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| EPoS Contribution |
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The Riddle of H2D+ in Massive Star Forming Regions
Thushara Pillai Caltech, Pasadena, USA | |
| Our research on dense gas tracers like N2H+ and NH3 in high mass star forming regions have shown that their deuterated analogues are excellent tracers of the "pre-protocluster" phase, which is the earliest stage in the formation of high mass stars. Such objects show very high deuteration (D/H). With the estimated high D/H ratios, we expected H2D+ to be abundant. Therefore, we followed up our brightest NH2D targets with JCMT to search for H2D+. The main result of our work (to our big surprise) is that H2D+ is detected only in a single source, and it is two orders of magnitude lower than that found in low mass cores (Pillai et al. prep, see Figure). This has the strong implication that the deuterium transfer in the high mass cores might occur not through ion-neutral exchange starting from H2D+, but via active grain chemistry. If this is indeed the case, we should detect abundant deuterated CO derivatives. I launched another project to test exactly this scenario and establish a viable reaction pathway for deuterium transfer that could explain the high deuteration, very low H2D+ abundance and the evolutionary status of the high mass "pre-protocluster" candidates. The observations covered low excitation transitions of a few CO derivatives in two well known active high mass star forming regions in DR21 and W48. From the analysis of the data, it has not been detected at a level that would require grain chemistry to be active. I will present the results based on this limit, coupled with our own temperature measurements, and recent lab experiments by other groups on molecular desorption. | |
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| Caption: Left Panel: SMA 1.3mm (grey scale), and SCUBA 850mu dust continuum map in DR21 (contours). Middle Panel: N2D+ 3--2 moment 0 map, and JCMT H2D+ S/N map (contours, 3 sigma in steps of 1.5 sigma). Right Panel: N2H+ 4--3 moment 0 map (weighted mean intensity, grey scale and black contours), and JCMT H2D+ S/N map. Stars denote the embedded population identified in the region with Spitzer. | |
| Collaborators: P. Caselli, U Leeds, UK J. Kauffmann, JPL, USA |
Suggested Session:
Chemistry, Massive Stars, Molecular Clouds, Turbulence |