Revealing the environs of the remarkable southern hot core G327.30.6
Coordinator: F. Wyrowski, K. Menten, P. Schilke, S. Thorwirth, P. Bergman
Program is available and data products can be downloaded
There is no generally accepted evolutionary scheme for high mass starformation yet, in contrast to the detailed framework of CLASSes thatexists for the early evolution of low mass stars. In the ninetiesultracompact HII regions and hot molecular cores were the youngestknown stages of massive star formation. In recent years, so called highmass protostellar objects (HMPOs) or massive young stellar objects(MYSOs) were recognized to be likely an even earlier stage of massivestar formation and in recent mm/submm bolometer array imaging evenmassive cold secondary cores not associated with freefree and NIR/MIRemission were found in the environs of UCHII regions or HMPOs. Hence,to understand the evolution of massive protostars, it is vital, tocover observationally the larger environs of known massive starformation, since this will likely reveal secondary cores in differentevolutionary stages.
One of the most prominent hot molecular cores in the southerncelestrial hemisphere is the core associated with the UCHII regionG327.3-0.6 at a kinematical distance of 2.9 kpc. It is associated withprominent H2O, OH and CH3OH masers and it chemistry has been studied intwo influencial papers, the ethylene oxide andacetaldehyde study of Nummelin et al. (1998) and the Gibb et al. (2000)study of the chemical inventory of this source. The source isremarkable for its line rich spectra with relatively narrow, wellbehaved (gaussian) line profiles, which reduces line blending and makesthe spectra easier to interpret than e.g. spectral scans of of SgrB2.
Given the interest in this hot core, it is surprising that almostnothing is known about its environs. Only in Per Bergman's thesis(1992) some SEST maps are reported, finding two adjacent dense cores inthis molecular cloud: one cold (kinetic temperature Tk=30 K) cloudcore, and one hot (Tk=100200 K) core, hence this cloud offers thepossibity to study cores that have formed from the same parential cloudbut are in different stages of evolution. See Fig. 1 for MIR images ofthe region.
Goals and strategy
Since the G327.30.6 hot core has thepotential of becoming a southern hemisphere hot core template forupcoming observatories like ALMA and Herschel, there will be largeinterest of the community in a chemical and physical study of themolecular environs of the source on a several parsec scale, coveringmost of the giant molecular cloud harboring the hot core, especiallysince there are up to now no published maps available, so that thiswould certainly be a pathfinding project. We will identify andcharacterize all secondary cores and determine with small high angularresolution maps the physical conditions within those cores.
Our strategy in detail is:
- Cover with OntheFly maps the whole cloud in 12CO and C18O (32)with the APEX2A receiver.This will reveal the global kinematics andcolumn density distribution of the cloud. We basically want to coverthe whole complex seen in the MSX 8mu image of the region which extendsover 6x6 arcmin**2.
- Zoom into indiviual cores with FLASH observations of CO(43) and 13CO(87) raster maps and APEX2A observations of N2H+ and HCN.
- Characterize the peaks of the found cores with transition bands of CH3CN and CH3OH.
We expect CO lines on a Ta* scale between 10 and 30 K, hence a RMS of1K issufficient, which is reached at 345GHz after 1s. For a fully sampledmap 1600 points have to be observed. We assume for the OTF observationsan ON efficiency of 0.5,including calibrations. Hence we need 1 houroberving time for the CO map. C18O intensities will be in the range 1to 5 K, hence at least 0.5 K RMS are needed. C18O emission will be lessextended, so that rougly half the size of the CO map has to be coveredwhich will cost a total of about 2 hours. 13CO (87) towards the coresis expected to be also 15 K. with 60s per positions we reach 0.35K and2 5x5 raster maps of the peaks take 1.5 hours. This leaves 3 hours fordeeper integrations towards the peaks in CH3CN and CH3OH. Additionally,we add 1 hour time for tuning. Note that some of the FLASH tuning canbe done during APEX2A observations to save time.
The whole observing program then requires a 8 hour, one transit, observation ofG327.