研究者業績
  1. 研究者検索結果一覧
  2. 本田 敏志

本田 敏志

ホンダ サトシ  (Satoshi Honda)

基本情報

所属
兵庫県立大学 自然・環境科学研究所 天文科学センター 准教授
学位
博士（理学）(2002年3月 総合研究大学院大学)
J-GLOBAL ID
202001012251638629
researchmap会員ID
R000007165

研究分野

 1

論文

 39
  • Yuta Notsu, Adam F. Kowalski, Hiroyuki Maehara, Kosuke Namekata, Kenji Hamaguchi, Teruaki Enoto, Isaiah I. Tristan, Suzanne L. Hawley, James R. A. Davenport, Satoshi Honda, Kai Ikuta, Shun Inoue, Keiichi Namizaki, Daisaku Nogami, Kazunari Shibata
    The Astrophysical Journal 961(2) 189-189 2024年1月25日  
    Abstract We conducted the time-resolved simultaneous optical spectroscopic and photometric observations of mid-M-dwarf flare stars YZ CMi, EV Lac, and AD Leo. Spectroscopic observations were obtained using Apache Point Observatory 3.5 m and Small and Moderate Aperture Research Telescope System 1.5 m telescopes during 31 nights. Among the 41 detected flares, seven flares showed clear blue wing asymmetries in the Hα line, with various correspondences in flare properties. The duration of the blue wing asymmetries range from 20 minutes to 2.5 hr, including a flare showing the shift from blue to red wing asymmetry. Blue wing asymmetries can be observed during both white-light and candidate non-white-light flares. All of the seven flares showed blue wing asymmetries also in the Hβ line, but there are large varieties on which other chromospheric lines showed blue wing asymmetries. One among the 7 flares was also observed with soft X-ray spectroscopy, which enabled us to estimate the flare magnetic field and length of the flare loop. The line-of-sight velocities of the blueshifted components range from –73 to –122 km s−1. Assuming that the blueshifts were caused by prominence eruptions, the mass of upward-moving plasma was estimated to be 1015–1019 g, which are roughly on the relation between flare energy and erupting mass expected from solar coronal mass ejections (CMEs). Although further investigations are necessary for understanding the observed various properties, these possible prominence eruptions on M-dwarfs could evolve into CMEs, assuming the similar acceleration mechanism with solar eruptions.
  • Wako Aoki, Haining Li, Nozomu Tominaga, Tadafumi Matsuno, Satoshi Honda, Gang Zhao
    The Astrophysical Journal 955(1) 28-28 2023年9月1日  査読有り
    Abstract We report on the chemical composition of the very metal-poor (VMP; [Fe/H] = −2.9) star LAMOST J1645+4357, which was identified as a red giant having peculiar abundance ratios by Li et al. The standard abundance analysis is carried out for this object and the well-studied metal-poor star HD 122563, which has similar atmospheric parameters. LAMOST J1645+4357 has a remarkable abundance set, highlighted by these features: (1) nitrogen is significantly enhanced ([N/Fe] = +1.4), and the total abundance of C and N is also very high ([(C+N)/Fe] = +0.9); (2) α-elements are overabundant with respect to iron, as generally found in VMP stars; (3) Ti, Sc, Co, and Zn are significantly deficient; (4) Cr and Mn are enhanced compared to most of VMP stars; and (5) Sr and Ba are deficient, and the Sr/Ba ratio ([Sr/Ba] = −1.0) is significantly lower than the value expected for the r-process. The overall abundance pattern of this object from C to Zn is well reproduced by a faint supernova model assuming spherical explosion, except for the excess of Cr and Mn, which requires enhancement of incomplete Si burning or small contributions from a Type Ia or pair-instability supernova. There remains, however, a question as to why the abundance pattern of this star is so unique among VMP stars.
  • Kai Ikuta, Kosuke Namekata, Yuta Notsu, Hiroyuki Maehara, Soshi Okamoto, Satoshi Honda, Daisaku Nogami, Kazunari Shibata
    The Astrophysical Journal 948(1) 64-64 2023年5月1日  査読有り
    Abstract Starspots and stellar flares are indicators of stellar magnetic activity. The magnetic energy stored around spots is thought to be the origin of flares, but the connection is not completely understood. To investigate the relation between spot locations deduced from light curves and the occurrence of flares therein, we perform starspot modeling for the TESS light curves of three M-dwarf flare stars, AU Mic, YZ CMi, and EV Lac, using the code implemented in Paper I. The code enables us to deduce multiple stellar/spot parameters by the adaptive parallel tempering algorithm efficiently. We find that flare occurrence frequency is not necessarily correlated with the rotation phases of the light curve for each star. The result of starspot modeling shows that any spot is always visible to the line of sight in all phases, and we suggest that this can be one of the reasons why there is no or low correlation between rotation phases and flare frequency. In addition, the amplitude and shape of the light curve for AU Mic and YZ CMi have varied in two years between different TESS cycles. The result of starspot modeling suggests that this can be explained by the variations of spot size and latitude.
  • Shun Inoue, Hiroyuki Maehara, Yuta Notsu, Kosuke Namekata, Satoshi Honda, Keiichi Namizaki, Daisaku Nogami, Kazunari Shibata
    The Astrophysical Journal 948(1) 9-9 2023年4月27日  査読有り
    Abstract Stellar coronal mass ejections (CMEs) have recently received much attention for their impacts on exoplanets and stellar evolution. Detecting prominence eruptions, the initial phase of CMEs, as the blueshifted excess component of Balmer lines is a technique to capture stellar CMEs. However, most of prominence eruptions identified thus far have been slow and less than the surface escape velocity. Therefore, whether these eruptions were developing into CMEs remained unknown. In this study, we conducted simultaneous optical photometric observations with Transiting Exoplanet Survey Satellite and optical spectroscopic observations with the 3.8 m Seimei Telescope for the RS CVn-type star V1355 Orionis that frequently produces large-scale superflares. We detected a superflare releasing 7.0 × 1035 erg. In the early stage of this flare, a blueshifted excess component of Hα extending its velocity up to 760–1690 km s−1 was observed and thought to originate from prominence eruptions. The velocity greatly exceeds the escape velocity (i.e., ∼350 km s−1), which provides important evidence that stellar prominence eruptions can develop into CMEs. Furthermore, we found that the prominence is very massive (9.5 × 1018 g < M < 1.4 × 1021 g). These data will clarify whether such events follow existing theories and scaling laws on solar flares and CMEs even when the energy scale far exceeds solar cases.
  • Keiichi Namizaki, Kosuke Namekata, Hiroyuki Maehara, Yuta Notsu, Satoshi Honda, Daisaku Nogami, Kazunari Shibata
    The Astrophysical Journal 945(1) 61-61 2023年3月1日  査読有り
    <jats:title>Abstract</jats:title> <jats:p>Active M-type stars are known to often produce superflares on the surface. Radiation from stellar (super)flares is important for exoplanet habitability, but the mechanisms are not well understood. In this paper, we report simultaneous optical spectroscopic and photometric observations of a stellar superflare on an active M dwarf, YZ Canis Minoris, with the 3.8 m Seimei telescope and the Transiting Exoplanet Survey Satellite. The flare bolometric energy is <jats:inline-formula> <jats:tex-math> <?CDATA ${1.3}_{-0.6}^{+1.6}\times {10}^{34}\,\mathrm{erg}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>1.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.6</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.6</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>34</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <mml:mi>erg</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjacb928ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and the H<jats:italic>α</jats:italic> energy is <jats:inline-formula> <jats:tex-math> <?CDATA ${3.0}_{-0.1}^{+0.1}\times {10}^{32}\,\mathrm{erg}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>3.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.1</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>32</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <mml:mi>erg</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjacb928ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. The H<jats:italic>α</jats:italic> emission line profile shows red asymmetry throughout the flare, with a duration of 4.6–5.1 hr. The velocity of the red asymmetry is ∼200–500 km s<jats:sup>–1</jats:sup> and the line width of H<jats:italic>α</jats:italic> broadens up to 34 ± 14 Å. The redshifted velocity and line width of H<jats:italic>α</jats:italic> line decay more rapidly than the equivalent width, and their time evolutions are correlated with that of the white-light emission. This indicates the possibility of the white light, the H<jats:italic>α</jats:italic> red asymmetry, and the H<jats:italic>α</jats:italic> line broadening originating from nearly the same site, i.e., the dense chromospheric condensation region, heated by nonthermal electrons. On the other hand, the flux ratio of the redshifted excess components to the central components is enhanced one hr after the flare’s onset. This may be due to the main source of the red asymmetry changing to post-flare loops in the later phase of the flare.</jats:p>
もっとみる

MISC

 98
  • Yuta Notsu, Satoshi Honda, Hiroyuki Maehara, Shota Notsu, Takuya Shibayama, Daisaku Nogami, Kazunari Shibata
    Publications of the Astronomical Society of Japan 67(3) 2015年4月8日  
    We conducted high dispersion spectroscopic observations of 50 superflare stars with Subaru/HDS. These 50 stars were selected from the solar-type superflare stars that we had discovered from the Kepler data. More than half (34 stars) of these 50 target superflare stars show no evidence of binarity, and we estimated stellar parameters of these 34 stars in our previous study (Notsu et al. 2015, PASJ, 67, 32). According to our previous studies using Kepler data, superflare stars show quasi-periodic brightness variations whose amplitude (0.1%-10%) is much larger than that of the solar brightness variations (0.01%-0.1%) caused by the existence of sunspots on the rotating solar surface. In this study, we investigated whether these quasi-periodic brightness variations of superflare stars are explained by the rotation of a star with fairly large starspots, by using stellar parameters derived in Paper I. First, we confirmed that the value of the projected rotational velocity, vsini, is consistent with the rotational velocity estimated from the period of the brightness variation. Next, we measured the intensity of Caii infrared triplet lines and Hα line, good indicators of the stellar chromospheric activity, and compared them with other stellar properties. The intensity of Caii infrared triplet lines indicates that the mean magnetic field strength ((fB)) of the target superflare stars can be higher than that of the Sun. A correlation between the amplitude of the brightness variation and the intensity of Caii triplet line was found. All the targets expected to have large starspots because of their large amplitude of the brightness variation show high chromospheric activities compared to the Sun. These results support the idea that the brightness variation of superflare stars is due to the rotation with large starspots.
