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.

Abstract
1. Introduction
2. Target Selection and Observations
3. Spectral Analysis
    3.1. Equivalent Widths and Stellar Parameters
    3.2. Analyzed Elements and Line List
    3.3. Comparison Stars
    3.4. Kinematical Properties
4. Elemental Abundances
5. Implications for Supernova Nucleosynthesis
    5.1. Comparison with the Pair-Instability SupernovaNucleosynthesis
    5.2. Comparison with the Core-Collapse SupernovaNucleosynthesis
6. Conclusions
Acknowledgments
References

• Hye-Eun Jang(Department of Physics and Astronomy, Seoul National University, Korea Astronomy and Space Science Institute) Corresponding author
• 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, National Astronomical Observatory of Japan)
• Tadafumi Matsuno(Department of Astronomical Science, School of Physical Sciences, SOKENDAI, The Graduate University for Advanced Studies, National Astronomical Observatory of Japan, Kapteyn Astronomical Institute, University of Groningen)
• 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, SNU Astronomy Research Center, Seoul National University)