COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2313 Konkoly Observatory Budapest 18 April 1983 HU ISSN 0374 - 0676 RADIAL VELOCITY VARIATION OF THE Be STAR 6 Cep (HD 203467) 6 Cep (HD 203467, HR 8171, BD+64d1527, SAO 019313, MWC 367) is a bright B emission star. Long-term spectral variation was disclosed by Hubert-Delplace and Hubert (1979) and by Slettebak (1982). Kodaira (1971) analyzed the radial velocity measurements of this star and concluded that 6 Cep is a spectroscopic binary (P = 1.12215d, K = 12 km/s). These parameters place 6 Cep at the edge of the region where the RV variation can still be interpreted as a consequence of the motion in a binary system containing B-type star. Recently, several Be stars showing periods close or shorter than 1 day were studied and other interpretation than binarity was proposed: 28 CMa- Baade (1982); Lambda Eri - Bolton (1982); EM Cep - Rachkovskaya (1975), Hilditch et al. (1982); LQ And - Percy (1983), Harmanec (1983). Our analysis of the data used by Kodaira (1971) revealed that the period 1.12215d is not the only one to fit the RV measurements. Moreover, the least- squares solution led to lower value of K (6.3 km/s), see Fig. 1a. Clearly, the problem of the interpretation of 6 Cep can only be further resolved by collecting new spectroscopic and also photometric (only few available so far) observations. This communication deals with a more detailed analysis of RV variation of 6 Cep. The results are based on 80 values of RV. 30 values are from the paper by Kodaira (1971). 18 values were measured on spectrograms obtained with the coude spectrograph of the 2 m PCC telescope (Ondrejov Observatory) and 32 values were derived from the measurements on spectra taken with the coude spectrograph of the 2 m RCC telescope (National Astronomical Observatory at Rozhen, Bulgaria). The data are not homogeneous. Different dispersions, emulsions, methods of RV determination and sets of lines were used. Therefore, two files were formed. File A contains all 80 values, while in the file B only the reliable measurements were included. File B is represented by 19 RV measured by Kodaira (1971) on Mt. Wilson plates and by 32 RV measured on Rozhen spectra. The second file is reasonably homogeneous. Kodaira (1971) determined the RV with the Grant machine from H lines, while the RV of the Rozhen plates were measured on tracings derived from Ondrejov five-channel microphotometer scans. Usually, the positions of 8 H lines (H8- H15) served for RV determination. [FIGURE 1] Figure 1. Radial velocity curves for 6 cep a) data used by Kodaira (1971), p=1.12215, K=6.3 km/s b) data of file A, p=2.438942d, K=7.0 km/s c) data of file B, p=0.708469, K=9.0 km/s Both files were analyzed for possible periods. The best-fit period to data of file A is 2.438942d. The least-square solution is presented in Fig. 1b (K = 7.0 km/s, f(m) = 0.875*10^-4 m_Sun). The data of file B were better fitted by the period 0.708469d. The least-square solution is shown in Fig. 1c (K=9.0 km/s, f(m) = 0.528*10^-4 m_Sun ). Both periods are interconnected but the ambiguity cannot be solved with the available data. The results can be used for testing the binarity of 6 Cep. Adopting the mass of the visible star (B2.5 Ve) m_1 = 10.4 m_Sun and inclination i= 25d (v*sini= 150 km/s), we derive the mass of the unseen component m_2= 0.5 m_Sun (file A), m_2= 0.4 m_Sun (file B). The derived values of m_2 are not in conflict with the binary interpretation of 6 Cep. But one should stress that the 0.7d period is close to the rotational period of the star. Obviously, further constraints could be placed on the model of 6 Cep if good photometric data are available. ZDRAVKA T. KRAJCEVA PAVEL KOUBSKY Department of Astronomy Astronomical Institute Bulgarian Academy of Sciences Czechoslovak Academy of Sciences 7 Nojabrja 1 Ondrejov Observatory 1000 Sofia 25165 Ondrejov Bulgaria Czechoslovakia References: Baade, D.: 1982, Astron. Astrophys., 105, 65. [BIBCODE 1982A&A...105...65B ] Bolton, C.T.: 1982, IAU Symp., No. 98 (Eds.: M. Jaschek and H.G. Groth), Reidel Publ. Co., Dordrecht, Holland, p. 181. [BIBCODE 1982IAUS...98..181B ] Harmanec, P.: 1983, Bull. Astron. Inst. Czech. (in press). [BIBCODE 1984BAICz..35..193H ] Hilditch, R.W., McLean, B.J., Reid, I.N.: 1982, Mon. Not.R.A.S., 200, 153. [BIBCODE 1982MNRAS.200.1153H ] Hubert-Delplace, A.M., Hubert, H.: 1979, An Atlas on Be Stars, Paris, Meudon Observatory. Kodaira, K.: 1971, Publ. Astr. Soc. Japan, 23, 159. [BIBCODE 1971PASJ...23..159K ] Percy, J.R.: 1983, Astron. J. (in press). [BIBCODE 1983AJ.....88..427P ] Rachkovskaya, T.M.: 1975, Izv. Krym Astrophys. Obs., 53, 168. Slettebak, A.: 1982, Astrophys. J. Suppl. Ser., 50, 55. [BIBCODE 1982ApJS...50...55S ]