arXiv subjects

S. Vig

Publications and source records attributed to S. Vig.

42 records · Page 3Linked to original sources

arXiv2006

A multiwavelength study of the massive star forming region IRAS 06055+2039 (RAFGL 5179)

We present a multiwavelength study of the massive star forming region associated with IRAS 06055+2039 which reveals an interesting scenario of this complex where regions are at different stages of evolution of star formation. Narrow band near-infrared (NIR) observations were carried out with UKIRT-UFTI in molecular hydrogen and Br$γ$ lines to trace the shocked and ionized gases respectively. We have used 2MASS $J H K_{s}$ data to study the nature of the embedded cluster associated with IRAS 06055+2039. We obtain a power-law slope of 0.43$\pm$0.09 for the $K_{s}$-band Luminosity Function (KLF) which is in good agreement with other young embedded clusters. We estimate an age of 2 -- 3 Myr for this cluster. The radio emission from the ionized gas has been mapped at 610 and 1280 MHz using the Giant Metrewave Radio Telescope (GMRT), India. Apart from the diffuse emission, the high resolution 1280 MHz map also shows the presence of several discrete sources which possibly represent high density clumps. The morphology of shocked molecular hydrogen forms an arc towards the N-E of the central IRAS point source and envelopes the radio emission. Submillimetre emission using JCMT-SCUBA show the presence of a dense cloud core which is probably at an earlier evolutionary stage compared to the ionized region with shocked molecular gas lying in between the two. Emission from warm dust and the Unidentified Infrared Bands (UIBs) have been estimated using the mid-infrared (8 -- 21 $μ$m) data from the MSX survey. From the submillimetre emission at 450 and 850 $μ$m the total mass of the cloud is estimated to be $\sim$ 7000 -- 9000 $\rm M_{\odot}$.

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arXiv2005

Post-outburst radio observation of the region around McNeil's nebula (V1647 Ori)

We present post-outburst (~ 100 days after outburst) radio continuum observation of the region (~ 30' x 30') around McNeil's nebula (V1647 Orionis). The observations were carried out using the Giant Metrewave Radio Telescope (GMRT), India, at 1272 MHz on 2004 Feb 14.5 UT. Although 8 sources have been detected within a circular diameter of 25' centred on V1647 Ori, we did not detect any radio continuum emission from McNeil's nebula. We assign a 5-sigma upper limit of 0.15 mJy/beam for V1647 Ori where the beam size is 5.6" x 2.7". Even at higher frequencies of 4.9 and 8.5 GHz (VLA archival data), no radio emission has been detected from this region. Three scenarios namely, emission from homogeneous HII region, ionised stellar wind and shock ionised gas, are explored in the light of our GMRT upper-limit. For the case of homogeneous HII region, the radius of the emitting region is constrained to be <~ 26 AU corresponding to a temperature >~ 2,500 K, which is consistent with the reported radio and H-alpha emission. In the ionised stellar wind picture, our upper limit of radio emission translates to the ratio of mass loss rate and terminal velocity, (M_dot/v_infinity) < 1.2-1.8 x 10^(-10) (M_sun/yr)/(km/s). On the other hand, if the stellar wind shocks the dense neutral (molecular) cloud, the radio upper limit implies that the fraction of the wind encountering the dense obstacle is <50%. Based on a recent measurement of X-ray outburst and later monitoring, the expected radio emission has been estimated. Using our radio limit, the radius (<~ 36 AU) and electron density (>~ 7.2 x 10^7 cm^(-3) of the radio emitting plasma have been constrained using a two phase medium in pressure equilibrium for a volume filling factor of 0.9.

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arXiv2005

Infrared and radio study of star forming regions associated with IRAS 19111+1048 and IRAS 19110+1045

A multiwavelength study of the star forming regions associated with IRAS 19111+1048 and IRAS 19110+1045 has been carried out. These have been simultaneously mapped in two far infrared bands at lambda_eff ~ 130 and 200 micron with ~1' angular resolution using the TIFR 1-m balloon borne telescope. The radio emission from the ionised gas of these regions has been imaged at 1280, 610 and 325 MHz using the Giant Metrewave Radio Telescope, India. A total of 20 compact radio sources have been detected from the high resolution radio map of IRAS 19111+1048 at 1280 MHz. Assuming these sources to represent exciting zero age main sequence (ZAMS) stars, the initial mass function is found to be quite steep, with the power law index of 5.3+-0.5 for the mass range 14 < m/M_sun < 33. The spectral types of the ZAMS stars inferred independently from the radio and NIR measurements match very well for a good fraction of the radio sources having NIR counterparts. For IRAS 19110+1045 region, seven radio sources have been detected of which two are associated with deeply embedded 2MASS objects. Self consistent radiative transfer modelling aimed at extracting important physical and geometrical details of the two IRAS sources has been carried out. A uniform density distribution of dust and gas is implied for both the sources. The extents of ionised gas, number of ZAMS stars, presence of deeply embedded sources and lower value of L/M for the cloud, support the youth of IRAS 19110+1045 vis-a-vis its neighbour, IRAS 19111+1048, consistent with earlier studies.