  • Yuta Notsu, Satoshi Honda, Hiroyuki Maehara, Shota Notsu, Takuya Shibayama, Daisaku Nogami, Kazunari Shibata
    Publications of the Astronomical Society of Japan 67(3) 2015年4月8日  
    We conducted high-dispersion spectroscopic observations of 50 superflare stars with Subaru High Dispersion Spectrograph (HDS), and measured the stellar parameters of them. These 50 targets were selected from the solar-type (G-type main sequence) superflare stars that we had discovered from the Kepler photometric data. As a result of these spectroscopic observations, we found that more than half (34) of our 50 targets have no evidence of binary systems. We then estimated the effective temperature (T&lt inf&gt eff&lt /inf&gt ), surface gravity (logg), metallicity ([Fe/H]), and projected rotational velocity (vsini) of these 34 superflare stars on the basis of our spectroscopic data. The accuracy of our estimations is higher than that of the Kepler Input Catalog (KIC) values, and the differences between our values and KIC values [(ΔT&lt inf&gt eff&lt /inf&gt )&lt inf&gt rms&lt /inf&gt ∼ 219 K, (Δlogg)&lt inf&gt rms&lt /inf&gt ∼ 0.37 dex, and (Δ[Fe/H])&lt inf&gt rms&lt /inf&gt ∼ 0.46 dex] are comparable to the large uncertainties and systematic differences of KIC values reported by the previous researchers. We confirmed that the estimated T&lt inf&gt eff&lt /inf&gt and logg values of the 34 superflare stars are roughly in the range of solar-type stars. In particular, these parameters and the brightness variation period (P&lt inf&gt 0&lt /inf&gt ) of nine of the stars are in the range of "Sun-like" stars (5600 ≤ T&lt inf&gt eff&lt /inf&gt ≤ 6000 K, logg ≥ 4.0, and P&lt inf&gt 0&lt /inf&gt &gt 10 d). Five of the 34 target stars are fast rotators (vsini ≥ 10 km s&lt sup&gt -1&lt /sup&gt ), while 22 stars have relatively low vsini values (vsini &lt 5 km s&lt sup&gt -1&lt /sup&gt ). These results suggest that stars that have spectroscopic properties similar to the Sun can have superflares, and this supports the hypothesis that the Sun might cause a superflare.
  • Wako Aoki, Takuma Suda, Timothy C. Beers, Satoshi Honda
    Astronomical Journal 149(2) 2015年2月1日  
    The fraction of binary systems in various stellar populations of the Galaxy and the distribution of their orbital parameters are important but not well-determined factors in studies of star formation, stellar evolution, and Galactic chemical evolution. While observational studies have been carried out for a large sample of nearby stars, including some metal-poor Population II stars, almost no constraints on the binary nature for extremely metal-poor (EMP [Fe/H] &lt -3.0) stars have yet been obtained. Here we investigate the fraction of double-lined spectroscopic binaries and carbon-enhanced metal-poor (CEMP) stars, many of which could have formed as pairs of low-mass and intermediate-mass stars, to estimate the lower limit of the fraction of binary systems having short periods. The estimate is based on a sample of very metal-poor stars selected from the Sloan Digital Sky Survey and observed at high spectral resolution in a previous study by Aoki et al. That survey reported 3 double-lined spectroscopic binaries and 11 CEMP stars, which we consider along with a sample of EMP stars from the literature compiled in the SAGA database. We have conducted measurements of the velocity components for stacked absorption features of different spectral lines for each double-lined spectroscopic binary. Our estimate indicates that the fraction of binary stars having orbital periods shorter than 1000 days is at least 10%, and possibly as high as 20% if the majority of CEMP stars are formed in such short-period binaries. This result suggests that the period distribution of EMP binary systems is biased toward short periods, unless the binary fraction of low-mass EMP stars is significantly higher than that of other nearby stars.
  • Yoichi Takeda, Satoshi Honda
    Publications of the Astronomical Society of Japan 67(2) 251-2516 2015年1月27日  
    With an aim to examine whether the surface oxygen composition suffers any appreciable change due to evolution-induced mixing of nuclear-processed material in the envelope of red giants, abundance determinations for O/Fe/Ni based on the synthetic spectrum-fitting method were performed by using the moderate-dispersion spectra in the 7770-7792 Å region (comprising O i 7771-5, Fe i 7780, and Ni i 7788 lines) for 16 stars of the old open cluster M 67 in various evolutionary stages from the turn-off point through the red giant branch. We could not find any meaningful difference in the oxygen abundances between the non-giant group (Teff &gt 5000 K) and the red-giant group (Teff &lt 5000 K), which are almost consistent with each other on average (despite that both have rather large dispersions of a few tenths dex caused by insufficient data quality), though only one giant star (S 1054) appears to show an exceptionally low O abundance and thus needs a more detailed study. This result may suggest that oxygen content in the stellar envelope is hardly affected (or any changes are insignificant) by the mixing of H-burning products in the red giant phase, as far as M 67 stars of low mass (∼ 1.3 M) are concerned, which is consistent with the prediction from the conventional stellar evolution theory of first dredge-up.
  • Masateru Ishiguro, Daisuke Kuroda, Hidekazu Hanayama, Jun Takahashi, Sunao Hasegawa, Yuki Sarugaku, Makoto Watanabe, Masataka Imai, Shuhei Goda, Hiroshi Akitaya, Yuhei Takagi, Kumiko Morihana, Satoshi Honda, Akira Arai, Kazuhiro Sekiguchi, Yumiko Oasa, Yoshihiko Saito, Tomoki Morokuma, Katsuhiro Murata, Daisaku Nogami, Takahiro Nagayama, Kenshi Yanagisawa, Michitoshi Yoshida, Kouji Ohta, Nobuyuki Kawai, Takeshi Miyaji, Hideo Fukushima, Jun-Ichi Watanabe, Cyrielle Opitom, Emmanu�l Jehin, Michael Gillon, Jeremie J. Vaubaillon
    Astrophysical Journal Letters 798(2) 2015年1月1日  
    We report a new observation of the Jupiter family comet 209P/LINEAR during its 2014 return. The comet is recognized as a dust source of a new meteor shower, the May Camelopardalids. 209P/LINEAR was apparently inactive at a heliocentric distance rh = 1.6 AU and showed weak activity at rh ≤ 1.4 AU. We found an active region of &lt 0.001% of the entire nuclear surface during the comet's dormant phase. An edge-on image suggests that particles up to 1 cm in size (with an uncertainty of factor 3-5) were ejected following a differential power-law size distribution with index q = -3.25 � 0.10. We derived a mass-loss rate of 2-10 kg s-1 during the active phase and a total mass of ≈5 � 107 kg during the 2014 return. The ejection terminal velocity of millimeter- to centimeter-sized particles was 1-4 m s-1, which is comparable to the escape velocity from the nucleus (1.4 m s-1). These results imply that such large meteoric particles marginally escaped from the highly dormant comet nucleus via the gas drag force only within a few months of the perihelion passage.
