On the Nature of the Optical Variations of HZ Her = Her X1статья

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[1] On the nature of the optical variations of hz her = her x1 / A. M. Cherepashchuk, Y. N. Efremov, N. E. Kurochkin et al. // Information Bulletin on Variable Stars. — 1972. — no. 720. — P. 1. COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 720 Konkoly Observatory Budapest 1972 September 29 ON THE NATURE OF THE OPTICAL VARIATIONS OF HZ Her=Her X1 The variable star HZ Her was recently identified with a close binary system, containing the X-ray pulsar Her X1 (1-3). Using 249 old plates (1907-1972) we investigated the optical periodical variability(4)(see Fig. 1). The moments of optical minima coincide with the epochs of X-ray eclipses derived in (5). The period p=1.70017d is stable during 65 years. The light variations are symmetrical to phase 180d; the light intensity monophonically increases from 0d to 180d and decreases from 180d to 360d. The hemisphere of the optical component turned to the X-ray source is three times brighter than the opposite one. Therefore we suggest that the reflection effect is the main cause of the light variations. The X-ray radiation, falling on the surface of the visible component is absorbed in the photosphere and reradiated in the optical and ultraviolet spectral bands. The importance of X-ray heating of the normal component in X-binary system was pointed out in (6,7). The spectral class lies in the range B2-A7 V (8-10), the earlier spectrum is at the brightness maximum. In this picture the latest observed spectrum reflects the properties of the visual star. Its mass must be of the order of 2M_Sun, its distance is about 1.5 kpc and its z coordinate is about 750 pc. At this distance the X-ray luminosity of the system will be about 3.10^35- 10^36 erg/sec and exceeds the optical luminosity of the A7V star (∼10^34 erg/sec). This is in rather good accordance with the estimation of X-ray energy needed for increasing the brightness of the optical component due to reflection effect. The dispersion of points near the maximum of the light curve is real and probably correlates with the cycle of the X-ray radiation, which is observed only 9 days during every 36 day cycle (5).If there is a real correlation, the maximal optical luminosity corresponds to the phase 0.5 of the 36 day cycle, when the X-ray flux in the direction to the Earth is absent. Sternberg Astronomical Institute, Moscow A.M. CHEREPASHCHUK, YU.N. EFREMOV, N.E. KUROCHKIN, N.I. SHAKURA, R.A. SUNYAEV. References: 1) W. Liller, 1972, IAU Circ. No. 2415. [BIBCODE (1972IAUC.2415....1L) ] 2) J.N. Bachcall, N.A. Bachcall, 1972, IAU Circ. No. 2427. [BIBCODE (1972IAUC.2427....1B) ] 3) N.E. Kurochkin, 1972, IAU Circ. No. 2436. [BIBCODE (1972IAUC.2436....1F) ] 4) N.E. Kurochkin, 1972, Astron.Circ. No. 717. [BIBCODE (1972ATsir.717....1K) ] 5) H. Tananbaum et al., 1972, Ap.J., 174, L 143. [BIBCODE (1972ApJ...174L.143T) ] 6) I.S. Shklowsky, 1967, Astron.Zh., 44, 930. [BIBCODE (1967AZh....44..930S) ] 7) N.I. Shakura, R.A. Sunyaev, 1972, Astron.Aph. (in press). [BIBCODE (1973A&A....24..337S) ] 8) B.W. Bopp, G. Grupsmith, P. Vanden Bout, 1972, IAU Circ. No. 2434. [BIBCODE (1972IAUC.2434....1B) ] 9) S.D. Crampton, C.L. Morbey, 1972, IAU Circ. No. 2428. [BIBCODE (1972IAUC.2428....1B) ] 10) A. Davidsen, J.P. Henry, J. Middleditch, H.E. Smith, 1972, preprint. [ DOI ]

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