A More Precise Mass for GJ 1214 b and the Frequency of Multiplanet Systems Around MidM Dwarfs
Abstract
We present an intensive effort to refine the mass and orbit of the enveloped terrestrial planet GJ 1214 b using 165 radial velocity (RV) measurements taken with the HARPS spectrograph over a period of 10 years. We conduct a joint analysis of the RVs with archival Spitzer/IRAC transits and measure a planetary mass and radius of 8.17 ± 0.43 M_{⊕} and ${2.742}_{0.053}^{+0.050}$ R_{⊕}. Assuming that GJ 1214 b is an Earthlike core surrounded by a H/He envelope, we measure an envelope mass fraction of X_{env} = ${5.24}_{0.29}^{+0.30}$ %. GJ 1214 b remains a prime target for secondary eclipse observations of an enveloped terrestrial, the scheduling of which benefits from our constraint on the orbital eccentricity of <0.063 at 95% confidence, which narrows the secondary eclipse window to 2.8 hr. By combining GJ 1214 with other midMdwarf transiting systems with intensive RV follow up, we calculate the frequency of midMdwarf planetary systems with multiple small planets and find that ${90}_{21}^{+5}$ % of midM dwarfs with a known planet with mass ∈ [1, 10] M_{⊕} and orbital period ∈ [0.5, 50] days, will host at least one additional planet. We rule out additional planets around GJ 1214 down to 3 M_{⊕} within 10 days, such that GJ 1214 is a singleplanet system within these limits. This result has a ${44}_{5}^{+9}$ probability given the prevalence of multiplanet systems around midM dwarfs. We also investigate midMdwarf RV systems and show that the probability that all reported RV planet candidates are real planets is <12% at 99% confidence, although this statistical argument is unable to identify the probable false positives.
 Publication:

The Astronomical Journal
 Pub Date:
 November 2021
 DOI:
 10.3847/15383881/ac1584
 arXiv:
 arXiv:2107.14732
 Bibcode:
 2021AJ....162..174C
 Keywords:

 Exoplanets;
 Exoplanet structure;
 M dwarf stars;
 Radial velocity;
 Transits;
 498;
 495;
 982;
 1332;
 1711;
 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 Accepted for publication in AAS journals. 16 pages (main) + 16 pages (appendices), 9 figures (main) + 24 figures (appendix B). Two additional figures in appendix B could not be included due to compilation errors. These figures are included in the source files