Abstract
We present the detection of a warm Neptune orbiting the M dwarf Gl 378, using radial velocity measurements obtained with the SOPHIE spectrograph at the Observatoire de Haute-Provence. The star was observed in the context of the SOPHIE exoplanet consortium’s sub-programme dedicated to finding planets around M dwarfs. Gl 378 is an M1 star, of solar metallicity, at a distance of 14.96 pc. The single planet detected, Gl 378 b, has a minimum mass of 13.02 MEarth and an orbital period of 3.82 days, which place it at the lower boundary of the hot Neptune desert. As one of only a few such planets around M dwarfs, Gl 378 b provides important clues to the evolutionary history of these close-in planets. In particular, the eccentricity of 0.1 may point to a high-eccentricity migration. The planet may also have lost part of its envelope due to irradiation.
Highlights
The mass-period diagram is an important diagnostic of the formation and evolution of planetary systems
We report the detection of a warm Neptune on the lower boundary of the hot Neptune desert, orbiting the M dwarf Gl 378, which was observed as part of this survey
The periodogram shows a clear peak at 3.82 d, which by bootstrap resampling we place below a 0.01% false alarm probability (FAP)
Summary
The mass-period diagram is an important diagnostic of the formation and evolution of planetary systems. There is a known dearth of Neptune-size exoplanets at short orbital periods compared to both Jupiter-size and Earth-size planets, which is generally referred to as the Neptune or sub-Jovian desert (Lecavelier Des Etangs 2007; Davis & Wheatley 2009; Szabó & Kiss 2011; Beaugé & Nesvorný 2013; Helled et al 2016; Mazeh et al 2016). Gillon et al 2017), SPECULOOS (Delrez et al 2018), and ExTrA (Bonfils et al 2015) in transits. It is clear that while hot Jupiters are rare around M dwarfs, short-period Earths and superEarths are numerous; hot Neptunes remain unusual, making up only about 3% of the sample of known exoplanets around M dwarfs It is clear that while hot Jupiters are rare around M dwarfs, short-period Earths and superEarths are numerous; hot Neptunes remain unusual, making up only about 3% of the sample of known exoplanets around M dwarfs (e.g. Bonfils et al 2013; Dressing & Charbonneau 2015; Hirano et al 2018)
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