COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3555 Konkoly Observatory Budapest 16 January 1991 HU ISSN 0374 - 0676 PHOTOELECTRIC LIGHTCURVE IN TWO COLOURS AND IMPROVED ELEMENTS FOR V724 AQUILAE (BAV-Mitteilung Nr. 57) V724 Aql = 798.1933 was detected by Hoffmeister as a short period variable in the range between 11.0m and 11.5m (Hoffmeister, 1934). First investigation of this variable was done by Ahnert on plates of the Sonneberg sky- survey. He classified the variable as a cepheid, communicated 11 times of maximum light with one digit accuracy and elements for maxima (Ahnert et al., 1949). In the course of a photoelectric survey of northern cepheids, the variable proved to be an eclipsing binary of W UMa type (Oosterhoff, 1960). He published a normal lightcurve and the elements: Min = JD 2436818.672 + 0.51752d * E. The low precision elements and the lack of further published observations made V724 Aql an interesting object for us. The variable was observed on eight nights from Aug. 1988 to July 1990 at the private observatory of F. Agerer, with an 0.35m automatic photoelectric telescope. For a description see Agerer (1988). The photometer was equipped with an uncooled EMI 9781 B PMT. Schott filters BG12 1mm + GG 385 2mm were used for B and GG 495 1mm for V. The diaphragm measured 32". BD+1d4146 (F0) served as comparison star and BD+1d4143 to check its constancy. Instrumental magnitude differences were converted to the international UBV-system. Minimum timings are calculated with the Kwee - van Woerden method. Two primary and three secondary minima were observed (Table I). As both minima are of nearly equal depth, the distinction between them is uncertain. From our observations and the normal minimum by Oosterhoff we calculated improved elements using the method of (weighted) least squares as: Min = JD 2436818.6721 + 0.51760028d * E. +-5 +-2 With these elements we reduced the photoelectric lightcurve (Fig. 1). Using the maximum timings by Ahnert, we calculated the times of the following minimum by adding P/4. The resulting O-C's seem to confirm the period found (Table I). [FIGURE 1] Figure 1 Differential B and V light and B-V color curves of V724 Aql Table 1. Observed times of minima for V729 Aql, epochs and residuals computed with respect to the ephemeris derived in this paper No. JD helioc. Weight Type Epoch (O-C) Observer Source 1 2426945.53 0 p -19075 0.08 P. Ahnert (+P/4) VSS 1.3 2 27277.53 0 p -18933.5 0.09 3 27633.53 0 p -17745.5 -0.07 9 28034.53 0 p -16971 0.05 5 28070.43 0 p -16901.5 -0.02 6 28422.43 0 p -16221.5 0.01 7 29024.73 0 p -15058 0.08 8 29102.63 0 p -14907.5 0.08 9 29158.53 0 p -14799.5 0.08 10 29923.43 0 p -13321.5 -0.03 11 30932.13 0 p -11373 0.13 12 2436818.672 10 E 0 -0.0001 P.T. Oosterhoff BAN 15.199 13 47905.415 2 E: 20453.5 0.0057 F. Agerer this paper 14 47912.3980 10 E 20467 0.0009 15 47913.4320 10 E 20469 -0.0003 16 48097.4413 10 E 21790.5 0.0002 17 48098.4744 10 E 21792.5 -0.0019 p denotes pg plate max. + P/4 to get time of next minimum (weight 0), E photoelectric min. The minimum marked ":" received reduced weight. F. AGERER D. LICHTENKNECKER + Berliner Arbeitsgemeinschaft fur veranderliche Sterne e.V. (BAV) Munsterdamm 90, D-1000 Berlin 41 References: Agerer, F.: 1988, BAV Rundbrief 37(2), 60. Ahnert, P., Hoffmeister, C., Rohlfs, E., van de Voorde, A.: 1949, Veröff. Sternw. Sonneberg, 1, Nr. 3. Hoffmeister, C.: 1934, Astron. Nachr., 251, 23. [BIBCODE 1934AN....251...19H ] Oosterhoff, P.Th.: 1960, Bull. Astron. Inst. Netherlands, 15, 199. [BIBCODE 1960BAN....15..199O ]