THE SPECTROPHOTOMETRIC VARIABILITY OF THE GALACTIC LUMINOUS BLUE VARIABLES AG CARINAE AND HR CARINAE FROM 1978 TO 1995

We present a long-term multiwavelength spectrophotometric study of two representative Galactic luminous blue variables (LBVs), AG Carinae an d HR Carinae. We find that the assumption of bolometric constancy lead s independently to an extinction of E(B - V) = 0.65+/-0.05 mag for AG Car and 1.0+/-0.1 mag for HR Car. We derive a luminosity for AG Car, o f order 10(6) L. for a distance of 6 kpc, that is consistent with mode l atmosphere analyses. During outburst, the wavelength at which antiph ase continuum variability occurs steadily increases as the optical dep th 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 f orming dust. For HR Car, we derive a similar luminosity to AG Car, of order 10(6) L. for a distance of 6 kpc. The optical depth in the circu mstellar environment appears to be greater, with the entire ultraviole t varying in antiphase with the visual. Both variables are characteriz ed by similar ultraviolet behavior during quiescence and similar times cales, of about one decade, between outbursts. Finally, we present evi dence for dust formation in the AG Car wind during the most recent out burst, which shows similar physical conditions to those encountered in classical dust-forming novae, and discuss the nature of the dust in t he circumstellar reflection nebula. (C) 1996 American Astronomical Soc iety.