HD219666b: a hot-Neptune from TESS Sector 1. (arXiv:1812.05881v1 [astro-ph.EP])

HD219666b: a hot-Neptune from TESS Sector 1. (arXiv:1812.05881v1 [astro-ph.EP])
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We report the discovery of a transiting planet orbiting the old and inactive
G7 dwarf star HD219666 (Mstar = 0.92 +/- 0.03 MSun, Rstar = 1.03 +/- 0.03 RSun,
tau_star = 10 +/- 2 Gyr). With a mass of Mb = 16.6 +/- 1.3 MEarth, a radius of
Rb = 4.71 +/- 0.17 REarth, and an orbital period of P ~ 6 days, HD219666b is a
new member of a rare class of exoplanets: the hot-Neptunes. The Transiting
Exoplanet Survey Satellite (TESS) observed HD219666 (also known as TOI-118) in
its Sector 1 and the light curve shows four transit-like events, equally spaced
in time. We confirmed the planetary nature of the candidate by gathering
precise radial velocity measurements with HARPS@ESO3.6m. We used the co-added
HARPS spectrum to derive the host star fundamental parameters (Teff = 5527 +/-
65 K, log g = 4.40 +/- 0.11 (cgs), [Fe/H]= 0.04 +/- 0.04 dex, log R’HK = -5.07
+/- 0.03), as well as the abundances of many volatile and refractory elements.
The host star brightness (V = 9.9) makes it suitable for further
characterization by means of in-transit spectroscopy. The determination of the
planet orbital obliquity, along with the atmospheric metal-to-hydrogen content
and thermal structure could provide us with important clues on the mechanisms
of formation of this class of objects.

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