  • Taichi Kato, Franz-Josef Hambsch, Hiroyuki Maehara, Gianluca Masi, Francesca Nocentini, Pavol A. Dubovsky, Igor Kudzej, Kazuyoshi Imamura, Minako Ogi, Kenji Tanabe, Hidehiko Akazawa, Thomas Krajci, Ian Miller, Enrique De Miguel, Arne Henden, Ryo Noguchi, Takehiro Ishibashi, Rikako Ono, Miho Kawabata, Hiroshi Kobayashi, Daisuke Sakai, Hirochika Nishino, Hisami Furukawa, Kazunari Masumoto, Katsura Matsumoto, Colin Littlefield, Tomohito Ohshima, Chikako Nakata, Satoshi Honda, Kenzo Kinugasa, Osamu Hashimoto, William Stein, Roger D. Pickard, Seiichiro Kiyota, Elena P. Pavlenko, Oksana I. Antonyuk, Aleksei V. Baklanov, Kirill Antonyuk, Denis Samsonov, Nikolaj Pit, Aleksei Sosnovskij, Arto Oksanen, Caisey Harlingten, Jenni Tyyskä, Berto Monard, Sergey Yu. Shugarov, Drahomir Chochol, Kiyoshi Kasai, Yutaka Maeda, Kenji Hirosawa, Hiroshi Itoh, Richard Sabo, Joseph Ulowetz, Etienne Morelle, Raul Michel, Genaro Suarez, Nick James, Shawn Dvorak, Irina B. Voloshina, Michael Richmond, Bart Staels, David Boyd, Maksim V. Andreev, Nikolai Parakhin, Natalia Katysheva, Atsushi Miyashita, Kazuhiro Nakajima, Greg Bolt, Stefano Padovan, Peter Nelson, Donn R. Starkey, Denis Buczynski, Peter Starr, William N. Goff, Denis Denisenko, Christopher S. Kochanek, Benjamin Shappee, Krzysztof Z. Stanek, Jose L. Prieto, Koh-Ichi Itagaki, Shizuo Kaneko, Rod Stubbings, Eddy Muyllaert, Jeremy Shears, Patrick Schmeer, Gary Poyner, Miguel Rodriguez-Marco
    Publications of the Astronomical Society of Japan 66(2) 2014年4月1日  
    Continuing the project described in Kato et al. (2009, PASJ, 61, S395), we collected times of superhump maxima for SU UMa-type dwarf novae mainly observed during the 2012-2013 season. We found three objects (V444 Peg, CSS J203937, and MASTER J212624) having strongly positive period derivatives despite the long orbital period (Porb). By using the period of growing stage (stage A) superhumps, we obtained mass ratios for six objects. We characterized nine new WZ Sge-type dwarf novae. We made a pilot survey of the decline rate in the slowly fading parts of SU UMa-type and WZ Sge-type outbursts. The decline time scale was found to generally follow an expected Porb 1/4 dependence, and WZ Sge-type outbursts also generally follow this trend. There are some objects which show slower decline rates, and we consider these objects good candidates for period bouncers. We also studied unusual behavior in some objects, including BK Lyn which made a transition from an ER UMa-type state to a novalike (standstill) state in 2013, and unusually frequent occurrences of superoutbursts in NY Ser and CR Boo. We applied the least absolute shrinkage and selection operator (Lasso) power spectral analysis, which has been proven to be very effective in analyzing the Kepler data, to the ground-based photometry of BK Lyn, and detected a dramatic disappearance of the signal of negative superhumps in 2013. We suggested that the mass-transfer rates did not strongly vary between the ER UMa-type state and novalike state in BK Lyn, and this transition was less likely caused by a systematic variation of the mass-transfer rate. © 2014 The Author.
  • Daisaku Nogami, Yuta Notsu, Satoshi Honda, Hiroyuki Maehara, Shota Notsu, Takuya Shibayama, Kazunari Shibata
    Publications of the Astronomical Society of Japan 66(2) 2014年4月1日  
    We report on the results of high dispersion spectroscopy of two superflare stars, KIC9766237 and KIC9944137 with Subaru/HDS. Superflare stars are G-type main sequence stars, but show gigantic flares compared to the Sun, which have recently been discovered in the data obtained with the Kepler spacecraft. Though most of these stars are thought to have a rotation period shorter than 10d on the basis of photometric variabilities, the two targets of the present paper are estimated to have rotation periods of 21.8d and 25.3d. Our spectroscopic results clarified that these stars have stellar parameters similar to those of the Sun in terms of the effective temperature, surface gravity, and metallicity. The projected rotational velocities derived by us are consistent with the photometric rotation period, indicating a fairly high inclination angle. The average strength of the magnetic field on the surface of these stars are estimated to be 1-20G, by using the absorption line of Caii 8542. We could not detect any hint of binarity in our spectra, although more data are needed to firmly rule out the presence of an unseen low-mass companion. These results claim that the spectroscopic properties of these superflare stars are very close to those of the Sun, and support the hypothesis that the Sun might cause a superflare. © 2014 The Author.
  • Masayuki Yamanaka, Keiichi Maeda, Miho Kawabata, Masaomi Tanaka, Katsutoshi Takaki, Issei Ueno, Kazunari Masumoto, Koji S. Kawabata, Ryosuke Itoh, Yuki Moritani, Hiroshi Akitaya, Akira Arai, Satoshi Honda, Koichi Nishiyama, Fujio Kabashima, Katsura Matsumoto, Daisaku Nogami, Michitoshi Yoshida
    Astrophysical Journal Letters 782(2) 2014年2月20日  
    We report photometric and spectroscopic observations of the nearby Type Ia Supernova (SN Ia) 2012ht from -15.8 days to +49.1 days after B-band maximum. The decline rate of the light curve is Δm 15(B) = 1.39 ± 0.05 mag, which is intermediate between normal and subluminous SNe Ia, and similar to that of the "transitional" Type Ia SN 2004eo. The spectral line profiles also closely resemble those of SN 2004eo. We were able to observe SN 2012ht at a very early phase, when it was still rising and was about three magnitudes fainter than at the peak. The rise time to the B-band maximum is estimated to be 17.6 ± 0.5 days and the time of the explosion is MJD 56277.98 ± 0.13. SN 2012ht is the first transitional SN Ia whose rise time is directly measured without using light curve templates, and the fifth SN Ia overall. This rise time is consistent with those of the other four SNe within the measurement error, even including the extremely early detection of SN 2013dy. The rising part of the light curve can be fitted by a quadratic function, and shows no sign of a shock-heating component due to the interaction of the ejecta with a companion star. The rise time is significantly longer than that inferred for subluminous SNe such as SN 1991bg, which suggests that a progenitor and/or explosion mechanism of transitional SNe Ia are more similar to normal SNe Ia rather than to subluminous SNe Ia. © 2014. The American Astronomical Society. All rights reserved..
  • 本田 敏志
    天文月報 107(2) 88-95 2014年2月  
  • 石黒正晃, 黒田大介, 花山秀和, 高橋隼, 高木悠平, 森鼻久美子, 本田敏志, 新井彰, 長谷川直, 秋田谷洋, 森谷友由希, 宇井崇紘, 神田優花, 高木勝俊, 伊藤亮介, 渡辺誠, 今井正尭
    日本天文学会年会講演予稿集 2014 2014年  
  • 大朝由美子, 高橋隼, 高木悠平, 本田敏志, 秋田谷洋, 黒田大介, 泉浦秀行, 筒井寛典, 関口和寛, 橋本修, 渡辺誠, 諸隈智貴, 斉藤嘉彦, 村田勝寛, 野上大作, 永山貴宏
    日本天文学会年会講演予稿集 2014 2014年  
  • Takuya Shibayama, Hiroyuki Maehara, Shota Notsu, Yuta Notsu, Takashi Nagao, Satoshi Honda, Takako T. Ishii, Daisaku Nogami, Kazunari Shibata
    Astrophysical Journal, Supplement Series 209(1) 2013年11月  
    By extending our previous study by Maehara et al., we searched for superflares on G-type dwarfs (solar-type stars) using Kepler data for a longer period (500 days) than that (120 days) in our previous study. As a result, we found 1547 superflares on 279 G-type dwarfs, which is much more than the previous 365 superflares on 148 stars. Using these new data, we studied the statistical properties of the occurrence rate of superflares, and confirmed the previous results, i.e., the occurrence rate (dN/dE) of superflares versus flare energy (E) shows a power-law distribution with dN/dE∝E -α, where α ∼ 2. It is interesting that this distribution is roughly similar to that for solar flares. In the case of the Sun-like stars (with surface temperature 5600-6000 K and slowly rotating with a period longer than 10 days), the occurrence rate of superflares with an energy of 10 34-1035 erg is once in 800-5000 yr. We also studied long-term (500 days) stellar brightness variation of these superflare stars and found that in some G-type dwarfs the occurrence rate of superflares was extremely high, ∼57 superflares in 500 days (i.e., once in 10 days). In the case of Sun-like stars, the most active stars show a frequency of one superflare (with 1034 erg) in 100 days. There is evidence that these superflare stars have extremely large starspots with a size about 10 times larger than that of the largest sunspot. We argue that the physical origin of the extremely high occurrence rate of superflares in these stars may be attributed to the existence of extremely large starspots. © 2013. The American Astronomical Society. All rights reserved..
  • Yuki Moritani, Daisaku Nogami, Atsuo T. Okazaki, Akira Imada, Eiji Kambe, Satoshi Honda, Osamu Hashimoto, Sahori Mizoguchi, Yuichi Kanda, Kozo Sadakane, Kohei Ichikawa
    Publications of the Astronomical Society of Japan 65(4) 2013年8月25日  
    We carried out optical high-dispersion spectroscopic monitoring of the Be disk in a Be/X-ray binary, A0535+262/V725 Tau, from 2009 to 2012, covering two giant outbursts and several normal ones. This monitoring was performed in order to investigate any variabilities of the Be disk due to interactions with the neutron star in the recent X-ray active phase from 2008 to 2011. Such variabilities give a clue to any uncleared detailed mechanism for very bright X-ray outbursts, which are unique to some Be/X-ray binaries with a relatively wide and eccentric orbit. In a previous letter (Moritani et al. 2011, PASJ, 63, L25), a brief overview of the line-profile variabilities around the 2009 giant outburst was given, and the possibility of a warped Be disk was discussed. In this paper, a full analysis of the H? line profiles as well as other line profiles is carried out. A bright blue component, or blue "shoulder," showing up after periastron indicates the presence of a dense gas stream toward the neutron star, which is associated with observed outbursts. We re-analyze the H? line profiles before 2009 (down to 2005) in order to investigate the variability of the disk structure in the innermost region, which seems to have detached from the Be star surface by 2008. A redshifted enhanced component is remarkable in all emission lines observed around the 2009 giant outburst, occasionally forming a triple peak. These features indicate that the Be disk was warped in the X-ray active phase. We estimated the position of the warped region from fitting the radial velocity of the redshifted enhanced component of H?, and found that it was very close to the periastron when two giant outbursts in 2009 and 2011 and a bright normal outburst in 2010 March occurred. These facts strongly suggest that the precessing warped Be disk triggered these giant outbursts. © 2013. Astronomical Society of Japan.
