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Do short-period gas giants predominantly form around metal-rich early M dwarfs?

Presentation #102.164 in the session Poster Session.

Published onJun 20, 2022
Do short-period gas giants predominantly form around metal-rich early M dwarfs?

M dwarfs are the most common type of stars in the Galaxy, and seem to host a higher number of planets on average, compared to FGK stars. Yet, due to their lower stellar (and disk) masses — and associated slower formation time scales — gas giants are expected to be infrequent around M dwarfs. In this presentation, we discuss the trends seen in a transiting sample of gas giants (Rp > 4 Re), with respect to the dependence on host stellar metallicity and mass. We then compare this dependence with a similar sample of non-transiting gas giants discovered by RV surveys.

While more detailed high resolution spectral synthesis routines are required to robustly determine abundances; using both empirical and photometric metallicities we note an emerging trend which suggests that the transiting planets (closer-in; warmer) typically orbit more metal-rich and massive M dwarfs compared to the RV sample (further-out; colder). We also compare the M dwarf giant planet sample (transiting + RV) with planets around FGK stars, and find statistically significant evidence that the metallicity distributions for the two differ. We contextualize these trends with planetary formation theories, and discuss future prospects for improving the robustness of studies such as this, with upcoming samples from TESS, and GAIA. We also note the potential of this sample for population level comparative studies using transmission spectroscopy due to the narrow range of stellar and planetary parameters it spans.

Finally, we present a new planet discovered using a combination of TESS photometry and radial velocities (RV) from the precision RV spectrographs — HPF and NEID. This low-density (rho ~ 0.3 g/cm3) Jovian sized planet around an early M dwarf presents a corner-case thereby testing the hypotheses of planet formation presented earlier. Furthermore, its large scale height (~ 400 km) makes it an excellent target for studies of atmospheric escape as well as transmission spectroscopy to determine atmospheric composition. Along these lines, we also present preliminary results from HPF observations which use Helium atomic transitions as a tracer to place upper limits on atmospheric escape.

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