COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 483 Konkoly Observatory Budapest 1970 November 5 HD 72754 - A NEW Be VARIABLE STAR OF BETA LYRAE TYPE The star HD 72754 (Bp; 8h29.4m, -49d16', 1900, with note "The line Hbeta is bright. The helium lines are faint") was found on Radcliffe slit spectra to have a remarkable early B type shell + stellar spectrum with variable velocity. A request for photometry was addressed to the Royal Observatory, Cape, and observations were secured over three successive seasons concurrently with Radcliffe spectroscopy. The Cape observations (in U,B,V: with the 1.02m Elizabeth reflector) are listed in Table I, the first 11 by one of us (P.W.H.) which showed the star to be variable with small amplitude; the remainder were made by many observers on the Cape staff including J.B.A. who also organised the reductions. The observations are plotted (V, B-V, U-B) in fig.1 against phase using the reciprocal period p^-1 = .029648 days^-1 or P = 33.72 days. This period was determined from a least-squares solution for the radial velocity measures (by A.D.T.). The photometry had first suggested a period of order 17 days but the spectroscopy clearly demonstrated that there must be two minima in a period twice as great. The numerous photometric observations now available confirm the difference between the two minima based on the longer period. The deeper of the minima in V occurs at about phase .16 when the spectra show that the visible star is in superior conjunction. Although the B-V colour remains remarkably constant through the cycle, U-B does not and has a greater variation during the secondary minimum of V (inferior conjunction). The spectroscopic orbit will be published elsewhere. The spectra have not demonstrated the nature of the secondary star but a massive system is indicated and the complex phenomena are strikingly reminiscent of beta Lyr and W Crucis. It is possible that the variations in V are entirely ellipsoidal in character; but the behaviour of U-B can be qualitatively understood if the U magnitude is dominated by H recombination beyond the Balmer limit in a gaseous stream which is partly obscured during both minima and more so pith the bright star in front. [FIGURE 1] Fig. 1 Light and Colour-curve of HD 72754 (V, B-V, U-B). Phases are computed from .029648 (JD - 2,400,000). First season's observations shown with open circles. The observed variations can be summarised as follows : V - 6.84 to 7.06 (1), 6.99 (2) B - V = +0.19 U - B = -0.73 to -0.67: (1), -0.65: (2). The scatter about the mean curves must be mainly intrinsic in character, as is often found in massive close binaries. It will be of interest to look for systematic variation in period such as has been found in beta Lyr as perhaps the most significant instance of rapid stellar evolution during a few decades. Our thanks are due to Dr R.H. Stoy and Mr G.Harding for access to the Royal Observatory equipment for these observations during the three relevant seasons, and to the Cape staff for much assistance in making the observations. One of us (P.W.H.) is indebted to the Science Research Council for a travel grant. Observations of HD 72754. Heliocentric V B-V U-B Phase J.D. 2439929.323 6.89m +0.20m -0.70m .825 9930.385 6.80 +0.22 -0.72 .855 9933.408 6.90: +0.22 -0.70 .946 9934.285 6.90 +0.18 -0.71 .972 9939.346 7.03 +0.21 -0.65 .122 9940.342 7.02 +0.20 -0.66 .151 9946.280 6.86 +0.20 -0.70 .327 9947.305 6.81 +0.20 -0.70 .357 9948.281 6.80 +0.20 -0.69 .387 9949.299 8.82 +0.21 -0.70 .417 9958.264 7.01 +0.19 -0.66 .683 2440081.585 8.88 +0.20 -0.72 .304 0187.587 6.84 +0.19 -0.70 .482 0190.574 8.87 +0.19 -0.70 .570 0196.567 7.04 +0.19 -0.63 .748 0200.588 6.8? +0.18 -0.71 .867 0210.586 7.10 +0.20 -0.68 .163 0221.525 8.87 +0.19 -0.71 .488 0224.425 6.94 +0.19 -0.68 .574 0228.516 6.97 +0.18 -0.68 .695 0235.426 6.90 +0.20 -0.73 .900 0252.432 o.84 +0.19 -0.71 .404 0257.430 6.88 +0.19 -0.68 .552 0258.435 6.91 +0.18 -0.68 .582 0267.451 6.85 +0.21 -0.71 .849 0270.481 6.81 +0.20 -0.73 .939 0274.419 6.95 +0.19 -0.68 .056 0278.403 7.04 +0.18 -0.68 .174 0284.339 6.88 +0.19 -0.70 .350 0285.371 6.88 +0.20 -0.69 .381 0288.321 6.88 +0.20 -0.70 .468 0291.417 6.86: +0.19 -0.68 .560 0302.330 6.86 +0.19 -0.72 .883 0306.313 6.94 +0.18 -0.72 .002 0311.300 7.02 +0.19 -0.71 .149 0312.342 7.05 +0.19 -0.69 .180 0336.286 6.93 +0.19 -0.72 .890 0343.246 6.95 +0.19 -0.70 .097 0344.273 6.97 +0.18 -0.69 .127 0361.248 7.00 +0.18 -0.63 .630 0362.233 6.96 +0.19 -0.63 .659 0365.218 6.97 +0.18 -0.65 .748 0613.424 7.05 +0.18 -0.67 .107 0616.502 6.96 +0.19 -0.67 .198 Heliocentric V B-V U-B phase J.D. 2440624.425 6.87m +0.18m -0.72m .433 0643.451 6.88 +0.18 -0.71 .997 0647.426 7.03 +0.18 -0.68 .115 0665.345 7.01 +0.18 -0.66 .646 0670.326 6.84 +0.18 -0.69 .794 0679.349 6.89 +0.19 -0.68 .061 0684.365 6.95 +0.19 -0.08 .210 0698.243 6.95 +0.19 -0.66 .622 0705.269 6.86 +0.19 -0.70 .830 1970 October A.D. THACKERAY (Radcliffe Observatory), J. B. ALEXANDER (Royal Observatory, Cape), and P.W. HILL (University Observatory, St Andrews).