  • Shota Notsu, Satoshi Honda, Yuta Notsu, Takashi Nagao, Takuya Shibayama, Hiroyuki Maehara, Daisaku Nogami, Kazunari Shibata
    2013年7月18日  
    We conducted the high-resolution spectroscopic observation with Subaru/HDS for a G-type star (KIC6934317). We selected this star from the data of the Kepler spacecraft. This star produces a lot of superflares, and the total energy of the largest superflare on this star is ~10^3 times larger (~2.2*10^35 erg) than that of the most energetic flare on the Sun (~10^32 erg). The core depth and emission flux of Ca II infrared triplet lines and Ha line show high chromospheric activity in this star, in spite of its low lithium abundance and the small amplitude of the rotational modulation. Using the empirical relations between emission flux of chromospheric lines and X-ray flux, this star is considered to show much higher coronal activity than that of the Sun. It probably has large starspots which can store a large amount of magnetic energy enough to give rise to superflares. We also estimated the stellar parameters, such as effective temperature, surface gravity, metallicity, projected rotational velocity (v sin_i), and radial velocity. KIC6934317 is then confirmed to be an early G-type main sequence star. The value of v sin_i is estimated to be ~1.91 km s^-1. In contrast, the rotational velocity is calculated to be ~20 km s^-1 by using the period of the brightness variation as the rotation period. This difference can be explained by its small inclination angle (nearly pole-on). The small inclination angle is also supported by the contrast between the large superflare amplitude and the small stellar brightness variation amplitude. The lithium abundance and isochrones implies that the age of this star is more than about a few Gyr, though a problem why this star with such an age has a strong activity remains unsolved.
  • Yuta Notsu, Takuya Shibayama, Hiroyuki Maehara, Shota Notsu, Takashi Nagao, Satoshi Honda, Takako T. Ishii, Daisaku Nogami, Kazunari Shibata
    Astrophysical Journal 771(2) 2013年7月10日  
    We performed simple spot-model calculations for quasi-periodic brightness variations of solar-type stars showing superflares using Kepler photometric data. Most of the superflare stars show quasi-periodic brightness modulations with a typical period of one to a few tens of days. Our results indicate that these brightness variations can be explained by the rotation of a star with fairly large starspots. Using the results of the period analysis, we investigated the relation between the energy and frequency of superflares and the rotation period. Stars with relatively slower rotation rates can still produce flares that are as energetic as those of more rapidly rotating stars although the average flare frequency is lower for more slowly rotating stars. We found that the energy of superflares is related to the total coverage of the starspot. The correlation between the spot coverage and the flare energy in superflares is similar to that in solar flares. These results suggest that the energy of superflares can be explained by the magnetic energy stored around the starspots. © 2013. The American Astronomical Society. All rights reserved..
  • Yoichi Takeda, Satoshi Honda, Takashi Ohnishi, Michiko Ohkubo, Ryuko Hirata, Kozo Sadakane
    Publications of the Astronomical Society of Japan 65(3) 2013年6月25日  
    In an attempt to carry out a systematic study on the behavior of the photospheric abundances of Li, C, and O (along with Fe) for Hyades main-sequence stars in the Teff range of ̃ 5000-7000 K, we conducted an extensive spectrum-synthesis analysis applied to four spectral regions (comprising lines of Fe-group elements, Li I 6708 line, C I 7111-7119 lines, and O I 6156-8 lines), based on the high-dispersion spectra of 68 selected F-G type stars belonging to this cluster. The abundances of C and O turned out to be fairly uniform in a marginally supersolar level, such as like the case of Fe: h[C=H]i = +0.15 (σ = 0.08), h[O=H]i = +0.22 (σ = 0.14), and h[Fe=H]i = +0.11 (σ = 0.08), suggesting that the primordial abundances are almost retained for these elements. Strictly, however, they show a slightly increasing trend with a decrease in Teff (typically on the order of ̃10-4 dexK-1) while this might be due to an improper choice of atmospheric parameters, we found it difficult to give a quantitatively reasonable explanation. Regarding Li, we confirmed the well-known Teff-dependent trend in the Li abundance reported so far (a conspicuous Li-trough at 6300K̃Teff̃6700K and a progressive decrease toward a lower Teff at Teff̃6000 K), which means that the surface Li of Hyades stars is essentially controlled only by Teff other parameters, such as the rotational velocity, are almost irrelevant. © 2013. Astronomical Society of Japan.
  • Kazunari Shibata, Hiroaki Isobe, Andrew Hillier, Arnab Rai Choudhuri, Hiroyuki Maehara, Takako T. Ishii, Takuya Shibayama, Shota Notsu, Yuta Notsu, Takashi Nagao, Satoshi Honda, Daisaku Nogami
    Publications of the Astronomical Society of Japan 65(3) 2013年6月25日  
    Recent observations of Sun-like stars, similar to our Sun in their surface temperature (5600-6000 K) and slow rotation (rotational period &gt 10 d), using the Kepler satellite by Maehara et al. (2012, Nature, 485, 478) have revealed the existence of superflares (with energy of 1033-1035 erg). From statistical analyses of these superflares, it was found that superflares with energy of 1034 erg occur once in 800 yr, and superflares with 1035 erg occur once in 5000 yr. In this paper, we examine whether superflares with energy of 1033-1035 erg could occur on the present Sun through the use of simple order-of-magnitude estimates based on current ideas related to the mechanisms of the solar dynamo. If magnetic flux is generated by differential rotation at the base of the convection zone, as assumed in typical dynamo models, it is possible that the present Sun would generate a large sunspot with a total magnetic flux of ̃2 ̃ 1023 Mx (= Gcm2) within one solar cycle period, and lead to superflares with an energy of 1034 erg. To store a total magnetic flux of ̃1024 Mx, necessary for generating 1035 erg superflares, it would take ̃40 yr. Hot Jupiters have often been argued to be a necessary ingredient for the generation of superflares, but we found that they do not play any essential role in the generation of magnetic flux in the star itself, if we consider only the magnetic interaction between the star and the hot Jupiter. This seems to be consistent with Maehara et al.'s finding of 148 superflare-generating solar-type stars that do not have a hot Jupiter-like companion. Altogether, our simple calculations, combined with Maehara et al.'s analysis of superflares on Sun-like stars, show that there is a possibility that superflares of 1034 erg would occur once in 800 yr on our present Sun. © 2013. Astronomical Society of Japan.
  • Wako Aoki, Timothy C. Beers, Young Sun Lee, Satoshi Honda, Hiroko Ito, Masahide Takada-Hidai, Anna Frebel, Takuma Suda, Masayuki Y. Fujimoto, Daniela Carollo, Thirupathi Sivarani
    Astronomical Journal 145(1) 2013年1月  
    Chemical compositions are determined based on high-resolution spectroscopy for 137 candidate extremely metal-poor (EMP) stars selected from the Sloan Digital Sky Survey (SDSS) and its first stellar extension, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). High-resolution spectra with moderate signal-to-noise (S/N) ratios were obtained with the High Dispersion Spectrograph of the Subaru Telescope. Most of the sample (approximately 80%) are main-sequence turnoff stars, including dwarfs and subgiants. Four cool main-sequence stars, the most metal-deficient such stars known, are included in the remaining sample. Good agreement is found between effective temperatures estimated by the SEGUE stellar parameter pipeline, based on the SDSS/SEGUE medium-resolution spectra, and those estimated from the broadband (V - K) 0 and (g - r)0 colors. Our abundance measurements reveal that 70 stars in our sample have [Fe/H] &lt -3, adding a significant number of EMP stars to the currently known sample. Our analyses determine the abundances of eight elements (C, Na, Mg, Ca, Ti, Cr, Sr, and Ba) in addition to Fe. The fraction of carbon-enhanced metal-poor stars ([C/Fe] &gt +0.7) among the 25 giants in our sample is as high as 36%, while only a lower limit on the fraction (9%) is estimated for turnoff stars. This paper is the first of a series of papers based on these observational results. The following papers in this series will discuss the higher-resolution and higher-S/N observations of a subset of this sample, the metallicity distribution function, binarity, and correlations between the chemical composition and kinematics of extremely metal-poor stars. © 2013. The American Astronomical Society. All rights reserved.
