Devendra K. Ojha

Deep Near-Infrared Observations of the W3 Main Star-forming Region

We present a deep JHKs-band imaging survey of the W3 Main star-forming region, using the near-infrared camera SIRIUS mounted on the University of Hawaii 2.2 m telescope. The near-infrared survey covers an area of ~24 arcmin2 with 10 σ limiting magnitudes of ~19.0, 18.1, and 17.3 in the J, H, and Ks bands, respectively. We construct JHK color-color and J versus J-H and K versus H-K color-magnitude diagrams to identify young stellar objects and estimate their masses. Based on these color-color and color-magnitude diagrams, a rich population of young stellar objects is identified that is associated with the W3 Main region. A large number of previously unreported red sources (H-K > 2) have also been detected around W3 Main. We argue that these red stars are most probably pre-main-sequence stars with intrinsic color excesses. We find that the slope of the Ks-band luminosity function (KLF) of W3 Main is lower than the typical values reported for young embedded clusters. The derived slope of the KLF is the same as that found in 1996 by Megeath and coworkers, from which analysis indicated that the W3 Main region has an age in the range of 0.3-1 Myr. Based on the comparison between models of pre-main-sequence stars and the observed color-magnitude diagram, we find that the stellar population in W3 Main is primarily composed of low-mass pre-main-sequence stars. We also report the detection of isolated young stars with large infrared excesses that are most probably in their earliest evolutionary phases.

A NEAR-INFRARED STUDY OF THE NGC 7538 STAR-FORMING REGION

We present subarcsecond (FWHM ~ 0farcs7), near-infrared (NIR) JHKs-band images and a high-sensitivity radio continuum image at 1280 MHz, using SIRIUS on the University of Hawaii 88 inch (2.2 m) telescope and the Giant Metrewave Radio Telescope (GMRT). The NIR survey covers an area of ~24 arcmin^2 with 10 σ limiting magnitudes of ~19.5, 18.4, and 17.3 in the J, H, and Ks bands, respectively. Our NIR images are deeper than any JHK surveys to date for the larger area of the NGC 7538 star-forming region. We construct JHK color-color and J - H/J and H - K/K color-magnitude diagrams to identify young stellar objects (YSOs) and to estimate their masses. Based on these color-color and color-magnitude diagrams, we identified a rich population of YSOs (Class I and Class II) associated with the NGC 7538 region. A large number of red sources (H - K > 2) have also been detected around NGC 7538. We argue that these red stars are most probably pre-main-sequence stars with intrinsic color excesses. Most of the YSOs in NGC 7538 are arranged from the northwest toward the southeast regions, forming a sequence in age: a diffuse H II region (northwest and oldest, where most of the Class II and Class I sources are detected), a compact IR core (center), and regions with an extensive IR reflection nebula and a cluster of red young stars (southeast and south). We find that the slope of the Ks-band luminosity function of NGC 7538 is lower than the typical values reported for young embedded clusters, although equally low values have also been reported in the W3 Main star-forming region. From the slope of the Ks-band luminosity function and the analysis by Megeath and coworkers, we infer that the embedded stellar population is composed of YSOs with an age of ~1 Myr. Based on the comparison of models of pre-main-sequence stars with the observed color-magnitude diagram, we find that the stellar population in NGC 7538 is primarily composed of low-mass pre-main-sequence stars similar to those observed in the W3 Main star-forming region. The radio continuum image from the GMRT observations at 1280 MHz shows an arc-shaped structure due to the interaction between the H II region and the adjacent molecular cloud. The ionization front at the interface between the H II region and the molecular cloud is clearly delineated by comparing the radio continuum, molecular line, and NIR images.

Near-Infrared Study of the Carina Nebula

We have carried out near-infrared (NIR) imaging observations of the Carina Nebula for an area of ~400 arcmin2 including the clusters Trumpler 14 and Trumpler 16, with 10 σ limits of J ~ 18.5, H ~ 17.5, and Ks ~ 16.5 mag. A total of 544 Class II candidates, 11 Class I candidates, and 40 red (H - Ks > 2) sources have been found. The majority of the Class II candidates are found to be distributed toward the clusters, whereas most of the red NIR sources are concentrated to the southeast of Trumpler 16, along the V-shaped dust lane. We found indications of ongoing star formation near the three MSX sources, G287.51-0.49, G287.47-0.54, and G287.63-0.72, where red NIR sources and X-ray sources are seen. In particular, two hard X-ray sources are identified near G287.47-0.54, one of which does not have an NIR counterpart and may be associated with a Class I/Class 0 object. The color-magnitude diagrams of the clusters suggest very young stellar population (<3 Myr). The Ks-band luminosity function (KLF) of Trumpler 14 shows a sharp peak at the faint end, likely due to the onset of deuterium burning. The KLF of Trumpler 16, in contrast, rises smoothly until it turns over. The slopes of the mass functions derived for the clusters are in agreement with the canonical Salpeter value for the field stars.

A MULTI-WAVELENGTH STUDY OF STAR FORMATION ACTIVITY IN THE S235 COMPLEX

We have carried out an extensive multi-wavelength study to investigate the star formation process in the S235 complex. The S235 complex has a sphere-like shell appearance at wavelengths longer than 2

A MULTIWAVELENGTH STUDY OF STAR FORMATION IN THE VICINITY OF GALACTIC H II REGION Sh 2-100

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Post-outburst phase of McNeil's nebula (V1647 Orionis)

m and harbors an O9.5V type star approximately at its center. Near-infrared extinction map traces eight subregions (having A

TIRSPEC: TIFR Near Infrared Spectrometer and Imager

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Age Sequence in Small Clusters Associated with Bright-Rimmed Clouds

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Sh2-138: physical environment around a small cluster of massive stars

8 mag), and five of them appear to be distributed in an almost regularly spaced manner along the sphere-like shell surrounding the ionized emission. This picture is also supported by the integrated