COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1600 Konkoly Observatory Budapest 1979 May 8 SPECTROSCOPIC EVIDENCE FOR THE BINARY NATURE OF THE Ap STAR ET ANDROMEDAE There are many indications in the literature that the Ap star ET And (= HD 219 749 = HR 8861 = BD +44d4373) is variable with the typical amplitudes ~0.02m (V), ~0.03m (B) and~0.05m (U) - see Renson (1977). Kizilirmak and Wood (1967) found the variability in their Hbeta and Hgamma photometry: Delta beta=0.035m and Delta gamma=0.049m. Several periods of light variability were suggested by various authors, namely 0.723d, 1.616d and 2.604d, but some of these periods must be definitely spurious since they are interrelated by Tanner's (1948) formula. Recently, Sezer (1978) found a period of 0.49925 days from his ubv photometry. Moreover, Panov (1978) claims that he has found short-time variability in UBV with a fundamental period of about 140 minutes and two harmonics at 70 and 35 minutes. Scarce spectroscopic data published until now (Palmer et al., 1968 and Hube, 1970) revealed some variations in radial velocities. We have obtained 23 high-dispersion spectrograms in coude focus of the Ondrejov 2m telescope between July 1974 and September 1978 with dispersions from 0.85 to 2.4 nm mm^-1 in blue and red regions of the spectrum. Radial velocities were determined from the repeated measurements of the hydrogen lines on the Abbe comparator and on the microdensitometer tracings. Probable error of one measurement of unit weight was 3,4 km s^-1. Radial velocities were determined by using a code written by Dr. P. Harmanec. The results are given in Table 1 where also the data from Hube's (1970) paper are added. We have then searched for periodicities in radial velocities in the time interval from 0.5 to 2000 days employing Dr. Harmanec's version of Morbey (1978) method. No periodicities suggested by the photometric data were found. However, the period of about 48 days is clearly present in the data. Table 1 ----------------------------------------------------- J.D. RV_obs O-C Cycle No. Phase 2400000.0+ (km s^-1) (km s^-1) ----------------------------------------------------- 36461.6860 15.0 5.6 -150 0.735 36470.6900 33.0 -0.5 -150 0.921 36509.5710 14.0 5.4 -149 0.726 36535.5960 - 7.0 7.2 -148 0.265 37864.8490 6.0 -8.1 -121 0.783 37867.8220 15.0 -6.7 -121 0.845 38990.7850 -14.0 -6.2 - 97 0.093 38993.7690 -12.0 1.9 - 97 0.154 39059.5670 -15.0 -10.1 - 96 0.516 42251.4414 0.7 1.3 - 30 0.595 42251.5331 0.3 0.9 - 30 0.597 42427.2617 -17.3 -2.7 - 26 0.235 42631.5417 - 5.4 1.9 - 22 0.464 42631.5743 - 8.9 -1.6 - 22 0.465 42636.5434 5.6 7.9 - 22 0.568 43016.3858 -12.9 -4.2 - 14 0.431 43016.5254 - 7.8 0.8 - 14 0.434 43389.5535 -15.4 -1.5 - 6 0.157 43393.4036 - 8.1 6.5 - 6 0.236 43448.4113 - 5.0 5.9 - 5 0.375 43454.3076 - 8.0 -2.2 - 5 0.497 43747.3747 - 7.9 -5.5 0 0.564 43748.4595 - 5.0 -3.9 0 0.587 43748.6060 - 8.9 -7.9 0 0.590 43757.4098 16.0 3.0 0 0.772 43757.5355 15.0 1.8 0 0.775 43760.4967 24.0 3.5 0 0.836 43760.6078 28.0 7.2 0 0.838 43767.4261 30.0 -4.3 0 0.980 43768.3011 27.0 -1.5 0 0.998 43768.5886 32.4 6.4 1 0.004 ----------------------------------------------------- Thus the radial velocity data from Table 1 were used for the calculation of the spectroscopic binary orbit by a code written by Dr. J. Horn. Elliptical orbit for a single-line spectroscopic binary yields the following elements (p.e. are quoted throughout): Period = (48.304 +- 0.007) days T (epoch of periastron passage) = (2 443 720.11 +- 0.64) J.D. T (max. RV) = 2 443 718.00 J.D. T (min. RV) = 2 443 730.10 J.D. T (pri. min.) = 2 443 721.76 J.D. T (sec.min.) = 2 443 708.11 J.D. omega = (49.8d +- 6.0d) epsilon = (0.50 +- 0.05) K_1 = (25.7 +- 2.0) km s^-1 V_0 = (+2.6 +- 0.7) km s^-1 f(m)= 0.0554 M_Sun a_1 sin i = 14.8 x 10^6 km Phases in Table 1 are computed from the time of periastron passage and O-C are referred to the above-mentioned elements; (see also Fig. 1 where dots represent Hube's data and open circles refer to our Ondrejov measurements). [FIGURE 1] Fig. 1. Radial velocity curve of the Ap star ET And. Further spectrographic observations, particularly in phases 0 to 0.1, would help to improve the orbit and to clarify whether the rather high eccentricity found in our solution is intrinsic. Photometry of the star extended over a long time span would be obviously most useful. We are much obliged to Drs. P. Harmanec and J. Horn for the permission of using their computing codes and for consultations. M. OUHRABKA and J. GRYGAR Astronomical Institute, Czechoslovak Academy of Sciences CS - 251 65 Ondrejov Czechoslovakia References: Hube, D.P., 1970: Mem. Roy. Astron. Soc. 72, 233 [BIBCODE 1970MmRAS..72..233H ] Kizilirmak, A., Wood, H.J., 1967: Astron.J. 72, 727 [BIBCODE 1967AJ.....72..727K ] Morbey, C.L., 1978: Publ. D.A.O. XV, No. 4, 105 [BIBCODE 1978PDAO...15..105M ] Palmer, D.R., Walker, E.N., Jones, D.H.P., Wallis, R.E., 1968: Roy.Obs.Bull. No. 135 [BIBCODE 1968RGOB..135..385P ] Panov, K., 1978: Publ.Astron.Inst.Czechosl.Acad.Sci. No. 54, 19 [BIBCODE 1978mast.conf...19P ] Renson, P., 1977: Astron. Astrophys. 54, 277 [BIBCODE 1977A&A....54..277R ] Sezer, C., 1978: I.B.V.S. No. 1384 Tanner, R.W., 1948: J. Roy. Soc. Canada 44, 177 [BIBCODE 1948JRASC..42..177T ]