  • Yoichi Takeda, Akito Tajitsu, Satoshi Honda, Satoshi Kawanomoto, Hiroyasu Ando, Takashi Sakurai
    2012年7月1日  
    Activity studies of solar-type stars, especially with reference to the status of our current Sun among them, have exposed the importance of (1) homogeneously selecting the sample stars and (2) reliably evaluating their activities down to a considerably low level. Motivated by these requirements, we conducted an extensive study on the activities of 118 solar-analog stars (of sufficiently similar properties to each other) by measuring the emission strength at the core of Ca II 3933.663 line (K line) on the high-dispersion spectrogram obtained by Subaru/HDS, where special attention was paid to correctly detecting the chromospheric emission by removing the wing-fitted photospheric profile calculated from the classical solar model atmosphere. This enabled us to detect low-level activities down to log R' ~ -5.4 (R' is the ratio of the chromospheric core emission flux to the total bolometric flux), by which we could detect subtle activity differences which were indiscernible in previous studies. Regarding the Sun, we found log R'sun = -5.33 near to the low end of the distribution, which means that it belongs to the distinctly low activity group among solar analogs. This excludes the once-suggested possibility for the high frequency of Maunder-minimum stars showing appreciably lower activities than the minimum-Sun.
  • Yuuki Moritani, Daisaku Nogami, Atsuo T. Okazaki, Akira Imada, Eiji Kambe, Satoshi Honda, Osamu Hashimoto, Kohei Ichikawa
    Publications of the Astronomical Society of Japan 63(4) L25-L29 2011年8月25日  
    We report on high-dispersion optical spectroscopic observations of the Be/X-ray binary A 0535+262/V725 Tau during a giant outburst in 2009 November/December, and after it. The observed emission line profiles, reflecting the structure of the geometrically thin circumstellar envelope of the Be star (Be disk), show drastic variabilities, and indicate the existence of a warped component. The enhanced blue shoulder seen after periastron passage implies a gas stream from a dense part of the Be disk to the neutron star. © 2011. Astronomical Society of Japan.
  • Yoichi Takeda, Akito Tajitsu, Satoshi Honda, Satoshi Kawanomoto, Hiroyasu Ando, Takashi Sakurai
    Publications of the Astronomical Society of Japan 63(3) 697-713 2011年6月25日  
    An extensive Be abundance analysis was conducted for 118 solar analogs (along with 87 FGK standard stars) by applying the spectrum synthesis technique to the near-UV region comprising the Be II line at 3131.066 Å , in an attempt to investigate whether Be suffers any depletion, such as in the case of Li showing a large diversity. We found that, while most of these Sun-like stars are superficially similar in terms of their A(Be) (Be abundances) around the solar value within∼±0.2 dex, 4 out of 118 samples turned out to be strikingly Be-deficient (by more than ∼2dex), and these 4 stars belong to the group of lowest v e sin i (projected rotation velocity). Moreover, even for the other majority showing an apparent similarity in Be, we can recognize a tendency that A(Be) gradually increases with an increase in v e sin i . These observational facts suggest that any solar analog star (including the Sun) generally suffers some kind of Be depletion during their lives, where the rotational velocity (or the angular momentum) plays an important role in the sense that the depletion tends to be enhanced by slower rotation. Hence, our findings require that the occasionally stated view "G-type dwarfs with Teff ≲6000K are essentially homogeneous in Be with their original composition retained" should be revised. Also, our analysis indicates that the difference of ∼0.2 dex in A(Be) between the solar photosphere and the meteorite really exists, implying that the "UV missing opacity" is irrelevant at least for this Be II line. © 2011. Astronomical Society of Japan.
  • Satoshi Honda, Wako Aoki, Timothy C. Beers, Masahide Takada-Hidai
    Astrophysical Journal 730(2) 2011年4月1日  
    We report Zn abundances for 18 very metal-poor stars studied in our previous work, covering the metallicity range -3.2&lt [Fe/H] &lt -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.
  • Honda Satoshi, Aoki Wako, Arimoto Nobuo, SADAKANE Kozo
    PASJ : publications of the Astronomical Society of Japan 63(2) S523-S529 2011年3月10日  
  • Yuuki Moritani, Daisaku Nogami, Atsuo T. Okazaki, Akira Imada, Eiji Kambe, Satoshi Honda, Osamu Hashimoto, Kazuhide Ichikawa
    ACTIVE OB STARS: STRUCTURE, EVOLUTION, MASS-LOSS, AND CRITICAL LIMITS 6(272) 618-+ 2011年  査読有り
    A giant outburst occurred in A0535+262/V725 Tau in November 2009, which lasted approximately 30 days. We carried out spectroscopic monitoring at OAO and GAO from November 2009 to March 2010, from before the giant outburst to the rising phase of the normal outburst which occurred after the next periastron. The obtained H-alpha, H-beta and He I emission lines exhibited drastic profile variability during the observations.
  • Wako Aoki, Timothy C. Beers, Satoshi Honda, Daniela Carollo
    Astrophysical Journal Letters 723(2) L201-L206 2010年11月10日  
    We report the discovery of a cool metal-poor, main-sequence star exhibiting large excesses of r-process elements. This star is one of the two newly discovered cool subdwarfs (effective temperatures of 5000 K) with extremely low metallicity ([Fe/H] &lt -3) identified from follow-up high-resolution spectroscopy of metal-poor candidates from the Sloan Digital Sky Survey. SDSS J2357-0052 has [Fe/H]= -3.4 and [Eu/Fe]= +1.9, and exhibits a scaled solar r-process abundance pattern of heavy neutron-capture elements. This is the first example of an extremely metal-poor, main-sequence star showing large excesses of r-process elements all previous examples of the large r-process-enhancement phenomena have been associated with metal-poor giants. The metallicity of this object is the lowest, and the excess of Eu ([Eu/Fe]) is the highest, among the r-process-enhanced stars found so far. We consider possible scenarios to account for the detection of such a star and discuss techniques to enable searches for similar stars in the future. © 2010. The American Astronomical Society. All rights reserved.
  • Kazuo Hiroi, Daisaku Nogami, Yoshihiro Ueda, Yuuki Moritani, Yuichi Soejima, Akira Imada, Osamu Hashimoto, Kenzo Kinugasa, Satoshi Honda, Shin-ya Narusawa, Makoto Sakamoto, Ryo Iizuka, Kentaro Matsuda, Hiroyuki Naito, Takashi Iijima, Mitsugu Fujii
    Publications of the Astronomical Society of Japan 61(4) 697-705 2009年4月22日  
    We carried out an international spectroscopic observation campaign of the dwarf nova GW Librae (GW Lib) during the 2007 superoutburst. Our observation period covered the rising phase of the superoutburst, maximum, slowly decaying phase (plateau), and long fading tail after the rapid decline from the plateau. The spectral features dramatically changed during the observations. In the rising phase, only absorption lines of H$\alpha$, H$\beta$, and H$\gamma$ were present. Around the maximum, the spectrum showed singly-peaked emission lines of H$\alpha$, He I 5876, He I 6678, He II 4686, and C III/N III as well as absorption lines of Balmer components and He I. These emission lines significantly weakened in the latter part of the plateau phase. In the fading tail, all the Balmer lines and He I 6678 were in emission, as observed in quiescence. We find that the center of the H$\alpha$ emission component was mostly stable over the whole orbital phase, being consistent with the low inclination of the system. Comparing with the observational results of WZ Sge during the 2001 superoutburst, the same type of stars as GW Lib seen with a high inclination angle, we interpret that the change of the H$\alpha$ profile before the fading tail phase is attributed to a photoionized region formed at the outer edge of the accretion disk, irradiated from the white dwarf and inner disk.
  • Hiroko Ito, Wako Aoki, Satoshi Honda, Timothy C. Beers
    Astrophysical Journal 698(1) L37-L41 2009年  
    We present a one-dimensional LTE chemical abundance analysis of the very bright (V = 9.1) carbon-enhanced metal-poor (CEMP) star BD+44°493, based on high-resolution, high signal-to-noise spectra obtained with Subaru/HDS. The star is shown to be a subgiant with an extremely low iron abundance ([Fe/H] = -3.7), while it is rich in C ([C/Fe] = +1.3) and O ([O/Fe] = +1.6). Although astronomers have been searching for extremely metal-poor stars for decades, this is the first star found with [Fe/H] &lt -3.5 and an apparent magnitude V &lt 12. Based on its low abundances of neutron-capture elements (e.g., [Ba/Fe] =-0.59), BD+44°493 is classified as a "CEMP-no" star. Its abundance pattern implies that a first-generation faint supernova is the most likely origin of its carbon excess, while scenarios related to mass loss from rapidly rotating massive stars or mass transfer from an asymptotic giant branch companion star are not favored. From a high-quality spectrum in the near-UV region, we set an very low upper limit on this star's beryllium abundance (A(Be) = log(Be/H) + 12 &lt -2.0), which indicates that the decreasing trend of Be abundances with lower [Fe/H] still holds at [Fe/H] &lt -3.5. This is the first attempt to measure a Be abundance for a CEMP star, and demonstrates that high C and O abundances do not necessarily imply high Be abundances. © 2009. The American Astronomical Society.
