Stars and Galaxies, Vol. 03 （2020年）

論文リスト：

Behaviors of Ca ii K line in A-type stars
　Author：Yoichi Takeda
　Affiliation：11–2 Enomachi, Naka-ku, Hiroshima-shi, Hiroshima 730–0851, Japan
　著者の電子メールアドレス: ytakeda@js2.so-net.ne.jp
　Received 2020 October 31; Accepted 2020 November 23

Abstract：
A synthetic spectrum-fitting analysis was applied to the resonance Ca ii line at 3933.68 Å for a large sample of 122 A-type main-sequence stars (7000 ≲ Teff ≲ 10000 K) in a wide range of projected rotational velocity (10 ≲ vsini ≲ 300 km s−1), with an aim of investigating the behaviors of Ca abundances ([Ca/H]39) determined from this strong Ca ii 3934 line, especially in context of (i) how they are related with the Am phenomenon (often seen in slow rotators) and (ii) whether they are consistent with the Ca abundances ([Ca/H]61) previously derived by the author from the weaker Ca i 6162 line. It was confirmed that Ca line strengths in Am stars tend to be weaker and associated abundances are lower compared to non-Am stars at the same Teff, indicating a deficiency of Ca in the photosphere of Am stars. However, an appreciable fraction of cool Am stars (Teff ≲ 8000 K) were found to show extraordinarily anomalous Ca ii 3934 line feature (i.e., unusually broad for its considerable weakness) which is hard to explain. Regarding the comparison between [Ca/H]39 and [Ca/H]61, while both are roughly consistent with each other for hotter stars (Teff ≳ 8000 K), the former tends to be lower (by up to −1 dex or even more) than the latter for cooler A stars (Teff ≲ 8000 K) including those “weak broad K line” objects, This fact suggests that some special mechanism reducing the strength of Ca ii 3934 line is involved at Teff ≲ 8000 K where [Ca/H]39 would be no more reliable. Whereas atomic diffusion causing the deficit of Ca in the photosphere as a result of element segregation in the deeper radiative envelope may be regarded as a promising explanation because it seems to fit in the qualitative trend of [Ca/H]61 in A-type stars, the well-known feature of considerably weak Ca ii K line in classical Am stars should not necessarily be attributed to only this element diffusion scenario, for which some unknown weakening mechanism specific to this resonance line may independently be operative.

　Key words：stars: abundances — stars: atmospheres — stars: chemically peculiar — stars: early-type — stars: rotation
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NIC から 2MASS の測光システムへの色変換係数の導出
Determination of color transformation coefficients from NIC to 2MASS photometric system
　著者：小野里 宏樹
　所属：兵庫県立大学 天文科学センター 西はりま天文台
　Author：Hiroki Onozato
　Affiliation：Nishi-Harima Astronomical Observatory, Center for Astronomy, University of Hyogo, 407–2 Nishigaichi, Sayo-cho, Hyogo 679–5313, Japan
　著者の電子メールアドレス: onozato@nhao.jp
　Received 2020 November 23; Accepted 2020 November 25

概要：
異なった望遠鏡、観測装置で取得された測光データを高精度に比較する際には、得られた等級を同一の測光システムに変換する必要がある。この論文ではなゆた望遠鏡のカセグレン焦点に搭載されている Nishiharima Infrared Camera (NIC) で観測した等級を近赤外線での事実上の標準システムとなっている Two Micron All Sky Survey (2MASS) のシステムに変換するための色変換式の変換係数を導出した。銀河面の星間減光の強い領域の観測データを含めることで、非常に赤い天体までを含んだ幅広い色指数の天体を用いて変換係数を導出することができた。その結果、変換係数は小さく、NIC と 2MASS の測光システムは似ていることが確認できた。

Abstract：
Accurate comparison of photometric data acquired by different telescopes and instruments requires the transformation of the magnitudes to the same photometric system. In this paper, I derived color transformation coefficients to convert the magnitudes observed with the Nishiharima Infrared Camera (NIC) equipped on the Cassegrain focus of the Nayuta telescope to the Two Micron All Sky Survey (2MASS) system, which has become the de facto standard system in the near-infrared. I was able to derive the color transformation coefficients using sources with a wide range of colors since the sample contains very red sources affected by strong interstellar extinction in the Galactic plane. As a result, the conversion coefficients are small, and it is confirmed that the NIC and 2MASS photometric systems are similar.

