C$^\mathsf{18}$O (3–2) observations of the Cometary Globule CG 12: a cold core and a C$^\mathsf{18}$O hot spot

Abstract

The feasibility of observing the C 18 O (3-2) spectral line in cold clouds with the APEX telescope has been tested. As the line at 329.330 GHz lies in the wing of a strong atmospheric H 2 O absorption it can be observed only at high altitude observatories. Using the three lowest rotational levels instead of only two helps to narrow down the physical properties of dark clouds and globules. The centres of two C 18 O maxima in the high latitude low mass star forming region CG 12 were mapped in C 18 O (3-2) and the data were analyzed together with spectral line data from the SEST. The T MB (3-2)/T MB (2-1) ratio in the northern C 18 O maximum, CG 12-N, is 0.8, and in the southern maximum, CG 12-S, ∼2. CG 12-N is modelled as a 120 diameter (0.4 pc) cold core with a mass of 27 M ⊙ . A small size maximum with a narrow, 0.8 km s -1 , C 18 O (3-2) spectral line with a peak temperature of T MB ∼ 11 K was detected in CG 12-S. This maximum is modelled as a 60-80 diameter (∼0.2 pc) hot (80 K? T ex ? 200 K) ∼1.6 M ⊙ clump. The source lies on the axis of a highly collimated bipolar molecular outflow near its driving source. This is the first detection of such a compact, warm object in a low mass star forming region.