Ammonia In Circumstellar Environment Of V Cyg

By Keith Cowing
Press Release
November 21, 2019
Filed under
Ammonia In Circumstellar Environment Of V Cyg
The averaged line profile of NH3 obtained from HIFI/Herschel observations. The black solid line shows the brightness for the model of ammonia in maximum phase of variability of VCyg, the black dashed line - in minimum phase of variability. The vertical arrow indicates the LSR velocity of the source[17].

The HIFI instrument on board of the Herschel Space Observatory (HSO) has been very successful in detecting molecular lines from circumstellar envelopes around evolved stars, like massive red supergiants, Asymptotic Giant Branch (AGB) and post-AGB stars, as well as planetary nebulae.

Among others, ammonia has been found in circumstellar envelopes of C-rich AGB stars in amounts that significantly exceeded theoretical predictions for C-rich stars. Few scenarios have been proposed to resolve this problem: formation of ammonia behind the shock front, photochemical processes in the inner part of the envelope partly transparent to UV background radiation due to the clumpy structure of the gas, and formation of ammonia on dust grains.

Careful analysis of observations may help to put constraints on one or another mechanism of ammonia formation. Here, we present results of the non-LTE radiative transfer modeling of ammonia transitions including a crucial process of radiative pumping via v2 = 1 vibrational band (at ∼10 μm) for V Cyg. Only ground-based ammonia transition NH3 J = 10 – 00 at 572.5 GHz has been observed by HIFI. Therefore, to determine abundance of ammonia we estimate a photodissociation radius of NH3 using chemical model of the envelope consistent with dust grain properties concluded from the spectral energy distribution.

B. Etmański, M. R. Schmidt, R. Szczerba
(Submitted on 21 Nov 2019)

Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:1911.09456 [astro-ph.SR] (or arXiv:1911.09456v1 [astro-ph.SR] for this version)
Submission history
From: Bartosz Etmański
[v1] Thu, 21 Nov 2019 13:10:45 UTC (828 KB)
Astrobiology, Astrochemistry

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