12C16O lines in Acturus IR spectru

Details 12C16O lines in Acturus IR spectru 12C16O lines in Acturus IR spectru

Jun 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009ycat..35040543t&link_type=abstract

VizieR On-line Data Catalog: J/A+A/504/543. Originally published in: 2009A&A...504..543T

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Stars: Giant, Spectra: Infrared, Abundances

Scientific paper

Based on the Infrared Atlas of the Arcturus Spectrum by Hinkle, Wallace, and Livingston (1995, Cat. ), 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.
(1 data file).

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