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Author (up) Bergsten, G.J.; Pascucci, I.; Hardegree-Ullman, K.K.; Fernandes, R.B.; Christiansen, J.L.; Mulders, G.D. doi  openurl
  Title No Evidence for More Earth-sized Planets in the Habitable Zone of Kepler's M versus FGK Stars Type
  Year 2023 Publication Astronomical Journal Abbreviated Journal Astron. J.  
  Volume 166 Issue 6 Pages 234  
  Keywords MAIN-SEQUENCE STARS; LOW-MASS STARS; M DWARFS; OCCURRENCE RATES; STELLAR-MASS; TERRESTRIAL PLANETS; GAIA DR2; CANDIDATES; SAMPLE; RELIABILITY  
  Abstract Reliable detections of Earth-sized planets in the habitable zone remain elusive in the Kepler sample, even for M dwarfs. The Kepler sample was once thought to contain a considerable number of M-dwarf stars ( T-eff < 4000 K), which hosted enough Earth-sized ([0.5, 1.5] R-circle plus) planets to estimate their occurrence rate (eta(circle plus)) in the habitable zone. However, updated stellar properties from Gaia have shifted many Kepler stars to earlier spectral type classifications, with most stars (and their planets) now measured to be larger and hotter than previously believed. Today, only one partially reliable Earth-sized candidate remains in the optimistic habitable zone, and zero in the conservative zone. Here we performed a new investigation of Kepler's Earth-sized planets orbiting M-dwarf stars, using occurrence rate models with considerations of updated parameters and candidate reliability. Extrapolating our models to low instellations, we found an occurrence rate of eta(circle plus) = 8.58( – 8.22 )(+ 17.94) % for the conservative habitable zone (and 14.22 (- 12.71) (+ 24.96 )% for the optimistic one), consistent with previous works when considering the large uncertainties. Comparing these estimates to those from similarly comprehensive studies of Sun-like stars, we found that the current Kepler sample does not offer evidence to support an increase in eta(circle plus) from FGK to M stars. While the Kepler sample is too sparse to resolve an occurrence trend between early and mid-to-late M dwarfs for Earth-sized planets, studies including larger planets and/or data from the K2 and TESS missions are well suited to this task.  
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  ISSN 0004-6256 ISBN Medium  
  Area Expedition Conference  
  Notes WOS:001103102000001 Approved  
  Call Number UAI @ alexi.delcanto @ Serial 1925  
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