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The Search for the 24.4 Day Planet Candidate Around HD79211 with HARPS-N

Presentation #102.316 in the session Poster Session.

Published onJun 20, 2022
The Search for the 24.4 Day Planet Candidate Around HD79211 with HARPS-N

M dwarfs are the focus of many exoplanet studies and as many as 46% of M dwarfs are members of binaries (Susemiehl & Meyer 2021), but only ~30 exoplanets have been detected around M dwarf binaries so far. HD79210 and HD79211 are two M0.0 members of a gravitationally-bound binary system 6.3 pc from Earth. Gonzalez-Alvarez 2020, using CARMENES radial velocities, detected a planet candidate signal with a period of 24.42 days around HD79211. We revisit this system by combining HARPS-N and HIRES RVs with the published CARMENES RVs, spanning a total of 23 years (June 1997-Feb 2020), and confirm the 24.4 day signal in the combined dataset. We analyze HARPS-N chromatic radial velocities and do not find evidence that this signal is caused by stellar activity. Using new photometric observations from KeplerCam we collected Feb-June 2021, however, we determine a rotational period for HD79211 of 17.6 days. Given that measured rotation periods can vary slightly depending on the active regions locations, stellar rotation period measurements are known to change over time as features evolve on the star’s surface, we cannot rule out an average stellar rotation period over the time of the RV observations closer to 16.3 days, which would have a 3/2 harmonic of 24.4 days. Ultimately, we confirm the 24.4 day RV signal in HD79211 RVs but cannot definitively attribute that signal to a planet or to stellar activity.

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