Interstellar Extinction and Long-Period Variables in the Galactic Center

TL;DR

This study maps interstellar extinction in the Galactic Center using IR data, analyzes long-period variable stars, and finds universal period-luminosity relations, indicating a younger stellar population in the GC.

Contribution

It provides a high-extinction map of the Galactic Center and demonstrates the universality of IRAC period-luminosity relations for LPVs across different regions.

Findings

Extinction map covers 2.0 x 1.4 degrees with high Av values.

LPVs follow well-defined IRAC period-luminosity relations.

GC contains more high-luminosity, long-period LPVs than the Bulge.

Abstract

We use the Spitzer IRAC catalogue of the Galactic Center (GC) point sources (Ramirez et al. 2008) and combine it with new isochrones (Marigo et al. 2008) to derive extinctions based on photometry of red giants and asymptotic giant branch (AGB) stars. This new extinction map extends to much higher values of Av than previoulsy available. Our new extinction map of the GC region covers 2.0 x 1.4 degree (280 x 200 pc at a distance of 8 kpc). We apply it to deredden the LPVs found by Glass et al. (2001) near the GC. We make period-magnitude diagrams and compare them to those from other regions of different metallicity. The Glass-LPVs follow well-defined period-luminosity relations (PL) in the IRAC filter bands at 3.6, 4.5, 5.8, and 8.0 micron. The period-luminosity relations are similar to those in the Large Magellanic Cloud, suggesting that the PL relation in the IRAC bands is universal. We use ISOGAL data to derive mass-loss rates and find for the Glass-LPV sample some correlation between mass-loss and pulsation period, as expected theoretically.The GC has an excess of high luminosity and long period LPVs compared to the Bulge, which supports previous suggestions that it contains a younger stellar population.