COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2422 Konkoly Observatory Budapest 24 October 1983 HU ISSN 0374 - 0676 FT LUPI: STUDY OF THE PERIOD AND LIGHT CURVE FT Lupi (S 5001= CoD -42d9876 (9.6) = CPD -42d6864 (9.3) = HD 132316 (F5) = BV 851= CSV 2228) is a close eclipsing binary of the southern hemisphere. It was discovered photographically and classified as an Algol system by Hoffmeister (Erg.A.N., 12,1,1949). Subsequently Hoffmeister (Veroff. Sonn. 6,3,132,1965) published a photographic light curve and 27 times of minima, eleven of which are visual determinations; he determined a period P = 0.4700903d days and reclassified FT Lupi as a beta Lyr system with amplitudes A1 = 0.8 and A2 = 0.3 mag and suggested that irregularities in the light curve were present. Strohmeier (Mitt. Verand. Sterne 3,1,1965) published an ephemeris with P = 0.4700895 days and indicated that no irregularities are superposed in the light curves. Further, Strohmeier (IBVS No.184, 1967) obtained an ephemeris (P = 0.470089d) from 34 photographic minima. Bauernfeind (Veroff. Bamberg, Band VIII,81,1968) gave 120 times of photographic minima; from these data he obtained a systematic trend of the residuals (O-C) in relation to the light elements given by Strohmeier in 1967. Strohmeier and Knigge (MNASSA 28, 75, 1969) catalogued S5001 (in Centaurus) as EA and quoted the ephemeris given in IBVS No. 184. It was reported in Bull.A.A.S. 3, 72, 1971 that Gleim gathered 3-colour photoelectric observation at Cerro Tololo. Mauder and Kappelmann (A.G.Mitt. 55, 72, 1982) discussed FT Lupi among other interesting contact double stars. They showed a V light curve and commented a preliminary photometric solution and absolute elements. They gave a photoelectric period P = 0.470073d +- 0.000002, as well as a period variation leading to a mass transfer of about 0.3x10^-6 M_Sun /year from the primary to the secondary component. Mauder and Kappelmann reproduced the O-C diagram of the minima given by Bauernfeind; they also plotted the minima obtained by Strohmeier (IBVS No. 184, 1967) and a minimum time found by themselves. The present study is based on 675 UBV photoelectric observations obtained by one of us (S.L.L.) along four years since 1980 with the 154 cm reflecting telescope at Bosque Alegre Station of Cordoba Observatory; 16 times of minimum light covering about 1700 cycles were derived for each colour, individual Table I Min. J.D. hel. Cycles (O-C) (O-C)' (2400000+) --------------------------------------------- II 44769.68020 -621.5 0.0021 0.0025 II 45002.83985 -125.5 0.0008 0.0010 II 45034.80671 -57.5 0.0023 0.0024 II 45060.65903 -2.5 0.0001 0.0002 II 45061.60021 -0.5 0.0011 0.0012 I 45061.83160 0.0 -0.0024 -0.0023 I 45063.71250 4.0 -0.0018 -0.0018 II 45064.88837 6.5 -0.0012 -0.0011 I 45090.50706 61.0 -0.0020 -0.0020 II 45090.74444 61.5 0.0003 0.0003 I 45116.83333 117.0 -0.0003 -0.0004 II 45117.53947 118.5 0.0006 0.0006 I 45117.77240 119.0 -0.0014 -0.0015 I 45531.44618 999.0 0.0001 -0.0008 II 45532.62285 1001.5 0.0017 0.0005 II 45533.56125 1003.5 -0.0001 -0.0009 --------------------------------------------- minima from the three light curves never differed by more than 0.0003 days; their averages are listed in Table I. A least squares linear ephemeris from these data gives: Min. I = J.D.Hel. 2445061.8340 + 0.4700820d * E (1) +-0.0003 +-0.0000007 The residuals (O-C) are listed in Table I. From these elements we computed the phases for the V-light and (B-V) colour curves shown in Figure 1. They are given differentially in relation to the comparison star HD 132201 (F0), in the sense variable minus comparison star. The light curve is precisely defined; no large scattering is observed (especially at minima) as found by Mauder and Kappelmann. The depth of primary minimum is 0.9 mag while for secondary is 0.28 mag. The maximum light following primary minimum is about 0.03 [FIGURE 1] mag higher than that following secondary one. Our observations show the secondary minimum to be flat, thus being an occultation; the duration of this total eclipse is at least 45 min. The (B-V) colour curve is almost constant, except at primary eclipse which is redder by 0.05 mag and bluer at secondary one by about 0.02 mag. Since there is a considerable number of minima published for FT Lupi during the last 80 years we included all of them in a period study. In the course of the analysis we found some trouble in identifying Bauernfeind's (1968) minima; a study of the data for different epochs and authors allowed a precise identification of all observations starting from the photoelectric data. Determination of the period for different epochs has clearly shown that it is becoming shorter; then all observations were included both in a linear and parabolic least squares ephemerides. The results are: Min. I = J.D.Hel. 2445061.880 + 0.470089d * E (2) +-0.038 +-0.000006 Min. I = J.D.Hel. 2445061.834 + 0.470083d * E - 0.114*10^-9 * E^2 (3) +-0.025 +-0.000002 +-0.029*10^-9 therefore the period is changing at a rate P = 0.0076 sec/year. The (O-C)' values of the photoelectric observations from the parabolic elements are listed in Table I. The residuals for all observations are given in Figure 2 for the ephemerides (2) and (3). It should be noted that the parabolic elements are well defined, even for photographic and visual observations. A fit to these values exactly predicts, within the errors, the period and slope of the photoelectric elements found for 1981-1983. In conclusion, we presented precise photoelectric V-light and (B-V) colour curves obtained during four years of observations. It was found that FT Lupi shows complete eclipses and that no seasonal changes of light were present. [FIGURE 2] A first detailed study of the period was made and its variation has been well established, though it is smaller by a factor of about 2 than that suggested by Mauder and Kappelmann (1982). The parabolic elements given by formula (3) should be used to predict future circumstances. Finally, we note that a periodic (O-C) light-time effect cannot be ruled out; this would be possible only for an orbital period larger than 160 years. S.L. LIPARI * and R.F. SISTERO Observatorio Astronomico and IMAF Laprida 854 - 5000 Cordoba Argentina * member of CONICET, R.A.