Universität zu Köln

Wong, K. T., Menten, K. M., Kaminski, T., Wyrowski, F., Lacy, J. H. and Greathouse, T. K. (2018). Circumstellar ammonia in oxygen-rich evolved stars. Astron. Astrophys., 612. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

Full text not available from this repository.

Abstract

Context. The circumstellar ammonia (NH3) chemistry in evolved stars is poorly understood. Previous observations and modelling showed that NH3 abundance in oxygen-rich stars is several orders of magnitude above that predicted by equilibrium chemistry.& para;& para;Aims. We would like to characterise the spatial distribution and excitation of NH3 in the oxygen-rich circumstellar envelopes (CSEs) of four diverse targets: IK Tau, VY CMa, OH 231.8+4.2, and IRC +10420.& para;& para;Methods. We observed NH3 emission from the ground state in the inversion transitions near 1.3 cm with the Very Large Array (VLA) and submillimetre rotational transitions with the Heterodyne Instrument for the Far-Infrared (HIFI) aboard Herschel Space Observatory from all four targets. For IK Tau and VY CMa, we observed NH3 rovibrational absorption lines in the v(2) band near 10.5 pm with the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). We also attempted to search for the rotational transition within the excited vibrational state (v(2) = 1) near 2 mm with the IRAM 30m Telescope. Non-LTE radiative transfer modelling, including radiative pumping to the vibrational state, was carried out to derive the radial distribution of NH3 in the CSEs of these targets.& para;& para;Results. We detected NH3 inversion and rotational emission in all four targets. IK Tau and VY CMa show blueshifted absorption in the rovibrational spectra. We did not detect vibrationally excited rotational transition from IK Tau. Spatially resolved VLA images of IK Tau and IRC +10420 show clumpy emission structures; unresolved images of VY CMa and OH 231.8+4.2 indicate that the spatial-kinematic distribution of NH 3 is similar to that of assorted molecules, such as SO and SO2, that exhibit localised and clumpy emission. Our modelling shows that the NH3 abundance relative to molecular hydrogen is generally of the order of 10(-7), which is a few times lower than previous estimates that were made without considering radiative pumping and is at least ten times higher than that in the carbon-rich CSE of IRC +10216. NH3 in OH 231.8+4.2 and IRC +10420 is found to emit in gas denser than the ambient medium. Incidentally, we also derived a new period of IK Tau from its V-band light curve.& para;& para;Conclusions. NH3 is again detected in very high abundance in evolved stars, especially the oxygen-rich ones. Its emission mainly arises from localised spatial-kinematic structures that are probably denser than the ambient gas. Circumstellar shocks in the accelerated wind may contribute to the production of NH3. Future mid-infrared spectroscopy and radio imaging studies are necessary to constrain the radii and physical conditions of the formation regions of NH3.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Wong, K. T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Menten, K. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kaminski, T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Wyrowski, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Lacy, J. H. UNSPECIFIED UNSPECIFIED UNSPECIFIED Greathouse, T. K. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-189168
DOI:	10.1051/0004-6361/201731873
Journal or Publication Title:	Astron. Astrophys.
Volume:	612
Date:	2018
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 VY-CANIS-MAJORIS; VIBRATIONALLY EXCITED AMMONIA; OPACITY-SAMPLING MODELS; MASS-LOSS HISTORY; MIDINFRARED INTERFEROMETRY; MOLECULAR ABUNDANCES; HYPERFINE-STRUCTURE; SPECTRAL-LINES; HCN EMISSION; SUBMILLIMETER OBSERVATIONS Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/18916