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| Paper: |
Probing NH3 Formation in Oxygen-rich Circumstellar
Envelopes |
| Volume: |
497, Why Galaxies Care about AGB Stars III: A Closer Look in Space and Time |
| Page: |
141 |
| Authors: |
Wong, K.; Menten, K. M.; Kamiński, T.; Wyrowski, F. |
| Abstract: |
The chemistry of ammonia (NH3) in the circumstellar envelopes (CSEs)
of AGB stars and red supergiants is poorly understood. Thermodynamic
equilibrium (TE) chemistry predicts an abundance of ≲10-8,
orders of magnitudes below values reported from observations
(∼10–7–10–6). To date, there is no consistent model
explaining the origin of such high abundances. To better understand
the physical conditions necessary for the formation of NH3, we
analysed the NH3 rotational and inversion lines observed in the
spectrum of IK Tauri. The strength of the rotational lines clearly
confirms the high abundances as compared to the TE predictions. From
1D radiative transfer modelling including infrared pumping via
vibrational bands, we infer a total NH3 abundance of 7.5×
10–7, along with an ortho-to-para ratio (OPR) of ≤ 1.5 : 1,
slightly above the statistical equilibrium value of 1. We discuss
these preliminary results and the possible origin of NH3 in
oxygen-rich CSEs. |
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