H₂O maser emission from bright rimmed clouds in the southern hemisphere

Abstract

Context. Water maser emission is a powerful tracer of the presence of embedded sources in dense clouds since it requires elevated temperatures (>100 K) and densities (>10 7 cm −3 ) that can be found in circumstellar disks and/or jets/outflows associated with Young Stellar Objects. Bright rimmed clouds compressed by ionization fronts from nearby massive stars are considered good examples of externally triggered star formation, possibly resulting in the formation of massive stars. Aims. We aim to determine the water maser emission frequency and characteristics of 45 bright rimmed clouds in the southern hemisphere identified by Sugitani & Ogura (1994, ApJS, 92, 163). Methods. We have used the Tidbinbilla 70-m radiotelescope to perform a high sensitivity survey at 22.2 GHz of the maser emission from the 6 16 −5 23 rotational transition of H 2 O molecules. Results. We found 7 water maser sources out of 44 (16% detection rate), 5 being new detections. With the exception of the maser associated with BRC 68, all the other maser are characterized by low integrated fluxes and luminosities. Conclusions. Most maser sources fall below the correlation between the H 2 O and far-infrared luminosity found in other studies towards a variety of star forming regions. These results are similar to those found in the companion survey of BRCs in the northern hemisphere by Valdettaro et al. (2005, A&A, 443, 535). The low detection frequency and the properties of water maser emission from BRCs indicate that low-mass star formation is the most natural outcome of the external compression induced by the ionization front from nearby massive stars.

High‐Resolution H2O Maser Observations towardIRASSources in Bright‐Rimmed Clouds

“…We believe that this is not a sensitivity effect, but reflects an intrinsic property of BRCs as a class of clouds, in agreement with the initial results of the less sensitive studies by Valdettaro et al (2005Valdettaro et al ( , 2007 in both hemispheres. Interestingly, we note that a recent study of the OH maser emission toward 46 BRCs has also given largely negative results ( Thomas et al 2006).…”

“…This result puts on firmer ground the initial findings of less sensitive, single-dish studies of Valdettaro et al (2005Valdettaro et al ( , 2007. BRCs seem to produce mostly low-luminosity Class I objects, which are presently in a more advanced evolutionary phase than Class 0 sources for which the frequency of occurrence of maser emission is high, albeit highly variable.…”

“…Recently, a similar, but more sensitive search (rms $ 0:1 Jy) for water maser emission from a sample of 44 BRCs in the southern hemisphere identified by Sugitani & Ogura (1994) was carried out by Valdettaro et al (2007) using the Tidbinbilla 70 m radio telescope. The results confirmed the previous findings, with only seven (16%) water masers detected in the single-epoch survey.…”

Observational study of sites of triggered star formation

“…H 2 O masers have been found in regions of high-and low-mass star formation and therefore act as a good general sign post of star formation. The Valdettaro et al (2007) search of the southern SFO catalogue detected H 2 O maser emission towards 7 clouds; due to the inherent variability of H 2 O masers this is a lower limit. In addition to H 2 O masers we searched the methanol maser catalogue of Pestalozzi et al (2005) and found three clouds coincident with Class II maser emission.…”

Maser science at Tidbinbilla

“…Maser science at Tidbinbilla 69 Valdettaro et al (2007) performed a high sensitivity survey of water masers in bright rimmed clouds compressed by ionization fronts from nearly massive stars. They found masers from seven bright rimmed interstellar clouds out of 44 such regions.…”