COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 357 Konkoly Observatory Budapest 1969 June 27 OBSERVATIONS OF HELIUM STARS At the Prague meeting of Commission 27 (1) I pointed out the similarity in composition between the hot helium stars and the R CrB variables. The compositions of hydrogen- poor stars have been summarized by Hack (2). Furthermore, MV Sgr has a light variation like R CrB and a spectrum like the helium stars BD +10deg2179 and HD 124448 (3). These observations suggest that helium stars may vary in a similar manner to R CrB, and that they should be regularly observed. I present here photoelectric observations of HD 124448, HD 160641 and HD 168476 made with the 24-inch (61 cm.) refractor and 40-inch (1.02 m.) reflector of the Royal Observatory, Cape of Good Hope, and with the 74-inch (1.88 m.) reflector of the Radcliffe Observatory, Pretoria. The 24-inch observations were made in the course of general photometric programmes and the mean results have been published (4, 5). A single observation is estimated to have a standard deviation about +/- 0.02m. I am grateful to the Officer-in-Charge at the Cape Observatory for permission to quote the individual results. Observations with the reflectors were made in the course of a photometric programme on blue stars. The results are at present being prepared for publication. All observations were made by the author except those prior to 1963 which were made by Dr. A. J. Wesselink. I am grateful for his permission to quote these. The standard deviation of a reflector observation determined from a large number of observations is +/-0.026m, +/-0.016m and +/-0.022m at Radcliffe and +0.016m, +0.009m and +0.012m at the Cape in V, B-V and U-B respectively. The observations are given in Table I transformed to the UBV system as defined by Cousins (6). Mean values of the reflector observations are as follows, giving double weight to the 40-inch results: V B-V U-B HD 124448 9.99m -0.09m -0.80m +/-0.014 +/-0.013 +/-0.018 (s.d.) HD 160641 9.86 +0.15 -0.85 +/-0.047 +/-0.011 +/-0.011 (s.f.) HD 168476 9.30 -0.01 -0.69 +/-0.046 +/-0.010 +/-0.019 (s.d.) TABLE I Date JD V B-V U-B (U-B)_C Tel. HD 124448 1960 June 6 2437094 9.98m -0.08m -0.80m 74 1961 Mar. 7 7366 10.01 -0.11 1.17 24 Mar.11 7370 10.01 -0.10 1.17 24 Apr.24 7414 9.98 -0.08 -0.79 74 May 17 7437 10.01 -0.09 -0.81 74 May 19 7439 9.99 -0.08 1.16 24 June 6 7457 10.02 -0.12 1.16 24 1962 Apr.29 7784 9.99 -0.08 -0.83 74 1964 Mar. 7 8462 10.00 -0.10 -0.77 74 July 14 8591 10.00 -0.09 -0.82 74 1968 Mar.19 9935 10.00 -0.11 -0.80 40 Mar.24 9940 9.98 -0.10 -0.79 40 Mar.30 9946 9.98 -0.08 -0.79 40 Mar.31 9947 9.98 -0.08 -0.78 40 Apr. 2 9949 9.97 -0.08 -0.80 40 1969 Apr. 5 2440317 9.98 -0.09 -0.80 40 Apr. 7 0319 9.98 -0.08 -0.79 40 HD 160641 1964 May 19 2438535 9.86 +0.15 -0.84 74 July 14 8591 9.81 +0.15 -0.86 74 Aug. 9 8617 9.82 +0.16 -0.84 74 1968 Mar.24 9940 9.89 +0.14 -0,84 40 Mar.30 9946 9.84 +0.14 -0.85 40 Apr.10 9957 9.90 +0.16 -0.85 40 HD 168476 1960 Sep.13 2437191 9.39 -0.01 -0.66 74 Sep.18 7196 9.40 -0.02 -0.68 74 1961 Apr.21 7411 9.31 -0.02 -0.66 74 1963 July 10 8221 9.26 -0.01 1.21 24 July 19 8230 9.33 -0.02 1.19 24 July 26 8237 9.32 -0.02 1.21 24 July 29 8240 9.33 -0.01 1.23 24 July 31 8242 9.33 -0.01 1.21 24 Sep. 9 8282 9.30 +0.01 -0.67 74 Sep.23 8296 9.26 -0.01 -0.67 74 1964 May 6 8522 9.30 0.00 -0.69 74 May 19 8535 9.33 -0.01 -0.66 74 June 14 8561 9.30 -0.03 -0.68 74 July 14 8591 9.29 -0.01 -0.69 74 Aug. 9 8617 9.30 -0.01 -0.68 74 Sep. 8 8647 9.33 -0.01 -0.68 74 1968 Mar.24. 9940 9.27 -0.03 -0.69 40 Mar.30 9946 9.27 -0.01 -0.70 40 Mar.31 9947 9.26 -0.01 -0.71 40 Apr.10 9957 9.30 0.00 -0.70 40 The errors are the internal standard deviations for each star for an observation of unit weight, determined from the observations themselves. Consequently for the 40-inch observations they should be divided by 2^(1/2). These results show that no large variations have occurred during the periods of observation. While the magnitude of HD 124448 has remained constant, both HD 160641 and HD 168476 show micro-variation in magnitude but not in colour, HD 160641 is an O star (7) and HD 168476 is suspected of having an extended atmosphere (8). The observations of HD 168476 made in 1960 September were significantly different from the mean. Other stars observed on these two nights do not differ significantly from their means. HD 168476 was observed spectroscopically at the Radcliffe Observatory in 1952 and 1953 (9), and in 1960, 1961, 1963 and 1964 (10). No significant changes in magnitude have been noted. A spectroscopic observation in 1969 April also showed no change. Because of the spectroscopic observations earlier in that year, the 1960 photometric observations would not appear to show HD 168476 emerging from a R CrB type minimum. The radial velocity may be variable with a small amplitude but no period has been found. I am grateful to the Science Research Council for a grant enabling me to visit the Radcliffe and Cape Observatories in 1968 and 1969. P. W. HILL 1969 May 19 University Observatory, St. Andrews, U.K, References (1) Trans. I.A.U. 13B, 152, 1967. (2) Hack. M., in Modern Astrophysics, ed. M. Hack. Gauthier- Villars, Paris, 1967, p 163. (3) Herbig, G.H., Ap. J. 140, 1317, 1964. [BIBCODE 1964ApJ...140.1317H ] (4) Cousins, A.W.J. and R.H. Stoy, R. Obs. Bull. No. 64, 1963. (5) Cousins, A.W.J., R. Lake and R.H. Stoy, R. Obs. Bull, No. 121, 1966. (8) Cousins, A.W.J., Mean Magnitudes and Colours of Bright Stars South of 10 deg Declination, Cape Mimeogram, 1967. [BIBCODE 1967mmcb.book.....C ] (7) Bidelman, W.P., Ap. J, 116, 227, 1952. [BIBCODE 1952ApJ...116..227B ] (8) Hill, P.W., M. N. R. A. S. 129, 137, 1965. [BIBCODE 1965MNRAS.129..137H ] (9) Thackeray, A.D., M. N. R. A. S. 114, 93, 1954. [BIBCODE 1954MNRAS.114...93T ] (10) Hill, P.W., M. N. R. A. S. 127, 113, 1964. [BIBCODE 1964MNRAS.127..113H ]