APEX SV projects

How hot are the organic molecules in the G327 hot core?

Coordinator: S. Bisschop, G. Fuchs, E.F. van Dishoeck, J. Jorgensen

Abstract:

Data:
Program is available and data products can be downloaded

Scientific justification:

Deeply embedded high-mass YSOs are known to be a rich source of complex organic, possibly prebiotic molecules. These molecules are thought to be produced by grain surface chemistry during the cold pre-stellar and collapse phases, followed by evaporation back into the gas phase. Subsequent high-temperature gas-phase chemistry can further enhance the chemical complexity. In order to test this chemical scheme and unravel the origin of complex organics, several groups world-wide (including our own) are pursuing observational programs on high- and low-mass hot cores, also in preparation for future line surveys with Herschel-HIFI and ALMA. Most of them have focussed on targets visible from the Northern hemisphere, but several of the popular template objects like SgrB2, W51 and W49 actually have large distances (~8 kpc) and intrinsically broad lines (~20 km/s). Thus, these data suffer heavily from beam dilution and line confusion.
G327.3-0.6 is a southern YSO surveyed at the SEST by Gibb et al. (2000, ApJ 545, 309) (see also Ikeda et al. 2001, ApJ 560, 792) and is particularly rich in organic molecules. It has a kinematical distance of only 2.9 kpc and its lines are relatively narrow, ~5 km/s, and symmetric. Thus it offers the opportunity to see weaker features, which in turn implies the possibility to observe lower abundances and/or different excitation regimes. We propose here two deep integrations on G327.2-0.6 with the 345 GHz receiver, to demonstrate the high quality, line-rich spectra that can be obtained with APEX on hot-core type objects. Compared with the 2 mm SEST survey, the 345 GHz band contains higher excitation lines and can thus better constrain the hot, high excitation gas.
The settings are chosen to cover high excitation lines (E_u up to 250 K) of C2H5OH and HCOOH, two critical species in the grain surface chemistry, and their lines are known to be relatively free from potential confusion by other species. Detection of these lines would imply higher excitation temperatures than inferred from the SEST data, which in turn provides constraints on their origin. Of course, the settings may also contain surprises of other, previously undetected molecules.

Observational details:
Source: G327.3-0.6 RA=15 49 15.6, DEC=-54 28 07 (B1950) V_LSR=-45 km/s
Receiver: 345 GHz facility receiver APEX-2a
Bandwidth: 512 MHz
Central frequencies: 348.050 GHz USB (contains C2H5OH 347.916 GHz, CH3OCHO, 13CH3OH)
346.850 GHz USB (contains HCOOH 346.719 GHz and many other species)
Observing mode: Beam or position switching by 120-180"
Required rms: 20 mK (T_A*) in 1 km/s bin
Required integration times: 40 minutes (on+off) per setting => 80 min total (assuming T_sys=400 K)
All times excluding overheads