The enigmatic object variable A in M33

Details The enigmatic object variable A in M33 The enigmatic object variable A in M33

Aug 1987

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987aj.....94..315h&link_type=abstract

Astronomical Journal (ISSN 0004-6256), vol. 94, Aug. 1987, p. 315-323. NASA-supported research.

Astronomy and Astrophysics

Astronomy

24

Blue Stars, Stellar Luminosity, Stellar Spectrophotometry, Variable Stars, Light Curve, Spectral Energy Distribution, Stellar Mass Ejection

Scientific paper

Variable A is a very luminous (about -9.5 mag), highly unstable star in M33. In 1950, it was one of the visibly brightest stars in M33, with the spectrum of a very luminous F supergiant. It then rapidly declined in brightness by 3.5 mag, becoming faint and red after slowly increasing in brightness during the previous 50 yr. This paper reports current spectroscopy and visual and infrared photometry. Variable A is still faint and red and now has the spectrum of an M supergiant. It also has a large infrared excess and is today as bright at 10 microns as it was at its visual maximum in 1950. Its energy distribution, luminosities, and mass-loss rate, which is quite large at 0.0002 solar mass/yr, are discussed. Its present late-type spectrum is probably produced in a cool pseudophotosphere, and it is shedding its mass in a high-density, low-velocity wind. A possible explanation is presented for Variable A's bizarre behavior as a massive star near the critical limit to its stabilty for its initial mass and temperature, where the balance between the radiation pressure, turbulence, and gravity of its atmosphere is very uncertain.

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