Investigation of the stellar content in the western part of the Carina nebula

Brajesh Kumar, Saurabh Sharma, Jean Manfroid, Eric Gosset, Gregor Rauw, Yael Naze, and Ram Kesh Yadav

1,2,7 : Aryabhatta Research Institute of 1,3,4,5,6 : Observational Sciences (India), University of Liege (Belgium)

We obtained deep $UBVRI$ H$alpha$ photometric data of the field situated to
the west of the main Carina nebula and centered on WR~22. Medium-resolution
optical spectroscopy of a subsample of X-ray selected objects along with
archival data sets from $Chandra$, $XMM-Newton$ and 2MASS surveys were used for
the present study. Different sets of color-color and color-magnitude diagrams
are used to determine reddening for the region and to identify young stellar
objects (YSOs) and estimate their age and mass. Our spectroscopic results
indicate that the majority of the X-ray sources are late spectral type stars.
The region shows a large amount of differential reddening with minimum and
maximum values of $E(B-V)$ as 0.25 and 1.1 mag, respectively. Our analysis
reveals that the total-to-selective absorption ratio $R rm_{V}$ is $sim$3.7
$pm$ 0.1, suggesting an abnormal grain size in the observed region. We
identified 467 YSOs and studied their characteristics. The ages and masses of
the 241 optically identified YSOs range from $sim$0.1 to 10 Myr and $sim$0.3
to 4.8M$_odot$, respectively. However, the majority of them are younger than 1
Myr and have masses below 2 M$_odot$. The high mass star WR 22 does not seem
to have contributed to the formation of YSOs in the CrW region. The initial
mass function slope, $Gamma$, in this region is found to be -1.13 $pm$ 0.20
in the mass range of 0.5 < M/M$_odot$ < 4.8. The $K$-band luminosity function
slope ($alpha$) is also estimated as 0.31 $pm$ 0.01. We also performed
minimum spanning tree analysis of the YSOs in this region, which reveals that
there are at least ten YSO cores associated with the molecular cloud, and that
leads to an average core radius of 0.43 pc and a median branch length of 0.28

Reference: 23 pages, 19 figures, 4 tables, Accepted for publication in Astronomy
& Astrophysics
Status: Manuscript has been accepted