COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3761 Konkoly Observatory Budapest 25 August 1992 HU ISSN 0374 - 0676 WHAT IS RX CEPHEI? RX Cephei is classified as a probable SRD variable in the General Catalogue of Variable Stars (GCVS), with an uncertain period of about 55 days. Its spectral type is G6 II (Keenan & McNeil 1989). Because of its classification it was included in a program of observing yellow semiregular variables (e.g. Zsoldos 1990; Zsoldos & Percy 1991). RX Cep was observed in 1990-91 with the 60-cm telescope of Konkoly Observatory in Budapest. The comparison and check stars were BD+81d27 and BD+82d30, respectively. The observations are listed in Table I. Their errors are usually smaller than 0.010m in V and 0.015m in B-V. Table I Observations of RX Cep J.D. V B-V 2440000+ 8151.516 7.440 1.101 8163.415 7.438 1.095 8176.364 7.442 1.103 8202.399 7.443 1.099 8502.524 7.440 1.107 8506.460 7.452 1.100 8508.465 7.440 1.107 8534.396 7.436 1.097 8536.399 7.447 1.081 8557.348 7.452 1.075 8561.339 7.448 1.086 8562.392 7.444 l.082 8573.380 7.444 1.093 8597.303 7.449 1.097 The amplitude of the star as given in the GCVS is about 1 magnitude. The observations given in Table I do not confirm this large amplitude, in fact they do not show any variation at all. Since the GCVS amplitude is too large to dismiss it as error of visual observations, it seemed worth to gather all information on the variation of RX Cep from the literature. Table II contains the published amplitudes of the variable between 1880 and 1937. Those marked with an asterisk are not real amplitudes, but the difference between the brightest and faintest points during the whole observing run. It is interesting to note that RX Cep was found constant by Payne-Gaposchkin (1952), too. Since the amplitudes in Table II are usually visual, the values smaller than 0.3m should be considered as (at least) doubtful (e.g. in 1908-12 or 1928-32). Table II Amplitudes of RX Cep Year Amplitude Reference 1880-87 1.0* Knott (1899) 1882 0.6 Knott (1882) 1908-12 0.2* Wendell (1913) 1911-23 0.7* Jost (1933) 1915-19 0.4* Luyten (1922) 1920-23 0.4* Hassenstein (1925) 1923-32 0.5 Parenago (1938) 1928-32 0.3* Carrasco (1935) 1931 0.3* Rybka (1937) 1931 0.3 Zverev (1936) 1933-36 - de Sitter (1937) 1937 0.4 Zverev (1938) Obviously further observations are needed to determine the nature of RX Cep. If the large amplitudes are real in Table II, then RX Cep is a star deserving more attention. E. ZSOLDOS Konkoly Observatory Budapest XII, P.O.Box 67 1525 Hungary References: Carrasco, R. 1935, Las Ciencias 2, No. 2 De Sitter, A. 1937, Bull. Astron. Inst. Netherlands 8, 185 [BIBCODE 1937BAN.....8..185D ] Hassenstein, W. 1925, Potsdam Publ. No. 81 Jost, E. 1933, Astron. Nachr. 249, 165 [BIBCODE 1933AN....249..165J ] Keenan, P. C., McNeil, R.C. 1989, Astrophys. J. Suppl. 71, 245 [BIBCODE 1989ApJS...71..245K ] Knott, G. 1882, Mon. Not. Royal Astron. Sor. 42, 384 [BIBCODE 1882MNRAS..42..384K ] Knott, G. 1899, Mem. Royal Astron. Soc. 52, 1 Luyten, W. J. 1922, Leiden Ann. 13, No. 2 Parenago, P. P. 1938, Sternberg Publ. 12, Part 1 Payne-Gaposchkin, C. 1952, Harvard Ann. 118, 217 [BIBCODE 1952AnHar.118..217P ] Rybka, E. 1937, Acta Astron. 2B, 54 Wendell, O. C. 1913, Harvard Ann. 69, Part II [BIBCODE 1913AnHar..69...99W ] Zsoldos, E. 1990, Astrophys. Space Sci. 165, 111 [BIBCODE 1990Ap&SS.165..111Z ] Zsoldos, E., Percy, J.R. 1991, Astron. Astrophys. 246, 441 [BIBCODE 1991A&A...246..441Z ] Zverev, M. 1936, Sternberg Publ. 8, Part I Zverev, M. 1938, Perem. Zv. 5, 190