Carbon star survey of Local Group galaxies

Abstract

We used the CFH12K wide field camera to survey the carbon star population of NGC 185 using the CN-TiO technique. 145 C stars are identified with a mean $\langle I \rangle = 19.99\pm0.05$, corresponding to $\langle M_I\rangle = -4.41\pm0.05$, a mean luminosity similar to what was recently found for the C star population of NGC 147. The stellar surface density profile of NGC 185 follows a power law with an exponential scale length of 2.53 ± 0.07 ' . The surface density of C stars follows also a power law but with a smaller scale length, $1.56 \pm 0.06$, demonstrating that the intermediate-age population of NGC 185 is more concentrated than its old population. A tidal radius, $r_{\rm t} = 22.5\pm2.2'$ is determined from red giant star counts. The C/M ratio of NGC 185 is $0.17 \pm 0.02$ with no apparent sign of a radial gradient. We compare the carbon star populations of NGC 185 and NGC 147 to conclude that it is unlikely that they form a close pair.