COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3048 Konkoly Observatory Budapest 14 July 1987 HU ISSN 0374-0676 PX Cep: A NEW LARGE AMPLITUDE ECLIPSING BINARY PX Cep (=GR 31) was discovered as an eclipsing binary by Romano (1958). Later Romano (1962) published a list of times corresponding to a brightness fainter than normal on photographic plates. The star was named as PX Cep (Kholopov et al., 1978). The fourth edition of the General Catalogue of Variable Stars (Khopolov et al., 1985) refers only to one time of minimum from Romano's list. Visual observations made by the author from 1983 to 1985 confirmed the eclipsing nature of PX Cep and provided a first preliminary ephemeris for this large amplitude (visually about 2.7 magnitude) EA star. During 5 nights in 1985 and 4 nights in 1986, PX Cep was measured photoelectrically, jointly with other stars from GEOS and Hipparcos programmes. Results on one of these stars (NSV 12040) were already published by the author (1986). The measures were made with a cooled photometer equipped with filters of the Geneva photometric system, attached to the Jungfraujoch Observatory's 76 cm telescope. 24 BV measurements of PX Cep were obtained (see Table I) by the GEOS members H. Boithias, M. Dumont, E. Joffrin, P. Louis, P. Rousselot and the author. Reductions of the observations were made using the method described by Dumont (1983). Transformation of the B-V values from Geneva system into Johnson and Morgan's system was made using Meylan and Hauck formulae (1981). A photoelectric time of minimum in 1985 along with a descending branch recorded in 1986, enables us to confirm the first visual ephemeris. Also using 7 visual times of minimum and Romano's photographic one, I obtained, by means of a leastsquares procedure, more accurate light-elements for PX Cep: Min I. = Hel. J.D. 2446270.440 + 3.126993d*E +/- 6 +/- 6 V and B-V light curves are constructed using the ephemeris above (see Fig.1). Only the measures between phases 0.8 - 1.2 are plotted. [FIGURE 1] Figure 1: V and B-V light curves of PX Cep, between phases 0.8-1.2 according to the ephemeris of this paper. Table I: V and B-V measures of PX Cep with phase according to the ephemeris of this paper. hel.J.D 24 46000+ V B-V phi 259.4812 12.31 0.32 0.495 260.5361 12.24 0.33 0.833 264.5751 12.24 0.36 0.124 270.3670 13.52 -- 0.976 .3815 13.82 0.38 0.981 .3913 14.02 0.54 0.984 .4010 14.29 0.59 0.987 .4093 14.33 0.70 0.990 .4288 14.64 0.95 0.996 .4378 14.60 0.91 0.999 .4656 14.18 0.81 0.008 .4885 13.77 0.54 0.015 .5142 13.24 0.47 0.024 .5378 12.92 0.38 0.031 .5670 12.56 0.37 0.040 271.5850 12.28 0.34 0.366 642.4179 12.77 0.32 0.957 .4471 13.08 0.37 0.966 .4672 13.50 0.38 0.973 .5005 14.15 0.62 0.983 .5318 14.63 0.97 0.993 .5561 14.63 0.79 0.001 645.5728 13.05 0.39 0.966 648.5841 12.23 0.32 0.929 655.5864 12.19 0.33 0.168 The star varies from 12.25 to 14.65 in V-light. The B-amplitude is 3.0 magnitude. From an inspection of the light curve, I estimate: D = 8 hours and d <= 0.5 hours. No secondary minimum could surely be detected, because the photoelectric measures are very scanty outside primary eclipse and visual estimates do not show variation greater than 0.2 magnitude around phase 0.5. The 2.4 V amplitude of the light variation and the B-V curve suggest a system composed of a main sequence A star with a giant K star. The limb- darkening effect is also visible. These parameters are somewhat inaccurate due to the paucity of measurements all along the period and due to the low signal/noise ratio during primary eclipse. Further investigations will be published in a future GEOS Circular on Eclipsing Binaries. R. BONINSEGNA Groupe Europeen d'Observation Stellaire (GEOS) 12, Rue Bezout F-75014 Paris References: Boninsegna R., 1986, Inf. Bull. on Var. Stars, No. 2966 Dumont M., 1983, GEOS Circular on RR Lyr type variables, 7 Kholopov P.N., Kukarkina N.P., Perova N.B, 1978, Inf. Bull. Var. Stars, No. 1414 Kholopov P.N., Samus N.N., Frolov M.S., Goranskij V.P., Gorynya N.A., Kireeva N.N., Kukarkina N.P., Kurochkin N.E., Medvedeva G.I., Perova N.B., Shugarov S. Yu., 1985, 4th Edition of the General Catalogue of Variable Stars ("Nauka", Moscow) Meylan G., Hauck B., 1981, Astron. Astrophys Suppl. Ser., 46, 281 [BIBCODE 1981A&AS...46..281M ] Romano G., 1958, Coelum, 26, 163 Romano G., 1962, Padova Publ. 125, 15