TOI-561 b: A Low-density Ultra-short-period Rocky Planet around a Metal-poor Star
Article
Brinkman, C., Weiss, L.M., Dai, F., Huber, D., Kite, E.S., Valencia, D., Bean, J., Beard, C., Behmard, A. and Isaacson, Howard. 2023. "TOI-561 b: A Low-density Ultra-short-period Rocky Planet around a Metal-poor Star." The Astronomical Journal. 165 (3).
Article Title | TOI-561 b: A Low-density Ultra-short-period Rocky Planet around a Metal-poor Star |
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ERA Journal ID | 1048 |
Article Category | Article |
Authors | Brinkman, C., Weiss, L.M., Dai, F., Huber, D., Kite, E.S., Valencia, D., Bean, J., Beard, C., Behmard, A. and Isaacson, Howard |
Journal Title | The Astronomical Journal |
Journal Citation | 165 (3) |
Number of Pages | 15 |
Year | 2023 |
Publisher | IOP Publishing |
Place of Publication | United States |
ISSN | 0004-6256 |
1538-3881 | |
Web Address (URL) | https://iopscience.iop.org/article/10.3847/1538-3881/acad83/meta |
Abstract | 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 Mb = 2.24 ± 0.20 M¤. We also used two new sectors of TESS photometry to improve the radius determination, finding Rb = 1.37 ± 0.04 R¤ and confirming that TOI-561 b is one of the lowest-density super-Earths measured to date (?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. © 2023. The Author(s). Published by the American Astronomical Society. |
Keywords | Exoplanet surface composition; Exoplanet atmospheric composition; Super Earths ; Exoplanets ; Extrasolar rocky planets |
ANZSRC Field of Research 2020 | 5101. Astronomical sciences |
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