J/A+A/504/543 12C16O lines in Arcturus IR spectrum (Tsuji, 2009)
The K giant star Arcturus: the hybrid nature of its infrared spectrum.
Tsuji T.
<Astron. Astrophys. 504, 543 (2009)>
=2009A&A...504..543T 2009A&A...504..543T
ADC_Keywords: Stars, giant ; Spectra, infrared ; Abundances
Keywords: stars: atmospheres - stars: chromospheres -
stars: individual: Acturus - stars: late-type - stars: mass-loss -
line: formation
Abstract:
We investigate the infrared spectrum of Arcturus to clarify the
nature of the cool component of its atmosphere, referred to as the
CO-mosphere, and its relationship to the warm molecular envelope or
the MOLsphere in cooler M (super)giant stars.
Description:
Based on the Infrared Atlas of the Arcturus Spectrum by Hinkle,
Wallace, and Livingston (1995, Cat. J/PASP/107/1042), we measured
line-depth, full-width at half-maximum (FWHM), and equivalent width
(EW) of 12C16O lines including fundamental, first and second
overtone bands, and the results are given in table2. We used the
electronic version of the ratioed spectra in our measurement and the
tabulated results are measured raw data without any correction yet.
The resulting data are used to investigate the nature of the infrared
spectrum of Arcturus. It is found that only the weak lines
(log(W/nu)←4.75) can be analyzed consistently on the basis of the
classical line-formation theory and hence can be used to extract the
nature of the photosphere: We found logAC=7.97 (on the scale of
log AH=12.00), micro and macro turbulent velocities to be 1.87 and
3.47km/s, respectively, for the photosphere.
The nature of CO lines, however, shows abrupt change at about
log(W/nu)=-4.75: The EWs of the lines larger than this limit can no
longer be accounted for by the photospheric parameters determined from
the weaker lines. A more simple demonstration of this fact is that the
curves-of-growth of overtone as well as of fundamental CO lines show
unpredictable upturn at about log(W/nu)=-4.75. Similar unusual
behaviors of empirical curves-of-growth are found in other red giant
and supergiant stars, and it looks as if the curves-of-growth are
composite of at least two components of different origins.
We think it difficult to understand such empirical data as due to the
classical photosphere alone, and infrared spectra of cool luminous
stars including Arcturus should be hybrid in nature. Although strong
lines of the CO fundamentals show strengthening, the weaker lines show
slight weakening, and we consider a possibility that these results are
due to absorption/emission by the molecular clouds formed in the
extended atmosphere. In cooler giant and supergiant stars in which CO
lines show similar unusual behaviors as in Arcturus, the presence of
molecular clouds (referred to as MOLsphere) in the outer atmospheres
has been demonstrated by direct observations of spatial
interferometry. The data compiled in table 2 are used to examine such
a possibility in Arcturus. Since the problem is far from solved yet,
we hope that these data can be of some use in understanding the origin
of the unusual behaviors of the CO spectra.
Objects:
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RA (2000) DE Designation(s)
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14 15 39.7 +19 10 57 Arcturus = alpha Boo
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 80 267 Measured spectroscopic data of 12C16O in Arcturus
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See also:
J/PASP/107/1042 : Infrared Arcturus atlas (Hinkle+ 1995)
J/ApJS/103/235 : Arcturus IR spectral atlas (Wallace+ 1996)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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2- 3 I2 --- v' Quantum number of the upper vibrational level
5- 6 I2 --- v" Quantum number of the lower vibrational level
9- 14 A6 --- Trans Identification of the rotational transition
17- 24 F8.3 cm-1 nu Wave number of the line
27- 32 F6.3 [-] loggf Logarithm of the gf-value
36- 44 F9.3 cm-1 LEP Lower excitation potential
47- 52 F6.3 [-] log(W/nu) Logarithm of the equivalent width to
wavenumber ratio (1)
56- 60 F5.3 [-] Depth Line depth normalized by the continuum
64- 68 F5.3 cm-1 FWHM Full-width at half-maximum
71- 76 F6.3 [-] lGam log(Γ), logarithm of the line
intensity integral (2)
80 I1 --- Ref [1/7] Identification of spectrum (in Table 1)
from which data are measured (3)
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Note (1): Where the equivalent width W is in unit of cm-1.
Note (2): The line intensity integral Γ is defined by eq. 2 in an
Appendix of Tsuji, 1991A&A...245..203T 1991A&A...245..203T, and used to evaluate
log(W/nu)wk=loggf+logΓ, as in Sect.4.1 (eq. 1) of this paper.
Note (3): Table 1: Observed data from the Arcturus IR Atlas
(Hinkle et al., 1995, Cat. J/PASP/107/1042)
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Ref Freq.Band Res Obs.Date Shift
cm-1 cm-1 km/s
------------------------------------------------------------------
1 1867-1965 0.02 1994/Jan/09 -30.52
2 1965-2021 0.02 1994/Jan/21 -30.52
3 2021-2098 0.02 1994/Jan/07 -31.66
4 2119-2189 0.02 1994/Jan/07 -31.39
5 2021-2098 0.02 1993/Jun/07 14.63
6 2119-2189 0.02 1993/Jun/07 14.90
7 4000-6675 0.04 1993/Jun/05 14.33
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Acknowledgements:
Takashi Tsuji, ttsuji(at)ioa.s.u-tokyo.ac.jp
(End) Patricia Vannier [CDS] 02-Jun-2009