Image of a BRC http://wiki.gb.nrao.edu/pub/Singledish/MorganAmmonia/SFO_04.eps

%META:FILEATTACHMENT{name="SFO_04.eps" attr="" comment="" date="1184272994" path="SFO_04.eps" size="249054" user="LarryMorgan" version="1.1"}%

TOC: No TOC in "Singledish.MorganAmmonia" Frequency Switched Ammonia Observations on Galactic Triggered Star-Formation Regions - Larry Morgan

Some Background

The rotational transition of ammonia seen at 23.69 GHz is generally only excited in regions that have high densities (10^4 cm^-3). Within molecular clouds these densities normally indicate the presence of conditions necessary for star-formation. By analysis of the ammonia transition and its hyperfine lines it is possible to determine the optical depth of the (presumed) star-forming cores. A comparison of the ammonia (1,1) line to its (2,2) counterpart at 23.72 GHz allows a determination of the rotation temperature of the region and thus the physical conditions of the region may be determined and the potential for star-formation ascertained. The details of the ammonia molecule and its usefulness to studies of the interstellar medium (ISM) are laid out in Ho and Townes (1983).

The Sugitani catalogue is a collection of bright infra-red (IR) sources associated with HII regions (Sugitani 1991, 1994)
These 'bright-rimmed clouds' (BRCs) are the suspected sites of triggered star formation caused by the propagation of photo-ionisation induced shocks into the interior of molecular clouds. The ionisation arising as the result of nearby massive stars.
This process is called 'radiatively-driven implosion' (RDI), some theoretical work describes the process (Bertoli 1989, Lefloch and Lazareff 1994) while observations are supportive, though not conclusive of the scenario (Thompson 2004, Morgan 2004, Thompson 2004a)
Observations have been made of individual objects that seem to show a split in the sample of molecular clouds between those likely to be sites of triggered star-formation and those likely to contain pre-existing star-formation regions (SFRs) that have simply been exposed to an ionisation front after the fact (Urquhart 2007, Urquhart 2006).

Objectives

GBTIDL

Method

• Step 1 - read in your data
• Step 2 - look at the data files, which scans are of which objects? You will want to average all scans of a single object at some point, first you may want to go through each scan alone so that you can eliminate any that are 'bad'.
  How are the data switched? This will affect how you reduce it using IDLs canned routines.
  How many IFs are used in each scan? You will need to look at each one separately
• Step 3 - you should now be able to average all valid scans for each object. Pick one object that looks like a promising candidate for detections at as many IFs as possible and average all the 'good' scans for it.
• Step 4 - do you want to smooth your data? If so, by how much? What resolution do you require? What smoothing method should you use?
• Step 5 - do you want to subtract a baseline? How should you accomplish this? What is the best method?
• Step 6 - due to a 'feature' of GBTIDL only the first IF's rest frequency is used when making velocity calculations, if you want to look at the other IF's in velocity space you will have to re-define the rest frequency of your line. Hint - type 'help,!g.s[0],/struct
• Step 7 - once you have the spectra smoothed, with any baseline removed, what then? Height and width of lines are normally the important factors, what is the best way of determining these?
• Step 8 - if you get this far and still have time on your hands, what are you going to do with the information you have gathered? Start reading Ho and Townes (1983) in combination with Longmore et al. (2007) to decide upon the best way to draw conclusions from your data.

Some Resources You May Need

References

• Ho, P. T. P. & Townes, C. H. 1983, Annual Review of Astronomy and Astrophysics
  Interstellar ammonia

• Bertoldi, Frank 1989, Astrophysical Journal
  The photoevaporation of interstellar clouds. I - Radiation-driven implosion

• Sugitani, Koji, Fukui, Yasuo, & Ogura, Katsuo 1991, Astrophysical Journal Supplement Series
  A catalog of bright-rimmed clouds with IRAS point sources: Candidates for star formation by radiation-driven implosion. I - The Northern Hemisphere

• Lefloch, B. & Lazareff, B. 1994, Astronomy and Astrophysics
  Cometary globules. 1: Formation, evolution and morphology

• Sugitani, Koji & Ogura, Katsuo 1994, Astrophysical Journal Supplement Series
  A catalog of bright-rimmed clouds with IRAS point sources: Candidates for star formation by radiation-driven implosion. 2: The southern hemisphere

• Morgan, L. K., Thompson, M. A., Urquhart, J. S., White, G. J., & Miao, J. 2004, Astronomy and Astrophysics
  A radio and mid-infrared survey of northern bright-rimmed clouds

• Thompson, M. A., White, G. J., Morgan, L. K., Miao, J., Fridlund, C. V. M., & Huldtgren-White, M. 2004, Astronomy and Astrophysics
  Searching for signs of triggered star formation toward IC 1848

• Thompson, M. A., Urquhart, J. S., & White, G. J. 2004, Astronomy and Astrophysics
  A Compact Array imaging survey of southern bright-rimmed clouds

• Urquhart, J. S., Thompson, M. A., Morgan, L. K., & White, G. J. 2004, Astronomy and Astrophysics
  High-mass star formation within the bright-rimmed cloud SFO 79

• Urquhart, J. S., Thompson, M. A., Morgan, L. K., & White, G. J. 2006, Astronomy and Astrophysics
  Radio continuum and molecular line observations of four bright-rimmed clouds

• Longmore, S. N., Burton, M. G., Barnes, P. J., Wong, T., Purcell, C. R., & Ott, J., 2007, Monthly Notices of the Royal Astronomical Society
  Multiwavelength observations of southern hot molecular cores traced by methanol masers - I. Ammonia and 24-GHz continuum data

• Urquhart, J. S., Thompson, M. A., Morgan, L. K., Pestalozzi, M. R., White, Glenn J., & Muna, D. N. 2007, Astronomy and Astrophysics
  A tale of two cores: triggered massive star formation in the bright-rimmed cloud SFO 75

%META:TOPICINFO{author="LarryMorgan" date="1184001197" format="1.0" version="1.1"}% %META:TOPICPARENT{name="CannedSignup"}% Canned Data Reduction Sessions Friday 13th July