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Upper limit for the D2H+ ortho-to-para ratio in the prestellar core 16293E (CHESS) | | C. Vastel
; P. Caselli
; C. Ceccarelli
; A. Bacmann
; D.C. Lis
; L. Pagani
; E. Caux
; C. Codella
; J. A. Beckwith
; T. Ridley
; | | Date: |
2 Oct 2012 | | Abstract: | The H3+ ion plays a key role in the chemistry of dense interstellar gas
clouds where stars and planets are forming. The low temperatures and high
extinctions of such clouds make direct observations of H3+ impossible, but lead
to large abundances of H2D+ and D2H+, which are very useful probes of the early
stages of star and planet formation. The ground-state rotational ortho-D2H+
111-000 transition at 1476.6 GHz in the prestellar core 16293E has been
searched for with the Herschel/HIFI instrument, within the CHESS (Chemical
HErschel Surveys of Star forming regions) Key Program. The line has not been
detected at the 21 mK km/s level (3 sigma integrated line intensity). We used
the ortho-H2D+ 110-111 transition and para-D2H+ 110-101 transition detected in
this source to determine an upper limit on the ortho-to-para D2H+ ratio as well
as the para-D2H+/ortho-H2D+ ratio from a non-LTE analysis. The comparison
between our chemical modeling and the observations suggests that the CO
depletion must be high (larger than 100), with a density between 5e5 and 1e6
cm-3. Also the upper limit on the ortho-D2H+ line is consistent with a low gas
temperature (~ 11 K) with a ortho-to-para ratio of 6 to 9, i.e. 2 to 3 times
higher than the value estimated from the chemical modeling, making it
impossible to detect this high frequency transition with the present state of
the art receivers. | | Source: | arXiv, 1210.0804 | | Services: | Forum | Review | PDF | Favorites | |
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