An ultra-short period rocky super-Earth orbiting the G2-star HD 80653

Abstract

Ultra-short period (USP) planets are a class of exoplanets with periods shorter than one day. The origin of this sub-population of planets is still unclear, with different formation scenarios highly dependent on the composition of the USP planets. A better understanding of this class of exoplanets will, therefore, require an increase in the sample of such planets that have accurate and precise masses and radii, which also includes estimates of the level of irradiation and information about possible companions. Here we report a detailed characterization of a USP planet around the solar-type star HD 80653≡EP 251279430 using the K2 light curve and 108 precise radial velocities obtained with the HARPS-N spectrograph, installed on the Telescopio Nazionale Galileo. From the K2 C16 data, we found one super-Earth planet (R b = 1.613 ± 0.071 R ⊕ ) transiting the star on a short-period orbit (P b = 0.719573 ± 0.000021 d). From our radial velocity measurements, we constrained the mass of HD 80653 b to M b = 5.60 ± 0.43 M ⊕ . We also detected a clear long-term trend in the radial velocity data. We derived the fundamental stellar parameters and determined a radius of R ⋆ = 1.22 ± 0.01 R ⊙ and mass of M ⋆ = 1.18 ± 0.04 M ⊙ , suggesting that HD 80653 has an age of 2.7 ± 1.2 Gyr. The bulk density (ρ b = 7.4 ± 1.1 g cm −3 ) of the planet is consistent with an Earth-like composition of rock and iron with no thick atmosphere. Our analysis of the K2 photometry also suggests hints of a shallow secondary eclipse with a depth of 8.1±3.7 ppm. Flux variations along the orbital phase are consistent with zero. The most important contribution might come from the day-side thermal emission from the surface of the planet at T ∼ 3480 K.

An unusually low density ultra-short period super-Earth and three mini-Neptunes around the old star TOI-561

“…If two or more observations are gathered during the same night and they span a large fraction of the orbital phase, the RV semi-amplitude of the USP planet can be precisely measured by just applying nightly offsets to remove all the other signals (e.g. Hatzes et al 2010;Howard et al 2013;Pepe et al 2013;Frustagli et al 2020 for a recent example). Such an approach, also known as floating chunk offset method (FCO; Hatzes 2014), has proven extremely reliable even in the presence of complex activity signals, as shown by Malavolta et al (2018).…”

Probing Kepler's hottest small planets via homogeneous search and analysis of optical secondary eclipses and phase variations

“…atmosphere (Frustagli et al 2020). Our analysis indicates a secondary eclipse depth of δ ec = 8.1 ± 3.7 ppm at a confidence level of 2.2 σ.…”

“…So far, a small number of USP planets have been well characterized thanks to space-based photometry and high-precision radial-velocity follow-up studies, such as Corot-7b (Léger et al 2011;Haywood et al 2014), Kepler-10b (Batalha et al 2011; vikash.singh@inaf.it Dumusque et al 2014;Weiss et al 2016), Kepler-78b (Sanchis-Ojeda et al 2013;Pepe et al 2013;Howard et al 2013), K2-141b (Malavolta et al 2018;Barragán et al 2018), 55 Cancri e (Demory et al 2016a;Nelson et al 2014), K2-229b (Santerne et al 2018), WASP-47e (Weiss et al 2017;Vanderburg et al 2017), K2-131b (Dai et al 2017), K2-106b (Sinukoff et al 2017;Guenther et al 2017), and K2-312b (Frustagli et al 2020). Most USP small planets have a rocky composition with varying silicateto-iron mass fractions (Dai et al 2019) and are generally less massive than 8 M ⊕ .…”

TKS X: Confirmation of TOI-1444b and a Comparative Analysis of the Ultra-short-period Planets with Hot Neptunes

“…Table 3 shows that there are three USPs that also have detected giant planet companions. They are 55 Cnc with a 14.6-day giant planet (Butler et al 1997); WASP-47 with with 4.2 and 600-day giant planets (Becker et al 2015b;Neveu-VanMalle et al 2016) and HD 80653 with a strong RV trend likely indicative of a giant planet 0.37±0.08 M Jup (a/AU) −2 (Frustagli et al 2020). The attentive reader might have already guessed that these three systems are also the most metal-rich among the USP sample with [Fe/H] = 0.31±0.04, 0.38±0.05 and 0.28±0.05 respectively (red points in Fig.…”