Long period variables in the VVV data

Abstract

The variable stars known as Ogle Small Amplitude Red Giants (OSARGs) are potentially one of the most numerous types of variable star but relatively little is known about them. OSARGs and other Long Period Variables (LPVs) are evolved low mass pulsating variable stars. The properties and variability of these objects in the NIR compared to the optical is examined. They are much more common than other pulsating variable stars such as Cepheids, whilst also obeying a Leavitt law styled period-luminosity relation.

To aid in the calculation of such a relation at the near-IR, I have compiled a catalogue of these objects. The variables in the catalogue were detected using two separate machine learning networks, trained on the OGLE catalogues of red giant stars.

The result is a catalogue of ∼ 34, 000 eclipsing binaries, ∼ 48, 000 LPVs and ∼ 25, 000 other pulsating variables. The periods calculated for these LPVs suffered due to a lack of epochs of observation, leading to a lack of a well-defined period- luminosity relation.

Unexpected behavior of the OSARGs in the Ks band was noticed, with them having ∼5x higher amplitudes in Ks than their OGLE counterparts in I band.

This goes against the pattern fit by other pulsating variables including Cepheids and Mira, where the amplitude of variation decreases at higher wavelengths. A number of observational or systematic explanations were examined but none fit the observed behavior. My current theory is some facet of the OSARGs outer layers dampens the variation amplitude in optical wavelengths, but this cannot be confirmed without further data.