Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/whats_on/workshops/mm_science2001/talks/Hunt.pdf Дата изменения: Tue Apr 23 11:34:12 2002 Дата индексирования: Wed Dec 26 02:51:06 2007 Кодировка: Поисковые слова: molecular cloud

Observations of Organic Molecules in Southern Molecular Clouds
Maria Hunt (UNSW, UWS, ATNF) John Whiteoak (ATNF) Paul Jones (UWS) Graeme White (UWS)


Investigating Star Formation in Southern Dense Molecular Cores l How?
­ Mopra and SEST observations of molecular transitions

between 1 and 3 mm. ­ Kinematic information from line profiles. ­ Temperatures and abundances from modelling of line emission.
l

Why?
­ To produce a statistical database of molecular emission

and abundances in southern molecular clouds. ­ To test theoretical predictions for molecular abundances in different physical regions of molecular clouds


SiO, SiO 2 , H2 O NO HCO+, N2 H+ CO, CS, HCN, HNC, HCO+, CN, C3 H2 , N2 H+, HC (2n+1)N T= 5- 25 K

CH3 OH, H2 CO, SO2 , H2CS, OH


As the gas density increases, molecules collide with and stick to the grain surfaces..... H+ HC5 N CS C HCO
+

HCN

HNC H+ O H+

C

HNC HC3 N

...new saturated molecules form on the grain surfaces such as CH3OH, OCS, NH3, H2CO ....


Ultracompact H II region

Hot Molecular Core T = 100 ­ 300 K

CS, SO, OCS, CH3 OH, SO2 , HCOOCH3 , CH3 CH2 OH


Observed Sample
l

27 bright galactic- plane molecular clouds with declinations south of ­30o
­ (250o< l < 2o).

l

Telescopes
­ The Mopra Telescope (86-116 GHz) ­ The SEST (84-250 GHz)


The Mopra Telescope ..
­ ­ ­ ­

Diameter 15 m (until 1999), 22 m (after 1999). 86 GHz ­ 116 GHz UNSW, ATNF Coonabarabran, NSW, Australia


Molecules
l

Transitions of the molecules CO, CS, HCN, HNC, HCO+, HC3 N, OCS, CH3OH and SO and several of their isotopomers with frequencies from 86 - 240 GHz Beam 30 ­ 60 arcsec

l




Calculating Abundances
l

Rotation Diagrams
­ Goldsmith, P.F. & Langer, W.D., 1999. Ap.J., 517,

209.
l

LVG Modelling
­ LVG code courtesy of Dr Peter Schilke, MPIFR. ­ Extension to LVG code for HC 3 N (Maria Hunt). ­ Castor, J.I., 1970. MNRAS, 149, 111. ­ Lampton, M., Margon, B. & Bowyers, S., 1976. Ap.J.,

208, 177.






Results
l

Most of the dense cores showed some evidence for recent or ongoing star formation:
­ Detection of thermal CH3 OH emission. ­ Detection of OCS emission. ­ Line wings suggestive of outflow.

l

G291.3-0.7, G345.5+1.5, NGC 6334(S), NGC 6334(N), NGC 6334(N1), G351.6-1.3 and G353.4-0.4 probably contain hot cores.


More Results
l

The Galactic-Centre cloud G1.6 -0.025 is probably undergoing a cloud- cloud collision. The molecular clouds G265.1+1.5, G291.3 0.7 and G1.6 -0.025 have self- absorbed line profiles in many molecules, suggesting a complex cloud structure and kinematics.

l


ATCA mm-observations
The higher resolution will enable the observation of more chemically homogeneous regions involved in starformation. l Thermal CH3 OH: At least 7 transitions within the 86 ­115 GHz range. l HC3N and OCS have 3 transitions each accessible with the ATCA.
l