  • Hideyuki Izumiura, Kunio Noguchi, Wako Aoki, Satoshi Honda, Hiroyasu Ando, Masahide Takada-Hidai, Eiji Kambe, Satoshi Kawanomoto, Kozo Sadakane, Bun'ei Sato, Akito Tajitsu, Wataru Tanaka, Ki'ichi Okita, Etsuji Watanabe, Michitoshi Yoshida
    Astrophysical Journal 682(1) 499-508 2008年7月20日  
    Balmer and Paschen continuum emission, as well as Balmer series lines of P Cygni-type profile from Hγ through H23, are revealed in the violet spectra of BM Gem, a carbon star associated with an oxygen-rich circumstellar shell ("silicate carbon star"). The blueshifted absorption in the Balmer lines indicates the presence of an outflow, the line-of-sight velocity of which is at least 400 km s-1. The Balmer lines show a significant change in profile over a period of 75 days. We argue that the observed unusual features in BM Gem are strong evidence for the presence of a companion, which should form an accretion disk that gives rise to both an ionized gas region and a high-velocity variable outflow. The estimated luminosity of ∼0.2 (0.03-0.6) L⊙ for the ionized gas can be maintained by a mass accretion rate for a dwarf companion of ∼10 -8 M⊙ yr-1, while ∼10-10 M⊙ yr-1 is sufficient for accretion to a white dwarf companion. These accretion rates are feasible for some detached binary configurations on the basis of the Bondi-Hoyle-type accretion process. Therefore, we conclude that the carbon star BM Gem is in a detached binary system with a companion of low mass and low luminosity. However, we are unable to determine whether this companion object is a dwarf or a white dwarf, although the gas outflow velocity of 400 km s-1, as well as the nondetection in the X-ray survey, favor its identity as a dwarf star. The upper limits for binary separation are 210 and 930 AU for a dwarf and a white dwarf, respectively, in the case of circular orbit. We also note that the observed features of BM Gem mimic those of Mira (o Cet), which may suggest actual similarities in their binary configurations and circumstellar structures. © 2008. The American Astronomical Society. All rights reserved.
  • Wako Aoki, Timothy C. Beers, Thirupathi Sivarani, Brian Marsteller, Young Sun Lee, Satoshi Honda, John E. Norris, Sean G. Ryan, Daniela Carollo
    Astrophysical Journal 678(2) 1351-1371 2008年5月10日  
    The chemical compositions of seven CEMP turnoff stars are determined from high-resolution spectroscopy. Five are selected from the SDSS SEGUE sample of metal-poor stars. Another star chosen from the SDSS SEGUE sample has only a weak upper limit on its carbon abundance obtained from the high-resolution spectrum. The effective temperatures are all higher than 6000 K, while the metallicities, parameterized by [Fe/H], are all below -2 the star with the lowest iron abundance has [Fe/H] = -3.1. Six of our objects exhibit high abundance ratios of barium ([Ba/Fe] &gt +1), suggesting large contributions of the products of former AGB companions via mass transfer across binary systems. One star (SDSS 1707+58) exhibits rapid variation in radial velocity, a strong signature that it belongs to a close binary. Combining our results with previous studies provides a total of 20 CEMP main-sequence turnoff stars for which the abundances of carbon and at least some neutron-capture elements are determined. The [C/H] ratios for this sample of CEMP turnoff stars are generally higher than those of CEMP giants and their dispersion is also smaller. These results indicate that the carbon-enhanced material from the companion AGB star is preserved at the surface of turnoff stars with no significant dilution, counter to expectations if processes such as thermohaline mixing have operated in unevolved CEMP stars. In contrast to the behavior of [C/H], a large dispersion in the observed [Ba/H] is found for the CEMP turnoff stars, suggesting that the efficiency of the s-process in very metal-poor AGB stars may differ greatly from star to star. Four of the six stars from the sample exhibit kinematics associated with membership in the outer-halo population, a remarkably high fraction. © 2008. The American Astronomical Society. All rights reserved.
  • Wako Aoki, Satoshi Honda
    Publications of the Astronomical Society of Japan 60(3) L7-L11 2008年  
    We determined lead (Pb) abundances for 12 red giants with the stellar metallicity [Fe/H] ranging between -2.1 and -1.3 and its upper limits for 2 lower-metallicity objects, as well as lanthanum (La) and europium (Eu) abundances. The averages of [Pb/Fe] and [Pb/Eu] were -0.3 and -0.6, respectively, and no clear increase of these ratios with increasing metallicity was found. The [La/Eu] values are only slightly higher than that of the r-process component in solar-system material. These results, together with the previous studies for globular clusters, suggest a small contribution of the s-process to the Pb abundance of the field stars studied here, supporting an estimate of Pb production by the r-process from the solar-system abundances. © 2008. Astronomical Society of Japan.
  • Wako Aoki, Satoshi Honda, Timothy C. Beers, Masahide Takada-Hidai, Nobuyuki Iwamoto, Nozomu Tominaga, Hldeyuki Umeda, Kenichi Nomoto, John E. Norris, Sean G. Ryan
    Astrophysical Journal 660(1 I) 747-761 2007年5月1日  
    A detailed elemental abundance analysis has been carried out for the very metal-poor ([Fe/H] = -2.7) star BS 16934-002, which was identified in our previous work as a star exhibiting large overabundances of Mg and Sc. A comparison of the abundance pattern of this star with that of the well-studied metal-poor star HD 122563 indicates excesses of O, Na, Mg, Al, and Sc in BS 16934-002. Of particular interest, no excess of C or N is found in this object, in contrast to CS 22949-037 and CS 29498-043, two previously known carbon-rich, extremely metal-poor stars with excesses of the α-elements. No established nucleosynthesis model exists that explains the observed abundance pattern of BS 16934-002. A supernova model, including mixing and fallback and assuming severe mass loss before explosion, is discussed as a candidate progenitor of BS 16934-002. © 2007. The American Astronomical Society. All rights reserved.
  • Anna Frebel, John E. Norris, Wako Aoki, Satoshi Honda, Michael S. Bessell, Masahide Takada-Hidai, Timothy C. Beers, Norbert Christlieb
    Astrophysical Journal 658(1 I) 534-552 2007年3月20日  
    We present a detailed chemical abundance analysis of HE 1300 + 0157, a subgiant with [Fe/H] = -3.9. From a high-resolution, high-S/N Subaru HDS spectrum we find the star to be enriched in C ([C/Fe]1D ∼ +1.4) and O ([O/Fe]1D ∼ + 1.8). With the exception of these species, HE 1300+0157 exhibits an elemental abundance pattern similar to that found in many other very and extremely metal-poor stars. The Li abundance is lower than the Spite plateau value, in agreement with expectation for its evolutionary status. Of particular interest, no neutron-capture elements are detected in HE 1300+0157. This type of abundance pattern has been found by recent studies in several other metal-poor giants. We suggest that HE 1300+0157 is an unevolved example of this group of stars, which exhibit high C abundances together with low (or absent) abundances of neutron-capture elements (CEMP-no). Several potential enrichment scenarios are presented. The nondetection of neutron-capture elements including Sr, Ba, and Pb suggests that the carbon excess observed in HE 1300+0157 is not due to mass transfer across a binary system. Such a scenario is applied to carbon-rich objects with excesses of s-process elements. The normal observed Li abundance supports this interpretation. Most likely, the high levels of C and O were produced prior to the birth of this star. It remains unclear whether a single faint SN is responsible for its overall chemical pattern, or whether one requires a superposition of yields from a massive Population 111 object and a hypernova. These scenarios provide important information on the C production in the early universe and on the formation of C-rich stars in the early Galaxy. © 2007. The American Astronomical Soeiety. All rights reserved.
  • Satoshi Honda, Wako Aoki, Yuhri Ishimaru, Shinya Wanajo
    Astrophysical Journal 666(2 I) 1189-1197 2007年  
    We obtained a high-resolution, high-signal-to-noise UV-blue spectrum of the extremely metal-poor red giant HD 88609 to determine the abundances of heavy elements. Nineteen neutron-capture elements are detected in the spectrum. Our analysis revealed that this object has large excesses of light neutron-capture elements, while heavy neutron-capture elements are deficient. The abundance pattern shows a continuously decreasing trend as a function of atomic number, from Sr to Yb, which is quite different from those in stars with excesses of r-process elements. Such an abundance pattern is very similar to that of HD 122563, which was studied in our previous work. The results indicate that the abundance pattern found in the two stars could represent the pattern produced by the nucleosynthesis process that provided light neutron-capture elements in the very early Galaxy. © 2007. The American Astronomical Society. All rights reserved.
  • Wako Aoki, Satoshi Honda, Kozo Sadakane, Nobuo Arimoto
    Publications of the Astronomical Society of Japan 59(3) L15-L19 2007年  
    The thorium abundance of the red giant COS 82 in the Ursa Minor dwarf spheroidal galaxy was determined based on the high-resolution spectrum. This is the first detection of actinides in an extragalactic object. A detailed abundance pattern was determined for 12 other neutron-capture elements from atomic number 39 to 68. These elements are significantly over-abundant with respect to other metals, like Fe (&gt 1 dex), and their abundance pattern agrees well with those of the r-process-enhanced, very metal-poor stars known in the galactic halo, while the metallicity of this object ([Fe/H] ∼ - 1.5) is much higher than these field stars ([Fe/H] ∼ - 3.0). The results indicate that the mechanism and the astrophysical site that are responsible for neutron-capture elements in COS 82 are similar to that for field r-process-enhanced stars, while the condition of low-mass star formation is quite different. An estimate of the age of this object based on the Th abundance ratio is discussed. © 2007. Astronomical Society of Japan.
