PHOTOMETRY OF A GALACTIC FIELD AT L = 232°, B = -6°. THE OLD OPEN CLUSTER AUNER 1, THE NORMA-CYGNUS SPIRAL ARM AND THE SIGNATURE OF THE WARPED GALACTIC THICK DISK

G. CARRARO; A. MOITINHO; M. ZOCCALI; R.A. VÁZQUEZ; G. BAUME

ASTRONOMICAL JOURNAL

IOP PUBLISHING LTD

Año: 2007 vol. 133 p. 1058 - 1066

0004-6256

We perform a detailed photometric study of the stellar populations in a Galactic field at l=232deg, b=-6deg in the Canis Major (CMa) constellation. We present the first U, B, V, I photometry of the old open cluster Auner 1 and determine it to be ~3.25 Gyr old and to lie 8.9 kpc from the Sun. In the background of the cluster, at more than 9 kpc, we detect a young population most likely associated with the Norma-Cygnus spiral arm. Furthermore, we detect the signature of an older population and identify its turnoff and red giant branch. This population is found to have a mean age of 7 Gyr and a mean metallicity of Z=0.006. We reconstruct the geometry of the stellar distribution and argue that this older population, often associated with the CMa ``galaxy,´´ in fact belongs to the warped old thin- and thick-disk components along this line of sight.