J/AZh/83/265 Optical spectral variability of IRAS 20508+2011 (Klochkova+, 2006)
Detection of spectral variability of the optical component of the IR-source
IRAS 20508+2011.
Klochkova V.G., Panchuk V.E., Tavolganskaya N.S., Zhao G.
<Astron. Zh. 83, 265 (2006)>
=2006AZh....83..265K 2006AZh....83..265K
=2006ARep..50...232K 2006ARep..50...232K
ADC_Keywords: Stars, atmospheres; Spectroscopy; Abundances
Abstract:
Based on high-resolution spectra we revealed variability of the
optical spectrum of the cool star identified with the IR source
IRAS 20508+2011. Over the five years of our observations, the radial
velocity derived from photospheric absorption lines varied in the
interval Vr=15-30km/s. In the same time, the H(alpha) profile varied
from an intense bell-shaped emission line with a small absorption to
2-peaked emission with a central absorption feature below the
continuum level. At all but one epoch, the positions of the metallic
photospheric lines were systematically shifted relative to the
H(alpha) emission: Delta Vr=Vr(met)-Vr(Halpha,emis)~-23km/s. The
NaD doublet lines shown a complex profile with broad (half-width about
120km/s) emission and photospheric absorption, as well as an
interstellar component. We used model atmospheres to determine the
physical parameters and chemical composition of the star's atmosphere:
Teff=4800K, logg=1.5, Vt=4.0km/s and metallicity [Fe/H]=-0.36. We
detected overabundances of oxygen [O/Fe]=+1.79 (with the ratio
[C/O]~-0.9), and alpha-process elements, as well as a deficit of heavy
metals. The totality of the parameters suggests that the optical
component of IRAS 20508+2011 is an "O-rich" AGB star with luminosity
Mv~-3mag that is close to its evolution transition to the post-AGB
stage.
Objects:
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RA (2000) DE Designation(s)
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20 53 08.68 +20 22 37.7 IRAS 20508+2011 = TYC 1655-558-1
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 40 375 Identification of lines and their intensities
in spectrum s25309 of IRAS 20508+2011,
along with the derived elemental abundances
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Table 1: Spectral observations of IRAS 20508+2011 with the 6m SAO telescope
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Spectrum Date UT Delta_lambda, Å Spectrograph
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s25309 28.07.1999 21/50 4550-7930 PFES
s28208 04.07.2000 23/13 4300-7820 PFES
s28412 06.07.2000 23/35 4320-7825 PFES
s40402 10.08.2003 23/05 5270-6760 NES
s43223 27.08.2004 22/51 5270-6760 NES
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Table 2: Mean heliocentric radial velocities for line groups and some individual
lines derived from IRAS 20508+2011 spectra obtained on various dates.
Uncertain values are given by colon.
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RV, km/s
Spectral features -------------------------------------------------------------
28.07.99 04.07.00 06.07.00 10.08.03 27.08.04
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Absorption lines:
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metallic 15.5 29.8 27.1 20.3 29.9
H(alpha) 23.1 38.6 40.7 21.4 38.0
H(beta) 16.5 27.0 24.4
H(gamma) 27.6 23.7
Emission lines:
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H(alpha) 39.3 51.6 57.1: 43.1 27.0
I.S. NaI(D1,D2) -4.6 -5.9 -5.5 -7.7 -7.3
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 7 F7.2 0.1nm Lambda Wavelength expressed in Angstroem (Å)
10- 13 A4 --- Ion Ion name and ionisation stage
16- 20 F5.2 eV EP Excitation potential of the lower level
23- 27 F5.2 [-] loggf Oscillator strength (loggf)
30- 32 I3 0.1pm EW Equivalent width, in mÅ
35- 40 F6.2 [-] log(eps(X)) Chemical composition log(epsilon(X))
(log(epsilon(H))=12.0)
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(End) Veta Avedisova [INASAN] 26-Jan-2007