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Searches for HCl and HF in comets 103P/Hartley 2 and C/2009 P1 (Garradd) with the Herschel Space Observatory

Bockelée-Morvan, D. and Biver, N. and Crovisier, J. and Lis, D. C. and Hartogh, P. and Moreno, R. and de Val-Borro, M. and Blake, G. A. and Szutowicz, S. and Boissier, J. and Cernicharo, J. and Charnley, S. B. and Combi, M. and Cordiner, M. A. and de Graauw, T. and Encrenaz, P. and Jarchow, C. and Kidger, M. and Küppers, M. and Milam, S. N. and Müller, H. S. P. and Phillips, T. G. and Rengel, M. (2014) Searches for HCl and HF in comets 103P/Hartley 2 and C/2009 P1 (Garradd) with the Herschel Space Observatory. Astronomy and Astrophysics, 562 . Art. No. A5. ISSN 0004-6361.

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Context. Hydrogen chloride (HCl) and hydrogen fluoride (HF) are expected to be the main reservoirs of fluorine and chlorine over a wide range of conditions, wherever hydrogen is predominantly molecular. They are found to be strongly depleted in dense molecular clouds, suggesting freeze-out onto grains in such cold environments. We can then expect that HCl and HF were also the major carriers of Cl and F in the gas and icy phases of the outer solar nebula, and were incorporated into comets. Aims. We aimed to measure the HCI and HF abundances in cometary ices as they can provide insights on the halogen chemistry in the early solar nebula. Methods. We searched for the J(1−0) lines of HCI and HF at 626 and 1232 GHz, respectively, using the Heterodyne Instrument for the Far-Infrared (HIFI) onboard the Herschel Space Observatory. HCI was searched for in comets 103P/Hartley 2 and C/2009 P1 (Garradd), whereas observations of HF were conducted in comet C/2009 P1 (Garradd). In addition, observations of H_2O and H_2^(18)O lines were performed in C/2009 P1 (Garradd) to measure the H_2O production rate at the time of the HCI and HF observations. Three lines of CH_3OH were serendipitously observed in the HCI receiver setting. Results. HCI is not detected, whereas a marginal (3.6-σ) detection of HF is obtained. The upper limits for the HCI abundance relative to water are 0.011% and 0.022%, for comet 103P/Hartley 2 and C/2009 P1 (Garradd), respectively, showing that HCI is depleted with respect to the solar Cl/O abundance by a factor more than 6_(-3)^(+6) in 103P/Hartley 2, where the error is related to the uncertainty in the chlorine solar abundance. The marginal HF detection obtained in C/2009 P1 (Garradd) corresponds to an HF abundance relative to water of (1.8 ± 0.5) × 10^(-4), which is approximately consistent with a solar photospheric F/O abundance. The inferred water production rate in comet C/2009 P1 (Garradd) is (1.1 ± 0.3) × 10^(29) s^(-1) and (0.75 ± 0.05) × 10^(29) s^(-1) on 17 and 23 February 2012, respectively. CH_3OH abundances relative to water are 2.7 ± 0.3% and 3.4  ± 0.6%, for comets 103P/Hartley 2 and C/2009 P1 (Garradd), respectively. Conclusions. The observed depletion of HCI suggests that HCl was not the main reservoir of chlorine in the regions of the solar nebula where these comets formed. HF was possibly the main fluorine compound in the gas phase of the outer solar nebula. However, this needs to be confirmed by future measurements.

Item Type:Article
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URLURL TypeDescription Paper
Lis, D. C.0000-0002-0500-4700
Blake, G. A.0000-0003-0787-1610
Additional Information:© 2014 ESO. Article published by EDP Sciences. Received 29 October 2013. Accepted 18 December 2013. Published online 30 January 2014. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important contribution from NASA. HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada and the United States (NASA) 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; Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astronómico Nacional (IGN), Centro de Astrobiología (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. Support for this work was provided by NASA through an award issued by JPL/Caltech. M.d.V.B. acknowledges partial support from grants NSF AST-1108686 and NASA NNX12AH91H. S.S. was supported by polish MNiSW funds (181/N-HSO/2008/0).
Funding AgencyGrant Number
Ministerstwo Nauki i Szkolnictwa Wyższego (MNiSW)181/N-HSO/2008/0
Subject Keywords:comets: general, submillimeter: planetary systems, comets: individual: C/2009P1 (Garradd), comets: individual: 103P/Hartley 2
Record Number:CaltechAUTHORS:20140428-132626126
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Official Citation:Searches for HCl and HF in comets 103P/Hartley 2 and C/2009 P1 (Garradd) with the Herschel Space Observatory D. Bockelée-Morvan, N. Biver, J. Crovisier, D. C. Lis, P. Hartogh, R. Moreno, M. de Val-Borro, G. A. Blake, S. Szutowicz, J. Boissier, J. Cernicharo, S. B. Charnley, M. Combi, M. A. Cordiner, T. de Graauw, P. Encrenaz, C. Jarchow, M. Kidger, M. Küppers, S. N. Milam, H. S. P. Müller, T. G. Phillips and M. Rengel A&A 562 A5 (2014) DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:45250
Deposited By: Ruth Sustaita
Deposited On:28 Apr 2014 21:20
Last Modified:30 Aug 2017 21:39

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