Obscured Asymptotic Giant Branch
variables in the Large
Magellanic Cloud and the period--luminosity relation
Whitelock P.A., Feast M.W., van Loon J.Th, Zijlstra A.A.,
Loup C., 2003, MNRAS,
342, 86
Abstract
The characteristics of oxygen-rich and carbon-rich, large-amplitude,
Asymptotic Giant Branch (AGB) variables in the Large Magellanic Cloud
are discussed, with an emphasis no those obscured by
dust. Near-infrared photometry, obtained over about 8 years, is
combined with published mid-infrared observations from IRAS and ISO to
determine bolometric magnitudes for 42 stars. Pulsation periods of the
O-rich stars are in the range 166-1393 days, while those for C-rich
stars have 298-939 days. In addition to teh regular pulsations, one
O-rich and four C-rich stars show large-amplitude, secular of very
long period variations, which may be associated with changes in their
mass-loss rates. We discuss and compare various methods of determining
the bolometric magnitudes, and show, perhaps surprisingly, that most
of the very-long-period stars seem to follow an extrapolation of the
period-luminosity relation determined for stars with shorter periods
-- although the details depend on how the bolometric magnitudes are
calculated.
Three stars with thin shells, which are clearly more luminous than the
obscured AGB stars, are undergoing hot bottom burning, while other
stars with similar luminosities have yet to be investigated in
sufficient detail to determine their status in this regard. We suggest
that an apparent change in slope of the period-luminosity relation
around 400-420 days is caused by variables with luminosities brighter
than the predictions of the core-mass--luminosity, owing to excess
flux from hot bottom burning.
paper (pdf, MNRAS reprint, 670k)
Last update: Jan 10, 2003