COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3913 Konkoly Observatory Budapest 28 July 1993 HU ISSN 0374 - 0676 DIFFERENTIAL UBV PHOTOMETRY OF THE CP3 STAR HD 89822 The CP3 star HD 89822 (HR4072, A0 HgSiSr) was selected from the paper of Gerbaldi, Floquet and Hauck (1985) to investigate the photometric period amongst Hg-Mn spectroscopic binaries. The membership of HD 89822 among the CP3 group has been definitely confirmed by Aikman (1976). Winzer (1974) found no evidence of significant variations and Catalano and Leone (1991) discovered a period of 7.5586 days which is substantially different from the known spectroscopic binary period of 11.5741 days. They used the same comparison stars as Winzer (HR 4026, HR, 4215). The observations have been carried out at Skalnate Pleso and Stara Lesna observatories with the photoelectric photometers attached to 0.6 m reflectors. The comparison star was HD 88983 (HR 4026, A8III) and the observations were made in the sequence 3xS-3xV- 3xS. Each observation of the star was followed by the sky background recording and the observations were corrected for differential extinction. The observations were made in overall number of 41 nights. Duration of a typical night run was 1.5 hour. However, weather conditions enabled us to obtain quality observations needed for searching for periodicities of low amplitudes around 0.02-0.03 mag as few as 10 nights and 15 nights for Skalnate Pleso and Stara Lesna observatories respectively. Table 1 lists the instrumental magnitudes in each filter. The night averages are given with corresponding rms errors. Raw data will be published elsewhere (Zboril 1994). Catalano and Leone (1991) were able to fit their observations of HD 89822 by two sinusoidal light curves represented by the function Delta m=A_0 + A_1 * sin(2pi((t - t_0 / p)+phi_1))+A_2 * sin(2pi((t - t_0 / p) + phi_2)) (1) where: Delta m is the magnitude difference in each filter, t Julian date of the observation, to is the initial epoch, p period in days and A_iota, phi_iota amplitudes and phases given in Table 2. They also established ephemeris elements JD(Delta U_min)=2441417.90+7.5586 x E (2) We determined the coefficients A_0 for our photometric systems as mean values of all nights considered in both observatories. Figures 1,2 give our observations in U and B filters against light curve according to formula 1 with the coefficients given in the Table 2 phased with respect to the above ephemeris formula. The largest amplitudes (around 0.03 mag) can be expected in U and B filters according to the values of A_1 in the Table 2 but we detect no variations within 0.01 mag in both filters respectively when data phased considering the period 7.5586 days. This goes for Table 1: Journal of observations Skalnate Pleso JD = 24400000+ -----------------------------|-----------------------------|----------------------------- U filter | B filter | V filter -----------------------------|-----------------------------|----------------------------- 8534.58 -1.253+-0.001 | 8534.58 -1.022 +-0.001 | 8534.58 -0.833 0.001 8562.64 -1.254 0.001 | 5562.64 -1.022 0.001 | 8562.64 -0.832 0.001 8588.65 -1.253 0.002 | 8588.65 -1.022 0.003 | 8588.65 -0.832 0.002 8625.51 -1.259 0.001 | 8625.51 -1.029 0.001 | 8625.51 -0.837 0.001 8643.57 -1.258 0.001 | 8643.57 -1.027 0.001 | 8643.57 -0.831 0.003 8680.57 -1.257 0.001 | 8680.57 -1.028 0.001 | 8680.57 -0.840 0.001 8723.45 -1.262 0.005 | 8723.45 -1.022 0.003 | 8723.45 -0.827 0.003 8758.41 -1.255 0.002 | 8758.41 -1.023 0.002 | 8758.41 -0.835 0.002 8759.39 -1.258 0.001 | 8759.39 -1.028 0.001 | 8759.39 -0.839 0.002 8993.69 -1.259 0.002 | 8993.69 -1.028 0.002 | 8993.69 -0.843 0.002 ----------------------------------------------------------------------------------------- Stara