The Properties of Long-Period Variables in the Large Magellanic Cloud From Macho

Abstract

We present a new analysis of the long-period variables in the Large Magellanic Cloud (LMC) from the MACHO Variable Star Catalog. Three-quarters of our sample of evolved, variable stars have periodic light curves. We characterize the stars in our sample using the multiple periods found in their frequency spectra. Additionally, we use single-epoch Two Micron All Sky Survey measurements to construct the average infrared light curves for different groups of these stars. Comparison with evolutionary models shows that stars on the red giant branch (RGB) or the early asymptotic giant branch (AGB) often show non-periodic variability, but begin to pulsate with periods on the two shortest period-luminosity sequences (3 & 4) when they brighten to K s ≈ 13. The stars on the thermally pulsing AGB are more likely to pulsate with longer periods that lie on the next two P-L sequences (1 & 2), including the sequence associated with the Miras in the LMC. The Petersen diagram and its variants show that multi-periodic stars on each pair of these sequences (3 & 4, and 1 & 2) typically pulsate with periods associated only with that pair. The periods in these multi-periodic stars become longer and stronger as the star evolves. We further constrain the mechanism behind the long secondary periods (LSPs) seen in half of our sample, and find that there is a close match between the luminosity functions of the LSP stars and all of the stars in our sample, and that these star's pulsation amplitudes are relatively

The mass-loss return from evolved stars to the Large Magellanic Cloud

“…The light curve available from the OGLE-III website 1 shows that LPV 28579 is multi-periodic, with a primary period of 356.2 d (peak-to-peak amplitude 1.587 mag) modulated by a slow variation of 5747 d (peak-to-peak amplitude 0.784 mag). Like many of our extreme AGB candidates identified in Paper I, LPV 28579 is absent from the Fraser et al (2008) MACHO catalog of LMC LPVs. This is most likely due to the moderately high circumstellar extinction at optical wavelengths.…”

“…This is most likely due to the moderately high circumstellar extinction at optical wavelengths. The primary period for LPV 28579 is very close to those of the sources in the "one year artifact" list, but the culling of these artifacts in Fraser et al (2008) was done in a manner as to avoid accidental removal of genuine sources. Based on its brightness (K s = 10.9 mag) and period, LPV 28579 would probably fall on period sequence 1, the sequence found by Wood et al (1999) to be predominantly populated by Miras in their fundamental mode of pulsation.…”

The optically bright post-AGB population of the LMC

“…Five of these SRVs -J045615.77-682042.3, J050733.83-692119.9, J053009.86-694655.6, J053416.45-695740.4 and J053455.93-694428.7 -show a long secondary period and hence they are sequence-D variables. Three were first recognised by Fraser et al (2008) and the other two by us. They are of K, M, or C spectral type, just like another five of the SRVs.…”

“…Of the remaining 194 post-AGB candidates in the LPV catalogue of Fraser et al (2008), 2 objects belong to sequence 4, 15 to sequence 3, 37 to sequence 2, 33 to sequence 1 and none to sequence E with the LMC period-luminosity sequences mentioned from shortest to longest period in the manner of Fraser et al (2008). All other objects are either part of the one-year artifact, which is caused by the annual observing schedule of the MACHO project (14 objects), fall outside the boundaries of any period-luminosity classification (39 objects), or were unable to be classified (54 objects).…”

“…For those objects for which we have an optical spectrum that enabled us to determine their spectral type, we made a detailed examination of the light curves because catalogues of variable stars (e.g., Fraser et al 2008) often miss low-amplitude variables. We downloaded light curves from the MACHO website for all post-AGB candidates with a spectral type and a spectrum (a few were missed, presumably because of close bright companions or bad positions on the MACHO CCDs) and we also obtained OGLE II and OGLE III light curves for the stars in the OGLE II and OGLE III variable star catalogues Soszyński et al 2008Soszyński et al , 2009a.…”