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Small Amplitude Variable Red Giants in the Magellanic Clouds
We present analysis of the large sample of variable red giants from the
Large and Small Magellanic Clouds detected during the second phase of the
Optical Gravitational Lensing Experiment (OGLE-II) and supplemented with
OGLE-III photometry. Comparing pulsation properties of detected objects we
find that they constitute two groups with clearly distinct features. In
this paper we analyze in detail small amplitude variable red giants (about
15400 and 3000 objects in the LMC and SMC, respectively). The vast majority
of these objects are multi-periodic. At least 30% of them exhibit two modes
closely spaced in the power spectrum, what likely indicates non-radial
oscillations. About 50% exhibit additional so called Long Secondary
Period.
To distinguish between AGB and RGB red giants we compare PL diagrams of
multi-periodic red giants located above and below the tip of the Red Giant
Branch (TRGB). The giants above the TRGB form four parallel ridges in the
PL diagram. Among much more numerous sample of giants below the TRGB we
find objects located on the low luminosity extensions of these ridges, but
most of the stars are located on the ridges slightly shifted in logP. We
interpret the former as the second ascent AGB red giants and the latter as
the first ascent RGB objects. Thus, we empirically show that the pulsating
red giants fainter than the TRGB are a mixture of RGB and AGB giants.
Finally, we compare the Petersen diagrams of the LMC, SMC and Galactic
bulge variable red giants and find that they are basically identical
indicating that the variable red giants in all these different stellar
environments share similar pulsation properties.
Full resolution paper is available from
the OGLE Internet
archive.
PLEASE cite the following paper when using the data or referring to these
OGLE results:
Soszynski et al., 2004,
Acta Astron., 54, 129.