Aims. We present a multiwavelength study of the massive star-forming region associated with IRAS 06055+2039. Methods. Narrow-band near-infrared (NIR) observations were carried out with UKIRT-UFTI in molecular hydrogen and Brγ lines to trace the shocked and ionized gases, respectively. We have used 2MASS JHK s data to study the nature of the embedded cluster associated with IRAS 06055+2039. The radio emission from the ionized gas was mapped at 610 and 1280 MHz using the Giant Metrewave Radio Telescope (GMRT), India. Emission from warm dust and the unidentified infrared bands (UIBs) was estimated using the mid-infrared (8-21 µm) data from the MSX survey. Submillimetre emission from the cold dust at 450 and 850 µm was studied using JCMT-SCUBA. Results. For the infrared cluster associated with IRAS 06055+2039, we obtain a power-law slope of 0.43 ± 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. Apart from the diffuse emission, the high-resolution 1280 MHz map also shows the presence of several discrete sources that 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 shows the presence of a dense cloud core that is probably at an earlier evolutionary stage compared to the ionized region with shocked molecular gas lying between the two. The total mass of the cloud is estimated to be ∼7000-9000 M from the submillimetre emission at 450 and 850 µm. Conclusions. The multiwavelength study of this star-forming complex reveals an interesting scenario where regions are at different stages in the evolution of star formation.Key words. infrared: ISM -radio continuum: ISM -ISM: H II regions -ISM: individual objects: IRAS 06055+2039 IntroductionMassive stars are preferentially formed in dense cores of molecular clouds. They remain deeply embedded in the prenatal molecular gas and obscuring dust and their pre-main-sequence (PMS) time scales are much shorter compared to the low mass stars. The luminous high-mass stars also affect the parent cloud. In addition, massive stars do not form in isolation but often in clusters and associations. All these factors contribute towards making the study of the formation mechanisms of these systems very difficult. Multiwavelength studies, therefore, hold the potential to probe these complexes at different depths and unravel the least understood aspects of massive star formation.IRAS 06055+2039 (G189.78+0.34, RAFGL 5179) is a massive star-forming region chosen from the catalog of massive young stellar objects by Chan et al. (1996). G189.78+0.34 is listed as an ultracompact (UC) HII region (Shepherd & Churchwell 1996;Bronfman et al. 1996). It belongs to the Gem OB1 molecular cloud complex and is a part of the extended HII region Sh 252. It is associated with S252 A, which is one of the six compact radio sources in Sh 252 revealed...

High‐resolution far‐infrared observations of a large area of the star‐forming complex RCW 106 obtained using the TIFR 1‐m balloon‐borne telescope are presented. Intensity maps have been obtained simultaneously in two bands centred around 150 and 210 μm. Intensity maps have also been obtained in the four IRAS bands using HIRES‐processed IRAS data. From the 150‐ and 210‐μm maps, reliable maps of dust temperature and optical depth have been generated. The star formation in this complex has occurred in five linear sub‐clumps. Using the map at 210 μm, which has a spatial resolution superior to that of IRAS at 100 μm, 23 sources have been identified. The spectral energy distribution (SED) and luminosity of these sources have been determined using the associations with the IRAS maps. The luminosity distribution of these sources has been obtained. Assuming these embedded sources to be zero‐age main‐sequence stars and using the mass–luminosity relation for these, the power‐law slope of the initial mass function is found to be −1.73±0.5. This index for this very young complex is about the same as that for more evolved complexes and clusters. Radiation transfer calculations in spherically symmetric geometry have been undertaken to fit the SEDs of 13 sources with fluxes in both the TIFR and the IRAS bands. From this, the r−2 density distribution in the envelopes is ruled out. Finally, a correlation is seen between the luminosity of embedded sources and the computed dust masses of the envelopes.

Large scale far-infrared (FIR) observations of the Orion complex at 205 and 138 µm are presented with an aim of studying the distribution of cold (<25 K) dust. The maps in these FIR bands extend over ∼3600 sq. arcmin and cover regions around OMC-1, 2, 3 in Orion A and NGC 2023 and NGC 2024 in Orion B. Some limited regions have also been mapped at 57 µm. A total of 15 sources in Orion A and 14 in Orion B (south) have been identified from our FIR maps. Dust temperature distribution in both Orion A and Orion B (south) have been determined reliably using the maps at 205 & 138 µm obtained from simultaneous observations using almost identical beams (1. ′ 6 dia). These temperatures have been used to generate map of τ 150 , the optical depth at 150 µm, for the Orion B region. The coldest source detected is in OMC-3 and has a temperature of ∼ 15 K. The diffuse FIR emission in the different sub-regions is found to vary between 25 % to 50 % of the total FIR emission from that sub-region.

We present a detailed study of the post-outburst phase of McNeil's nebula (V1647 Orionis) using optical B, V, R, I and near-infrared (NIR) J, H, K photometric and low-resolution optical spectroscopic observations. The observations were carried out with the Himalaya Faint Object Spectrograph Camera (HFOSC), NIR camera (NIRCAM), the Tata Institute of Fundamental Research (TIFR) Near-Infrared Camera (TIRCAM) and NICMOS cameras on the 2-m Himalayan Chandra Telescope (HCT) and 1.2-m Physical Research Laboratory (PRL) telescopes during the period 2004 February-2005 December. The optical and NIR observations show a general decline in the brightness of the exciting source of McNeil's nebula (V1647 Ori). Our recent optical images show that V1647 Ori has faded by more than 3 mag since February 2004. McNeil's nebula has also faded considerably. The optical/NIR photometric data also show a significant variation in the magnitudes ( V = 0.78, R = 0.44, I = 0.21, J = 0.24 and H = 0.20 mag) of V1647 Ori within a period of one month, which is possibly undergoing a phase similar to eruptive variables, like EXors or FUors. The optical spectra show a few features such as strong Hα emission with blue-shifted absorption and the Ca II IR triplet (8498, 8542 and 8662 Å) in emission. As compared to the period just after outburst, there is a decrease in the depth and extent of the blue-shifted absorption component, indicating a weakening in the powerful stellar wind. The presence of the Ca II IR triplet in emission confirms that V1647 Ori is a pre-main-sequence star. The long-term, post-outburst photometric observations of V1647 Ori suggest an EXor rather than an FUor event. An optical/IR comparison of the region surrounding McNeil's nebula shows that the optical nebula is more widely and predominantly extended to the north, whereas the IR nebula is relatively confined (diameter ∼60 arcsec), but definitely extended, to the south, too. The large colour gradient from north to south and the sudden absence of an optical nebula to the south are suggestive of a large-scale disc-like structure (or envelope) surrounding the central source that hides the southern nebula.

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 k eA ¼ 130 and 200 m with $1 0 angular resolution using the TIFR 1 m balloon-borne telescope. The radio emission from the ionized gas of these regions has been imaged at 1280, 610, and 325 MHz using the Giant Metrewave Radio Telescope, India. Assuming the detected compact sources to represent exciting zero-age main sequence ( ZAMS) stars, the initial mass function [(m) / m Àa ] for the IRAS 19111+1048 region is found to be quite steep, with a ¼ 5:3 AE 0:5 for the mass range 14 < m/M < 33. The near-infrared ( NIR) source coincident with the IRAS 19111+1048 peak is likely to be an embedded pre-main-sequence star. 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. The best-fit radiative transfer models of the two IRAS sources are in good agreement with the observed spectral energy distributions. A uniform density distribution of dust and gas is implied for both the sources. The extents of ionized 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-à-vis its neighbor, IRAS 19111+1048, consistent with earlier studies.