  • Yuji Shirasaki, Masahiro Tanaka, Satoshi Honda, Satoshi Kawanomoto, Masatoshi Ohishi, Yoshihiko Mizumoto, Naoki Yasuda, Yoshifumi Masunaga, Yasuhide Ishihara, Jumpei Tsutsumi, Hiroyuki Nakamoto, Yuusuke Kobayashi, Michito Sakamoto
    2006年11月17日  
    We present our activity on making the Subaru Data Archive accessible through the Japanese Virtual Observatory (JVO) system. There are a lot of demand to use the archived Subaru data from various fields of astronomers. To be used by those who are not familiar with the way to reduce the Subaru data, the data reduction should be made before providing for them, or at least it should be easily done without precise knowledge about instrument's characteristic and environment where data are taken. For those purposes, data quality assessment system NAQATA is developed, which is presented in this meeting by Nakata et al. (2006), and the science-ready image data are provided for some of the SuprimeCam data at SMOKA data service which is presented by Enoki et al (2006). JVO portal will provide the way to access the reduce data, and also provides the way to reduce from raw data with very few efforts through the user-friendly web browser I/F. To provide such a CPU-intensive service, we have developed a GRID computing system. The architecture of this Subaru Data and Analysis system are discussed.
  • 本田 敏志
    天文月報 99(7) 358-364 2006年6月20日  
  • Kaori Otsuki, Satoshi Honda, Wako Aoki, Toshitaka Kajino, Grant J. Mathews
    Astrophysical Journal 641(2) L117-L120 2006年4月20日  
    We report on observations of six giants in the globular cluster M15 (NGC 7078) using the Subaru Telescope to measure neutron-capture elemental abundances. Our abundance analyses, based on high-quality blue spectra, confirm the star-to-star scatter in the abundances of heavy neutron-capture elements (e.g., Eu), and we found no significant s-process contribution to them, as was found in previous studies. We have found that, for the first time, there are anticorrelations between the abundance ratios of light to heavy neutron-capture elements ([Y/Eu] and [Zr/Eu]) and the heavy neutron-capture elements (e.g., Eu). This indicates that the light neutron-capture elements in these stars cannot be explained by only a single r-process. Another process that contributed significantly to the light neutron-capture elements is required in M15. Our results suggest a complicated enrichment history for M15 and its progenitor. © 2006. The American Astronomical Society. All rights reserved.
  • W Aoki, A Frebel, N Christlieb, JE Norris, TC Beers, T Minezaki, PS Barklem, S Honda, M Takada-Hidai, M Asplund, SG Ryan, S Tsangarides, K Eriksson, A Steinhauer, CP Deliyannis, K Nomoto, MY Fujimoto, H Ando, Y Yoshii, T Kajino
    ASTROPHYSICAL JOURNAL 639(2) 897-917 2006年3月  
    We present the elemental abundances of HE 1327-2326, the most iron-deficient star known, determined from a comprehensive analysis of spectra obtained with the Subaru Telescope High Dispersion Spectrograph. HE 1327-2326 is either in its main-sequence or subgiant phase of evolution. Its non-LTE-corrected iron abundance is [Fe/H] = -5.45, 0.2 dex lower than that of HE 0107-5240, the previously most iron-poor object known, and more than 1 dex lower than those of all other metal-poor stars. Both HE 1327-2326 and HE 0107-5240 exhibit extremely large overabundances of carbon ([C/Fe] similar to +4). The combination of extremely high carbon abundance with outstandingly low iron abundance in these objects clearly distinguishes them from other metal-poor stars. The large carbon excesses in these two stars are not the result of a selection effect. There also exist important differences between HE 1327-2326 and HE 0107-5240. While the former shows remarkable overabundances of the light elements (N, Na, Mg, and Al), the latter shows only relatively small excesses of N and Na. The neutron-capture element Sr is detected in HE 1327-2326, but not in HE 0107-5240; its Sr abundance is significantly higher than the upper limit for HE 0107-5240. The Li I gamma 6707 line, which is detected in most metal-poor dwarfs and warm subgiants having the same temperature as HE 1327-2326, is not found in this object. The upper limit of its Li abundance [log epsilon(Li) &lt; 1.5] is clearly lower than the Spite plateau value. These data provide new constraints on models of nucleosynthesis processes in the first-generation objects that were responsible for metal enrichment at the earliest times. We discuss possible scenarios to explain the observed abundance patterns.
  • Wako Aoki, Satoshi Honda, Timothy C. Beers, Toshitaka Kajino, Hiroyasu Ando, John E. Norris, Sean G. Ryan, Hideyuki Izumiura, Kozo Sadakane, Masahide Takada-Hidai
    Astrophysical Journal 632(1 I) 611-637 2005年10月10日  
    Elemental abundance measurements have been obtained for a sample of 18 very metal-poor stars using spectra obtained with the Subaru Telescope High Dispersion Spectrograph. Seventeen stars, among which 16 are newly analyzed in the present work, were selected from candidate metal-poor stars identified in the HK survey of Beers and colleagues. The metallicity range covered by our sample is -3.1 ≲ [Fe/H] ≲ -2.4. The abundances of carbon, α-elements, and iron-peak elements determined for these stars confirm the trends found by previous work. One exception is the large overabundance of Mg, Al, and Sc found in BS 16934-002, a giant with [Fe/H] = -2.8. Interestingly, this is the most metal-rich star (by about 1 dex in [Fe/H]) known with such large overabundances in these elements. Furthermore, BS 16934-002 does not share the large overabundances of carbon that are associated with the two other, otherwise similar, extremely metal-poor stars CS 22949-037 and CS 29498-043. By combining our new results with those of previous studies, we investigate the distribution of neutron-capture elements in very metal-poor stars, focusing on the production of the light neutron-capture elements (e.g., Sr, Y, and Zr). Large scatter is found in the abundance ratios between the light and heavy neutron-capture elements (e.g., Sr/Ba, Y/Eu) for stars with low abundances of heavy neutron-capture elements. Most of these stars have extremely low metallicity ([Fe/H] ≲ -3). By contrast, the observed scatter in these ratios is much smaller in stars with excesses of heavy neutron-capture elements and with higher metallicity. These results can be naturally explained by assuming that two processes independently enriched the neutron-capture elements in the early Galaxy. One process increases both light and heavy neutron-capture elements and affects stars with [Fe/H] ≳ -3, while the other process contributes only to the light neutron-capture elements and affects most stars with [Fe/H] ≳ -3.5. Interestingly, the Y/Zr ratio is similar in stars with high and low abundances of heavy neutron-capture elements. These results provide constraints on modeling of neutron-capture processes, in particular, those responsible for the nucleosynthesis of light neutron-capture elements at very low metallicity. © 2005. The American Astronomical Society. All rights reserved.
  • Anna Frebel, Wako Aoki, Norbert Christlieh, Hiroyasu Ando, Martin Asplund, Paul S. Barklem, Timothy C. Beers, Kjell Eriksson, Cora Fechner, Masayuki Y. Fujimoto, Satoshi Honda, Toshitaka Kajino, Takeo Minezaki, Ken'ichi Homoto, John E. Horris, Sean G. Ryan, Masahide Takada-Hidal, Steilos Tsangarides, Yuzuru Yoshii
    Nature 434(7035) 871-873 2005年4月14日  
    The chemically most primitive stars provide constraints on the nature of the first stellar objects that formed in the Universe elements other than hydrogen, helium and traces of lithium present within these objects were generated by nucleosynthesis in the very first stars. The relative abundances of elements in the surviving primitive stars reflect the masses of the first stars, because the pathways of nucleosynthesis are quite sensitive to stellar masses. Several models have been suggested to explain the origin of the abundance pattern of the giant star HE0107-5240, which hitherto exhibited the highest deficiency of heavy elements known. Here we report the discovery of HE1327-2326, a subgiant or main-sequence star with an iron abundance about a factor of two lower than that of HE0107-5240. Both stars show extreme overabundances of carbon and nitrogen with respect to iron, suggesting a similar origin of the abundance patterns. The unexpectedly low Li and high Sr abundances of HE1327-2326, however, challenge existing theoretical understanding: no model predicts the high Sr abundance or provides a Li depletion mechanism consistent with data available for the most metal-poor stars.
  • Yoichi Takeda, Osamu Hashimoto, Hikaru Taguchi, Kazuo Yoshioka, Masahide Takada-Hidai, Yuji Saito, Satoshi Honda
    Publications of the Astronomical Society of Japan 57(5) 751-768 2005年  
    Extensive statistical-equilibrium calculations on S I and Zn I were carried out, in order to investigate how the non-LTE effect plays a role in the determination of their abundances in F-K stars. Having checked on the spectra of representative F-type stars (Polaris, Procyon, α Per) and the Sun that our non-LTE corrections yield a reasonable consistency between the abundances derived from different lines, we tried an extensive non-LTE reanalysis of published equivalent-width data of S I and Zn I lines for metal-poor halo/disk stars. According to our calculations, S I 9212/9228/9237 lines suffer significant negative non-LTE corrections (≲ 0.2-0.3 dex), while LTE is practically valid for S I 8683/8694 lines. As far as the very metal-poor regime is concerned, a marked discordance is observed between the [S/Fe] values from these two abundance indicators, in the sense that the former attains a nearly flat plateau (or even a slight downward bending) while the latter shows an ever-increasing trend with a further lowering of metallicity. The characteristics of [Zn/Fe] reported from recent LTE studies (i.e., an evident/slight increase of [Zn/Fe] with a decrease of [Fe/H] for very metal-poor/disk stars) were almost confirmed, since the non-LTE corrections for the Zn I 4722/4810 and 6362 lines (tending to be positive and gradually increasing toward lower [Fe/H]) are quantitatively of less significance (≲ 0.1 dex). © 2005. Astronomical Society of Japan.
