Search for H-3(+) isotopologues toward CRL2136 IRS 1

Goto, Miwa; Geballe, Thomas R.; Harju, Jorma; Caselli, Paola; Sipila, Olli; Menten, Karl M. und Usuda, Tomonori (2019): Search for H-3(+) isotopologues toward CRL2136 IRS 1. In: Astronomy & Astrophysics, Bd. 632, A29

Abstract

Context. Deuterated interstellar molecules frequently have abundances relative to their main isotopologues much higher than the overall elemental D-to-H ratio in the cold dense interstellar medium. H-3(+) and its isotopologues play a key role in the deuterium fractionation;however, the abundances of these isotopologues have not been measured empirically with respect to H-3(+) to date. Aims. Our aim was to constrain the relative abundances of H2D+ and D-3(+) in the cold outer envelope of the hot core CRL 2136 IRS 1. Methods. We carried out three observations targeting H-3(+) and its isotopologues using the spectrographs CRIRES at the VLT, iSHELL at IRTF, and EXES on board SOFIA. In addition, the CO overtone band at 2.3 mu m was observed by iSHELL to characterize the gas on the line of sight. Results. The H-3(+) ion was detected toward CRL 2136 IRS 1 as in previous observations. Spectroscopy of lines of H2D+ and D-3(+) resulted in non-detections. The 3 sigma upper limits of N(H2D+)/N(H-3(+)) and N(D-3(+))=N(H-3(+)) are 0.24 and 0.13, respectively. The population diagram for CO is reproduced by two components of warm gas with the temperatures 58 and 530 K, assuming a local thermodynamic equilibrium (LTE) distribution of the rotational levels. Cold gas (<20 K) makes only a minor contribution to the CO molecular column toward CRL 2136 IRS 1. Conclusions. The critical conditions for deuterium fractionation in a dense cloud are low temperature and CO depletion. Given the revised cloud properties, it is no surprise that H-3(+) isotopologues are not detected toward CRL 2136 IRS 1. The result is consistent with our current understanding of how deuterium fractionation proceeds.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Physik
• Themengebiete: 500 Naturwissenschaften und Mathematik > 530 Physik
• ISSN: 0004-6361
• Sprache: Englisch