Vastel, C. and Caselli, P. and Ceccarelli, C. and Bacmann, A. and Lis, D. C. and Caux, E. and Codella, C. and Beckwith, J. A. and Ridley, T. (2012) Upper limit for the D_2H^+ ortho-to-para ratio in the prestellar core 16293E (CHESS). Astronomy and Astrophysics, 547 . Art. No. A33. ISSN 0004-6361 http://resolver.caltech.edu/CaltechAUTHORS:20130116-130437278
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The H^+_3 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 H^+_3 impossible, but lead to large abundances of H_2D^+ and D_2H^+, which are very useful probes of the early stages of star and planet formation. The ground-state rotational ortho-D_2H^+ 1_(1,1)–0_(0,0) 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^(-1) level (3σ integrated line intensity). We used the ortho-H_2D^+ 1_(1,0)–1_(1,1) transition and para-D_2H^+ 1_(1,0)–1_(0,1) transition detected in this source to determine an upper limit on the ortho-to-para D_2H^+ ratio as well as the para-D_2H^+/ortho-H_2D^+ ratio from a non-local thermodynamic equilibrium 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 5 × 10^5 and 10^6 cm^(-3). Also the upper limit on the ortho-D_2H^+ 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.
|Additional Information:||© 2012 ESO. Received 16 May 2012. Accepted 28 September 2012. Published online 24 October 2012. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada and the United States under the leadership of SRON Netherlands Institute for Space Research, Groningen, The Netherlands and with major contributions from Germany, France and the US. Consortium members are: Canada: CSA, U. Waterloo; France: CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland, NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di Arcetri-INAF; The Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astronomico Nacional (IGN), Centro de Astrobiologia (CSIC-INTA). Sweden: Chalmers University of Technology – MC2, RSS & GARD; Onsala Space Observatory; Swedish National Space Board, Stockholm University – Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. We thank CNES for financial support. We thank Valentine Wakelam for providing the reduced Nahoon chemical network and for carefully checking the self-consistency of the program. We thank Laurent Loinard for kindly providing the data published in 2001. Support for this work was provided by NASA through an award issued by JPL/Caltech.|
|Subject Keywords:||astrochemistry ISM: individual objects: 16293E ISM: abundances line: identification radiative transfer|
|Official Citation:||Upper limit for the D2H+ ortho-to-para ratio in the prestellar core 16293E (CHESS) A33 C. Vastel, P. Caselli, C. Ceccarelli, A. Bacmann, D. C. Lis, E. Caux, C. Codella, J. A. Beckwith and T. Ridley Published online: 24 October 2012 DOI: http://dx.doi.org/10.1051/0004-6361/201219616|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||16 Jan 2013 21:44|
|Last Modified:||16 Jan 2013 21:44|
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