The distance to the young cluster NGC 7129 and its age

Abstract

The dust cloud TGU H645 P2 and embedded in it young open cluster NGC 7129 are\ninvestigated using the results of medium-band photometry of 159 stars in the\nVilnius seven-colour system down to V = 18.8 mag. The photometric data were\nused to classify about 50 percent of the measured stars in spectral and\nluminosity classes. The extinction A_V vs. distance diagram for the 20x20\narcmin area is plotted for 155 stars with two-dimensional classification from\nthe present and the previous catalogues. The extinction values found range\nbetween 0.6 and 3.4 mag. However, some red giants, located in the direction of\nthe dense parts of the cloud, exhibit the infrared extinction equivalent up to\nA_V = 13 mag. The distance to the cloud (and the cluster) is found to be 1.15\nkpc (the true distance modulus 10.30 mag). For determining the age of NGC 7129,\na luminosity vs. temperature diagram for six cluster members of spectral\nclasses B3 to A1 was compared with the Pisa pre-main-sequence evolution tracks\nand the Palla birthlines. The cluster can be as old as about 3 Myr, but star\nforming continues till now as witnessed by the presence in the cloud of many\nyounger pre-main-sequence objects identified with photometry from 2MASS,\nSpitzer and WISE infrared surveys.\n