Volume 589, May 2016
|Number of page(s)||11|
|Section||Planets and planetary systems|
|Published online||15 April 2016|
1 LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
2 Stockholm Observatory, AlbaNova University Center, 106 91 Stockholm, Sweden
3 LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, 75014 Paris, France
4 IRAM, 300, rue de la Piscine, 38406 Saint-Martin-d’Hères, France
5 IRAM, Avd. Divina Pastora, 7, 18012 Granada, Spain
6 NASA Goddard Space Flight Center, Astrochemistry Laboratory, Code 691.0, Greenbelt, MD 20771, USA
7 Onsala Space Observatory, Chalmers University of Technology, 439 92 ONSALA, Sweden
8 OHB Sweden, PO Box 1269, 164 29 Kista, Sweden
9 Omnisys Instruments, August Barks Gata 6B, 421 32 Västra Frölunda, Sweden
10 Dept. of Radio and Space Science, Chalmers Technical University, 41258 Gothenburg, Sweden
Received: 24 December 2015
Accepted: 4 March 2016
The apparition of bright comets C/2012 F6 (Lemmon) and C/2014 Q2 (Lovejoy) in March-April 2013 and January 2015, combined with the improved observational capabilities of submillimeter facilities, offered an opportunity to carry out sensitive compositional and isotopic studies of the volatiles in their coma. We observed comet Lovejoy with the IRAM 30 m telescope between 13 and 26 January 2015, and with the Odin submillimeter space observatory on 29 January–3 February 2015. We detected 22 molecules and several isotopologues. The H216O and H218O production rates measured with Odin follow a periodic pattern with a period of 0.94 days and an amplitude of ~25%. The inferred isotope ratios in comet Lovejoy are 16O/18O = 499 ± 24 and D/H = 1.4 ± 0.4 × 10-4 in water, 32S/34S = 24.7 ± 3.5 in CS, all compatible with terrestrial values. The ratio 12C/13C = 109 ± 14 in HCN is marginally higher than terrestrial and 14N/15N = 145 ± 12 in HCN is half the Earth ratio. Several upper limits for D/H or 12C/13C in other molecules are reported. From our observation of HDO in comet C/2014 Q2 (Lovejoy), we report the first D/H ratio in an Oort Cloud comet that is not larger than the terrestrial value. On the other hand, the observation of the same HDO line in the other Oort-cloud comet, C/2012 F6 (Lemmon), suggests a D/H value four times higher. Given the previous measurements of D/H in cometary water, this illustrates that a diversity in the D/H ratio and in the chemical composition, is present even within the same dynamical group of comets, suggesting that current dynamical groups contain comets formed at very different places or times in the early solar system.
Key words: radio lines: planetary systems / submillimeter: planetary systems / comets: individual: C/2012 F6 (Lemmon) / comets: individual: C/2014 Q2 (Lovejoy) / comets: general
Based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).
Odin is a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and the Centre National d’Études Spatiales (CNES, France). The Swedish Space Corporation is the prime contractor, also responsible for Odin operations.
The spectra dataset is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A78
© ESO, 2016
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