APEX SV projects

Revealing the environs of the remarkable southern hot core G327.30.6

Coordinator: F. Wyrowski, K. Menten, P. Schilke, S. Thorwirth, P. Bergman

Data:
Program is available and data products can be downloaded

Scientific justification:

There is no generally accepted evolutionary scheme for high mass star formation yet, in contrast to the detailed framework of CLASSes that exists for the early evolution of low mass stars. In the nineties ultracompact HII regions and hot molecular cores were the youngest known stages of massive star formation. In recent years, so called high mass protostellar objects (HMPOs) or massive young stellar objects (MYSOs) were recognized to be likely an even earlier stage of massive star formation and in recent mm/submm bolometer array imaging even massive cold secondary cores not associated with freefree and NIR/MIR emission were found in the environs of UCHII regions or HMPOs. Hence, to understand the evolution of massive protostars, it is vital, to cover observationally the larger environs of known massive star formation, since this will likely reveal secondary cores in different evolutionary stages.
One of the most prominent hot molecular cores in the southern celestrial hemisphere is the core associated with the UCHII region G327.3-0.6 at a kinematical distance of 2.9 kpc. It is associated with prominent H2O, OH and CH3OH masers and it chemistry has been studied in two influencial papers, the ethylene oxide and acetaldehyde study of Nummelin et al. (1998) and the Gibb et al. (2000) study of the chemical inventory of this source. The source is remarkable for its line rich spectra with relatively narrow, well behaved (gaussian) line profiles, which reduces line blending and makes the spectra easier to interpret than e.g. spectral scans of of SgrB2.
Given the interest in this hot core, it is surprising that almost nothing is known about its environs. Only in Per Bergman's thesis (1992) some SEST maps are reported, finding two adjacent dense cores in this molecular cloud: one cold (kinetic temperature Tk=30 K) cloud core, and one hot (Tk=100200 K) core, hence this cloud offers the possibity to study cores that have formed from the same parential cloud but are in different stages of evolution. See Fig. 1 for MIR images of the region.

Goals and strategy
Since the G327.30.6 hot core has the potential of becoming a southern hemisphere hot core template for upcoming observatories like ALMA and Herschel, there will be large interest of the community in a chemical and physical study of the molecular environs of the source on a several parsec scale, covering most of the giant molecular cloud harboring the hot core, especially since there are up to now no published maps available, so that this would certainly be a pathfinding project. We will identify and characterize all secondary cores and determine with small high angular resolution 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 and column density distribution of the cloud. We basically want to cover the whole complex seen in the MSX 8mu image of the region which extends over 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.

Time estimate
We expect CO lines on a Ta* scale between 10 and 30 K, hence a RMS of 1K is sufficient, which is reached at 345GHz after 1s. For a fully sampled map 1600 points have to be observed. We assume for the OTF observations an ON efficiency of 0.5,including calibrations. Hence we need 1 hour oberving time for the CO map. C18O intensities will be in the range 1 to 5 K, hence at least 0.5 K RMS are needed. C18O emission will be less extended, so that rougly half the size of the CO map has to be covered which will cost a total of about 2 hours. 13CO (87) towards the cores is expected to be also 15 K. with 60s per positions we reach 0.35K and 2 5x5 raster maps of the peaks take 1.5 hours. This leaves 3 hours for deeper integrations towards the peaks in CH3CN and CH3OH. Additionally, we add 1 hour time for tuning. Note that some of the FLASH tuning can be done during APEX2A observations to save time.
The whole observing program then requires a 8 hour, one transit, observation of G327.