New observations of the CP stars in the spectral regions of Li I 6708 Å and 6104 Å lines with the 6m BTA telescope N. Polosukhina 1, D. Kudryavtzev 2, N.A. Drake 3,4, Y. Lyubchik 5, A. Shavrina 5, M. Hack 6 1 Crimean Astrophysical Observatory, Ukraine 2 Special Astrophysical Observatory, Russian Academy of Sciences, Russia 3 Observatório Nacional/MCT, Rio de Janeiro, Brazil 4 Sobolev Astronomical Institute, St. Petersburg State University, Russia 5 Main Astronomical Observatory, Ukraine 6 Department of Astronomy, Trieste University, Italy

Introduction The international Cooperation Program "Lithium in Magnetic CP Stars" (see poster FP7 of Polosukhina et al. in this Symposium) has been aimed to study the behaviour of the Li I 6708 Å resonance doublet and the subordinate 6104 Å line in the spectra of CP stars. For a long time, the results of Li line observations in the CP stars were a controversial subject because of the lack of observational data. Obviously, the increase of the amount of the high resolution (R~100000, S/N~100) spectral observations and the appearance of modern methods for spectra processing, present an opportunity for a detailed study of the CP stars spectra in the vicinity of the Li I 6708 Å and 6104 Å lines, and, therefore, to get closer to the comprehension of the Li problem in CP stars.

Main objectives of the Program The Program of Li observations in CP stars which was set up on BTA has the following objectives: Test observations - search for Li I 6708 Å line in the spectra of selected CP stars Monitoring of slowly rotating roAp stars (with sharp lines) Monitoring of rapidly rotating roAp stars for the study of the Li I 6708 Å line behaviour with the rotation phase – search for CP stars with “Li spots” Identification of some faint spectral lines of REE in the region of the Li I 6708 Å line in the spectra of slowly rotating CP stars Determination of the Li abundance using the Li I 6708 Å and 6104 Å lines taking into account the magnetic field effects Determination of the Li isotopic ratio 6 Li/ 7 Li using the Li I 6708 Å line This long term program is designed to substantially increase the amount of the observational data on Li and to build a reliable database of the CP stars spectra in the regions of Li I 6708 Å and 6104 Å lines. This may lead to a better understanding of the anomaly behaviour of these lines in CP stars. Additional monitoring of γ Equ (with exposure times of min) was carried out with the purpose to search for oscillations in the spectral region of the Li I 6708 Å and Pr III Å lines and to compare them with the oscillations in other REE lines (Kochukhov, Ryabchikova, Piskunov, 2004).

First preliminary results of the observations with the 6m telescope BTA on April 8-9, 2004 Observations have been carried out in NASMYTH focus of 6 m BTA telescope with the echelle spectrometer NES (Panchuk & Klochkova 1999) in the spectral region of Å, with the signal-to-noise ratio S/N ~ For spectra reduction the software package REDUCE (Piskunov & Valenti 2002) was used. The spectra of observed stars in the regions of the Li I lines at 6104 Å and 6708 Å are shown in Figures 1a, 1b, and 1c. a) Testing observations of the stars HD 49976, HD 62140, HD (53 Cam), HD 81009, HD , and HD permitted us to add two new Ap-CP stars with Li lines, HD and HD , to the old list of “Lithium Ap-CP stars’’. As can be seen in Figure 2, the spectra of HD and HD contain the Li I 6708 Å line. In the next set of observations, we plan to carry out the monitoring of these stars in order to study a behaviour of the Li I line as a function of the rotation phase.

b) Sharp-lined CP stars have been included into the program of observation on BTA (this program is similar to Wade’s). These stars are slowly rotating and very rich in REE lines and have strong magnetic fields (~1500 – 5000 G). As a first approximation, the modelling calculations have been carried out with atmospheric parameters T eff = 7700 – 8100 K and log g = 4.2 – 4.4, taking into account Zeeman splitting of the resonance Li I 6708 Å doublet and a contribution of both 6 Li and 7 Li isotopes (Zverko et al. 2000). More recent analysis of slowly rotating stars was performed taking into account magnetic splitting for two Li I lines 6708 Å and 6104 Å and all blending lines (see poster FP14 of Shavrina et al.) For a detailed analysis of the Li line profiles and synthetic spectra calculations, precise measurements of the magnetic field for each rotation phase, as well as corrected data for REE lines in the vicinity of the Li I 6708 Å and 6104 Å lines are needed. We plan to carry out the observations of the sharp-lined stars accompanied by the magnetic field observations of the same stars according to Wade’s program. Figure 3 shows the first observations of these stars on the BTA telescope. Strong Li I 6708 Å and Pr III Å lines are clearly seen in the spectra. Further detailed study and surface modelling of the slowly rotating roAp stars with the strong non- variable Li I 6708 Å line (taking into account the blending by the REE lines, magnetic field structure and Li stratification in the star atmosphere) will be done in the future.

c) We present here for the first time the high-time resolution observations of γ Equ in the Li I 6708 Å spectral region, obtained during two nights, on April 8 - 9, About 60 spectra with a time resolution of 1.5 – 2 min were obtained. Our preliminary results of time variations of the spectra of γ Equ are shown on Figure 4. The dispersograms for some CP stars obtained by Polosukhina et al. (1999) clearly show, that the largest amplitudes of the short time variations are to be found in the intensities of the Li I 6708 Å and Pr III Å lines. We thank Drs. I. Romanyuk, V. Panchuk, and V. Klochkova for support of our observational project. References Kochukhov, O, Ryabchikova, T., Piskunov, N. 2004, A&A, 415, L13 Panchuk, V., Klochkova, V. et al. 1999, Preprint of SAO, N135 Piskunov, N.E., Valenti, J.A. 2002, A&A, 385, 1095 Polosukhina, N., Khalak V., Shavrina, A., North, P. 1999, Astron. Letters, 25, No.9, 608. Zverko, J., Ziznovski, J., Polosukhina, N., North P. 2000, IAU JD 5, 35

HD HD Cam HD Figure 1a. Spectra of HD 62140, HD and HD in the spectral regions of Li I 6104 Å and 6708 Å lines.

Figure 1b. Spectra of HD , HD , and HD in the spectral regions of Li I 6104 Å and 6708 Å lines. HD Lib HD HD

HD Aql HD ί Peg HD Figure 1c. Spectra of HD , HD and HD in the spectral regions of Li I 6104 Å and 6708 Å lines.

Testing observations Figure 2. Spectra of the rapidly rotating CP stars in the spectral regions of Li I 6104 Å and 6708 Å lines.

Figure 3. Spectra of the slowly rotating CP stars in the spectral regions of Li I 6104 Å and 6708 Å lines. Sharp-line CP stars

Figure 4. The dispersogram for γ Equ in the Li I 6708 Å line spectral region. The noticeable variability of the Li I line is evident. γ Equ