Abstract
ABSTRACTWe present the bright (Vmag = 9.12), multiplanet system TOI-431, characterized with photometry and radial velocities (RVs). We estimate the stellar rotation period to be 30.5 ± 0.7 d using archival photometry and RVs. Transiting Exoplanet Survey Satellite (TESS) objects of Interest (TOI)-431 b is a super-Earth with a period of 0.49 d, a radius of 1.28 ± 0.04 R⊕, a mass of 3.07 ± 0.35 M⊕, and a density of 8.0 ± 1.0 g cm−3; TOI-431 d is a sub-Neptune with a period of 12.46 d, a radius of 3.29 ± 0.09 R⊕, a mass of $9.90^{+1.53}_{-1.49}$ M⊕, and a density of 1.36 ± 0.25 g cm−3. We find a third planet, TOI-431 c, in the High Accuracy Radial velocity Planet Searcher RV data, but it is not seen to transit in the TESS light curves. It has an Msin i of $2.83^{+0.41}_{-0.34}$ M⊕, and a period of 4.85 d. TOI-431 d likely has an extended atmosphere and is one of the most well-suited TESS discoveries for atmospheric characterization, while the super-Earth TOI-431 b may be a stripped core. These planets straddle the radius gap, presenting an interesting case-study for atmospheric evolution, and TOI-431 b is a prime TESS discovery for the study of rocky planet phase curves.
Highlights
The discoveries of the Kepler Space Telescope (Borucki et al 2010) provided us with the means to make statistical studies on the exoplanet population for the first time: Kepler has shown us that Neptune-sized planets are more common than large gas giants (Fressin et al 2013), and that super-Earths are the most abundant planet type (Petigura, Howard & Marcy 2013)
We searched for stellar companions to TESS Objects of Interest (TOIs)-431 with speckle imaging with the 4.1-m Southern Astrophysical Research (SOAR) telescope (Tokovinin 2018) on UT 2019 March 17, observing in the Cousins Iband, a similar visible bandpass to TESS
We use a normal distribution with this model as the mean and a standard deviation set by the jitter parameter, and this is fit to the observed Spitzer flux
Summary
The discoveries of the Kepler Space Telescope (Borucki et al 2010) provided us with the means to make statistical studies on the exoplanet population for the first time: Kepler has shown us that Neptune-sized planets are more common than large gas giants (Fressin et al 2013), and that super-Earths are the most abundant planet type (Petigura, Howard & Marcy 2013). TOI431 b and d are a super-Earth and sub-Neptune, respectively, discovered first by TESS and confirmed via extensive follow up: highprecision Doppler spectroscopy from the High Accuracy Radial velocity Planet Searcher (HARPS; Pepe et al 2002) and the HIgh REsolution Spectrograph (HIRES; Vogt et al 1994), which allows us to determine their masses; additional Doppler spectroscopy from iSHELL (Rayner et al 2016a), Fiberfed Extended Range Optical Spectrograph (FEROS; Kaufer & Pasquini 1998), and MINERVAAustralis (Addison et al 2019a); ground-based transit detections from Generation Transit Survey (NGTS; Wheatley et al 2018) and the LCOGT 1m network (Brown et al 2013); and a double-transit from the Spitzer space telescope.
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