AMBER/VLTI observations of 5 giant stars

TL;DR

This study used VLTI/AMBER observations to measure diameters and temperatures of five giant stars, including one with a known exoplanet, providing data to calibrate stellar models and investigate planet formation around massive stars.

Contribution

First interferometric measurements of diameters and temperatures for five giant stars, including a star with a known exoplanet, to improve stellar mass and size estimates independent of models.

Findings

Measured angular diameters and effective temperatures of 4 giant stars.

Discovered an unknown companion star near HD12438.

Found lower effective temperatures compared to spectroscopic data.

Abstract

While the search for exoplanets around main sequence stars more massive than the Sun have found relatively few such objects, surveys performed around giant stars have led to the discovery of more than 30 new exoplanets. The interest in studying planet hosting giant stars resides in the possibility of investigating planet formation around stars more massive than the Sun. Masses of isolated giant stars up to now were only estimated from evolutionary tracks, which led to different results depending on the physics considered. To calibrate the theory, it is therefore important to measure a large number of giant star diameters and masses as much as possible independent of physical models. We aim in the determination of diameters and effective temperatures of 5 giant stars, one of which is known to host a planet. AMBER/VLTI observations with the ATs were executed in low resolution mode on 5 giant stars. In order to measure high accurate calibrated squared visibilities, a calibrator-star-calibrator observational sequence was performed. We measured the uniform disk and limb-darkened angular diameters of 4 giant stars. The effective temperatures were also derived by combining the bolometric luminosities and the interferometric diameters. Lower effective temperatures were found when compared to spectroscopic measurements. The giant star HD12438 was found to have an unknown companion star at an angular separation of ~ 12 mas. Radial velocity measurements present in the literature confirm the presence of a companion with a very long orbital period (P ~ 11.4 years).}