Stars and Galaxies, Vol. 06 （2023年）

論文リスト：

Long-term evolution of the Hα emission line of Pleione between Jan 2009 and Mar 2023 in the BeSS database
Author：Junichi Katahira
著者の電子メールアドレス: atak@db3.so-net.ne.jp
Received 2023 September 29; Accepted 2023 November 10

Abstract：
Using the Hα double peak emission lines of Pleione in the BeSS database from January 2009 to March 2023, we have measured the characteristic three point intensities of the line: the intensities at the blue and red emission peaks, and the intensity of the central minimum between the peaks, and calculated the radial velocities of these three points. These values are shown over a period of 14 years. The long-term variations shown are interpreted to be split into (a) the short-term variations when the companion of Pleione is close to periastron, and (b) the long-term variations in the background. For the (b) variation, we try to explain the trajectory of the central minimum intensity by the disk precession, and discuss the occurrence of the V/R phenomenon.

　Key words：stars: Be star— stars: Pleione— stars: Be disk
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Learning Based on Shared Experience: A Proof of Concept at the SAGI summer school in Observational Astronomy
Author：Quang NGUYEN-LUONG1,2, Van Trung DINH3, Kazuhito DOBASHI4, Anh DUONG-TUAN2, Yuya HIRANO5, John HOANG6,7, Ngoc Duy HOANG8, Yoichi ITOH5, Mikio KURITA9, Minh Tan LE10, Ngoc Tram LE11, Quang Thuy LE12, Thierry MONTMERLE13, Binh NGUYEN14, Huu Ha NGUYEN12, Thi Thao NGUYEN15, Tung Lam NGUYEN16, Van Tue NGUYEN12, Nicolas PERETTO17, Jungjoo SOHN18, Quang Vinh TRAN19, Thanh Son TRAN16
Affiliation : 1) Department of Computer Sciences, Math, & Environmental Science, The American University of Paris, 75007, Paris, France
2) Universit´e Paris-Saclay, Universit´e Paris Cit´e, CEA, CNRS, AIM, 91191, Gif-sur-Yvette, France
3) Institute of Physics, Viet Nam Academy of Science and Technology, Viet Nam
4) Department of Astronomy & Earth Sciences, Tokyo Gakugei University, Nukuiki Tamachi, Koganei, Tokyo, 184-8501, Japan
5) Nishi-Harima Astronomical Observatory, Center for Astronomy, University of Hyogo, Japan
6) Department of Astronomy, University of California Berkeley, USA
7) Santa Cruz Institute for Particle Physics, University of California Santa Cruz, USA
8) Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
9) Department of Astronomy, Kyoto University, Kyoto, Japan
10) Department of Physics, Tay Nguyen University, Daklak, Viet Nam
11) Max Plank Institute for Radio Astronomy, Germany
12) Quy Nhon Observatory, Explorascience Quy Nhon, Quy Nhon City, Viet Nam
13) Institut d’Astrophysique de Paris, F-75014 Paris, France
14) Department of Astronomy, University of Washington, Washington, USA
15) Nha Trang Observatory, Nha Trang City, Viet Nam
16) IFIRSE, ICISE, Quy Nhon City, Viet Nam
17) School of Physics & Astronomy, Cardiff University, UK
18) Dept. of Earth Science of Education, Korea National University of Education, Cheongju-si, ChungBuk, Korea
19) Massachusetts Institute of Technology, USA
著者の電子メールアドレス: qnguyen@aup.edu
Received 2023 October 31; Accepted 2023 November 28

Abstract：
The SAGI summer school 2023 (3S23) in observational astronomy is organized in the Summer 2023, at the International Center for Interdisciplinary Science and Education (ICISE) in Quy Nhon, Viet Nam. The goal of 3S23 is to promote astronomy research in Viet Nam and to teach astronomy to students. We report the activities of the school and also highlight its pedagogical approach. Using narrative and observational analysis of participants’ own words, we analyze the impacts of the school on participants and on astronomy in Viet Nam. From these results, we propose a new form of teaching, namely Learning Based on Shared Experience (LBSE). LBSE takes into account the diversities in students’ backgrounds, languages, analytical, mathematical, abilities, and experiences and create an environment where learners learn and share from each others’ experience. This approach is likely effective in teaching subjects that requires collaborations such as sciences and technologies.

