Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998a%26as..133...29h&link_type=abstract
Astronomy and Astrophysics Supplement, v.133, p.29-49
Astronomy and Astrophysics
Astrophysics
91
Ism: Molecules, Ism: Clouds, Ism: Hii Regions, Radio Lines: Ism, Stars: Formation, Molecular Processes
Scientific paper
We have used the JCMT to survey molecular line emission towards 14 ultracompact HiI\ regions (G5.89, G9.62, G10.30, G10.47, G12.21, G13.87, G29.96, G31.41, G34.26, G43.89, G45.12, G45.45, G45.47, and G75.78). For each source, we observed up to ten 1 GHz bands between 200 and 350 GHz, covering lines of more than 30 species including multiple transitions of CO isotopes, CH_3OH, CH_3CCH, CH_3CN and HCOOCH_3, and sulphuretted molecules. The number of transitions detected varied by a factor of 20 between sources, which were chosen following observations of high-excitation ammonia (Cesaroni et al. 1994a) and methyl cyanide (Olmi et al. 1993). In half our sample (the line-poor sources), only C(17) O, C(18) O, SO, C(34) S and CH3OH were detected. In the line-rich sources, we detected over 150 lines, including high excitation lines of CH_3CN, HCOOCH_3, C_2H_5CN, CH_3OH, and CH_3CCH. We have calculated the physical conditions of the molecular gas. To reproduce the emission from the line-rich sources requires both a hot, dense compact core and an ambient cloud consisting of less dense, cooler gas. The hot cores, which are less than 0.1 pc in size, reach densities of at least 10(8) cm(-3) and temperatures of more than 80 K. The line-poor sources can be modelled without a hot core by a 20-30 K, 10(5) cm(-3) cloud. We find no correlation between the size of the HiI\ region and the current physical conditions in the molecular environment. A comparison with chemical models (Millar et al. 1997) confirms that grain surface chemistry is important in hot cores. Tables 10-18 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html}$^,$\thanks{Figures 6-12 are only available in the electronic version of the journal at http://www.edpsciences.com
Hatchell Jennifer
Macdonald G. H.
Millar Thomas J.
Thompson Maggie A.
No associations
LandOfFree
A survey of molecular line emission towards ultracompact HII regions does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with A survey of molecular line emission towards ultracompact HII regions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A survey of molecular line emission towards ultracompact HII regions will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1073842