COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2049 Konkoly Observatory Budapest 1981 December 3 HU ISSN 0374-0676 PHOTOELECTRIC MINIMA OBSERVATIONS OF THE ECLIPSING BINARY ST CARINAE The eclipsing character of the tenth photographic magnitude star ST Carinae (HD 89234, CD-59d2985, CPD-59d2007, HV 1270, A0 + F6) was discovered photographically by Pickering (1906) from Harvard patrol plates. The system was later observed photographically by Leavitt (1908) who described it as an Algol-like eclipsing binary and found a period of 0.901652d. Shapley (1915) obtained a preliminary orbital solution based on photographic data. Further photographic observations carried out by Hertzsprung (1925) confirmed the existence of a secondary minimum of about 0.06m in depth predicted by Shapley (1912). Hertzsprung obtained the following ephemeris: JD Hel Min I = 2423901.675d + 0.9016498d E (1) More recently Gaposchkin (1953) obtained new photographic minima from which he found the following revised ephemeris: JD Hel Min I = 2428915.756d + 0.9016495d E (2) So far, no photoelectric light curve of ST Car has been obtained. During the period from February 1980 to March 1981, we made 650 UBV photoelectric observations at the Bosque Alegre Station (BAS) of the National University of Cordoba (Argentina). The measurements were carried out with the BAS 154-cm telescope provided with a conventional design photometer. These data were supplemented with 100 photoelectric observations in each color, obtained during April-May 1980 with the 61-cm Lowell telescope at the Cerro Tololo Inter-American Observatory (CTIO, Chile). RCA 1P21 photomultipliers refrigerated with dry ice were used in both observatories. All the observations of ST Car were made differentially in relation to HD 89234, whose spectral type is A0. Mean atmospheric extinction coefficients were used to correct for first and second-order differential extinction. No variation in the light of the comparison star was detected. Using the bisection-of-chords method we derived a total of 17 new times of minimum light. A linear least squares solution, including the above photoelectric minima and three older photographic ones, leads to the following improved ephemeris: JD Hel Min I = 2444317.7292d + 0.90164965d E (3) +-.0004 +-.00000004 Table I Times of minimum light of ST Carinae JD Hel. 2440000+ E (O-C) Reference ------------------------------------------- -25739.666 -33336.0 -0.002 A -16098.325 -22643.0 -0.001 B -11084.244 -17082.0 0.006 C 4282.5654 -39.0 0.0006 D 4282.5653 -39.0 0.0005 D 4282.5636 -39.0 -0.0012 D 4317.7288 0.0 -0.0004 D 4317.7290 0.0 -0.0002 D 4317.7290 0.0 -0.0002 D 4365.5156 53.0 -0.0010 D 4365.5155 53.0 -0.0011 D 4365.5155 53.0 -0.0011 D 4647.7330 366.0 0.0001 D 4647.7333 366.0 0.0004 D 4647.7328 366.0 -0.0001 D 4675.6850 397.0 0.0009 D 4675.6844 397.0 0.0003 D 4675.6846 397.0 0.0005 D 4698.6733 422.5 -0.0028 D 4698.6785 422.5 0.0023 D ------------------------------------------- References to Table I A: Leavitt (1908) B: Hertzsprung (1925) C: Gaposchkin (1953) D: This study It is clearly seen that the period of ST Car does not seem to have varied over the past seventy years. Table I gives in succession the available times of minima, epoch numbers, residuals (O-C) computed from equation (3), and sources of reference. Orbital phases have been calculated from the revised ephemeris given in equation (3) and light and color curves have been obtained. The differential light curves in the V-magnitude and (B-V) color are shown in Figure 1. The differences DeltaV and Delta(B-V) are in the sense variable minus comparison star. The light curve in the V-magnitude reveals partial eclipses; the depths of primary and secondary minima are about 1.2 and 0.3, respectively. In addition, the variation in the maxima due to ellipticity and reflection effects is also evident. [FIGURE 1] Figure 1: V and (B-V) light curves of the eclipsing binary ST Carinae A detailed analysis of ST Carinae by means of the classical Russell-Merrill procedure will be published elsewhere. We are very grateful to the Director of CTIO for the time allocation and facilities at CTIO. The assistance of H. Moyano, J. R. Puerta, and J. E. Laborde during the observations is also gratefully acknowledged. J. J. CLARIA * E. LAPASSET ** Observatorio Astronomico Laprida 854 - 5000 Cordoba Argentina * Visiting astronomer, Cerro Tololo Inter-American Observatory, which is supported by the NSF under contract No. 74-04128. ** Member of the Carrera del Investigador Cientifico del Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) de Argentina. References: Gaposchkin, S. 1953 Harvard Ann. 113, No. 2, 70. Hertzsprung, E. 1925, Bull. Astr. Netherlands, Vol. II, No. 77, 209. [BIBCODE 1925BAN.....2..212H ] Leavitt, H. S. 1908, Harvard Ann. 60, No. 5, 109. Pickering, E. C. 1906, Harvard Circ. 122. Shapley, H. 1912 Astr. Nach. 192, No. 4589, 79. [BIBCODE 1912AN....192...79S ] Shapley, H. 1915, Contr. Princeton Univ. Obs. No. 3. [BIBCODE 1915CoPri...3....1S ]