　Key words：optical astronomy — astronomy education — science development – experiential learning
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京都大学飛騨天文台ドームレス太陽望遠鏡を用いたエラーマンボムの高度詳細解析
Detailed altitude analysis of Ellerman bomb using the domeless solar telescope at the Hida Observatory, Kyoto University
著者：市川椋大1, 野澤恵1
所属： 1) 茨城大学理学部
Authors：Ryota ICHIKAWA1, Satoshi NOZAWA1
Affiliation： 1) 1Ibaraki University College of Science, 2-1-1, Bunkyo, Mito, Ibaraki, Japan, 310-8512
著者の電子メールアドレス: 23nm302at@vc.ibarakia.ac.jp
Received 2023 September 25; Accepted 2023 November 29

概要：
エラーマンボムは彩層底部で起こる小規模爆発現象であり、Hα線中心では吸収、ウィング部では顕著 な増光が見られる特徴的なスペクトルプロファイルを示す。発生メカニズムは磁気リコネクションと考え られているが、その詳細は未だに未解明のままである。そこで、エラーマンボムのスペクトル特性から立 体的な構造の時間変動を解明することが本研究の狙いである。2022年10月に京都大学付属飛騨天文台の水 平分光器を用いて、Hα線とCa II K線で観測した活動領域NOAA13124とNOAA13135の黒点近傍で発生し たエラーマンボムを分光観測し、各波長から速度・温度・明るさの物理量の時間変動を求めた。結果、Hα 線では彩層下部で磁気リコネクションが発生し、それによる双方向流を観測した。また、ウィング部の速 度と明るさに関して、明るさが増加したタイミングで速度が上昇するような相関が確認できた。Ca II K線 では彩層中部以下で磁気リコネクションが発生したと考えられ、K2コンポーネントに関してはHα線ウィ ング部と同様に速度と明るさに相関が確認できた。

Abstract：
The Ellerman bombs are small-scale explosive events that occur at the base of the chromosphere and exhibit a characteristic spectral profile, showing absorption in the Hα line center and significant brightening in the wing. While magnetic reconnection is considered to be the mechanism of their occurrence, the details remain unresolved. Therefore, the aim of this study is to elucidate the temporal evolution of the three-dimensional structure of Ellerman bombs through their spectral characteristics. Using the horizontal spectrograph at the Hida Observatory, Kyoto University, in October 2022, we conducted spectroscopic observations of Ellerman bombs that occurred in the vicinity of sunspots in active regions NOAA13124 and NOAA13135, using the Hα and Ca II K lines, and obtained the temporal variations of physical quantities such as velocity, temperature, and brightness at each wavelength. As a result, we observed magnetic reconnection at the base of the chromosphere in the Hα line, and bi-directional flow resulting from it. Furthermore, we confirmed a correlation between the increase in brightness and the subsequent rise in velocity in the wing. In the Ca II K line, we considered magnetic reconnection to occur below the middle of the chromosphere, and we found a similar correlation between the velocity and brightness of the K2 component as in the Hα line wing.

　Key words：Sun : Chromosphere –Sun : Magnetic Reconnection – Sun : Ellerman Bomb
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なゆた望遠鏡MALLSによるBe星δ Scorpii、π Aquariiの中分散分光観測
Medium resolution Spectroscopic Observations of Be stars δ Scorpii and π Aquarii with the Nayuta Telescope MALLS
著者：石田光宏
所属： 横浜市立戸塚高等学校
Authors：Mitsuhiro ISHIDA
Affiliation： Yokohama Municipal Totsuka High School, 2–27–1 Gumizawa, Totsuka-ku, Yokohama-shi, 245–0061, Japan
著者の電子メールアドレス: mi06-ishida@city.yokohama.jp
Received 2023 October 31; Accepted 2023 November 29

