The Spectrophotometric Variability of the Galactic Luminous Blue Variables AG Carinae and HR Carinae from 1978 to 1995

Abstract

We present a long-term multiwavelength spectrophotometric study of two representative Galactic luminous blue variables (LBVs), AG Carinae and HR Carinae. We find that the assumption of bolometric constancy leads independently to an extinction of E(B-V)=0.65±0.05 mag for AG Car and 1.0±0.l mag for HR Car. We derive a luminosity for AG Car, of order 10⁶ L_sun for a distance of 6 kpc, that is consistent with model atmosphere analyses. During outburst, the wavelength at which antiphase continuum variability occurs steadily increases as the optical depth of the envelope increases. The star is now in the largest outburst of the last 20 years and we suggest that it may be in the process of forming dust. For HR Car, we derive a similar luminosity to AG Car, of order 10⁶ L_sun for a distance of 6 kpc. The optical depth in the circumstellar environment appears to be greater, with the entire ultraviolet varying in antiphase with the visual. Both variables are characterized by similar ultraviolet behavior during quiescence and similar timescales, of about one decade, between outbursts. Finally, we present evidence for dust formation in the AG Car wind during the most recent outburst, which shows similar physical conditions to those encountered in classical dust-forming novae, and discuss the nature of the dust in the circumstellar reflection nebula.