Multiwavelength study of a young open cluster NGC7419

Abstract

Using new UBVRIHα CCD photometric observations and the archival infrared and X-ray data, we have carried out a multiwavelength study of a Perseus arm young open star cluster NGC7419. An age of 22.5 +/- 3.0Myr and a distance of 3230⁺³³⁰_-430pc are derived for the cluster. Our photometric data indicate a higher value of colour excess ratio E(U - B)/E(B - V) than the normal one. There is an evidence for mass segregation in this dynamically relaxed cluster and in the range 1.4-8.6M_solar, the mass function slope is in agreement with the Salpeter value. Excess emissions in near-infrared and Hα support the existence of a young (<=2Myr) stellar population of Herbig Ae/Be stars (>=3.0M_solar) indicating a second episode of star formation in the cluster region. Using XMM-Newton observations, we found several X-ray sources in the cluster region but none of the Herbig Ae/Be stars is detected in X-rays. We compare the distribution of upper limits for Herbig Ae/Be stars with the X-ray distribution functions of the T Tauri and the Herbig Ae/Be stars from previous studies, and found that the X-ray emission level of these Herbig Ae/Be stars is not more than L_X ~ 5.2 × 10³⁰ergs^-1, which is not significantly higher than for the T Tauri stars. Therefore, X-ray emission from Herbig Ae/Be stars could be the result of either unresolved companion stars or a process similar to T Tauri stars. We report an extended X-ray emission from the cluster region NGC7419, with a total X-ray luminosity estimate of ~1.8 × 10³¹ergs^-1arcmin^-2. If the extended emission is due to unresolved emission from the point sources then we estimate ~288 T Tauri stars in the cluster region each having X-ray luminosity ~1.0 × 10³⁰ergs^-1. Investigation of dust attenuation and¹²CO emission map of a square degree region around the cluster indicates the presence of a foreground dust cloud which is most likely associated with the local arm star-forming region (Sh2-154). This cloud harbours uniformly distributed pre-main-sequence stars (0.1-2.0M_solar), with no obvious trend of their distribution with either (H - K) excess or A_V. This suggests that the star formation in this cloud depend mostly upon the primordial fragmentation.