Supergiant Temperatures and Linear Radii from Near-Infrared Interferometry

TL;DR

This study provides empirical calibrations of effective temperature and linear radii for supergiant stars using near-infrared interferometry, improving understanding of their physical properties across spectral types and colors.

Contribution

It presents the first extensive empirical calibration of supergiant temperatures and radii based on interferometric measurements, linking these parameters to spectral type and color.

Findings

Empirical temperature calibration with median deviation of 70K for LC I stars.

Radius measurements up to 400 solar radii, limited by distance uncertainties.

Effective temperature versus spectral type shows more scatter than temperature versus color.

Abstract

We present angular diameters for 42 luminosity class I stars and 32 luminosity class II stars that have been interferometrically determined with the Palomar Testbed Interferometer. Derived values of radius and effective temperature are established for these objects, and an empirical calibration of these parameters for supergiants will be presented as a functions of spectral type and colors. For the effective temperature versus $(V-K)_0$ color, we find an empirical calibration with a median deviation of $\Delta T = 70$K in the range of $0.7 < (V-K)_0 < 5.1$ for LC I stars; for LC II, the median deviation is $\Delta T = 120$K from $0.4 < (V-K)_0 < 4.3$. Effective temperature as a function of spectral type is also calibrated from these data, but shows significantly more scatter than the $T_{\rm EFF}$ versus $(V-K)_0$ relationship. No deviation of $T_{\rm EFF}$ versus spectral type is seen for these high luminosity objects relative to luminosity class II giants. Directly determined diameters range up to $400 R_\odot$, though are limited by poor distance determinations, which dominate the error estimates. These temperature and radii measures reflect a direct calibration of these parameters for supergiants from empirical means.