J/A+A/314/585 NaI/KI scattering in circumstellar envelopes (Guilain+ 1996)
NaI/KI scattering observations in circumstellar envelopes: constraints on
ionization and mass-loss rates.
Guilain C., Mauron N.
<Astron. Astrophys. 314, 585 (1996)>
=1996A&A...314..585G 1996A&A...314..585G (SIMBAD/NED BibCode)
ADC_Keywords: Mass loss ; Stars, atmospheres
Keywords: stars: AGB - stars: mass loss - stars: circumstellar matter -
stars: W Hya; R Hya
Abstract:
We investigate KI or NaI fluorescent emission in circumstellar shells
to study their ionization and mass-loss rates. First-time KI
detections around the mira-type stars W Hya and R Hya are presented.
Together with the previously analysed cases of α Ori, α
Her and o Cet (Mauron and Caux 1992) and other observations, this
gives an extended sample of 10 envelopes which includes µ Ce p, CE
Tau, β Peg, ρ Per and g Her. A few non-detections are also
considered. In order to compare observed with expected values of KI
intensities, the ionization model of Glassgold and Huggins (1986) is
used, and the relevant parameters such as distance d, mass-loss rate
{dot}(M), gas temperature, fractional electron abundance xe and
stellar photoionizing rates G_⊕ _have to be known. Using data
found in the literature, we estimate these parameters in detail for
each case. The values of xe are obtained with a hypothesized simple
rule based on the circumstellar abundance of molecules and grains
which could lock electron donors, giving either xe∼3x10-4 or
∼2x10-5. The G_⊕ _values depend on the rare ultraviolet
spectrophotometric data available for red giants. The kinetic
temperature was assumed to be 30K at the probed impact parameters
robs∼0.5 to 5x1016cm. Despite real uncertainties, the predicted KI
intensities with our best estimates of the parameters are in very
reasonable agreement with observations in 8 cases in 10. The largest
discrepancy concerns the red supergiant µ Cep (M2Ia): our KI data
suggest that, similar to α Ori, CO and dust are incompletely
formed; for this object we favor {dot}(M)=5x10-6M☉/yr. The
wind of β Peg is the second case for which a larger mass-loss
and/or a larger xe than primarily believed is suggested, but
confirming observations are needed. Finally there is no indication
that K or Na might be depleted in silicate grains.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
appen.tex 84 427 LaTeX version of appendix
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Courtesy: Nicolas Mauron
(End) Patricia Bauer [CDS] 19-Sep-1996