COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2179 Konkoly Observatory Budapest 1982 July 20 HU ISSN 0374-0676 INVESTIGATION OF THE PULSATIONAL PECULIARITIES OF THE HOTTER COMPONENT IN THE ECLIPSING BINARY SYSTEM AB Cas Already five eclipsing binary systems containing Delta Scuti pulsating component are known today: AB Cas, Y Cam, RS Cha, AI Hya and UX Mon (ZZ Cyg is not such a system as was recently shown by Frolov et al., 1982).The places of the pulsating components of these systems on the HR diagramme are shown in Figure 1. [FIGURE 1] The parameters needed to construct this diagramme were taken from various sources, the borders of the instability strip are from Breger (1979). Because of large interstellar reddenings in the cases of AB Cas and UX Mon we used the known uvby index calibrations for the determination of the (b-y)_0 values. One can see from Figure 1 that all the five stars are indeed inside the Delta Scuti instability strip. The two M_v values for the hotter component of AB Cas plotted in Figure 1 (taken from different sources) suggest that this star is on the ZAMS and is unlike SX Phe. Supposing that synchronism between rotation and revolution takes place for all the five systems we calculated rotation velocities V_rot of their pulsating components using radius and orbital period values. Pulsation constants Q were calculated for AB Cas, Y Cam, AI Hya and RS Cha using radius, mass, and pulsational period values (pulsational period of UX Mon is practically unknown). These values along with the physical parameters adopted are given in Table I. Table I Star AB Cas Y Cam RS Cha AI Hya UX Mon Spectrum A3V A9IV-V A5V F5 A6V Mass 2.56_Sun 2.15 1.86 2.0 3.47 Radius 1.48_Sun 3.03 2.14 3.88 4.30 P_puls 0.0582874d 0.06646 0.084: 0.13803 0.02:: P_orb 1.3658783d 3.30553 1.6698684 8.289676 5.90450 M_v +2.75,+2.2 +1.42 +1.69 +1.18 +0.59 V_rot 55 km/sec 46 65 24 37 Q 0.046 0.018 0.037: 0.026 - The values of V_rot and Q confirm that these pulsating components are Delta Scuti type stars. One can also suppose that variable components of AB Cas and RS Cha are pulsating in the fundamental mode, but first and maybe second overtone are excited in AI Hya and Y Cam consequently (in the frames of the radial oscillation hypothesis). The eclipsing binary AB Cas was observed photoelectrically during 11 nights from November 1/2, 1980 to November 21/22, 1981. The 48-cm reflector of the High altitude station of Sternberg Astronomical Institute near Alma-Ata and a one-channel photometer with photon counting were used. The star was observed in the BV standard system. Fragments of the light curve of AB Cas in B light versus Phases of the P_orb = 1.3668783d are shown in differential magnitudes in Figure 2. One can see a small reflection effect in this system, the same effect was discovered by Ando (1980). Tempesti (1971) was the first who discovered the pulsational nature of the brighter (hotter) component in the AB Cas system. Ando (1980) confirmed this discovery. [FIGURE 2] [FIGURE 3] On the basis of our photoelectric data in B light (n ~~ 900) we calculated the best single mean pulsational period: 0.0582874d. The mean B light curve of the hotter (brighter) pulsating component of AB Cas is shown in Figure 3.b in differential magnitudes. The light elements are: Max hel = JD 2444912.1759 + 0.0582874d.E. +-2 Our light elements are in accordance with maxima of light variability from B.N. Irkaev's unpublished observations made in the year 1977 (JD 2443065-2443066) and with maxima from the light curve fragments published by Tempesti (1971). Time differences of these two data samples concerning ours are more than 31000 and about 70000 pulsation cycles respectively. Maybe only the small pulsation cycle statistics in Ando's (1980) paper is just the reason of the difference between his mean period 0.054d+-0.005 and ours. The scatter seen in the mean light curve in Figure 3.b is not surprising because even consecutive individual pulsation cycles have often different period lenghts and different light amplitudes. Only one exception is noticed by us: the observations made during the last night on 1981 November 21/22 (JD 2444930) are are disagreement with our mean light curve: see Figure 3.a. We do not know what is the reason of this because one can see the usual appearance of pulsations during this night (Figure 2). We can conclude that a high degree of the Delta Scuti pulsational macrostability does exist in the case of the hotter (brighter) component of AB Cas. M.S. FROLOV, E.N. PASTUKHOVA A.V. MIRONOV Astronomical Council of the Sternberg Astronomical USSR Academy of Sciences Institute, USSR References: Ando H., 1980, Astrophys. and Space Sci., 71, 249 [BIBCODE 1980Ap&SS..71..249A ] Breger M., 1979, Publ. Astron. Soc. Pacif., 91, 5 [BIBCODE 1979PASP...91....5B ] Frolov M.S., Mironov A.V. and Pastukhova E.N., 1982, I.B.V.S. No. 2117 Tempesti P., 1971, I.B.V.S. No. 596