planets iota Dra b, HD 5608 b, and HD 14067 b.

We report the detection of a double planetary system around the evolved intermediate-mass star HD 47366 from precise radial-velocity measurements at the Okayama Astrophysical Observatory, Xinglong Station, and Australian Astronomical Observatory. The star is a K1 giant with a mass of 1.81 ± 0.13 M⊙, a radius of 7.30 ± 0.33 R⊙, and solar metallicity. The planetary system is composed of two giant planets with minimum masses of 1.75-0.17 +0.20 MJ and 1.86-0.15 +0.16 MJ, orbital periods of 363.3-2.4 +2.5 days and 684.7-4.9 +5.0 days, and eccentricities of 0.089-0.060 +0.079 and 0.278-0.094 +0.067, respectively, which are derived by a double Keplerian orbital fit to the radial-velocity data. The system adds to the population of multi-giant-planet systems with relatively small orbital separations, which are preferentially found around evolved intermediate-mass stars. Dynamical stability analysis for the system revealed, however, that the best-fit orbits are unstable in the case of a prograde configuration. The system could be stable if the planets were in 2:1 mean-motion resonance, but this is less likely, considering the observed period ratio and eccentricity. A present possible scenario for the system is that both of the planets have nearly circular orbits, namely the eccentricity of the outer planet is less than ∼0.15, which is just within 1.4σ of the best-fit value, or the planets are in a mutually retrograde configuration with a mutual orbital inclination larger than 160°.

We carried out optical high-resolution spectroscopy of T Tauri stars using the Subaru Telescope. Using archived data from the Keck Telescope and the Very Large Telescope, we detected forbidden lines of [S II] at 4069 Å, in addition to those of [O I] at 5577 Å and 6300 Å, for 13 T Tauri stars. We consider that low-velocity components of these forbidden lines emanate from the wind associated with T Tauri stars. Using two flux ratios of the three lines, we simultaneously determined the hydrogen density and temperature of the winds. The winds of T Tauri stars have a hydrogen density of 2.5 × 106 cm-3 - 2.5 × 109 cm-3 and a temperature of 10800 -18 000 K. The mass loss rates by the wind are estimated to lie in the range from 2.0 × 10-10 Mo yr-1 to 1.4 × 10-9 Mo yr-1. The mass loss rates are found to increase with increasing mass accretion rates. The ratio of the mass loss rate to the mass accretion rate is 0.001-0.1 for classical T Tauri stars and 0.1-1 for transitional disk objects.

We present our optical follow-up observations to search for an electromagnetic counterpart of the first gravitational wave source GW150914 in the framework of the Japanese collaboration for Gravitational wave ElectroMagnetic follow-up (J-GEM), which is an observing group utilizing optical and radio telescopes in Japan, as well as in New Zealand, China, South Africa, Chile, and Hawaii. We carried out a wide-field imaging survey with the Kiso Wide Field Camera (KWFC) on the 1.05m Kiso Schmidt telescope in Japan and a galaxy-targeted survey with Tripole5 on the B&amp C 61cm telescope in New Zealand. Approximately 24 deg2 regions in total were surveyed in i-band with KWFC and 18 nearby galaxies were observed with Tripole5 in g-, r-, and i-bands 4-12 days after the gravitational wave detection. Median 5 σ depths are i 18.9mag for the KWFC data and g 18.9mag, r 18.7mag, and i 18.3mag for the Tripole5 data. The probability for a counterpart to be in the observed area is 1.2% in the initial skymap and 0.1% in the final skymap. We do not find any transient source associated to an external galaxy with spatial offset from its center, which is consistent with the local supernova rate.

We present the results of an age determination study for pre-main sequence stars in the Ophiuchus molecular cloud. The ages of eight pre-main sequence stars were estimated from surface gravities derived from high-resolution spectroscopy. The average age of the target stars was 0.7 Myr. By comparing the individual age and the near-infrared color excess, we found that color excess decreases gradually with a constant rate and the lifetime of the inner disk was determined to be 1.2 Myr. The estimated lifetime is nearly a half of the time compared to that of the pre-main sequence stars in the Taurus molecular cloud estimated with the same method. This result indicates that the disk evolution timescale depends on the environment of the star-forming region.

