Eri Toyota

The N2K Consortium. II. A Transiting Hot Saturn around HD 149026 with a Large Dense Core

Doppler measurements from Subaru and Keck have revealed radial velocity variations in the V = 8.15, G0 IV star HD 149026 consistent with a Saturn-mass planet in a 2.8766 day orbit. Photometric observations at Fairborn Observatory have detected three complete transit events with depths of 0.003 mag at the predicted times of conjunction. HD 149026 is now the second-brightest star with a transiting extrasolar planet. The mass of the star, based on interpolation of stellar evolutionary models, is 1.3 ± 0.1 M_☉; together with the Doppler amplitude K_1 = 43.3 m s^(-1), we derive a planet mass M sin i = 0.36M_J and orbital radius 0.042 AU. HD 149026 is chromospherically inactive and metal-rich with spectroscopically derived [Fe/H] = +0.36, T_(eff) = 6147 K, log g = 4.26, and v sin i = 6.0 km s^(-1). Based on T_(eff) and the stellar luminosity of 2.72 L_☉, we derive a stellar radius of 1.45 R_☉. Modeling of the three photometric transits provides an orbital inclination of 85o.3 ± 1o.0 and (including the uncertainty in the stellar radius) a planet radius of (0.725 ± 0.05)R_J. Models for this planet mass and radius suggest the presence of a ~67 M_⊕ core composed of elements heavier than hydrogen and helium. This substantial planet core would be difficult to construct by gravitational instability.

A planetary companion to the hyades giant ε tauri

Wereportthedetection of anextrasolarplanet orbitingTau,oneof thegiantstarsintheHyadesopencluster.This is the first planet ever discovered in an open cluster. Precise Doppler measurements of this star from Okayama Astrophysical Observatory have revealed Keplerian velocity variations with an orbital period of 594:9 � 5:3 days, a semiamplitude of 95:9 � 1: 8ms � 1 , and an eccentricity of 0:151 � 0:023. The minimum mass of the companion is 7:6 � 0:2MJ,andthesemimajoraxisis1:93 � 0:03AUadoptingastellarmassof 2:7 � 0:1M� .Theageof 625Myr for the cluster sets the most secure upper limit ever on the timescale of giant planet formation. The mass of 2.7 Mfor thehoststarisrobustlydeterminedbyisochronefitting,whichmakesthestartheheaviestamongplanet-harboringstars. Puttingtogetherthefactthatnoplanetshavebeenfoundaroundabout100low-massdwarfsinthecluster,thefrequency of massive planets is suggested to be higher around high-mass stars than around low-mass ones. Subject headingg open clusters and associations: individual (Hyades) — planetary systems — stars: individual (� Tauri) — techniques: radial velocities

Five intermediate-period planets from the N2K sample

We report the detection of five Jovian-mass planets orbiting high-metallicity stars. Four of these stars were first observed as part of the N2K program, and exhibited low rms velocity scatter after three consecutive observations. However, follow-up observations over the last 3 years now reveal the presence of longer period planets with orbital periods ranging from 21 days to a few years. HD 11506 is a G0 V star with a planet of M sin i = 4.74 M_(Jup) in a 3.85 yr orbit. HD 17156 is a G0 V star with a 3.12 M_(Jup) planet in a 21.2 day orbit. The eccentricity of this orbit is 0.67, one of the highest known for a planet with a relatively short period. The orbital period for this planet places it in a region of parameter space where relatively few planets have been detected. HD 125612 is a G3 V star with a planet of M sin i = 3.5 M_(Jup) in a 1.4 yr orbit. HD 170469 is a G5 IV star with a planet of M sin i = 0.67 M_(Jup) in a 3.13 year orbit. HD 231701 is an F8 V star with planet of 1.08 M_(Jup) in a 142 day orbit. All of these stars have supersolar metallicity. Three of the five stars were observed photometrically, but showed no evidence of brightness variability. A transit search conducted for HD 17156 was negative, but covered only 25% of the search space, and so is not conclusive.

A SUBSTELLAR COMPANION TO THE INTERMEDIATE-MASS GIANT 11 COMAE

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 ± 0.32 days, a semiamplitude of 302.8 ± 2.6 m s−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 MJ, 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 programs 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.

