Wolf 503 b: Characterization of a Sub-Neptune Orbiting a Metal-poor K Dwarf

Creators: Polanski, Alex S.; Crossfield, Ian J. M.; Burt, Jennifer A.; Nowak, Grzegorz; López-Morales, Mercedes; Mortier, Annelies; Poretti, Ennio; Behmard, Aida; Benneke, Björn; Blunt, Sarah; Bonomo, Aldo S.; Butler, R. Paul; Chontos, Ashley; Cosentino, Rosario; Crane, Jeffrey D.; Dumusque, Xavier; Fulton, Benjamin J.; Ghedina, Adriano; Gorjian, Varoujan; Grunblatt, Samuel K.; Harutyunyan, Avet; Howard, Andrew W.; Isaacson, Howard; Kosiarek, Molly R.; Latham, David W.; Luque, Rafael; Martinez Fiorenzano, Aldo F.; Mayor, Michel; Mills, Sean M.; Molinari, Emilio; Nagel, Evangelos; Palle, Enric; Petigura, Erik A.; Shectman, Stephen A.; Sozzetti, Alessandro; Teske, Johanna K.; Wang, Sharon Xuesong; Weiss, Lauren M.

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Abstract

Using radial-velocity measurements from four instruments, we report the mass and density of a 2.043 ±0.069 R_⊕ sub-Neptune orbiting the quiet K-dwarf Wolf 503 (HIP 67285). In addition, we present improved orbital and transit parameters by analyzing previously unused short-cadence K2 campaign 17 photometry and conduct a joint radial-velocity-transit fit to constrain the eccentricity at 0.41 ± 0.05. The addition of a transit observation by Spitzer also allows us to refine the orbital ephemeris in anticipation of further follow-up. Our mass determination, 6.26^(+0.69)_(-0.70)M_⊕ , in combination with the updated radius measurements, gives Wolf 503 b a bulk density of ρ = 2.92^(+0.50)_(-0.44) g cm⁻³. Using interior composition models, we find this density is consistent with an Earth-like core with either a substantial H₂O mass fraction (45^(+19)_(-16)%) or a modest H/He envelope (0.5% ± 0.3%). The low H/He mass fraction, along with the old age of Wolf 503 (11 ± 2 Gyr), makes this sub-Neptune an opportune subject for testing theories of XUV-driven mass loss while the brightness of its host (J = 8.3 mag) makes it an attractive target for transmission spectroscopy.

Additional Information

© 2021. The American Astronomical Society. Received 2021 February 24; revised 2021 July 14; accepted 2021 July 15; published 2021 November 11. The authors thank the anonymous referee whose thorough review greatly increased the quality of this publication. We also thank the time assignment committees of the University of California, the California Institute of Technology, NASA, and the University of Hawaii for supporting the TESS-Keck Survey with observing time at Keck Observatory and on the Automated Planet Finder. We thank NASA for funding associated with our Key Strategic Mission Support project. We gratefully acknowledge the efforts and dedication of the Keck Observatory staff for support of HIRES and remote observing. We recognize and acknowledge the cultural role and reverence that the summit of Maunakea has within the indigenous Hawaiian community. We are deeply grateful to have the opportunity to conduct observations from this mountain. Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundacion Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. The HARPS-N project has been funded by the Prodex Program of the Swiss Space Office (SSO), the Harvard University Origins of Life Initiative (HUOLI), the Scottish Universities Physics Alliance (SUPA), the University of Geneva, the Smithsonian Astrophysical Observatory (SAO), and the Italian National Astrophysical Institute (INAF), the University of St Andrews, Queen's University Belfast, and the University of Edinburgh. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA) This work is based in part on observations made with the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. A.M. acknowledges support from the senior Kavli Institute Fellowships. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement SCORE No. 851555). This research made use of Lightkurve, a Python package for Kepler and TESS data analysis (Lightkurve Collaboration et al.2018). Facilities: Keck:I (HIRES) - KECK I Telescope, Magellan:Clay (PFS) - , Observatorio del Roque de los Muchachos:TNG (HARPS-N) - , Calar Alto:Zeiss 3.5m (CARMENES) - , Spitzer. - Software: exoplanet (Foreman-Mackey et al. 2021), radvel (Fulton et al. 2018), Lightkurve (Lightkurve Collaboration et al. 2018), batman (Kreidberg 2015), isoclassify (Huber et al. 2017), emcee (Foreman-Mackey et al. 2013), PandExo (Batalha et al. 2017), ExoTransmit (Kempton et al. 2017), smint (Piaulet et al. 2021).

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