Star formation in young star cluster NGC 1893

Abstract

We present a comprehensive multiwavelength study of the star‐forming region NGC 1893 to explore the effects of massive stars on low‐mass star formation. Using near‐infrared colours, slitless spectroscopy and narrow‐band Hα photometry in the cluster region we have identified candidate young stellar objects (YSOs) distributed in a pattern from the cluster to one of the nearby nebulae Sim 129. The V, (V−I) colour–magnitude diagram of the YSOs indicates that majority of these objects have ages between 1 and 5 Myr. The spread in the ages of the YSOs may indicate a non‐coeval star formation in the cluster. The slope of the K‐band luminosity function for the cluster is estimated to be 0.34 ± 0.07, which agrees well with the average value (∼0.4) reported for young clusters. For the entire observed mass range 0.6 < M/M⊙≤ 17.7 the value of the slope of the initial mass function, ‘Γ’, comes out to be −1.27 ± 0.08, which is in agreement with the Salpeter value of −1.35 in the solar neighbourhood. However, the value of ‘Γ’ for pre‐main‐sequence phase stars (mass range 0.6 < M/M⊙≤ 2.0) is found to be −0.88 ± 0.09 which is shallower than the value (−1.71 ± 0.20) obtained for main‐sequence stars having mass range 2.5 < M/M⊙≤ 17.7 indicating a break in the slope of the mass function at ∼2 M⊙. Estimated ‘Γ’ values indicate an effect of mass segregation for main‐sequence stars, in the sense that massive stars are preferentially located towards the cluster centre. The estimated dynamical evolution time is found to be greater than the age of the cluster, therefore, the observed mass segregation in the cluster may be the imprint of the star formation process. There is evidence for triggered star formation in the region, which seems to govern initial morphology of the cluster.

Star formation in the outer Galaxy: membership and fundamental parameters of the young open cluster NGC 1893

“…In this section we complement our optical photometric catalog by using the V and I magnitudes by Sharma et al (2007) for the objects detected in X-rays with Chandra/ACIS-I or in the NIR with NICS and/or IRAC falling outside our optical fields or in saturated or corrupted regions of the V and I images. This is only for the purpose of finding as complete a list of cluster candidate members as possible, while in the next sections, where we derive cluster parameters, stellar masses, and ages, we only use our photometry to make certain we have a homogeneous photometric system.…”

“…8, showing all objects in the FoV with error in V − I smaller than 0.1 and diskless candidate cluster members. The Massey et al (1995) and Sharma et al (2007) photometry (dots); filled circles are diskless candidate members, squares are those compatible with reddening 0.5 < E(B − V) < 0.7 based on the expected photospheric colors by Kenyon & Hartmann (1995) drawn at the E(B − V) values indicated on each line. The reddening vector obtained using the Munari & Carraro (1996) reddening law is also shown.…”

“…We have identified NGC 1893 as a very promising cluster for this kind of investigations since it is very young (∼1-2 Myr), about 12 Kpc distant from the Galactic center, with known massive members and indication of a large PMS population (Vallenari et al 1999;Sharma et al 2007). This SF region, located at the center of the Aur OB2 associations, is associated with the HII region IC 410 and the two pennant nebulae, Sim 19 and Sim 130 (Gaze & Shajn 1952).…”

“…Evidence of a large population of PMS stars in this cluster has been found by Vallenari et al (1999) by using near-infrared photometry, even if their data did not allow them to distinguish the young population from the contaminating field stars. Only recently, Sharma et al (2007) presented a study about the low-mass population in NGC 1893 based on deep optical photometry down to V ∼ 22 and NIR 2MASS (Cutri et al 2003) catalog. Several conclusions have been drawn in this work about the IMF, the dynamical evolution and the effects of massive cluster stars on the low-mass population.…”

A multiwavelength investigation of the H ii region S311: young stellar population and star formation

“…In order to evaluate the completeness limit of the photometric data in J, H, Ks, ch1, ch2, ch3 and ch4 bands, we performed "ADDSTAR" experiments of DAOPHOT II. The procedures have been outlined in detail by several authors (see, e.g., Pandey et al 2001;Sharma et al 2007;Jose et al 2016, and references therein). Briefly, in this method artificial stars of known magnitudes and positions are added randomly into the original frame.…”