概要：
長年、Be星（γ Cas型変光星)の測光・分光観測が行われているが、星周円盤への角運動量輸送機構（連 星系の場合、伴星の寄与もあるのか）等、明らかになっていないことも多い。2018年9月から学校天文台に ある小口径望遠鏡+低分散分光器を用いて、複数のBe星の分光モニター観測を行った。観測結果より「Be 星の伴星が近星点を通過するときの潮汐力で円盤がリング化する」という仮説を立てた(石田2022, Stars and Galaxies, 5, 10)。これを検証するため、兵庫県立大学西はりま天文台のなゆた望遠鏡を用い、Be星δ Sco とπ Aqrにおいて、それぞれの伴星が近星点を通過した時と後で中分散分光観測を行った。BeSS database の解析結果も合わせると、円盤のリング化は見られなかった。学校天文台での観測と合わせると、δ Scoの 円盤は、有効温度が下がって膨張していると予想され、今後は消滅に向かう可能性がある。π Aqrの円盤 は、近星点前後で円盤の有効温度が変化する傾向がある。これらより、Be星の円盤への角運動量輸送機構 に、伴星が大きく影響を与えている可能性がある。

Abstract：
Although photometric and spectroscopic observations of Be stars (γ Cas-type variable stars) have been carried out for many years, there are many things that remain unclear, such as the mechanism of angular momentum transport to the circumstellar disk (in the case of binary systems, is there also a contribution from the companion star). Spectroscopic monitoring observations of several Be stars were performed using the Small Aperture Telescope + low-dispersion spectrograph at the school observatory starting in September 2018. As a result, we hypothesized that “the disk is ringed by tidal forces when the Be star’s companion passes through the perihelion point” (石田2022, Stars and Galaxies, 5, 10). To test this hypothesis, we performed medium-dispersion spectroscopic observations of Be stars δ Sco and π Aqr using the Nayuta Telescope at the Nishi-Harima Observatory, University of Hyogo, during and after the periastron passage of their respective companion stars. Combined with the results of the BeSS database analysis, no ring formation of the disk was observed. Combined with the observations at the School Observatory, the disk at δ Sco is expected to be expanding due to a decrease in effective temperature, and may be headed for extinction in the future. In the disk of π Aqr, the effective temperature of the disk tends to change around the perihelion. From these results, it is possible that the companion star has a significant effect on the angular momentum transport mechanism of the Be star to the disk.

　Key words：emission-line—Be Star—optical astronomy—spectroscopic
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太陽活動はダルトン極小期以降4回衰退した
Four Times Solar Activity Decline since the Dalton Minimum
著者：杉谷康雄
Authors：Yasuo SUGITANI
著者の電子メールアドレス: ys1951@live.jp
Received 2023 October 31; Accepted 2023 December 1

概要：
太陽活動には、約11年の周期が存在しているが、その強さは周期によって大きく変動する。この周期 の強さを、周期の始まりが分かった時点で予測する式を、旧バージョンの黒点相対数を使い、重回帰分析 の手法を使って探してきた。そして二つの重回帰式を見つけたが、少なくともどちらかの式が、過去の全 周期の強さをピンポイントで言い当てている。二つの式が存在する事から導かれる結論は、周期の強さを 予測するという当初の目的とは異なる副産物ではあるが、太陽活動の衰退時期が特定できる事、活動衰退 は予測可能である事、黒点相対数だけでは判断できない極めて弱い衰退が存在する事である。新バージョ ンの黒点相対数についても同様の2式が存在するので報告する。

Abstract：
Solar activity has a cycle of ∼11 years, and its strength greatly varies depending on the cycle. I have been seeking for a formula that predicts the strength of this cycle once the beginning of the cycle is known using the old version of the relative sunspot numbers and multiple regression analysis techniques. Two multiple regression formulas have been discovered, and at least one of these pinpoints the strength of all past cycles. From these two formulas, the author concludes that while they are the byproduct of the objective of predicting the strength of the cycle, which differed from the original objective, the timing of the decline in solar activity can be identified. Furthermore, the decline in solar activity is predictable, and extremely weak declines cannot be determined merely using the relative sunspot numbers. The same two formulas exist for the new version of the relative sunspot numbers and are reported in this study.

　Key words：sunspots, solar activity
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Period modulations of the long secondary periods on the AGB stars
Author： Masaki Takayama
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: takayama@nhao.jp Received 2023 October 31; Accepted 2023 December 5

Abstract：
30%–50% of the luminous pulsating red-giant stars show light variations of a longer period than the pulsation periods. Those periods are called long secondary periods (LSP). There has been debated for many years but the origin of the LSP is still unknown. To explain the LSP variations, there have been many approaches in not only observations but also theoretical studies. However, the invariance of the length of the LSPs has been investigated little. Thus, we studied the temporal variations of the period by performing the weighted wavelet-Z-transform analysis. Using the OGLE-III database, the I-band light curves of 6904 and 1945 LSP candidates in the Large/Small Magellanic Clouds, respectively, were analyzed. Most of our sample stars indicated that the period corresponding to the LSP was constant during the observation term. However, 101 and 44 LSP stars in the LMC and SMC, respectively, showed the signature of the temporal variations of the LSPs. There were diversities of the period modulations i.e. monotonic increase or decrease, or constant until the middle and then increase, etc. The comet-like companion is one of the possible explanations for the LSP variations, but this hypothesis cannot explain the period modulations because the LSP is determined by the orbital period.

