COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2171 Konkoly Observatory Budapest 1982 June 25 HU ISSN 0374-0676 VARIABLE STARS IN THE GLOBULAR CLUSTER MESSIER 28 (NGC 6626) The investigation of variables in this cluster (C1821-249) has continued at the David Dunlap Observatory since the paper by Sawyer (1949, A.J. 54, 193) and during the past decade in collaboration with researchers at the University of Western Ontario. Otherwise the variables in this cluster have received little attention except in the work of Dr. Dorrit Hoffleit in the field, summarized in IBVS 660, 1972 and some recent work by Dr. T. Lloyd Evans (1980, private communication). Because of the cluster's southern declination, observations from our latitudes have proved somewhat inconclusive in determination of periods, and we await further plates from the University of Toronto 0.6 m telescope at Las Campanas, Chile. About six new or suspected cluster variables have been found by Vicki Watt at the DDO as well as five new long period field variables. Two additional new variables have been found by the authors of this paper. Accordingly it seems useful now to upgrade the list of variables in this cluster in the Third Catalogue of Sawyer Hogg in 1973 (Pub. D.D.O. 3, 6). The new list is given in Table I, but does not include the new field variables. Periods are based on magnitude measures by the two of us as well as those of Roslyn Moorhead of the University of Western Ontario. At the time of writing we have periods for 10 RR Lyrae stars and for V 4 the known W Vir type. In addition, a new variable, V 21, appears to have a long W Vir period of about 29 days and V 17 seems to be RV Tau type. Four variables are red and irregular. V 7 is not visible on most of our plates and is probably a field variable. The full paper, with observations and light curves of the variables, will be completed in 1983. The standard sequence used for our measures may be revised from comparison with the work of G. Alcaino (1981, Astron. Astrophys.Suppl. 44, 191). Our sequences are in general agreement down to the 15th magnitude but then begin to diverge. Therefore in Table 2 the magnitudes listed for the RR Lyrae stars, especially at minimum, are probably too bright. Table I Variable Stars in Messier 28 No x" y" Max Min Epoch Period Remarks 1 +174.0 + 88.5 15.25 16.1 42590.853 0.491753 2 - 47.3 + 63.1 14.3 14.9 irr, red 3 - 32.9 +111.0 14.5 15.2 irr, red 4 - 34.5 + 33.6 13.7 14.7 44371.894 13.457 5 - 44.8 + 16.4 14.8 15.8 36040.674 0.644360 6 + 34.1 + 50.4 14.3 15.1 irr, red 7 +172.2 +102.7 14.8 17.0 f 8 +227.3 -222.3 15.1 16.2 44428.860 0.565995 9 -158.6 -252.4 14.75 15.7 35696.652 0.661544 10 + 96 - 79 14.0 14.7 irr, red 11 - 14 + 35 15.1 16.3 44429.835 0.542782 12 +148 - 49 15.0 16.1 35335.633 0.578242 13 - 92 - 24 15.5 15.9 42225.798 0.33599 14 -131 -100 15.6 16.2 42589.850 0.418274 15 -472 -186 15.5 16.6 42229.732 0.448331 16 +432 -372 15.8 16.5 RR 17 + 42 - 68 12.9 14.5 RV Tau 18^* + 55 + 20 15.3 16.4 new var, Watt, RR 19 + 66 + 15 15.3 15.9 new var, AW, RRc 20 + 7 + 29 14.6 15.7 new var, Watt 21 + 7 + 11 14.1 15.8 44429.835 27.6 or 29.9 new var, Watt 22 + 6 + 2 15.2 16.4 44432.666 0.498828 new var, HSH 23 + 26 - 53 15.5 16.1 new var, Watt, RRc 24 -452 +109 15.7 16.1 new var, Watt, RRc * V18 in 3rd Catalogue is same as V12. AMELIA WEHLAU HELEN SAWYER HOGG Department of Astronomy David Dunlap Observatory University of Western Ontario Richmond Hill,Ontario, Canada London, Canada, N6A 3K7 L4C 4Y6