We compared the number of faint stars detected in deep survey fields with the current stellar distribution model of the Galaxy and found that the detected number in the H band is significantly smaller than the predicted number. This indicates that M-dwarfs, the major component, are fewer in the halo and the thick disk. We used archived data of several surveys in both the north and south field of GOODS (Great Observatories Origins Deep Survey), MODS (MOIRCS Deep Survey) in GOODS-N, and ERS (Early Release Science) and CANDELS (Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey) in GOODS-S. The number density of M-dwarfs in the halo has to be 20%+/- 13% relative to that in the solar vicinity, in order for the detected number of stars fainter than 20.5 mag in the H band to match with the predicted value from the model. In the thick disk, the number density of M-dwarfs must be reduced (52%+/- 13%) or the scale height must be decreased (similar to 600 pc). Alternatively, overall fractions of the halo and thick disks can be significantly reduced to achieve the same effect, because our sample mainly consists of faint M-dwarfs. Our results imply that the M-dwarf population in regions distant from the Galactic plane is significantly smaller than previously thought. We then discussed the implications this has on the suitability of the model predictions for the prediction of non-companion faint stars in direct imaging extrasolar planet surveys by using the best-fitting number densities.

We present a Subaru/Infrared Camera and Spectrograph H-band image of the edge-on debris disk around the F2V star HD 15115. We detected the debris disk, which has a bow shape and an asymmetric surface brightness, at a projected separation of 1″-3″ (∼ 50-150 au). The disk surface brightness is ∼ 0.5-1.5 mag brighter on the western side than on the eastern side. We use an inclined annulus disk model to probe the disk geometry. The model fitting suggests that the disk has an inner hole with a radius of 86 au and an eccentricity of 0.06. The disk model also indicates that the amount of dust on the western side is 2.2 times larger than that on the eastern side. A several Jupiter-mass planet may exist at ≥ 45 au and capture grains at the Lagrangian points to open the eccentric gap. This scenario can explain both the eccentric gap and the difference in the amount of dust. In case of the stellar age of several 100 Myr, a dramatic planetesimal collision possibly causes the dust to increase in the western side. Interstellar medium interaction is also considered as a possible explanation of the asymmetric surface brightness, however, it hardly affects large grains in the vicinity of the inner hole.

We present new L′ (3.8 μm) and Brα (4.05 μm) data and reprocessed archival L′ data for the young, planet-hosting star HR 8799 obtained with Keck/NIRC2, VLT/NaCo, and Subaru/IRCS. We detect all four HR 8799 planets in each data set at a moderate to high signal-to-noise ratio (S/N ≳ 6-15). We fail to identify a fifth planet, "HR 8799 f," at r &lt 15 AU at a 5σ confidence level: one suggestive, marginally significant residual at 0.″2 is most likely a point-spread function artifact. Assuming companion ages of 30 Myr and the Baraffe planet cooling models, we rule out an HR 8799 f with a mass of 5 MJ (7 MJ ), 7 MJ (10 MJ ), or 12 MJ (13 MJ ) at r proj 12 AU, 9 AU, and 5 AU, respectively. All four HR 8799 planets have red early T dwarf-like L′-[4.05] colors, suggesting that their spectral energy distributions peak in between the L′ and M′ broadband filters. We find no statistically significant difference in HR 8799 cde's color. Atmosphere models assuming thick, patchy clouds appear to better match HR 8799 bcde's photometry than models assuming a uniform cloud layer. While non-equilibrium carbon chemistry is required to explain HR 8799 b and c's photometry/spectra, evidence for it from HR 8799 d and e's photometry is weaker. Future, deep-IR spectroscopy/spectrophotometry with the Gemini Planet Imager, SCExAO/CHARIS, and other facilities may clarify whether the planets are chemically similar or heterogeneous.

A high angular resolution near-infrared image that shows the intensity of polarization for the GG Tau A binary system was obtained with the Subaru Telescope. The image shows a circumbinary disk scattering the light from the central binary. The azimuthal profile of the intensity of polarization for the circumbinary disk is roughly reproduced by a simple disk model with the Henyey-Greenstein phase function and the Rayleigh function, indicating there are small dust grains at the surface of the disk. Combined with a previous observation of the circumbinary disk, our image indicates that the gap structure in the circumbinary disk orbits counterclockwise, but material in the disk orbits clockwise. We propose that there is a shadow caused by material located between the central binary and the circumbinary disk. The separations and position angles of the stellar components of the binary in the past 20 yr are consistent with the binary orbit with a = 33.4 AU and e = 0.34.

