Protostars and Planets VI, Heidelberg, July 15-20, 2013

Poster 1B022

Maser and Molecular Line Surveys of Massive Star-forming Regions

Kim, Won-Ju (Korea Astronomy and Space science Institute)
Kim, Kee-Tae (Korea Astronomy and Space science Institute)

Abstract:
We made twice a simultaneous 22 GHz H2O and 44 GHz Class I CH3OH maser surveys of 103 ultra-compact HII regions (UCHIIs) in 2010 and 2011. We also performed a SiO (J=1-0, v=0) line survey of three samples of massive star-forming regions in different evolutionary stages from 2010 to 2013: 134 infrared dark cores (IRDCs), 135 high-mass proto-stellar objects (HMPOs) and 103 UCHIIs . H2O and CH3OH masers were detected in 70 (68%) and 48 (47%) UCHIIs, respectively. Among them, six H2O and twenty-four CH3OH masers are new detections. These high detection rates of both masers strongly suggest that their occurrence periods are significantly overlapped with the UCHII phase. CH3OH masers always have smaller relative velocities than 10 km s−1 with respect to the ambient molecular gas, while H2O masers frequently show larger relative velocities. Eighteen UCHIIs show H2O maser lines at relative velocities > 30 km s−1. The occurrence and disappearance of H2O masers are frequent over one-year time interval. In contrast, CH3OH masers rarely show significant variation in peak velocity, peak intensity, and line shape. The isotropic luminosities of both masers well correlate with the bolometric luminosities of the central stars in the case that data points of low- and intermediate-mass proto-stars are added. They also tend to increase with the 2/6 cm radio continuum luminosities of UCHIIs and the 850 m continuum luminosity of the parent dense cores. SiO thermal emission was detected in 52 IRDCs (39 %), 22 HMPOs (16 %), and 24 UCHIIs (23 %). Almost SiO emission–detected UCHIIs (96%) have H2O and/or CH3OH maser emissions. SiO luminosity is proportional to bolometric luminosity and maser (H2O and CH3OH) luminosities. LSiO/Lbol ratio tend to decrease as central (proto)stars evolved.

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