Journal of The Korean Astronomical Society (천문학회지)

The Korean Astronomical Society (한국천문학회)
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GRACES Observations of Mg-Enhanced Metal-Poor Stars in the Milky Way

  • Hye-Eun Jang (Department of Physics and Astronomy, Seoul National University) ;
  • Young Sun Lee (Department of Astronomy and Space Science, Chungnam National University) ;
  • Wako Aoki (Department of Astronomical Science, School of Physical Sciences, SOKENDAI, The Graduate University for Advanced Studies) ;
  • Tadafumi Matsuno (Department of Astronomical Science, School of Physical Sciences, SOKENDAI, The Graduate University for Advanced Studies) ;
  • Wonseok Kang (Metaspace) ;
  • Ho-Gyu Lee (Korea Astronomy and Space Science Institute) ;
  • Sang-Hyun Chun (Korea Astronomy and Space Science Institute) ;
  • Miji Jeong (Department of Astronomy and Space Science, Chungnam National University) ;
  • Sung-Chul Yoon (Department of Physics and Astronomy, Seoul National University)
  • Received : 2022.10.25
  • Accepted : 2023.01.11
  • Published : 2023.12.30
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Abstract

We report the result of a high-resolution spectroscopic study on seven magnesium (Mg) enhanced stars. The high Mg abundances in these stars imply that they were born in an environment heavily affected by the nucleosynthesis products of massive stars. We measure abundances of 16 elements including Mg and they show various abundance patterns implying their diverse origin. Three of our program stars show a very high Mg to Si ratio ([Mg/Si] ≈ 0.18-0.25), which might be well explained by fall-back supernovae or by supernovae with rapid rotating progenitors having an initial mass higher than about 20 M⊙. Another three of our program stars have high light to heavy s-process element ratios ([Y/Ba] ≈ 0.30-0.44), which are consistent with the theoretical prediction of the nucleosynthesis in rapidly rotating massive stars with an initial mass of about M = 40 M⊙. We also report a star having both high Y ([Y/Fe] = 0.2) and Ba ([Ba/Fe] = 0.28) abundance ratios, and it also shows the highest Zn abundance ratio ([Zn/Fe] = 0.27) among our sample, implying the nucleosynthesis by asymmetric supernova explosion induced by very rapid rotation of a massive progenitor having an initial mass between 20 M⊙ ≲ M ≲ 40 M⊙. A relative deficiency of odd-number elements, which would be a signature of the pair-instability nucleosynthesis, is not found in our sample.

Keywords

Acknowledgement

We acknowledge support from the National Research Foundation (NRF) of Korea grant funded by the Ministry of Science and ICT (NRF-2019R1A2C2010885). This work was partly supported by the Korea Astronomy and Space Science Institute grant funded by the Korea government (MSIT) (No. 2022186003). We also acknowledge support from KGMT Science Program (PID: GN-2016A-Q-1) of Korea Astronomy and Space Science Institute (KASI). Y.S.L. acknowledges support from the National Research Foundation (NRF) of Korea grant funded by the Ministry of Science and ICT (NRF-2021R1A2C1008679). Y.S.L. also gratefully acknowledges support by research fund of Chungnam National University. W.A. was supported by JSPS KAKENHI grant Nos. 21H04499. This work is based on observations obtained through the Gemini Remote Access to CFHT ESPaDOnS Spectrograph (GRACES). ESPaDOnS is located at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawai'i. ESPaDOnS is a collaborative project funded by France (CNRS, MENESR, OMP, LATT), Canada (NSERC), CFHT and ESA. ESPaDOnS was remotely controlled from the international Gemini Observatory, a program of NSF's NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), Agencia Nacional de Investigacion y Desarrollo (Chile), Ministerio de Ciencia, Tecnologia e Innovacion (Argentina), Ministerio da Ciencia, Tecnologia, Inovacoes e Comunicacoes (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea).

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