GJ 3929: High-precision Photometric and Doppler Characterization of an Exo-Venus and Its Hot, Mini-Neptune-mass Companion
Cochran, William D.; Endl, Michael; Mahadevan, Suvrath; Wisniewski, John; Wright, Jason T.; Logsdon, Sarah E.; Ford, Eric B.; McElwain, Michael W.; Cañas, Caleb I.; Kanodia, Shubham; Ninan, Joe P.; Hebb, Leslie; Everett, Mark; Bender, Chad F.; Fredrick, Connor; Halverson, Samuel; Metcalf, Andrew J.; Robertson, Paul; Roy, Arpita; Schwab, Christian; Terrien, Ryan C.; Li, Dan; Libby-Roberts, Jessica E.; Lin, Andrea S. J.; Beard, Corey; Holcomb, Rae; Lubin, Jack; Blake, Cullen H.; Rajagopal, Jayadev; Stefánsson, Guđmundur; Gupta, Arvind F.; Jones, Sinclaire; Schutte, Maria; Luhn, Jacob
United States, India, Australia
Abstract
We detail the follow-up and characterization of a transiting exo-Venus identified by TESS, GJ 3929b (TOI-2013b), and its nontransiting companion planet, GJ 3929c (TOI-2013c). GJ 3929b is an Earth-sized exoplanet in its star's Venus zone (P b = 2.616272 ± 0.000005 days; S b = ${17.3}_{-0.7}^{+0.8}$ S ⊕) orbiting a nearby M dwarf. GJ 3929c is most likely a nontransiting sub-Neptune. Using the new, ultraprecise NEID spectrometer on the WIYN 3.5 m Telescope at Kitt Peak National Observatory, we are able to modify the mass constraints of planet b reported in previous works and consequently improve the significance of the mass measurement to almost 4σ confidence (M b = 1.75 ± 0.45 M ⊕). We further adjust the orbital period of planet c from its alias at 14.30 ± 0.03 days to the likely true period of 15.04 ± 0.03 days, and we adjust its minimum mass to $m\sin i$ = 5.71 ± 0.92 M ⊕. Using the diffuser-assisted ARCTIC imager on the ARC 3.5 m telescope at Apache Point Observatory, in addition to publicly available TESS and LCOGT photometry, we are able to constrain the radius of planet b to R p = 1.09 ± 0.04 R ⊕. GJ 3929b is a top candidate for transmission spectroscopy in its size regime (TSM = 14 ± 4), and future atmospheric studies of GJ 3929b stand to shed light on the nature of small planets orbiting M dwarfs.