2010A&A...510A..96O

This work aims at investigating the molecular and infrared components in the massive young stellar object (MYSO) candidate IRAS 18544+0112. The purpose is to determine the nature and the origin of this infrared source. To analyze the molecular gas towards IRAS 18544+0112, we have carried out observations in a 90''x90'' region around l=34.69°, b=-0.65°, using the Atacama Submillimeter Telescope Experiment (ASTE) in the ¹²CO J=3-2, ¹³CO J=3-2, HCO⁺J=4-3 and CS J=7-6 lines with an angular resolution of 22''. The infrared emission in the area has been analyzed using 2MASS and Spitzer public data. From the molecular analysis, we find self-absorbed ¹²CO J=3-2 profiles, which are typical in star forming regions, but we do not find any evidence of outflow activity. Moreover, we do not detect either HCO⁺J=4-3 or CS J=7-6 in the region, which are species normally enhanced in molecular outflows and high density envelopes. The ¹²CO J=3-2 emission profile suggests the presence of expanding gas in the region. The Spitzer images reveal that the infrared source has a conspicuous extended emission bright at 8µm with an evident shell-like morphology of ∼1.5' in size (∼1.4pc at the proposed distance of 3kpc) that encircles the 24µm emission. The non-detection of ionized gas related to IRAS 18544+0112 together with the fact that it is still embedded in a molecular clump suggest that IRAS 18544+0112 has not reached the UCHII region stage yet. Based on near infrared photometry we search for YSO candidates in the region and propose that 2MASS 18565878+0116233 is the infrared point source associated with IRAS 18544+0112. Finally, we suggest that the expansion of a larger nearby HII region, G034.8-0.7, might be related to the formation of IRAS 18544+0112.