Period changes of Mira variables in the M16-M17 region

TL;DR

This study examined period stability and luminosity changes in Mira variables near M16-M17 over 50 years, finding no significant period changes but notable luminosity variations in some stars, and refining star identifications.

Contribution

It provides updated classifications, identifications, and luminosity assessments of Mira variables in the M16-M17 region, comparing historical and modern data.

Findings

No significant period changes in the studied stars over 50 years.

Some stars, notably KZ Ser, show substantial luminosity variations.

New classifications and identifications for several Mira variables.

Abstract

We analyzed the light curves of 165 AGB variables, mostly Miras, in the sky area centered between M16 and M17 (l=16, b=0), using the OGLE GVS database in the I_C band. Comparison with the published light curves, derived about 50 years earlier by P.~Maffei using Kodak I-N photographic plates, allowed us to find no significant period changes in any star. Remarkably, a few stars of the sample appear to have substantially changed their average luminosity, the most striking case being KZ Ser. We provide a better identification for three stars: IX Ser, NSV 10522, and NSV 10326, all of them being Miras. We classify the light curves of 6 stars, discovered but not classified by Maffei, (GL Ser, NSV 10271, NSV 10326, NSV 10522, NSV 10677, and NSV 10772) five of them being new Miras, and confirm the R CrB nature of V391 Sct. The magnitude scale used by Maffei is compared to the modern I_C one.