Spectral observations using a BTA telescope of chemically peculiar stars in the spectral region near the Li I (6708 Å) resonance doublet

Abstract

New spectral observations of chemically peculiar (CP) magnetic stars were obtained using an NES echelle spectrometer with a BTA telescope in the Special Astrophysical Observatory (Russian Academy of Sciences). Several stars were shown to have anomalous Li abundances. Testing and monitoring the stars with Doppler shifts Vsini > 10 km/s indicated that the lithium 6708 A line was variable in the spectra of some roaAP-CP stars. To distinguish variable features in the spectra, the dispersogram technique was used. The most peculiar among the stars studied is HD 12098. The strong and variable lithium 6708 A line was detected in the spectrum of this star. The star has been shown to have greatly different lithium abundances in two rotation phases corresponding to opposite surface areas. As mentioned earlier, a similar behavior of the Li blend was found in the spectra of HD 83368 and HD 60435 which have lithium spots on their surface. Spectral observations of slowly rotating CP stars with the Doppler shifts Vsini < 10 km/s revealed the strong and nonvariable lithium 6708 A line in the spectra of these stars. Quantitative spectral analysis using the Li I 6708 A resonance doublet and the Li I 6103 A line shows the lithium abundance, as determined by the 6103 A line, to be somewhat greater than that determined by the 6708 A line. A higher ratio of 6Li/7Li amounting to ∼0.3–0.5 was found in these stars. 6Li production is assumed to be due to spallation reactions on the surface of magnetic CP stars; this isotope ratio remained in strong magnetic fields.