We present near-infrared high-contrast imaging photometry and integral field spectroscopy of ROXs 42B, a binary M0 member of the 1-3 Myr old ρ Ophiuchus star-forming region, from data collected over 7 years. Each data set reveals a faint companion - ROXs 42Bb - located 1.″16 (rproj 150 AU) from the primaries at a position angle consistent with a point source identified earlier by Ratzka et al. ROXs 42Bb's astrometry is inconsistent with a background star but consistent with a bound companion, possibly one with detected orbital motion. The most recent data set reveals a second candidate companion at 0.″5 of roughly equal brightness, though preliminary analysis indicates it is a background object. ROXs 42Bb's H and Ks band photometry is similar to dusty/cloudy young, low-mass late M/early L dwarfs. K band VLT/SINFONI spectroscopy shows ROXs 42Bb to be a cool substellar object (M8-L0 Teff 1800-2600 K), not a background dwarf star, with a spectral shape indicative of young, low surface gravity planet-mass companions. We estimate ROXs 42Bb's mass to be 6-15 MJ, either below the deuterium-burning limit and thus planet mass or straddling the deuterium-burning limit nominally separating planet-mass companions from other substellar objects. Given ROXs 42b's projected separation and mass with respect to the primaries, it may represent the lowest mass objects formed like binary stars or a class of planet-mass objects formed by protostellar disk fragmentation/disk instability, the latter slightly blurring the distinction between non-deuterium-burning planets like HR 8799 bcde and low-mass, deuterium-burning brown dwarfs. © 2014. The American Astronomical Society. All rights reserved.

We propose a new high contrast imager for Kyoto 4m segmented telescope called SEICA (Second-generation Exoplanet Imager with Coronagraphic Adaptive optics), aiming at detection and characterization of selfluminous gas giants within 10AU around nearby stars. SEICA is aggressively optimized for high performance at very small inner working angle, 10-6 detection contrast at 0".1 in 1-hour integration. We start the on-sky commissioning test in 2016 and the science observations in 2017. Since it is the first time to realize the highcontrast imaging on the segmented telescope, SEICA is an important step toward future high contrast sciences on Extremely Large Telescopes (ELTs). This paper presents an overall of the SEICA program and the conceptual design for ultimate performance under given atmospheric conditions.

We have developed a visible imager and spectrograph, Nayoro Optical Camera and Spectrograph (NaCS), installed at the f/12 Nasmyth focus of the 1.6-m Pirka telescope of the Hokkaido University in Hokkaido, Japan. The optical and mechanical design is similar to that of WFGS2 of the University of Hawaii 2.2-m telescope (UH88), however the camera is newly designed. The spectral coverage is 380-970 nm, and the field of view is 8.4 x 4.5 arcmin with a pixel scale of 0.247 arcsec pixel(-1). The SDSS (g', r', i', z') filters, Johnson (B, V) filters and a replica grism (R similar to 300 at 650 nm) are equipped. The slit width can be selected from 2, 3, and 4 arcsec. We selected a 2k x 1k fully-depleted back-illuminated Hamamatsu CCD as a detector, because it has a high quantum efficiency (>= 80 %) over optical wavelength. The Kiso Array Controller (KAC) is used as a CCD controller. The first light observation was done on November 2011. NaCS is used mainly for long-term spectroscopic monitor of active galactic nuclei. It is also used for several astronomical observations such as light-curve measurements of asteroids and search of pre-main-sequence stars and brown dwarfs by slit-less spectroscopy as a major facility instrument of the Pirka telescope. We present the design, construction, integration, and performance of this instrument.

We present the results of our JHKs photometry of asteroid 2012 DA14 at its closest approach to Earth on 2013 February 15. Possible spectral changes associated with resurfacing by planetary encounters are of great interest. The Earth flyby of 2012 DA14 provided a rare opportunity to investigate this effect. Our observations were conducted using the Nishiharima Infrared Camera (NIC) attached to the 2.0 m Nayuta telescope at the Nishi-Harima Astronomical Observatory. Despite the extraordinarily fast sky motion of up to near 50″ s-1, the telescope successfully tracked the asteroid. The NIC achievement of three-band simultaneous observations allowed us to reliably deduce the colors of this fast-moving object. The derived near-infrared relative reflectances are flat, which is consistent with the classification of the asteroid as L-type. The J́-H and H́-Ks colors at 0.5-1 hr after the closest approach are compared with those observed by de León (2013, A&amp A, 555, L2) at́ ∼ 10 hr after the closest time. We did not detect color changes significantly exceeding the photometric errors, which aré ∼ 0.1 mag. This project has demonstrated the potential of the NIC as a three-band simultaneous imager, especially for observations of rapidly time-variable phenomena. © 2014 The Author.