Universität zu Köln

Csengeri, T., Wyrowski, F., Menten, K. M., Wiesemeyer, H., Guesten, R., Stutzki, J., Heyminck, S. and Okada, Y. (2022). SOFIA/GREAT observations of OD and OH rotational lines towards high-mass star forming regions. Astron. Astrophys., 658. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. Only recently, OD, the deuterated isotopolog of hydroxyl, OH, has become accessible in the interstellar medium; spectral lines from both species have been observed in the supra-Terahertz and far infrared regime. Studying variations of the OD/OH abundance amongst different types of sources can deliver key information on the formation of water, H2O. Aims. With observations of rotational lines of OD and OH towards 13 Galactic high-mass star forming regions, we aim to constrain the OD abundance and infer the deuterium fractionation of OH in their molecular envelopes. For the best studied source in our sample, G34.26+0.15, we were able to perform detailed radiative transfer modelling to investigate the OD abundance profile in its inner envelope. Methods. We used the Stratospheric Observatory for Infrared Astronomy (SOFIA) to observe the (2)pi(3/2) J = 5/2-3/2 ground-state transition of OD at 1.3 THz (215 mu m) and the rotationally excited OH line at 1.84 THz (163 mu m). We also used published high-spectral-resolution SOFIA data of the OH ground-state transition at 2.51 THz (119.3 mu m). Results. Absorption from the (2)pi(3/2) OD J = 5/2-3/2 ground-state transition is prevalent in the dense clumps surrounding active sites of high-mass star formation. Our modelling suggests that part of the absorption arises from the denser inner parts, while the bulk of it as seen with SOFIA originates in the outer, cold layers of the envelope for which our constraints on the molecular abundance suggest a strong enhancement in deuterium fractionation. We find a weak negative correlation between the OD abundance and the bolometric luminosity to mass ratio, an evolutionary indicator, suggesting a slow decrease of OD abundance with time. A comparison with HDO shows a similarly high deuterium fractionation for the two species in the cold envelopes, which is of the order of 0.48% for the best studied source, G34.26+0.15. Conclusions. Our results are consistent with chemical models that favour rapid exchange reactions to form OD in the dense cold gas. Constraints on the OD/OH ratio in the inner envelope could further elucidate the water and oxygen chemistry near young high-mass stars.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Csengeri, T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Wyrowski, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Menten, K. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Wiesemeyer, H. UNSPECIFIED UNSPECIFIED UNSPECIFIED Guesten, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Stutzki, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Heyminck, S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Okada, Y. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-678619
DOI:	10.1051/0004-6361/202140577
Journal or Publication Title:	Astron. Astrophys.
Volume:	658
Date:	2022
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language WATER DEUTERIUM FRACTIONATION; DISSOCIATIVE RECOMBINATION; HERSCHEL/HIFI OBSERVATIONS; EXCHANGE-REACTION; RATE COEFFICIENTS; OXYGEN CHEMISTRY; CROSS-SECTIONS; RATE CONSTANTS; OF-SIGHT; INTERSTELLAR Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/67861