Key words：infrared: stars – stars: AGB and post-AGB – stars: late-type
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First detection of exoplanet transit in Vietnam
Author: Tue Nguyen-Van†1, Hai Ngo-Ngoc2, Yuya Hirano3, Yoichi Itoh3, Thuy Le-Quang1, An Nguyen-Khanh4, Felix Wood5, John Hoang6,7, D. N. Hoang8, Thierry Montmerle9, Quang Nguyen-Luong10,11
Affiliation：
1) Quy Nhon Observatory, Explorascience Quy Nhon, Quy Nhon city, Vietnam
2) University of Science, Vietnam National University, HCM city, Vietnam
3) Nishi-Harima Astronomical Observatory, Center for Astronomy, University of Hyogo, Japan
4) Department of Physics, International University, Vietnam National University, HCM city, Vietnam
5) Cardiff University, UK
6) Department of Astronomy, University of California Berkeley, USA
7) Santa Cruz Institute for Particle Physics, University of California Santa Cruz, USA
8) Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
9) Institut d’Astrophysique de Paris, F-75014 Paris, France
10) CSMES, The American University of Paris, PL111, 2 bis, passage Landrieu, 75007, Paris, France
11) Universit´e Paris-Saclay, Universit´e Paris Cit´e, CEA, CNRS, AIM, 91191, Gif-sur-Yvette, France
著者の電子メールアドレス: nguyenvantue0996@gmail.com
　Received 2023 October 31; Accepted 2023 December 6

Abstract：
In this paper, we report the results obtained from the first observations of exoplanet transit conducted with the 600 mm telescope at Quy Nhon Observatory (QNO) in Vietnam. The object of our observation is the exoplanet WASP- 3b, transiting its host starWASP-3 with a period of approximately 1.8468 Earth days. Through our observations and modeling, we obtained a magnitude depth of 0.0121 ± 0.007 mag and a planet radius of 1.42 ± 0.05 RJupiter for WASP-3b. This result is consistent with the previous published results and it implies that QNO 600 mm telescope is capable of monitoring short-period exoplanet transits, even at the atmospheric conditions of Quy Nhon city.

Key words：WASP-3b — Exoplanets — Exoplanet transits —Techniques: photometry — Quy Nhon Observatory (QNO)
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教員志望学生を対象とした天文分野の理解度や興味・関心に関する継続調査：10 年間の変遷
Continuous research on understanding and interests in astronomy for prospective teacher students: Changes over the decade
著者：大朝由美子1,2
所属： 1) 埼玉大学教育学部
2) 埼玉大学大学院理工学研究科
Authors：Yumiko Oasa1,2
Affiliation： 1) Saitama University,Faculty of Education, 255, Shimo-Okubo, Sakura, Saitama, Saitama 338–8570, Japan
2) Saitama University,Graduate School of Science and Technology, 255, Shimo-Okubo, Sakura, Saitama, Saitama 338–8570, Japan 著者の電子メールアドレス: yumiko.oasa@mail.saitama-u.ac.jp
Received 2023 November 8; Accepted 2023 December 7

