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CH Cygni: TiO molecule as a probe of temperature variations in the atmosphere of the cool component
D. Kotnik-Karuza and
Received 7 July 1999 / Accepted 10 November 1999
We report our determination of from band systems of TiO in the visible spectra of the symbiotic star CH Cygni during its 1987-89 quiescent phase as well as And and 30 Her, which are taken as comparison stars. The problems usually met by attempting to perform quantitative analysis of the atmospheres of late M-type stars have been taken into account and discussed in detail. Assuming the LTE, Born-Oppenheimer approximation, constant electronic transition moment for an electronic band and neglecting the vibration-rotation interaction but thanks to the sensitivity of the method used, the vibrational temperature of the outer atmospheric layers of the cool component of CH Cygni has been determined to be changing from about to during the observed two year period. The errors of the applied method are small enough to allow the interpretation of this temperature variation as a result of intrinsic variariability of the cool component. The possible influence of the symbiotic mechanism has been excluded. The results obtained for CH Cygni fit well with the temperatures of the two comparison stars determined from the spectra on one hand and taken from the literature on the other.
Key words: stars: atmospheres stars: binaries: symbiotic stars: fundamental parameters stars: individual: CH Cyg stars: late-type
Send offprint requests to: Dr. Dubravka Kotnik-Karuza, Physics Department, Faculty of Philosophy Omladinska 14, HR-51000 Rijeka, Croatia
Online publication: March 9, 2000