The occurrence rate of giant planets orbiting low-mass stars with TESS

Abstract

We present a systematic search for transiting giant planets ($0.6R_{\mathrm{J}}\le R_{\mathrm{P}}\le 2.0R_{\mathrm{J}}$) orbiting nearby low-mass stars ($M_{\ast }\le 0.71M_{\odot }$). The formation of giant planets around low-mass stars is predicted to be rare by the core-accretion planet formation theory. We search 91,306 low-mass stars in the TESS 30 minute cadence photometry detecting fifteen giant planet candidates, including seven new planet candidates which were not known planets or identified as TOIs prior to our search. Our candidates present an exciting opportunity to improve our knowledge of the giant planet population around the lowest mass stars. We perform planet injection-recovery simulations and find that our pipeline has a high detection efficiency across the majority of our targeted parameter space. We measure the occurrence rates of giant planets with host stars in different stellar mass ranges spanning our full sample. We find occurrence rates of $0.137\pm 0.097$% (0.088 - 0.26 $M_{\odot }$), $0.108\pm 0.083$% (0.26 - 0.42 $M_{\odot }$), and $0.29\pm 0.15$% (0.42 - 0.71 $M_{\odot }$). For our full sample (0.088 - 0.71 $M_{\odot }$) we find a giant planet occurrence rate of $0.194\pm 0.072$%. We have measured for the first time the occurrence rate for giant planets orbiting stars with $M_{\ast }\le 0.4M_{\odot }$ and we demonstrate this occurrence rate to be non-zero. This result contradicts currently accepted planet formation models and we discuss some possibilities for how these planets could have formed.

20 pages, 14 figures. Accepted for publication in MNRAS

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