Fundamental properties of red-clump stars from long-baseline H-band interferometry

TL;DR

This study uses long-baseline H-band interferometry to precisely measure the angular diameters of 48 red-clump stars, improving fundamental stellar parameter determinations and testing stellar evolution models.

Contribution

It provides highly accurate angular diameters and combines them with spectroscopic and Gaia data to refine stellar parameters and compare with isochrone models, highlighting current limitations.

Findings

Half the angular diameters have errors below 1.2%.

Derived stellar parameters are consistent with previous studies.

Significant scatter in age estimates indicates uncertainties in atmospheric parameters.

Abstract

Observations of 48 red-clump stars were obtained in the H band with the PIONIER instrument installed at the Very Large Telescope Interferometer. Limb-darkened angular diameters were measured by fitting radial intensity profile I(r) to square visibility measurements. Half the angular diameters determined have formal errors better than 1.2%, while the overall accuracy is better than 2.7%. Average stellar atmospheric parameters (effective temperatures, metallicities and surface gravities) were determined from new spectroscopic observations and literature data and combined with precise Gaia parallaxes to derive a set of fundamental stellar properties. These intrinsic parameters were then fitted to existing isochrone models to infer masses and ages of the stars. The added value from interferometry imposes a better and independent constraint on the R-Teff plane. Our derived values are consistent with previous works, although there is a strong scatter in age between various models. This shows that atmospheric parameters, mainly metallicities and surface gravities, still suffer from a non-accurate determination, limiting constraints on input physics and parameters of stellar evolution models.