The Habitable Zone Planet Finder Reveals a High Mass and Low Obliquity for the Young Neptune K2-25b,The Astronomical Journal

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The Habitable Zone Planet Finder Reveals a High Mass and Low Obliquity for the Young Neptune K2-25b
The Astronomical Journal ( IF 5.1 ) Pub Date : 2020-09-30 , DOI: 10.3847/1538-3881/abb13a
Gudmundur Stefansson _{1,

2,

3} , Suvrath Mahadevan _{1,

2} , Marissa Maney ₁ , Joe P. Ninan _{1,

2} , Paul Robertson ₄ , Jayadev Rajagopal ₅ , Flynn Haase ₅ , Lori Allen ₅ , Eric B. Ford _{1,

2,

6} , Joshua Winn ₃ , Angie Wolfgang _{1,

2} , Rebekah I. Dawson _{1,

2} , John Wisniewski ₇ , Chad F. Bender ₈ , Caleb Caas _{1,

2} , William Cochran ₉ , Scott A. Diddams _{10,

11} , Connor Fredrick _{10,

11} , Samuel Halverson ₁₂ , Fred Hearty _{1,

2} , Leslie Hebb ₁₃ , Shubham Kanodia _{1,

2} , Eric Levi ₁ , Andrew J. Metcalf _{10,

11,

14} , Andrew Monson _{1,

2} , Lawrence Ramsey _{1,

2} , Arpita Roy ₁₅ , Christian Schwab ₁₆ , Ryan Terrien ₁₇ , Jason T. Wright _{1,

2}

Affiliation

Department of Astronomy & Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA
Center for Exoplanets & Habitable Worlds, University Park, PA 16802, USA
Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08540, USA
Department of Physics and Astronomy, University of California–Irvine, Irvine, CA 92697, USA
NSF’s OIR Lab, 950 North Cherry Avenue, Tucson, AZ 85719, USA
Institute for Computational & Data Sciences, The Pennsylvania State University, 203 Computer Building, University Park, PA 16802, USA
Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019, USA
Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
McDonald Observatory and Center for Planetary Systems Habitability, The University of Texas at Austin, Austin, TX 78712, USA
Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, CO 80305, USA
Department of Physics, University of Colorado, 2000 Colorado Avenue, Boulder, CO 80309, USA
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
Department of Physics, Hobart and William Smith Colleges, 300 Pulteney Street, Geneva, NY 14456, USA
Space Vehicles Directorate, Air Force Research Laboratory, 3550 Aberdeen Avenue SE, Kirtland AFB, NM 87117, USA
California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA
Department of Physics and Astronomy, Macquarie University, Balaclava Road, North Ryde, NSW 2109, Australia
Department of Physics and Astronomy, Carleton College, Northfield, MN 55057, USA

Using radial velocity data from the Habitable Zone Planet Finder, we have measured the mass of the Neptune-sized planet K2-25b, as well as the obliquity of its M4.5 dwarf host star in the 600–800 Myr Hyades cluster. This is one of the youngest planetary systems for which both of these quantities have been measured and one of the very few M dwarfs with a measured obliquity. Based on a joint analysis of the radial velocity data, time-series photometry from the K2 mission, and new transit light curves obtained with diffuser-assisted photometry, the planet's radius and mass are 3.44 ± 0.12 R_⊕ and 24.5_(-5.2)^(+5.7) M_⊕. These properties are compatible with a rocky core enshrouded by a thin hydrogen–helium atmosphere (5% by mass). We measure an orbital eccentricity of e = 0.43 ± 0.05. The sky-projected stellar obliquity is λ = 3° ± 16°, compatible with spin–orbit alignment, in contrast to other "hot Neptunes" that have been studied around older stars.

中文翻译：

宜居带行星探测器揭示了年轻海王星 K2-25b 的高质量和低倾角

使用来自宜居带行星探测器的径向速度数据，我们测量了海王星大小的行星 K2-25b 的质量，以及它在 600-800 Myr Hyades 星团中 M4.5 矮主星的倾角。这是最年轻的行星系统之一，这两个量都被测量过，也是极少数具有测量倾角的 M 矮星之一。根据对径向速度数据、K2 任务的时间序列测光和漫射辅助测光获得的新过境光曲线的联合分析，行星的半径和质量分别为 3.44 ± 0.12 R_⊕ 和 24.5_(-5.2) ^(+5.7) M_⊕。这些特性与被稀薄的氢氦气氛（5% 的质量）包围的岩石核相容。我们测量的轨道偏心率为 e = 0.43 ± 0.05。天空投影的恒星倾角为 λ = 3° ± 16°，

更新日期：2020-09-30

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