　Key words：instrumentation: detectors — instrumentation: photometers
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Detection of intermediate-mass black holes in globular clusters using gravitational lensing
　Authors：Takayuki Tatekawa1,2, Yuuki Okamura3
　Affiliation：
　　1) Department of Social Design Engineering, National Institute of Technology, Kochi College, 200–1 Monobe Otsu, Nankoku, Kochi 783–8508, Japan
　　2) Research Institute for Science and Engineering, Waseda University, 3–4–1 Okubo, Shinjuku, Tokyo 169–8555, Japan
　　3) Department of Electrical Engineering and Information Science, National Institute of Technology, Kochi College, 200–1 Monobe Otsu, Nankoku, Kochi 783–8508, Japan
　著者の電子メールアドレス: tatekawa@kochi-ct.ac.jp
　Received 2020 October 26; Accepted 2020 December 23

Abstract：
Recent observations suggest the presence of supermassive black holes at the centers of many galaxies. The existence of intermediate-mass black holes (IMBHs) in globular clusters has also been predicted. We focus on gravitational lensing as a new way to explore these entities. It is known that the mass distribution of a self-gravitating system such as a globular cluster changes greatly depending on the presence or absence of a central massive object. After considering possible mass distributions for a globular cluster belonging to the Milky Way galaxy, we estimate that the effect on the separation angle of gravitational lensing due to an IMBH would be of milliarcsecond order.

　Key words：gravitational lensing — intermediate-mass black holes — globular clusters
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Estimation of the mass and luminosity of Polaris from resonance hypothesis
　Author：Toshihito Ishida
　Affiliation：Nishi-Harima Astronomical Observatory, Center for Astronomy, University of Hyogo, 407–2 Nishigaichi, Sayo-cho, Hyogo 679–5313, Japan
　著者の電子メールアドレス: ishida@nhao.jp
　Received 2020 November 16; Accepted 2020 December 24

Abstract：
The resonance hypothesis for the cause of the decreasing event in the pulsation amplitude of the Cepheid component of Polaris is proposed. If Polaris is at the center of the 2:1 resonance between the first and the fourth overtone modes, we can estimate the mass and luminosity from the results of the linear nonadiabatic pulsation models using resonance conditions. The estimated stellar parameters from the resonance hypothesis are within the possible parameter range.

　Key words：stars: indivisual (Polaris) — stars : oscillations — stars: variables: Cepheids
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京都女子大学の望遠鏡から見た日本の天文学史
Japanese history of astronomy looked through the telescope of Kyoto Women’s University
　著者：河村 聡人1、中尾 真弓2、道越 秀吾2
　所属：1) 京都大学付属天文台 2) 京都女子大学
　Authors：Akito D. Kawamura1, Mayumi Nakao2, Shugo Michikoshi2
　Affiliation：
　　1) Astronomical Observatory, Kyoto University, 17–1 Kitakazan-ohmine-cho, Yamashina-ku, Kyoto 607–8471, Japan
　　2) Kyoto Women’s University, 35 Kitahiyoshi-cho, Imakumano, Higashiyama-ku, Kyoto 605–8501, Japan
　著者の電子メールアドレス: akitodk@kwasan.kyoto-u.ac.jp
　Received 2020 November 6; Accepted 2020 December 24

概要：
京都女子大学附属小学校の反射望遠鏡 (以下、京女望遠鏡) の調査を発端とし、大正から昭和にかけての日本の天文学の発展を考察する。天文学史研究において重要なのは、論文だけでなく、研究を支えた人々の調査である。本研究において、西村末雄という重要な鏡製作者が発見された。この発見は日本の天文学の歴史を考察する上で重要である。当論文では、京女望遠鏡の調査結果とともに、京都女子大学視点での日本の天文学史を読み解き、天文学史研究の多角的な将来性について議論する。

Abstract：
Starting with our investigation of the telescope settled in the Elementary School Attached to Kyoto Women’s University (hereafter Kyojo telescope), we examine the development history of Japanese astronomy during Taisho and Showa era. For the history of astronomy, studying people behind published papers and works is as important as studying those papers. In this paper, with the results of the Kyojo telescope investigation, we try to reconstruct the history of Japanese astronomy from the viewpoint of Kyoto Women’s University and discuss the potential of this kind of study in multiple perspectives.

　Key words：general: history and philosophy of astronomy
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