Search

We present high-angular resolution observations of OH maser emission towards the high-mass star-forming region IRAS 06056+2131. The observations were carried out using the UK radio interferometer array, Multi-Element Radio Linked Interferometer Network (MERLIN) in the OH main lines at 1665 and 1667 MHz, in addition to the OH satellite line at 1720 MHz. The results of this study reveal the small upper limit to the size of emission in the 1665-MHz line with an estimated total intensity of ∼4 Jy. We did not detect any emission from the 1667 and 1720-MHz lines. The full polarization mode of MERLIN enables us to investigate the magnetic field in the OH maser region. In this transition, a Zeeman pair is identified from which a magnetic strength of ∼−1.5 mG is inferred. Our results show that IRAS 06056+2131 is highly polarized, with ∼ 96 |${{\ \rm per\ cent}}$| circular polarization and ∼6 |${{\ \rm per\ cent}}$| linear polarization. The linear polarization angle is ∼29°, implying a magnetic field which could be aligned with the outflow direction detected towards this region, but the actual magnetic field direction has an uncertainty of up to 110° due to the possible effects of Faraday rotation. The star-forming evolutionary status of the embedded protostellar object is discussed. [ABSTRACT FROM AUTHOR]

We have carried out a near-infrared imaging survey of luminous young stellar outflow candidates using the United Kingdom Infrared Telescope. Observations were obtained through the broad-band K (2.2 μm) and narrow-band filters at the wavelengths of H = 1–0 S(1) (2.1218 μm) and Brγ (2.166 μm) lines. 50 regions were imaged with a field of view of 2.2 × 2.2 arcmin2. Several young embedded clusters are unveiled in our near-infrared images. 76 per cent of the objects exhibit H2 emission and 50 per cent or more of the objects exhibit aligned H2 emission features suggesting collimated outflows, many of which are new detections. These observations suggest that disc accretion is probably the leading mechanism in the formation of stars, at least up to late O spectral types. The young stellar objects (YSOs) responsible for many of these outflows are positively identified in our images based on their locations with respect to the outflow lobes, Two-Micron All-Sky Survey colours and association with Midcourse Space Experiment, Infrared Astronomical Satellite, millimetre and radio sources. The close association of molecular outflows detected in CO with the H2 emission features produced by shock excitation by jets from the YSOs suggests that the outflows from these objects are jet-driven. Towards strong radio emitting sources, H2 jets were either not detected or were weak when detected, implying that most of the accretion happens in the pre-ultracompact (pre-UC) H ii phase; accretion and outflows are probably weak when the YSO has advanced to its UC H ii stage. [ABSTRACT FROM AUTHOR]

IRAS 21413+5442 and IRAS 21407+5441 are two massive star-forming regions of high luminosity, likely associated with each other. Near-infrared (NIR) photometry on these two IRAS sources was performed at United Kingdom Infrared Telescope (UKIRT) using the UFTI under excellent seeing conditions yielding an angular resolution of ∼0.5 arcsec. Our results reveal details of stellar content to a completeness limit (90 per cent) of and mag in the two regions. In IRAS 21413+5442, we identify a late O-type star, having large colour, to be near the centre of the CO jets observed by earlier authors. The UKIRT images reveal in IRAS 21407+5441, a faint but clear compact H ii region around a central high- and intermediate-mass star cluster. We have detected a number of sources with large colour which are not detected in J band. We also present the GMRT radio continuum map at 1.28 GHz covering the entire region surrounding the two star-forming clouds. The radio continuum fluxes are used to estimate the properties of H ii regions which seem to support our NIR photometric results. Based on our radio continuum map and the archival Midcourse Space Experiment (MSX) 8.2-μm image, we show that the two IRAS sources likely belong to the same parent molecular cloud and conjecture that a high-mass star of large IR colours, present in between the two sources, might have triggered star formation in this region. However, one cannot rule out the alternative possibility that Star A could be a nearby foreground star. [ABSTRACT FROM AUTHOR]