Aims: We present a study of the silicon-bearing species detected in a line-confusion limited survey towards Orion KL performed with the IRAM 30-m telescope. The analysis of the line survey is organized by families of molecules. Our aim is to derive physical and chemical conditions for each family taking all observed lines into account from all isotopologs of each species. The large number of transitions in different vibrationally excited states covered by our data, which range from 80 to 280 GHz, let us provide reliable source-average column densities (hence, isotopolog abundances and vibrational temperatures) for the detected molecules. In addition, we provide a wide study of the physical properties of the source based on the different spectral components found in the emission lines.
Methods: We modeled the lines of the detected molecules using a radiative transfer code, which permit us to choose between large velocity gradient (LVG) and local thermodynamic equilibrium (LTE) approximations depending on the physical conditions of the gas. We used appropriate collisional rates for the LVG calculations. To qualitatively investigate the origin of the SiS and SiO emissions in Orion KL we ran a grid of chemical models.
Results: For the v = 1 state of SiO, we detected the J = 2-1 line and, for the first time in this source, emission in the J = 4-3 transition, both of them showing a strong masering effect. For SiO v = 0, we detected 28SiO, 29SiO, and 30SiO; in addition, we have mapped the J = 5-4 SiO line. For SiS, we have detected the main species, 29SiS, and SiS v = 1. Unlikely other species detected in Orion KL (
Astronomy and Astrophysics
- Pub Date:
- April 2011
- stars: formation;
- ISM: abundances;
- ISM: clouds;
- ISM: molecules;
- radio lines: ISM;
- Astrophysics - Astrophysics of Galaxies
- Astronomy and Astrophysics, in press