Lesna JD = 24400000+ -----------------------------|-----------------------------|----------------------------- 8274.54 -1.239 0.002 | 8274.54 -1.004 0.001 | 8274.54 -0.826 0.001 8331.43 -1.243 0.003 | 8331.43 -1.002 0.002 | 8331.43 -0.822 0.002 8350.54 -1.248 0.004 | 8350.54 -1.013 0.003 | 8350.54 -0.834 0.002 8645.71 -1.251 0.006 | 8645.71 -1.017 0.002 | 8645.71 -0.835 0.004 8646.63 -1.230 0.004 | 8646.63 -1.011 0.001 | 5646.63 -0.830 0.001 8683.52 -1.245 0.003 | 8683.52 -1.007 0.001 | 8683.52 -0.826 0.001 8691.53 -1.230 0.003 | 8691.53 -1.008 0.001 | 8691.53 -0.827 0.001 8692.52 -1.236 0.006 | 8692.52 -1.007 0.001 | 8692.52 -0.826 0.001 8701.53 -1.246 0.006 | 8701.53 -1.014 0.003 | 8701.53 -0.837 0.002 8993.63 -1.237 0.003 | 8993.63 -1.006 0.001 | 8993.63 -0.825 0.001 9023.36 -1.227 0.008 | 9023.36 -1.012 0.005 | 9023.36 -0.827 0.006 9030.69 -1.242 0.003 | 9030.66 -1.007 0.001 | 9030.66 -0.827 0.001 9031.37 -1.223 0.006 | 9031.37 -0.997 0.002 | 9031.37 -0.822 0.001 9149.44 -1.244 0.004 | 9149.44 -1.004 0.002 | 9149.44 -0.828 0.003 9178.43 -1.255 0.008 | 9178.43 -1.011 0.004 | 9178.43 -0.828 0.005 ----------------------------------------------------------------------------------------- Skalnate Pleso observatory (1783m above sea level), while the observations from Stara Lesna observatory are of larger scatter (900m above sea level). Since there is a gap around phase 0.45 the observations are being continued to improve the phase diagram. Anyhow, we should point out that we did not consider HR 4215 as another comparison star for its considerable distance from HD 89822. The quality of the data observed due to various altitudes warn us when searching for low amplitude variations. Our data (Skalnate Pleso) are probably consistent with the latest observations of Adelman and Pyper (1993) using Four College APT who considered both comparison stars as in Winzer's thesis. They also do not confirm the light variability of this star in Stromgren Table 2: Parameters of the light curve fit -------------------------------------------------------------------------------- A_0 coeff. Filter A_0 A_1 A_2 phi_1 phi_2 sigma Sk. Pleso St. Lesna -------------------------------------------------------------------------------- U -1.23739 0.01629 0.00301 -0.229 -0.773 0.008 -1.240 -1.257 B -1.01655 -0.01563 0.00209 0.220 0.111 0.007 -1.008 -1.025 V -0.82746 -0.00955 0.00473 -0.320 0.863 0.008 -0.828 -0.835 -------------------------------------------------------------------------------- [FIGURE 1] Figure 1: The U filter observations at Skalnate Pleso (bottom) and Stara Lesna observatories [FIGURE 2] Figure 2: The B filter observations at Skalnate Pleso (bottom) and Stara Lesna observatories system. Thus, we cannot probably confirm the period of 7.5586 days predicted by Catalano and Leone (1991). Moreover, Adelman and Pyper's (1993) observations of another Hg-Mn star (HR 1331) do not give evidence for photometric variability of CP3 stars and this provoke us to reconsider the constancy in light of these objects. Milan ZBORIL Jan BUDAJ Astronomical Institute Slovak Academy of Sciences 059 60 Tatranska Lomnica Slovakia astrmizb @ asu.savba.cs References: Adelman S. J. and Pyper D. M. 1993 in Astron. Soc. of the Pacific Conf. Ser. 44, 644 [BIBCODE 1993ASPC...44..644A ] Aikman G. C. L. 1976 Publ. Dominion Astrophys. Obs. 14, 379 [BIBCODE 1976PDAO...14..379A ] Catalano F. A., Leone F. 1991 Astron. Astrophys. 244, 327 [BIBCODE 1991A&A...244..327C ] Gerbaldi M., Floquet M., Hauck B. 1985 Astron. Astrophys. 146, 341 [BIBCODE 1985A&A...146..341G ] Winzer J. E. 1974 Ph. D. Thesis, University of Toronto [BIBCODE 1974PhDT........61W ] Zboril M. 1994 Contrib. Astron. Obs. Skalnate Pleso, in press [BIBCODE 1994CoSka..24..141Z ]