Radii, masses, and ages of 18 bright stars using interferometry and new estimations of exoplanetary parameters

Abstract

Context. Accurate stellar parameters are needed in numerous domains of astrophysics. The position of stars on the HertzsprungRussell diagram is an important indication of their structure and evolution, and it helps improve stellar models. Furthermore, the age and mass of stars hosting planets are required elements for studying exoplanetary systems. Aims. We aim at determining accurate parameters of a set of 18 bright exoplanet host and potential host stars from interferometric measurements, photometry, and stellar models. Methods. Using the VEGA/CHARA interferometer operating in the visible domain, we measured the angular diameters of 18 stars, ten of which host exoplanets. We combined them with their distances to estimate their radii. We used photometry to derive their bolometric flux and, then, their effective temperature and luminosity to place them on the H-R diagram. We then used the PARSEC models to derive their best fit ages and masses, with error bars derived from Monte Carlo calculations. Results. Our interferometric measurements lead to an average of 1.9% uncertainty on angular diameters and 3% on stellar radii. There is good agreement between measured and indirect estimations of angular diameters (either from SED fitting or from surface brightness relations) for main sequence (MS) stars, but not as good for more evolved stars. For each star, we provide a likelihood map in the mass-age plane; typically, two distinct sets of solutions appear (an old and a young age). The errors on the ages and masses that we provide account for the metallicity uncertainties, which are often neglected by other works. From measurements of its radius and density, we also provide the mass of 55 Cnc independently of models. From the stellar masses, we provide new estimates of semimajor axes and minimum masses of exoplanets with reliable uncertainties. We also derive the radius, density, and mass of 55 Cnc e, a super-Earth that transits its stellar host. Our exoplanetary parameters reflect the known population of exoplanets. Conclusions. This work illustrates how precise interferometric measurements of angular diameters and detailled modeling allow fundamental parameters of exoplanet host stars to be constrained at a level permiting analysis of the planet's parameters.

A near-infrared interferometric survey of debris-disc stars

“…The K-band interferometric data, obtained with the 65 m baseline, are compatible with the stellar photosphere parameters derived by Ligi et al (2016), and therefore consistent with a nonexcess as shown in Fig. 5.…”

Empirical Relations for the Accurate Estimation of Stellar Masses and Radii

“…The study did not provide an estimate of ρ. All 4 stars are on the MS. Ligi et al (2016), using the VEGA optical interferometer at the CHARA array, determined the angular diameter of 18 stars and estimated R with an error of less than 5%. By fitting SEDs taken from the VizieR SED Viewer, they determined the total flux and derived L and T eff .…”

“…The first group of accurate stellar radii obtained using interferometry from the VEGA optical interferometer at the CHARA array has been published (Ligi et al 2016) 3. Tens of accurate stellar densities have been confirmed thanks to planetary transits.…”

The Compositional Diversity of Low-Mass Exoplanets

“…Upper limits on the masses of ultra-short period planets, given their proximity to the stellar Roche limit indicate a likely rocky composition (Rappaport et al 2013). Furthermore, several ultra-short period exoplanets have low masses, as characterized via RV spectroscopy, including 55 Cancri e (Ligi et al 2016), CoRoT-7 b (Faria et al 2016), Kepler-10 b (Weiss et al 2016), Kepler-78 b (Pepe et al 2013;Howard et al 2013), K2-106 b (Guenther et al 2017), K2-131 b ), K2-229 b (Santerne et al 2018) and WASP-47 e (Vanderburg et al 2017); all of these planets orbit G or early-K dwarfs. Both 55 Cancri e and WASP-47 e (both in multiplanet systems with close-in Neptune and Jovian-mass planets) are less dense than would be with an Earth-like composition, hinting at a water-rich composition.…”

“…The resonant configuration of the system is consistent with planet formation further out, followed by migration to their current orbits, all within 0.07 AU of the star. R⊕ (Ligi et al 2016). Its density is consistent with rock although it appears likely that there are some volatiles.…”