Dense Cores in the HH24-26 Outflow Region [chapter]

K. M. Menten, C. M. Walmsley, R. Mauersberger
1987 Circumstellar Matter  
We have made observations of the (1,1) and (2,2) inversion lines of ammonia (NH3) towards the dark cloud region containing the Herbig-Haro (HH) objects 24-27. These transitions are only excited at H 2 densities >10 4 cm -3 , and thus probe high density gas. From the observed hyperfine splitting one can calculate optical depths. The optical depth ratio can be used to determine the rotational temperature T 2 i which is equal to the kinetic temperature under dark cloud conditions. With the 40"
more » ... s. With the 40" beam of the Effelsberg l00-m telescope we are able to detect a wealth of fine structure in the NH3 distribution not seen in earlier lower resolution studies of the region ( Matthews and Little 1983, Torrelles et al. 1983). Our map in the (l,l) line (see Fig. I) shows a general elongation of the NH 3 emission in the N-S direction forming a ridge which connects the northern cluster of Herbig-Haro objects (HH24 Α-D), the 1^ emission line star no. 140, and HH25 and 26 with their exciting star, the embedded IR-source SSV59 (Strom et al. 1976). No enhancement in the NH3 emission is seen towards HH27 which lies just outside our eastern map boundary. Like HH objects, high velocity CO line wings are manifestations of outflow activity and Fig. I is an overlay of our NH3 map and the CO high velocity emission detected by Snell and Edwards (1982) which suggests the existence of two distinct outflow centers in the region. There is a conspicuous correlation of the ammonia emission peaks with the positions of the HH objects (except HH27) and the embedded IRsources. There also is a local emission maximum near no. 140, the star which may be driving the northern outflow. We have found evidence for an interaction of the outflow with the dense N H 3 clumps: A high S/N spectrum taken towards the position of SSV59, between HH25 and 26 shows evidence for broad line wings. Moreover, the linewidth towards the peak close to HH25 is significantly larger than towards neighbouring positions (l.O km s~1 compared to typically 0.6 km s~1). Also, the NH 3 rotational temperature at this position is higher than elsewhere in the cloud (I5±l Κ compared to Π-12 K). A possible explanation for the enhanced temperature and broader lines towards HH25 is that these phenomena reflect the existence of an embedded heating source other than SSV59 which lies close to HH25. Evi-179 /. Appenzellerand C. Jordan (eds.), Circumstellar Matter, 179-180. ©1987 by the IAU. available at https://doi.
doi:10.1007/978-94-009-3887-8_48 fatcat:tszfasrknjcslf5m7w7cnemxlq