TOI-561 b: A Low-density Ultra-short-period “Rocky” Planet around a Metal-poor Star
TOI-561 b: A Low-density Ultra-short-period “Rocky” Planet around a Metal-poor Star
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DOI：
10.3847/1538-3881/acad83
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发表时间：
2022-10
期刊：
影响因子：
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通讯作者：
C. Brinkman;L. Weiss;F. Dai;D. Huber;E. Kite;D. Valencia;J. Bean;C. Beard;A. Behmard;S. Blunt;M. Brady;B. Fulton;S. Giacalone;A. Howard;H. Isaacson;D. Kasper;J. Lubin;M. Macdougall;Joseph M. Akana Murphy;Mykhaylo Plotnykov;A. Polanski;M. Rice;A. Seifahrt;G. Stefansson;J. Stürmer
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文献类型：
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作者：
C. Brinkman;L. Weiss;F. Dai;D. Huber;E. Kite;D. Valencia;J. Bean;C. Beard;A. Behmard;S. Blunt;M. Brady;B. Fulton;S. Giacalone;A. Howard;H. Isaacson;D. Kasper;J. Lubin;M. Macdougall;Joseph M. Akana Murphy;Mykhaylo Plotnykov;A. Polanski;M. Rice;A. Seifahrt;G. Stefansson;J. Stürmer
TOI-561是一颗银河系厚盘恒星，拥有一颗半径为1.37R⊕的超短周期(0.45日轨道)行星，使其成为发现地球大小行星的最缺乏金属([Fe/H]=−0.41)和最古老(≈10 Gyr)的地点之一。我们给出了双子座N/马龙X和Keck/HiRes的新的同步径向速度(RV)测量，并与文献中的RV相结合，得到质量为Mb=2.2 4±0.2 0M⊕。我们还使用了两个新的TESS测光扇区来改进半径测定，得到Rb=1.37±0.04R⊕，并确认TOI-561b是迄今测量到的密度最低的超地球之一(ρb=4.8±0.5g cm−3)。这种密度与反映宿主星的铁和造岩元素丰度的贫铁岩石成分是一致的；然而，它也与一颗具有挥发性包层的低密度行星一致。行星的平衡温度(∼2300K)表明，这个包层可能由高平均分子量物种组成，如水蒸气、二氧化碳或硅酸盐蒸气，可能不是原始的。我们还证明了成分测定对恒星参数的选择是敏感的，还需要进一步的测量来确定TOI-561b是一颗裸露的岩石行星，还是一颗具有光学稀薄大气的岩石行星，还是半径小于1.5R⊕的行星上罕见的非原始包络的例子。
TOI-561 is a galactic thick-disk star hosting an ultra-short-period (0.45-day-orbit) planet with a radius of 1.37 R ⊕, making it one of the most metal-poor ([Fe/H] = −0.41) and oldest (≈10 Gyr) sites where an Earth-sized planet has been found. We present new simultaneous radial velocity (RV) measurements from Gemini-N/MAROON-X and Keck/HIRES, which we combined with literature RVs to derive a mass of M b = 2.24 ± 0.20 M ⊕. We also used two new sectors of TESS photometry to improve the radius determination, finding R b = 1.37 ± 0.04 R ⊕ and confirming that TOI-561 b is one of the lowest-density super-Earths measured to date (ρ b = 4.8 ± 0.5 g cm−3). This density is consistent with an iron-poor rocky composition reflective of the host star’s iron and rock-building element abundances; however, it is also consistent with a low-density planet with a volatile envelope. The equilibrium temperature of the planet (∼2300 K) suggests that this envelope would likely be composed of high mean molecular weight species, such as water vapor, carbon dioxide, or silicate vapor, and is likely not primordial. We also demonstrate that the composition determination is sensitive to the choice of stellar parameters and that further measurements are needed to determine whether TOI-561 b is a bare rocky planet, a rocky planet with an optically thin atmosphere, or a rare example of a nonprimordial envelope on a planet with a radius smaller than 1.5 R ⊕.