M33's Variable A: A Hypergiant Star More Than 35 YEARS in Eruption

Variable A in M33 is a member of a rare class of highly luminous, evolvedstars near the upper luminosity boundary that show sudden and dramatic shiftsin apparent temperature due to the formation of optically thick winds in highmass loss episodes. Recent optical and infrared spectroscopy and imaging revealthat its ``eruption'' begun in $\sim$1950 has ended, {\it lasting $\approx$ 45yrs}. Our current observations show major changes in its wind from a cool,dense envelope to a much warmer state surrounded by low density gas with rareemission lines of Ca II, [Ca II] and K I. Its spectral energy distribution hasunexpectedly changed, especially at the long wavelengths, with a significantdecrease in its apparent flux, while the star remains optically obscured. Weconclude that much of its radiation is now escaping out of our line of sight.We attribute this to the changing structure and distribution of itscircumstellar ejecta corresponding to the altered state of its wind as the starrecovers from a high mass loss event.Comment: 26 pages, 6 figure