  • Yuji Shirasaki, Masatoshi Ohishi, Yoshihiko Mizumoto, Masahiro Tanaka, Satoshi Honda, Masafumi Oe, Naoki Yasuda, Yoshifumi Masunaga
    2004年11月19日  
    Currently two query languages are defined as standards for the Virtual Observatory (VO). Astronomical Data Query Language (ADQL) is used for catalog data query and Simple Image Access Protocol (SIAP) is for image data query. As a result, when we query each data service, we need to know in advance which language is supported and then construct a query language accordingly. The construct of SIAP is simple, but they have a limited capability. For example, there is no way to specify multiple regions in one query, and it is difficult to specify complex query conditions. In this paper, we propose a unified query language for any kind of astronomical database on the basis of SQL99. SQL is a query language optimized for a table data, so to apply the SQL to the image and spectrum data set, the data structure need to be mapped to a table like structure. We present specification of this query language and an example of the architecture for the database system.
  • E Kambe, B Sato, Y Takeda, H Ando, K Noguchi, W Aoki, H Izumiura, S Wada, S Masuda, N Okada, Y Shimizu, E Watanabe, M Yoshida, S Honda, S Kawanomoto
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 54(6) 865-871 2002年12月  
    We have developed iodine (I-2) cells for the High Dispersion Spectrograph (HDS) on the Subaru telescope and for the HIgh Dispersion Echelle Spectrograph (HIDES) on the Okayama 1.88 m reflector. The cell is put into a compact vacuum vessel, which fits into a small space behind the entrance slit of the HDS. The cell assembly is designed to minimize heat losses from the cell, which is heated during observations, to keep I-2 vapor from condensation. The amount Of I-2 in the cell is determined to be best suited for radial-velocity measurements of solar-type stars. We also report on some performances of the HDS and HIDES as well as their instrumental profiles based on tests of our I-2 cells. Lastly, we discuss future improvements of our instruments and data-analysis softwares for \I-2 observations, and also describe the scientific goals of our project.
  • K Noguchi, W Aoki, S Kawanomoto, H Ando, S Honda, H Izumiura, E Kambe, K Okita, K Sadakane, B Sato, A Tajitsu, M Takada-Hidai, W Tanaka, E Watanabe, M Yoshida
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 54(6) 855-864 2002年12月  
    We present the design and performance of the High Dispersion Spectrograph (HDS) of the Subaru Telescope. HDS is an echelle spectrograph located at the Nasmyth focus of the telescope. The collimated beam size is 272 mm, and the echelle is 300 mm by 840 mm in total size (31.6 gr mm(-1), R = 2.8). HDS has two cross-dispersing gratings with 400 gr mm(-1) and 250 gr mm(-1), which are optimized for the blue and red wavelength regions, respectively. The camera is of the catadioptric type system, consisting of three corrector lenses and a mirror. Two EEV-CCD's with 4100 x 2048 pixels and a pixel size of 13.5 mum are used as the detector. A standard configuration with a 0."4 slit gives a spectral resolution of R = 90000, and a narrower slit width enables higher resolution of up to R similar to 160000. The spectrograph has sensitivities from 3000 Angstrom to 1 mum, and one exposure covers a range of 1500-2500 Angstrom, depending on the wavelength region. The throughput of the telescope and the spectrograph, including the efficiency of the detector, is about 13% in 5000-6000 Angstrom and about 8% at 4000 Angstrom. The stability of the spectrograph and scattered light level are also reported.
  • W Aoki, H Ando, S Honda, M Iye, H Izumiura, T Kajino, E Kambe, S Kawanomoto, K Noguchi, K Okita, K Sadakane, B Sato, Shelton, I, M Takada-Hidai, Y Takeda, E Watanabe, M Yoshida
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 54(3) 427-449 2002年6月  
    We have obtained high-resolution (R similar to 90000) spectra of the carbon- and s-process-element-rich, very metal-poor ([Fe/H] = -2.7) subgiant LP 625-44, as well as those of HD 140283 (a metal-poor subgiant with normal abundance ratio) for a comparison, with the High Dispersion Spectrograph (HDS) for the Subaru Telescope for detailed abundance study. The excess of oxygen in LP 625-44 seems to be remarkable (perhaps by nearly a factor 10) compared with that of HD 140283 derived from the O I triplet around 7770 A, though the oxygen abundance derived from these lines is uncertain. The Na enhancement in LP 625-44 is by about a factor 50, suggesting hydrogen burning in the Ne-22-rich layer in an asymptotic giant branch star which produced the abundance pattern of this object, In our new spectrum of LP 625-44, the Pb I lambda3683 Angstrom line has been detected, confirming the Pb abundance [logepsilon(Pb) similar to 1.9] derived from the Pb 1; 4057 Angstrom line by previous work. The abundance ratio of s-process elements at the second peak (e.g., La, Cc, and Nd) to that at the third peak (Pb) in LP 625-44 is significantly higher (by a factor 5) than that in other three s-process element-rich objects recently studied by van Eck et al. Recent theoretical studies have modeled s-process nucleosynthesis in the radiative layer of asymptotic giant branch stars in the inter-pulse phase. The above results mean that these processes produced a large scatter in the abundance ratios, or different processes (e.g., s-process nucleosynthesis during thermal pulses) contributed to heavy elements in the early Galaxy.
  • Y Takeda, B Sato, E Kambe, W Aoki, S Honda, S Kawanomoto, S Masuda, H Izumiura, E Watanabe, H Koyano, H Maehara, Y Norimoto, T Okada, Y Shimizu, F Uraguchi, K Yanagisawa, M Yoshida, SM Miyama, H Ando
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 53(6) 1211-1221 2001年12月  
    By using the high-dispersion spectra of 14 bright planet-harboring stars (along with 4 reference stars) observed with the new coude echelle spectrograph at Okayama Astrophysical Observatory, we investigated the abundances of volatile elements (C, N, 0, S, Zn; low condensation temperature T-c) in order to examine whether these show any significant difference compared to the abundances of other refractory elements (Si, Ti, V, Fe, Co, Ni; high T-c), which are known to be generally overabundant in those stars with planets, since a T-c-dependence is expected if the cause of such a metal-richness is due to the accretion of solid planetesimals onto the host star. We found, however, that all elements which we studied behave themselves quite similarly to Fe (i.e., [X/Fe] similar or equal to 0), even for the case of volatile elements. This may suggest that the enhanced metallicity in those planet-bearing stars is not so much an acquired character (by accretion of rocky material) as rather primordial.
  • H Kawakita, J Watanabe, H Ando, W Aoki, T Fuse, S Honda, H Izumiura, T Kajino, E Kambe, S Kawanomoto, K Noguchi, K Okita, K Sadakane, B Sato, M Takada-Hidai, Y Takeda, T Usuda, E Watanabe, M Yoshida
    SCIENCE 294(5544) 1089-1091 2001年11月  
    A high-dispersion spectrum of Comet C/1999S4 (LINEAR) was obtained in the optical region with the high-dispersion spectrograph on the Subaru telescope when the comet was 0.863 astronomical units from the Sun before its disintegration. We obtained high signal-to-noise ratio emission tines of the cometary NH2 bands from which an ortho-to-para ratio (OPR) of 3.33 +/- 0.07 was derived on the basis of a fluorescence excitation model. Assuming that cometary NH2 mainly originates from ammonia through photodissociation, the derived OPR of NH2, molecules should reflect that of ammonia, which provides information on the environment of molecular formation or condensation and of the thermal history of cometary ices. Assuming that the OPR of ammonia in comets was unchanged in the nucleus, the derived spin temperature of ammonia (28 +/- 2 kelvin) suggests that a formation region of the cometary ammonia ice was between the orbit of Saturn and that of Uranus in the solar nebula.
  • K Sadakane, T Yokoo, J Arimoto, K Matsumoto, S Honda, K Tanabe, K Wakamatsu, M Nishida, M Yoshida, M TakadaHidai
    PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 48(1) 51-57 1996年2月  
    Optical light curves in the V, R, and I bands, starting 10 days before the maximum light, and the optical spectra near to the V maximum phase of supernova SN 1995D in NGC 2962 are presented. The spectra taken near to the optical maximum are similar to the prototypical type-Ia supernova SN 1981B, and show no trace of the interstellar Nar D Line. The expansion velocity at the maximum phase was 10000 +/- 200 km s(-1). The supernova reached maximum light in the I band about four days earlier than in the V band. A distinct secondary peak is observed in the I band about 30 days after the V maximum. This secondary peak occurred about one week delayed from the published template light curve. A clear shoulder is detected in the R band light curve corresponding to the secondary peak in the I band. The initial rate of decline is slow [Delta m(15)(V) = 0.66 mag], and it is suggested that the supernova belongs to a group of the intrinsically brightest type-Ia supernovae. From the initial declining rate in the V band, we estimated the absolute magnitude M(V) to be -18.8 +/- 0.3 mag, and the distance modulus of the parent galaxy (NGC 2962) to be 32.2 +/- 0.3 mag.

共同研究・競争的資金等の研究課題

 10
もっとみる
一覧へ戻る