概要：
本論文では，将来教員になる大学生の天文分野の基本的な知識・理解度や認識，興味の変化などを調査 することを目的として，教員養成系である教育学部生（3432名）を対象に，天文分野の興味関心や小中学 校で学ぶ天文分野の理解度調査を，2013年度から2023年度まで継続的に実施した。その結果，教育学部， 及び理科専修の学生の理科好きの割合は8，9割前後で推移しており，ここ十年における明確な理科離れ・ 理科嫌いの傾向は見られないことが明らかになった。日周運動・年周運動等の「天体の動き」，及び太陽や 月など「天体の分類」については知識の定着率が比較的高い一方で，「天体の大きさ」や「天体の光り方」 等の天体の物理的特徴を扱う事項については理解度が低いことがわかった。理科・天文への興味関心の度 合い，望遠鏡で天体観測・観望を行なった経験，天の川の観望経験等の天文に関する直接的体験や高校地 学分野の履修状況などを考慮した分析から，全体の正答率が高い「天体の動き」や「天体の分類」には大 きな違いはないが，「天体の大きさ」「天体の光り方」や全問正解の割合には，それぞれの経験/履修内容に よる違いが見られた。回答者の属性，経験，天文分野の理解度についてロジスティック回帰分析を行なっ た結果，天文に関する直接的な体験や興味・関心，高等学校で地学関連を学ぶこと等が知識や理解度へ影 響を及ぼすことが示唆された。さらに，将来小中高の理科教員を志望している理科専修の学生について， 1年次に加えて，2，3，4年次に調査を行なった結果を比較したところ，入学時から卒業前までで理解度が 向上していることが明らかになった。多くの学生にとって，高等学校において地学関連の科目を学ぶ機会 がない現在の状況を考慮すると，天文学を学ぶ最後の機会となり得る大学で学ぶことは，教員として必要 な科学的知識，及び科学的素養を育成できる可能性が示唆された。 以上の結果を踏まえると，教員養成系の大学生について天文学の基本的な理解度を向上し，定着させ るためには，（1） 天体望遠鏡等を用いた観望・観測体験， （2） 高等学校での「地学・地学基礎」の履修， （3）大学での天体観測を活用した教育が望まれる。

Abstract：
This paper aims to investigate the the fundamental knowledge, comprehension, awareness, and interest in the realm of astronomy among university students aspiring to become teachers. We have conducted questionnaire surveys from 2013 to 2023 among 3432 students in the Faculty of Education, a teacher-training department, in order to assess their interest in science and astronomy and their understanding of astronomical concepts studied during elementary/junior-high school. As a result, there has been a consistent interest around 80-90% in science among education and science major students over the past decade. There appears to be no clear trend of “decline in students’ positive attitude toward science” during this period. While there was a relatively high retention of knowledge regarding diurnal/annual motions and the classification of the Sun and Moon, there was a lower comprehension of astrophysical characteristics. From comparisons of the percentage of correct responses, interest in science/astronomy, direct experiences in astronomical observations using telescopes and/or gazing our Milky Way, and learning “earth science” in high school, it was found that there existed a discernible gap in understanding astrophysical characteristics, while there were no significant differences in understanding diurnal/annual motions and the classification of the Sun/Moon. The logistic regression analyses on the students’ interests, experiences, and understanding of astronomy indicated that direct experiences, interests, and/or curiosity in astronomy, as well as studying “earth science” in high school, could have a impact on knowledge and understanding of astronomy. Furthermore, a comparison between first-year and subsequent years’ surveys for science major students aspiring to become science teachers at elementary, junior high, and high schools revealed a progressive improvement in understanding. The results suggest that studying astronomy during university, often considered the final opportunity to learn astronomy, could significantly contribute to nurturing essential knowledge and scientific literacy for teachers. In summary, in order to enhance and retain the fundamental understanding of astronomy among university students in teacher training programs, it is recommended to implement the following strategies: （1） observational experiences and hands-on learning utilizing telescopes, （2） studying “earth science （basic）” in high school, and （3） educational practices involving astronomical observations at the university level.

　Key words：天文教育，地学教育，理科教育，理解度調査，教員養成，学習指導要領
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嘉永六年クリンカーヒューズ彗星にみる土御門家・間家の観測精度比較
Observation of Klinkerfues comet in Japan on 1853 - Evaluation of the technical arts of astronomical observations at Tsuchimikado (Kyoto) and Hazama (Osaka) -
著者：玉澤春史1, 2 岩橋清美3 北井礼三郎4
所属：
1) 1東京大学生産技術研究所、〒153-8505 東京都目黒区駒場4-6-1
2) 京都市立芸術大学、〒610-1197 京都市西京区大枝沓掛町13-6
3) 國學院大學、〒150-8440 東京都渋谷区東4丁目10-28
4) 立命館大学、〒603-8577 京都市北区等持院北町56-1
Author： Harufumi Tamazawa1, 2, Kiyomi Iwahashi3, and Reizaburou Kitai4
Affiliation：
1) Institute of Industrial Science, the University of Tokyo, 4-6-1 Komaba Meguro-ku, Tokyo 153-8505, Japan
2) Kyoto City University of Arts, 13-6 Kutsukake-cho, Oe, Nishikyo-ku, Kyoto 610-1197, Japan
3) Kokugakuin University, 10-28 Higashi 4-cyoume, Shibuya-ku, Tokyo 150-8440
4) Ritsumeikan University,56-1, Toujiinkita-cyou, Kita-ku, Kyoto 603-8587
著者の電子メールアドレス: tamazawa@iis.u-tokyo.ac.jp
　Received 2023 October 31; Accepted 2023 December 12

