Detection of interstellar NH towards zeta Ophiuchi by means of ultra-high-resolution spectroscopy
Abstract
We have obtained an ultra-high-resolution (0.38 km s^-1 FWHM) spectrum of the R_1(0) (3358.053 Angstroms) line of interstellar NH towards zeta Oph. These observations comprise the first detection of NH towards zeta Oph, and the third reported detection of this molecule by absorption-line spectroscopy towards any star. The equivalent width (036+/-0.05 mAngstroms) corresponds to a column density of 808+/-1.2x10^11 cm^-2. This is more than an order of magnitude higher than that expected on the basis of equilibrium gas-phase models, but is consistent with models incorporating grain-surface chemistry. The line profile is fully resolved, and has an intrinsic velocity dispersion characterized by b=1.15+/-0.12 km s^-1. This is sufficiently narrow to exclude the possibility of hot NH formation through the endothermic reaction N+H_2-->NH+H. There is evidence that the NH line is split into two velocity components (separation 1.26+/-0.17 km s^-1), with relative strengths mirroring those of the two CN components towards this star. We argue that this correlation also supports the case for grain surface reactions dominating the nitrogen chemistry of diffuse molecular clouds.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- November 1997
- DOI:
- 10.1093/mnras/291.3.L53
- Bibcode:
- 1997MNRAS.291L..53C
- Keywords:
-
- Interstellar Matter;
- Astronomical Spectroscopy;
- Spectral Line Width;
- Molecular Clouds;
- Nitrogen Compounds;
- Interstellar Chemistry;
- Absorption Spectra;
- High Resolution;
- Stellar Models;
- Exothermic Reactions;
- Astrophysics;
- STARS: INDIVIDUAL: ZETA OPH;
- ISM: MOLECULES