Near-Infrared photometry of carbon stars in the Sagittarius dwarf irregular galaxy and DDO 210

Abstract

We investigate the intermediate-age asymptotic giant branch stellar population of two Local Group dwarf irregular galaxies to characterize their carbon star population in near-infrared (IR). Our work is based on J and K-band SOFI near-IR photometry complemented with optical ground based and HST photometry. We show that near-IR photometry is a very powerful tool for carbon star detection. We recovered two out of three previously-known carbon stars in DDO 210 and discovered six additional objects in this galaxy which have optical and near-IR colors consistent with carbon giants. This brings the total number of bona-fide C-star candidates in DDO 210 to nine. We detected a large population of C-star candidates in SagDIG, 18 of which were previously identified in Demers & Battinelli (2002) and Cook (1987), and six new bona-fide carbon stars. We present their optical and near-IR colors and use their luminosity function to put constraints on the star formation history (SFH) in this dwarf irregular galaxy.

Accepted for publication in Astronomy & Astrophysics, 15 pages, 11 figures