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

December 2021 • 2021AJ....162..238P

Authors • 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 • Pallé, Enric • Petigura, Erik A. • Shectman, Stephen A. • Sozzetti, Alessandro • Teske, Johanna K. • Wang, Sharon Xuesong • Weiss, Lauren M.

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 ${}_{-0.70}^{+0.69}$ M _⊕ , in combination with the updated radius measurements, gives Wolf 503 b a bulk density of $\rho ={2.92}_{-0.44}^{+0.50}$ 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 ${}_{-16}^{+19}$ %) 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.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2021AJ....162..238P
• DATA http://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/162/238
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2021AJ....162..238P
• PREPRINT http://arxiv.org/abs/2107.08092
• ELECTR https://doi.org/10.3847%2F1538-3881%2Fac1590