Planetary Companions around Three Intermediate-Mass G and K Giants: 18 Delphini, ξ Aquilae, and HD 81688

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), � Aql (K0 III) and HD 81688 (K0 III–IV), are located in the clump region on the HR diagram with estimated masses of 2.1–2.3Mˇ .1 8 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. � Aq lb and HD 81688 b have minimum masses of 2.8 and 2.7MJ ,a nd reside in nearly circular orbits with periods of 137 and 184 d, respectively, which are the shortest ones around evolved stars. All of the substellar companions ever discovered around intermediate-mass (1.7–3.9Mˇ )c lump 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

Planetary Companions to Evolved Intermediate-Mass Stars: 14 Andromedae, 81 Ceti, 6 Lyncis, and HD167042

We report on the detection of four extrasolar planets orbiting evolved intermediate-mass stars from a precise Doppler survey of G-K giants at Okayama Astrophysical Observatory. All of the host stars are considered to be formerly early F-type or A-type dwarfs when they were on the main sequence. 14 And (K0 III) is a clump giant with a mass of 2.2 Mand has a planet of minimum mass m2 sin i = 4.8 MJ in a nearly circular orbit with a 186 d period. This is one of the innermost planets around evolved intermediate-mass stars, and such planets have only been discovered in clump giants. 81 Cet (G5 III) is a clump giant with 2.4 Mhosting a planet of m2 sin i = 5.3 MJ in a 953 d orbit with an eccentricity of e = 0.21. 6 Lyn (K0 IV) is a less-evolved subgiant with 1.7Mˇ, and has a planet of m2 sin i = 2.4 MJ in a 899 d orbit with e = 0.13. HD 167042 (K1 IV) is also a less-evolved star with 1.5 Mˇ hosting a planet of m2 sin i = 1.6 MJ in a 418 d orbit with e = 0.10. This planet was independently announced by Johnson et al. (2008, ApJ, 675, 784). All of the host stars have solar or sub-solar metallicity, which supports the lack of a metal-rich tendency in planet-harboring giants in contrast to the case of dwarfs.

Substellar Companions to Evolved Intermediate-Mass Stars: HD 145457 and HD 180314

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 K0 giant with a mass of 1.9 Mˇ, 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 K0 giant with 2.6Mˇ, and hosts a substellar companion of m2 sin i = 22 MJ, which falls in the brown-dwarf mass regime, in an orbit with P = 396 d and e = 0.26. HD 145457 b 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.

A Substellar Companion in a 1.3 yr Nearly-circular Orbit of HD 16760

We report the detection of a substellar companion orbiting the G5 dwarf HD 16760 from the N2K sample. Precise Doppler measurements of the star from Subaru and Keck revealed a Keplerian velocity variation with a period of 466.47 ± 0.35 d, a semiamplitude of 407.71 ± 0.84 m s^(–1), and an eccentricity of 0.084 ± 0.003. Adopting a stellar mass of 0.78 ± 0.05 M_☉, we obtain a minimum mass for the companion of 13.13 ± 0.56 M_(JUP), which is close to the planet/brown-dwarf transition, and the semimajor axis of 1.084 ± 0.023 AU. The nearly circular orbit despite the large mass and intermediate orbital period makes this companion unique among known substellar companions.

A Planetary Companion to the Intermediate-Mass Giant HD 100655

A precise radial-velocity survey conducted by a Korean–Japanese planet search program revealed a planetary companion around the intermediate-mass clump giant HD 100655. The radial velocity of the star exhibits a periodic Keplerian variation with a period, semi-amplitude, and eccentricity of 157.57 d, 35.2 m s � 1 , and 0.085, respectively. Adopting an estimated stellar mass of 2.4 Mˇ, we confirmed the presence of a planetary companion with a semimajor axis of 0.76 AU and a minimum mass of 1.7 MJ. The planet is the lowest-mass planet yet discovered around clump giants with masses greater than 1.9 Mˇ.

DETERMINATION OF ORBITAL ELEMENTS OF SPECTROSCOPIC BINARIES USING HIGH-DISPERSION SPECTROSCOPY

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 {approx}10 m s{sup -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.