Confirmation of the luminous blue variable nature of AFGL 2298

Abstract

We present new photometric and spectroscopic observations of the stellar source AFGL 2298 (= IRAS 18576-0341) that has recently been proposed as a candidate Luminous Blue Variable (LBV). Our data confirm that the star is a highly luminous B supergiant which is both spectroscopically and photometrically variable. Assuming a distance of 10 kpc, comparison of the 2001 June data to synthetic spectra suggest stellar parameters of T = 12.5 kK, log(L/L⊙) = 6.2 and Ṁ = 5 × 10-5 M⊙ yr-1. Data obtained in 2002 August indicate an increase in both temperature (=15 kK) and mass loss rate (=1.2 × 10-4 M⊙ yr-1) at constant bolometric luminosity. These physical parameters place AFGL 2298 at the Humphreys-Davidson limit for the most luminous stars known. We conclude that the position of AFG 2298 in the HR diagram, the significant variability observed between 1999-2002 and presence of a massive ejection nebula are consistent with a classification of AFGL 2298 as a bona fide LBV.