J/A+A/606/A67 Circumstellar envelopes CO photodissociation (Groenewegen, 2017)
The photodissociation of CO in circumstellar envelopes.
Groenewegen M.A.T
<Astron. Astrophys. 606, A67 (2017)>
=2017A&A...606A..67G 2017A&A...606A..67G (SIMBAD/NED BibCode)
ADC_Keywords: Radio lines ; Stars, late-type ; Mass loss
Keywords: astrochemistry - stars: AGB and post-AGB - stars: winds, outflows -
radio lines: stars
Abstract:
Carbon monoxide is the most abundant molecule after H2 and is
important for chemistry in circumstellar envelopes around late-type
stars. The size of the envelope is important when modelling low-J
transition lines and deriving mass-loss rates from such lines. Now
that ALMA is coming to full power the extent of the CO emitting region
can be measured directly for nearby asymptotic giant branch (AGB)
stars. In parallel, it has become obvious in the past few years that
the strength of the interstellar radiation field (ISRF) can have a
significant impact on the interpretation of the emission lines. In
this paper an update and extension of the classical Mamon et al.
(1988ApJ...328..797M 1988ApJ...328..797M) paper is presented; these authors provided the
CO abundance profile, described by two parameters, as a function of
mass-loss rate and expansion velocity. Following recent work an
improved numerical method and updated H2 and CO shielding functions
are used and a larger grid is calculated that covers more parameter
space, including the strength of the ISRF. The effect of changing the
photodissociation radius on the low-J CO line intensities is
illustrated in two cases.
Description:
The results of extensive CO photodissociation calculations are
presented. The CO profile is described by the radius at which the
abundance has dropped to half its initial value (R1/2) and a shape
parameter (alpha).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 50 20262 CO photodissociation parameters
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 E8.3 Msun/yr dM/dt Mass-loss rate
10- 13 F4.1 km/s V Gas expansion velocity
15- 22 E8.3 --- fCO CO abundance relative to H2
24- 29 F6.2 --- chi Strength of the radiation field
31- 35 F5.1 K Tex Excitation temperature
37- 44 F8.2 10+15cm R1/2 Half radius
46- 50 F5.2 --- alpha ?=- Shape parameter of the CO profile
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Acknowledgements:
Martin Groenewegen, martin.groenewegen(at)oma.be
(End) Martin Groenewegen [Belgium], Patricia Vannier [CDS] 12-Oct-2017