COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2555 Konkoly Observatory Budapest 18 July 1984 HU ISSN 0374-0676 FK OPHIUCHI = V2 (NGC 6273) The variability of FK Oph (HV 4337 = HV 9196) was first discovered by I.E. Woods (Swope, 1928). Swope found changes between 14.8m and 15.6m m(pg) exhibited by this star near the globular cluster NGC 6273 (M 19). Later the star was independently discovered by Luyten (1973, 1938), with the photographic range 13.5m - 14.5m. At first Luyten was not able to identify his star with FK Oph because of the wrong value of right ascension (by one hour) he originally determined. No information concerning the type of variability is contained in the General Catalogue of Variable Stars. Sawyer (1943) discovered four variable stars in NGC 6273, as well as two more variables in the surrounding field. Among these variables, V2 in NGC 6273 is identical with FK Oph, as we were able to find by comparison of photographs published by Sawyer and by Swope (1932). Sawyer published 12 observations (13.4m - 14.7m m(pg)) and considered the star to be a possible long-period Cepheid. The star enters the Third Catalogue of Variable Stars in Globular Clusters (Sawyer Hogg, 1973). I have made 42 eye-estimates of FK Ophiuchi on the plates obtained with the 40-cm astrograph of the Sternberg Institute Crimean Observatory. The observations are presented in Table I. The three observations marked with asterisks are based on photographs obtained at the same observatory with the 50-cm Maksutov camera. The system of B magnitudes is based on the photometric study of NGC 6273 by Harris, Racine and de Roux (1976). On our plates, the three brightest comparison stars from Sawyer's list are situated too deep in the dense unresolved part of the cluster and cannot be used. Five of Sawyer's comparison stars (d, f, g, h, k) were measured by Harris et al., as the brightest comparison star I used the star ZNG 5 (cf. Harris et al.). FK Ophiuchi belongs to CW type stars. Its elements are found to be Max = 2445133.7 + 14.138d E M - m = 0.35p. The Maksutov camera observations were not used for the period determination. The earlier observations published by Sawyer (1943) do not Table I J.D.24... B J.D.24... B J.D.24... B 37109.43 14m21 44015.45 13m76 44815.31 14m41 130.35 13.79 020.44 13.72 818.31 15.35 138.32 14.16 023.42 13.76 819.30 14.66 139.33 14.37 028.43 14.37 820.29 14.33 144.33 13.76 041.38 15.21 45087.52 14.53 145.33 13.59 406.38 15.15 134.41 13.52 40738.50 13.76 409.41 14.58 464.52 13.84 745.44 14.98 410.40 14.37 469.52 14.49 42922.48* 15.12 430.36 13.76 494.43 14.33 43700.36* 15.04 435.34 14.78 496.42 15.37 701.35* 15.04 438.36 14.33 496.45 15.44 989.52 13.59 789.36 15.24 499.41 14.25 992.52 13.79 811.32 13.76 523.38 14.49 993.45 13.79 812.31 13.64 546.32 13.67 994.55 13.81 813.31 13.79 552.3 14.78: contradict our elements, and their limited number does not give a possibility to improve the elements. The light curve is shown in Figure I. [FIGURE 1] It is worth noting that FK Oph is the star No. 509 (V = 13.40m, B-V=0.78m) in the M 19 photometric catalogue by Harris et al. (1976). Their values are compatible with possible cluster membership of this Cepheid. I am grateful to Prof. P.N. Kholopov for the possibility to use his computer program for period determination. N.N. SAMUS' Astronomical Council of the USSR Academy of Sciences 48, Pyatnitskaya Str. Moscow 109017, USSR References: Harris W.E., Racine R., de Roux J., 1976, Astrophys.J.Suppl. 31, No. 1, 13 [BIBCODE 1976ApJS...31...13H ] Luyten, W.J., 1937, Astron.Nachr. 261, 451 [BIBCODE 1937AN....261..451L ] Luyten, W.J., 1938, Minnesota Obs.Publ. II, No. 6 [BIBCODE 1938POMin...6....1L ] Sawyer, H.B., 1943 Publ. David Dunlap Obs. I, No. 14 [BIBCODE 1943PDDO....1..283S ] Sawyer Hogg, H., 1973, Publ. David Dunlap Obs. 3, No. 6. [BIBCODE 1973PDDO....3....6S ] Swope, H.H., 1928, Harvard Obs.Bull. No. 857, 1 [BIBCODE 1928BHarO.857....1S ] Swope, H.H., 1932, Harvard Obs.Bull. No. 887, 6 [BIBCODE 1932BHarO.887....6S ]