Volume 618, October 2018
|Number of page(s)||11|
|Section||Interstellar and circumstellar matter|
|Published online||03 October 2018|
Linking interstellar and cometary O2: a deep search for 16O18O in the solar-type protostar IRAS 16293–2422
INAF, Osservatorio Astrofisico di Arcetri,
Largo E. Fermi 5,
2 Leiden Observatory, Leiden University, PO Box 9531, 2300 RA Leiden, The Netherlands
3 Max-Planck-Institut für Extraterretrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
4 Centre for Star and Planet Formation, Niels Bohr Institute & Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K., Denmark
5 I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
6 Physikalisches Institut, Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
7 Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA
8 Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, Allée Geoffroy Saint-Hilaire, 33615 Pessac, France
9 Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
10 Center for Computer Sciences, University of Tsukuba, 305-8577 Tsukuba, Japan
11 Department of Space, Earth, and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
12 School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
Accepted: 31 May 2018
Recent measurements carried out at comet 67P/Churyumov–Gerasimenko (67P) with the Rosetta probe revealed that molecular oxygen, O2, is the fourth most abundant molecule in comets. Models show that O2 is likely of primordial nature, coming from the interstellar cloud from which our solar system was formed. However, gaseous O2 is an elusive molecule in the interstellar medium with only one detection towards quiescent molecular clouds, in the ρ Oph A core. We perform a deep search for molecular oxygen, through the 21−01 rotational transition at 234 GHz of its 16O18O isotopologue, towards the warm compact gas surrounding the nearby Class 0 protostar IRAS 16293–2422 B with the ALMA interferometer. We also look for the chemical daughters of O2, HO2, and H2O2. Unfortunately, the H2O2 rotational transition is dominated by ethylene oxide c-C2H4O while HO2 is not detected. The targeted 16O18O transition is surrounded by two brighter transitions at ± 1 km s−1 relative to the expected 16O18O transition frequency. After subtraction of these two transitions, residual emission at a 3σ level remains, but with a velocity offset of 0.3−0.5 km s−1 relative to the source velocity, rendering the detection “tentative”. We derive the O2 column density for two excitation temperatures Tex of 125 and 300 K, as indicated by other molecules, in order to compare the O2 abundance between IRAS 16293 and comet 67P. Assuming that 16O18O is not detected and using methanol CH3OH as a reference species, we obtain a [O2]/[CH3OH] abundance ratio lower than 2−5, depending on the assumed Tex, a three to four times lower abundance than the [O2]/[CH3OH] ratio of 5−15 found in comet 67P. Such a low O2 abundance could be explained by the lower temperature of the dense cloud precursor of IRAS 16293 with respect to the one at the origin of our solar system that prevented efficient formation of O2 in interstellar ices.
Key words: astrochemistry / molecular processes / stars: formation / ISM: abundances / ISM: molecules / ISM: individual objects: IRAS 16293–2422
© ESO 2018
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