COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 443 Konkoly Observatory Budapest 1970 July 3 THE PERIOD OF TW DRACONIS FROM 1880 TO 1970 It is long known that the period of this eclipsing binary is increasing. In 1910 Graff found the period 2.80654d (1910) In the last edition of Rocznik Astronomiczny (SAC 40, 1969) the following period is given: 2.806687d (1958) If new elements were calculated in the past 50 years, a few years later the O-C has become positive. As a part of a joint photoelectric programme of the Observatories Nurnberg (Germany) and Izmir (Turkey) a few minima of TW Dra were determined. Table 1 gives the observed time of minima and the O-C against the elements given in SAC 40. Table 1 Min (helioc) O-C (SAC 40) 2438 539.4451 + 0d009 Nurnberg, pe 671.3698 + 0.011 " " 39 979.3515 - 0,009 Izmir, " 40 080.3995 - 0.009 " " 473.352 - 0.018 Nurnberg, " The last 3 minima show negative (O-C)-values. It appears that the period of TW Dra is now becoming shorter. That is why we reconsider here the O-C diagram using all published minima. From 134 published minima I formed 14 normal minima listed in Table 2.The minima 15 to 19 are the photoelectric minima from Table 1. Table 2 Normalminima and photoelectric minima No. Min (helioc.) E n O-C(P) O-C(I-IV) 1 2414 935.225 0 2 pg 0.000d +0.005d 2 18 754.885 1361 5 pg -0.253 -0.019 3 19 543.538 1642 39 vis -0.282 0.000 I. 4 20 169.407 1865 28 vis -0.306 +0.014 5 22 810.398 2806 5 vis -0.416 +0.005 6 23 711.324 3127 6 vis -0.439 +0.002 7 24 746.958 3496 5 vis -0.476 -0.012 II. 8 26 627.422 4166 3 vis -0.499 +0.007 9 27 629.414 4523 3 pg -0.497 - 10 33 310.238 6547 8 vis -0.426 0.000 11 33 759.340 6707 13 vis -0.395 +0.002 12 34 208.438 6867 8 vis -0.369 0.000 III. 13 34 876.4683 7105 1 pe -0.332 -0.005 14 35 951.510 7488 7 vis -0.255 +0.003 15 38 539.4451 8410 1 pe -0.093 -0.0006 16 38 671.3698 8457 1 pe -0.083 +0.0028 17 39 979.3515 8923 1 pe -0.021 -0.0006 IV. 18 40 080.3995 8959 1 pe -0.015 +0.0013 19 40 473.352 9099 1 pe 0.000 -0.003 Column 4 (_n) gives the number of single minima used for forming a normal minimum, The O-C values in column 5 were calculated with a mean period and the normal minimum 1 as E = 0, i.e. Min = 2414 935.225 + 2d8066960.E (s. Figure 1.) For the epochs I to IV linear elements were calculated using the method of least squares. Table 3 gives the corresponding elements together with the mean errors and the mean epochs. Table 3 Min = 2414 935.220 + 2d806527.E (I) E= 930 +-16 +-12 Min = 2422 810.393 + 2d806634.E (II) E=3490 +-8 +-10 Min = 2433 310.238 + 2d8068742.E (III) E=7020 +-26 +-43 Min = 2438 539.4457+ 2d8068352.E (IV) E=8750 [FIGURE 1] [FIGURE 2] The O-C values are given in column 3 of Table 2;the elements (IV) give a good representation of the observed minima from 1964-1970. Figure 2 shows the change of period; dots give the periods I to IV (Table 3), the period represented by a dot in circle at E = -2800 was calculated only from 2 minima. Crosses represent the periods published by Schneller (MVS 1, page 187; 1966) which are in very good accordance with our values. Figure 2 and Table 3 show very clearly that 1) Between E = -3000 and +1000 (1876-1907) the period of TW Dra was nearly constant. 2) Between E,= +1000 and +7500 (1908-1958) the period has considerable increased. 3) At present (E > 8000) the period of TW Dra is decreasing. E. POHL Nurnberg Observatory 85 Nurnberg, Lutzowstr. 10 Germany BD +28 838 Dans le Bulletin No. 409, j'ai publie une liste de 13 variables nouvelles, dont l'une, BD +28d838, etait signalee comme Algolide avec un seul minimum observe le j.j. 2440 267 . Trois observateurs suisses, N.N. Locher, Disthelm et Walke, n'ayant pas remarque d'eclipse, j'ai fait un fort agrandissement de la photo du minimum (x17): une legere aureole blanche autour de BD +28d838 indique peut- etre un defaut dans l'emulsion, ce qui fait que la variable est douteuse. A. BRUN 03, Le Breuil France [From IBVS 460] Corrections to Inf. Bull. No. 443 (TW Her) Elements (III) and (IV) in Table 3 should be read: Min = 2433 310.238 + 2.8068742d. E ; E = 7020 (III) +- .0026 +-.0000043 Min = 2438 539.4457 + 2.8068352d. E ; E = 8750 (IV) +- .0018 +- 0000040