概要：
嘉永6(1853)年に出現したクリンカーヒューズ彗星の日本における観測記録は、日本では京都土御門家 と大坂間家に伝来しており、これらは観測数値が記されていることから西洋における観測記録と比較可能 である。観測精度の相互比較を行った結果、(1) 土御門家の測量では、測量機器の設定誤差が方位角で4◦、高 度角で−2◦あること、およびこのことが赤道座標値での軌道の系統的なエラーの原因であることが分かっ た。測量機器の設定誤差を補正すると、土御門家観測は、西欧観測との残差は±2◦のランダムエラーの範 囲内であり、赤道座標での彗星の軌道は十分把握できていた。(2)間家の観測結果は、西欧観測結果に比し て±5◦のランダムエラーがあり、土御門家観測より精度が劣ることが分かった。

Abstract：
Klinkerfues comet (1853) was observed at Tsuchimikado in Kyoto and Hazama in Osaka in Japan. Their daily observational records were found to give us numerical data of apparent positions of the comet and permit us to get equatorial coordinates of daily positions of the comet. By mutual comparison of observational accuracies , we found that (1) there are error of +4◦ in azimuth and −2◦ in altitude in Tsuchimikado’s measureing device setting and that after the correction of device setting error, the orbit of the comet well fit the western observational result with a random error of 2◦. (2) The orbit derived from Hazama measurement is less well fit the western observational result than Tsuchimikado’s measurements, with a random error of 5◦.

　Key words：Comet Donati - Historical records in Japan - Technical arts of observation
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Long term variability of light-pollution in Bisei Town
Authors：Ryosuke ITOH1, 2 and Syota MAENO1
Affiliation： 1) Bisei Astronomical Observatory, Bisei, Ibara, Okayama, 715-1411, Japan
2) Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan
著者の電子メールアドレス: itoh@bao.city.ibara.okayama.jp
Received 2023 November 4; Accepted 2023 December 15

Abstract：
Bisei town, located in the west part of Japan, is known as a place where the local community protects its beautiful night sky from light pollution through its unique ordinances and the efforts of the local residents. It is also important to monitor in the quantity and quality of light pollution for precise measurement of astronomical observations. The fluorescent lamps in the city were gradually replaced with light emitting diode (LED) lamps. In order to investigate how much light pollution is affecting astronomical observation, we analyzed the archival photometric and spectroscopic data taken by the 101 cm telescope that has been installed at Bisei Astronomical Observatory (BAO) since 2006. As a result, we found that there is no significant variability in sky brightness in optical bands, but from spectroscopic observation, we observed a blue humps around 4500 ˚A originating from LED lights from 2017 to 2023. The brightness of light pollution observed at BAO is not varied but the origin of light has gradually changed from fluorescent lamps toLED lamps.

　Key words：light pollution
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Linear Nonadiabatic Pulsation Models of Ultra-Long-Period Cepheids
Authors：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 2023 October 31; Accepted 2023 December 20

Abstract：
Ultra-Long-Period Cepheids (Periods longer than 80 days) are examined using linear nonadiabatic pulsation models. We found models with ultra-long-periods even with Z = 0.02 models, so such a Cepheid may exist in our Galaxy, which has not been discovered yet. We seem to need a survey of the far side of our Galaxy or a survey in the other galaxy with a similar chemical composition to discover such an object. It is also shown that the models with periods longer than 200 days need to be more massive than the Cepheid upper mass limit, inferred from the stellar evolution theory. It is pointed out that the Cepheid’s nature of HV 1956 in SMC, which has over-200 days period, needs careful confirmation.

　Key words：Stars: individual (HV 1956 in SMC) — stars: oscillations — stars: variables: Cepheids
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