A Very Metal-poor RR Lyrae Star with a Disk Orbit Found in the Solar Neighborhood
A Very Metal-poor RR Lyrae Star with a Disk Orbit Found in the Solar Neighborhood
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DOI：
10.3847/1538-4357/ac3483
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发表时间：
2022-01
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通讯作者：
N. Matsunaga;Akinori Itane;Kohei Hattori;J. Crestani;V. Braga;G. Bono;D. Taniguchi;J. Baba;H. Maehara;N. Ukita;T. Sakamoto;N. Kobayashi;T. Aoki;T. Soyano;K. Tarusawa;Y. Sarugaku;H. Mito;S. Sako;M. Doi;Y. Nakada;Natsuko Izumi;Y. Ita;H. Onozato;M. Jian;S. Kondo;S. Hamano;C. Yasui;T. Tsujimoto;S. Otsubo;Y. Ikeda;H. Kawakita
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作者：
N. Matsunaga;Akinori Itane;Kohei Hattori;J. Crestani;V. Braga;G. Bono;D. Taniguchi;J. Baba;H. Maehara;N. Ukita;T. Sakamoto;N. Kobayashi;T. Aoki;T. Soyano;K. Tarusawa;Y. Sarugaku;H. Mito;S. Sako;M. Doi;Y. Nakada;Natsuko Izumi;Y. Ita;H. Onozato;M. Jian;S. Kondo;S. Hamano;C. Yasui;T. Tsujimoto;S. Otsubo;Y. Ikeda;H. Kawakita
缺乏金属的恒星是了解银河系早期形成的重要示踪物。最近利用光度和光谱数据进行的大规模调查报告了越来越多的缺乏金属的恒星，它们的运动学特征与盘状恒星群的运动特征一致。我们报告发现了一个RR天琴座变星(以下简称RRL)，它位于厚盘内，其轨道与厚盘运动学一致。我们的目标RRL(高清331986)位于距离太阳约1kpc的位置，V≃为11.3，是目前已知的∼130最亮的RRL之一。然而，这个天体几乎没有被研究过，因为它位于银河系的中面，在银河系的纬度约为-1°。其近红外光谱(0.91-1.32μm)除巴氏系列氢线外，无其他吸收峰，提示为[Fe/H]≲-2.5。它是最缺乏金属的RRL，至少在其轨道与盘运动学一致的RRL中是如此，尽管我们无法确定它属于哪个盘和光环。这种独特的RRL将为我们研究内银河系恒星的早期形成提供必要的线索，并进行进一步的研究，包括高分辨率光学光谱。
Metal-deficient stars are important tracers for understanding the early formation of the Galaxy. Recent large-scale surveys with both photometric and spectroscopic data have reported an increasing number of metal-deficient stars whose kinematic features are consistent with those of the disk stellar populations. We report the discovery of an RR Lyrae variable (hereafter RRL) that is located within the thick disk and has an orbit consistent with the thick-disk kinematics. Our target RRL (HD 331986) is located at around 1 kpc from the Sun and, with V ≃ 11.3, is among the ∼130 brightest RRLs known so far. However, this object has scarcely been studied because it is in the midplane of the Galaxy, at a Galactic latitude around –1°. Its near-infrared spectrum (0.91–1.32 μm) shows no absorption line except hydrogen lines of the Paschen series, suggesting [Fe/H] ≲ –2.5. It is the most metal-deficient RRL, at least among RRLs whose orbits are consistent with the disk kinematics, although we cannot determine to which of the disk and the halo it belongs. This unique RRL would provide us with essential clues for studying the early formation of stars in the inner Galaxy with further investigations, including high-resolution optical spectroscopy.