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arXiv2005

Warp signatures of the Galactic disk as seen in mid infrared from Midcourse Space Experiment

The gross features in the distribution of stars as well as warm (T >~ 100 K) interstellar dust in the Galactic disk have been investigated using the recent mid infrared survey by Midcourse Space Experiment (MSX) at 8, 12, 14 & 21 micron bands. An attempt has been made to determine the location of the Galactic mid-plane at various longitudes, using two approaches : (i) fitting exponential functions to the latitude profiles and (ii) statistical indicators.The former method is successful for the inner Galaxy (-90 < l < 90), and quantifies characteristic angular scales along latitude, which have been translated to linear scale heights (z_h) and radial length scales (R_l) using geometric description of the Galactic disk. The distribution of warm dust in the Galactic disk is found to be characterised by R_l < 6 kpc and 60 < z_h <~ 100 pc, in agreement with other studies. The location of the Galactic mid-plane as a function of longitude, for stars as well as warm dust, has been searched for signatures of warp-like feature in their distribution, by fitting sinusoid with phase and amplitude as parameters. In every case, the warp signature has been detected. An identical analysis of the DIRBE/COBE data in all its ten bands covering the entire infrared spectrum (1.25-240 micron), also leads to detection of warp signatures with very similar phase as found from the MSX data. Our results have been compared with those from other studies.

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arXiv2004

A near-infrared study of the NGC 7538 star forming region

We present sub-arcsecond (FWHM ~ 0".7), NIR JHKs-band images and a high sensitivity radio continuum image at 1280 MHz, using SIRIUS on UH 88-inch telescope and GMRT. The NIR survey covers an area of ~ 24 arcmin^2 with 10-sigma limiting mags of ~ 19.5, 18.4, and 17.3 in J, H, and Ks-band, respectively. Our NIR images are deeper than any JHK surveys to date for the larger area of NGC 7538 star forming region. We construct JHK CC and J-H/J and H-K/K CM diagrams to identify YSOs and to estimate their masses. Based on these CC and CM 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 PMS stars with intrinsic color excesses. Most of YSOs in NGC 7538 are arranged from the N-W toward S-E regions, forming a sequence in age: the diffuse H II region (N-W, oldest: where most of the Class II and Class I sources are detected); the compact IR core (center); and the regions with the extensive IR reflection nebula and a cluster of red young stars (S-E and S). We find that the slope of the KLF of NGC 7538 is lower than the typical values reported for the young embedded clusters, although equally low values have also been reported in the W3 Main star forming region. From the slope of the KLF and the analysis by Megeath et al. (1996), we infer that the embedded stellar population is comprised of YSOs with an age of ~ 1 Myr. Based on the comparison between models of PMS stars with the observed CM diagram we find that the stellar population in NGC 7538 is primarily composed of low mass PMS stars similar to those observed in the W3 Main star forming region.

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arXiv2003

A study of the Galactic star forming region IRAS 02593+6016 / S 201 in infrared and radio wavelengths

We present infrared and radio continuum observations of S 201 star forming region. A massive star cluster is observed in this region, which contains different classes of young stellar objects. The near-infrared colour-colour and colour-magnitude diagrams are studied to discuss the nature of these sources. We have discovered the knots of molecular hydrogen emission at 2.122 micron in the central region of S 201. These knots are clearly seen along the diffuse emission in north-west direction which are probably the obscured Herbig-Haro objects. High sensitivity and high resolution radio continuum images from GMRT observations at 610 and 1280 MHz show an interesting 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 seen by comparing the radio, molecular hydrogen and Br Gamma images. The emission from the carriers of Unidentified Infrared Bands in the mid-infrared 6-9 micron (possibly due to PAHs) as extracted from the Midcourse Space Experiment survey (at 8, 12, 14 and 21 micron) is compared with the radio emission. The HIRES processed IRAS maps at 12, 25, 60, and 100 micron, have also been used for comparison. The spatial distribution of the temperature and the optical depth of the warm dust component around S 201 region, has been generated from the mid-infrared images.

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