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Honda S.,Gunma Astronomical Observatory | Honda S.,Kyoto University | Aoki W.,Japan National Astronomical Observatory | Aoki W.,Graduate University for Advanced Studies | And 2 more authors.
Astrophysical Journal

We report Zn abundances for 18 very metal-poor stars studied in our previous work, covering the metallicity range -3.2< [Fe/H] <-2.5. The [Zn/Fe] values of most stars show an increasing trend with decreasing [Fe/H] in this metallicity range, confirming the results found by previous studies. However, the extremely metal-poor star BS 16920-017([Fe/H] =-3.2) exhibits a significantly high [Zn/Fe] ratio ([Zn/Fe] = +1.0). Comparison of the chemical abundances of this object with HD 4306, which has similar atmospheric parameters to BS 16920-017, clearly demonstrates a deficiency of α elements and neutron-capture elements in this star, along with enhancements of Mn and Ni, as well as Zn. The association with a hypernova explosion that has been proposed to explain the high Zn abundance ratios found in extremely metal-poor stars is a possible explanation, although further studies are required to fully interpret the abundance pattern of this object. © 2011. The American Astronomical Society. All rights reserved. Source

Sadakane K.,Osaka Kyoiku University | Kambe E.,Japan National Astronomical Observatory | Hashimoto O.,Gunma Astronomical Observatory | Honda S.,University of Hyogo | Sato B.,Tokyo Institute of Technology
Publications of the Astronomical Society of Japan

Frequent high-resolution spectroscopic observations of ε Aur during the 2009-2011 eclipse revealed temporal appearances of low-excitation absorption lines of neutral iron peak elements. Several 0 eV lines of Fe I were detected near the end of the first half of the eclipse. They had migrated toward shorter wavelength, became much strong after the third contact, and then disappeared after the fouth contact. Curiously, the widths of these temporal absorption lines became broader for about a 100-d period just before the third contact. The radial velocity measured for these lines follows that of the KI line at 7699 A°, implying that these lines originated in a rotating disk around the secondary star, which occulted the primary star. Weak and sharp absorption lines of low excitation neutral metals, such as Sc I, Ti I, VI, Cr I, and MnI, were observed only for a short period from the third contact to the fourth contact, and they were all blue-shifted by ∼40 km s-1. These observations show that the rotating disk around the secondary star is not axially symmetric, but suggest that a clump of cool gas concentrated in a region observed projected on the primary star near at the end of the eclipse. © 2013 Astronomical Society of Japan. Source

Maciejewski G.,Astrophysikalisches Institute und Universitats Sternwarte | Maciejewski G.,Nicolaus Copernicus University | Dimitrov D.,Bulgarian Academy of Science | Neuhauser R.,Astrophysikalisches Institute und Universitats Sternwarte | And 14 more authors.
Monthly Notices of the Royal Astronomical Society

Transit timing analysis may be an effective method of discovering additional bodies in extrasolar systems that harbour transiting exoplanets. The deviations from the Keplerian motion, caused by mutual gravitational interactions between planets, are expected to generate transit timing variations of transiting exoplanets. In 2009, we collected nine light curves of eight transits of the exoplanet WASP-10b. Combining these data with those published, we have found that transit timing cannot be explained by a constant period but by a periodic variation. Simplified three-body models, which reproduce the observed variations of timing residuals, were identified by numerical simulations. We have found that the configuration with an additional planet with a mass of ∼0.1MJ and an orbital period of ∼5.23 d, located close to the outer 5:3 mean motion resonance, is the most likely scenario. If the second planet is a transiter, the estimated flux drop will be ∼0.3 per cent and can be observed with a ground-based telescope. Moreover, we present evidence that the spots on the stellar surface and the rotation of the star affect the radial-velocity curve, giving rise to a spurious eccentricity of the orbit of the first planet. We argue that the orbit of WASP-10b is essentially circular. Using the gyrochronology method, the host star was found to be 270 ± 80 Myr old. This young age can explain the large radius reported for WASP-10b. © 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS. Source

Stonkute R.,Lithuanian Academy of Sciences | Arimoto N.,Japan National Astronomical Observatory | Arimoto N.,Graduate University for Advanced Studies | Hasegawa T.,Gunma Astronomical Observatory | And 4 more authors.
Astrophysical Journal, Supplement Series

We have surveyed a complete extent of Leo A - an apparently isolated gas-rich low-mass dwarf irregular galaxy in the Local Group. The B, V, and I passband CCD images (typical seeing ∼0.″8) were obtained with the Subaru Telescope equipped with the Suprime-Cam mosaic camera. The wide-field (20′ × 24′) photometry catalog of 38,856 objects (V ∼ 16-26 mag) is presented. This survey is also intended to serve as "a finding chart" for future imaging and spectroscopic observation programs of Leo A. © 2014. The American Astronomical Society. All rights reserved. Source

Sadakane K.,Osaka Kyoiku University | Kambe E.,Japan National Astronomical Observatory | Sato B.,Tokyo Institute of Technology | Honda S.,Gunma Astronomical Observatory | And 2 more authors.
Publications of the Astronomical Society of Japan

A detailed abundance analysis of the primary star of ε Aur before an eclipse was carried out using a very high signal-to-noise ratio optical-region spectrum. An A7 Iab supergiant HD 81471, presumably a member of the Vela OB1 association, was used as a reference. We obtained atmospheric parameters (T eff, logg, and ξt) to be (8025K, 1.0 and 10 km s -1) and (8050K, 1.0 and 7 kms-1) for ε Aur and HD 81471, respectively. The abundances of Mg, Si, S, Ca, Sc, Ti, Cr, and Fe were very close to the solar abundances in both stars. Light elements C and O were under-abundant, while N and Na were over-abundant in both stars, after correcting for non-LTE effects. Definite under-abundances of Sr were detected in both stars. Slight, but definite, over-abundances were found in ε Aur for the s-process elements Y, Zr, and Ba, when compared with the results of HD 81471. Enhancements in the abundances of N, Na, and s-process elements might indicate the occurences of thermal dredge-up and the s-process nucleosynthesis in ε Aur during the past evolution. © 2010. Astronomical Society of Japan. Source

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