The Sequence of Mass-Losing AGB Stars in the Magellanic Clouds
Surveys of variable stars in the Magellanic Clouds, such as those by MACHO, EROS, OGLE and MOA, have revealed red variable stars with amplitudes from a few hundredths of a magnitude (SR variables) up to roughly six magnitudes (Mira variables). The MSX survey found large numbers of mass-losing, dust-enshrouded AGB stars in the Magellanic Clouds and the MACHO data shows them to be pulsating stars in a more advanced evolutionary state than the Mira variables. In this paper, these results are described and compared with theories of the pulsation and evolution of AGB stars. One particularly interesting group of variables in the LMC are the SR variables with long secondary periods (sequence D stars). It is argued that these are red giants with brown dwarf or planetary companions in elliptic orbits. A cloud of dust and gas loosely associated with the orbiting companion is assumed to cause the photometric variability at the long secondary period.
KeywordsStars: AGB stars: variable stars: binary
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