Variability in Proto-Planetary Nebulae: III. Light Curve Studies of Magellanic Cloud Carbon-Rich Objects

TL;DR

This study analyzes light variability in 22 carbon-rich post-AGB stars in the Magellanic Clouds, revealing similarities and differences with Milky Way PPNs, and identifying distinct variability patterns related to temperature and spectral type.

Contribution

It provides the first detailed comparison of Magellanic Cloud PPN light curves with those of the Milky Way, highlighting similarities and potential differences in variability trends.

Findings

Eight stars show periodic variability similar to MWG PPNs

Most stars are redder when fainter, indicating pulsation

Shorter timescale variability suggests hotter PPNs or young planetary nebulae

Abstract

We have investigated the light variability in a sample of 22 carbon-rich post-AGB stars in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC), based primarily on photometric data from the OGLE survey. All are found to vary. Dominant periods are found in eight of them; these periods range from 49 to 157 days, and most of these stars have F spectral types. These eight are found to be similar to the Milky Way Galaxy (MWG) carbon-rich proto-planetary nebulae (PPNs) in several ways: (a) they are in the same period range of ~38 to ~160 days, (b) they have similar spectral types, (c) they are (all but one) redder when fainter, (d) they have multiple periods, closely spaced in time, with a average ratio of secondary to primary period of ~1.0, and as an ensemble, (e) they show a trend of decreasing period with increasing temperature, and (f) they show a trend of decreasing amplitude with decreasing period. However, they possibly differ in that the decreasing trend of period with temperature may be slightly offset from that of the MWG. These eight are classified as PPNs. The other 14 all show evidence of variability on shorter timescales. They are likely hotter PPNs or young planetary nebulae. However, in the MWG the numbers of PPNs peak in the F-G spectral types, while it appears that in the LMC they peak at a hotter B spectral type. One of the periodic ones shows a small, R Coronae Borealis-type light curve drop.