COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2569 Konkoly Observatory Budapest 3 August 1984 HU ISSN 0374-0676 ULTRAVIOLET ANS PHOTOMETRY FOR THE FIVE SUSPECTED LONG PERIOD Ap STARS HD 89 822, HD 137 389, HD 187 474, HD 204 411 AND HD 221 760 The main problem of the very long period magnetic CP stars is whether the nature of those stars is the same as for the "normal " short period ones. To answer this question it is necessary to determine the periods and then to compare their characteristics of variability, which certainly should be different, if different mechanisms are working. The Ap stars show pronounced typical characteristics in their UV variability, e.g. large amplitudes and antiphase relations to the visible spectral regions. For five of the suspected long period Ap stars given by Hensberge et al. (1984), more than two single UV observations from ANS (Wesselius et al., 1982) are available (Table I). Table I ANS UV observations J.D. 2400000+ 15W 18 22 24 33 HD 89822 Mg 42350.328 4.231+- 4 4.207+-3 4.326+-2 4.696+-3 4.836+-4 42527.971 4.222 3 4.200 3 4.317 1 4.684 3 4.831 2 42528.176 4.226 2 4.199 3 4.315 1 4.691 2 4.827 3 HD 137389 Si 42400.006 5.302 11 5.299 7 5.523 5 5.831 15 5.964 8 .623 5.306 5 5.314 4 5.520 2 5.811 7 5.951 5 .623 5.314 6 5.311 5 5.521 3 5.814 5 5.959 6 42580.355 5.316 7 5.332 4 5.516 2 5.803 4 5.947 5 42581.507 5.328 5 5.324 4 5.519 2 5.803 4 5.955 4 .977 5.327 6 5.319 6 5.520 3 5.798 3 5.959 6 42583.872 5.315 5 5.326 3 5.515 2 5.805 4 5.956 5 HD 187474 Si Cr Eu 42336.792 5.341 6 5.103 4 4.873 2 5.275 4 5.100 2 337.004 5.331 5 5.118 5 4.877 3 5.271 5 5.102 3 515.907 5.179 6 4.972 5 4.819 2 5.207 5 5.123 3 .907 5.186 4 4.967 4 4.815 2 5.218 3 5.121 3 880.397 5.158 2 4.966 3 4.841 1 5.216 2 5.135 2 .861 5.153 9 4.968 5 4.838 2 5.211 8 5.129 3 HD 204411 Cr Si 42575.899 7.892 18 6.165 8 5.887 5 6.181 5 5.783 6 .899 - - 6.144 5 5.885 3 6.193 5 5.773 4 42576.914 7.863 29 6.157 7 5.879 3 6.190 6 5.771 5 Table I (cont.) J.D. 2400000+ 15W 18 22 24 33 HD 204411 Cr Si 42576.914 7.866+- 19 6.157+-8 5.884+- 4 6.186+- 6 5.782+-5 42578.134 7.891 16 6.169 7 5.877 3 6.194 7 5.771 4 .134 - - 6.160 6 6.879 2 6.198 6 5.770 4 HD 221760 Sr Cr Eu 42377.901 6.222 9 5.259 6 5.048 2 5.407 4 5.045 3 .901 6.196 9 5.257 6 5.048 2 5.413 4 5.039 3 42378.105 6.226 10 5.258 5 5.055 2 5.407 4 5.044 3 .105 6.229 10 5.266 5 5.053 2 5.410 4 5.049 4 42558.656 6.180 10 5.232 4 5.048 3 5.401 4 5.037 4 42559.466 6.278 10 5.232 5 5.049 3 5.408 4 5.050 4 .466 6.292 9 5.245 4 5.050 2 5.411 4 5.050 4 .470 6.274 10 5.235 5 5.052 2 5.414 5 5.048 4 42743.556 6.202 8 5.263 4 5.044 4 5.410 6 5.047 4 .556 6.187 10 5.257 4 5.041 3 5.406 4 5.050 3 42744.626 6.236 10 5.267 5 5.050 2 5.411 3 5.044 2 .630 6.218 12 5.268 5 5.051 3 5.409 4 5.048 3 For three of the stars (HD 89822, HD 137389, HD 204411) no significant variations have been found. That means that HD 89822 and HD 137389, if variable, have periods, much longer than 180 days. For HD 204411 found to be constant in the visible by different authors, one can exclude UV variability with a period less than 10 days. For HD 221760 the observed magnitude differences, at least in the wide 1550 A band are significantly greater than the errors. The short time scale of variations suggests a period length in the order of days. The star HD 187474 clearly shows variations which agree with the time scale given by Hensberge et al. (1984). Assuming similar shapes of the light curves in u and in the near-by 3300 A band and shifting the magnitude scale to fit the two sets of observations, we can correct the period given by the above mentioned authors. This leads also to a little better agreement between the uvby observations. The obtained elements are: JD (phase zero) = 2444457.77 + 2300 E +-50 Figure 1 shows the observations plotted in the phase diagram. The visible magnitudes were taken from Figure 1 of Hensberge et al. (1984), the phases were computed from the mean time of the corresponding observing runs, given there (+absolute measurement). The dashed lines indicate our interpretation of the observations. The distribution of the observations at different wavelengths in the phase diagram suggests a double wave in the light curves. The variations in the UV have large amplitudes and are in antiphase to the [FIGURE 1] variations in the visible spectral region including the 3300 A band. The characteristics of the photometric variability of this very long period (6.2 years) star are very similar to normal short periodic Ap stars, suggesting intrinsic slow rotation and rotational variability for HD 187 474. The intermediate long period Ap stars HD 221 568 (P = 159 d) and HD 188041 (P = 224 d) clearly show rotational variability. Now HD 187 474 extends this property to much longer periods. Therefore it does not seem to be necessary to assume generally any other mechanism for explaining the very long period Ap stars. On the other hand, the expected short rotational period, estimated by Kurtz (1983) from his oblique pulsator model for Gamma Equ in connection with the long time scale variations of the magnetic field (s. Krause, Scholz, 1981) might indicate that for different long period magnetic CP stars different mechanisms can be responsible for their variability. We thank Dr. Wesselius, who made it possible to use the individual observations from ANS. WERNER SCHONEICH Zentralinstitut fur Astrophysik 1502 Potsdam-Babelsberg Rosa-Luxemburg-Str. 17a GDR References: Hensberge, H., Manfroid, J., Schneider, H., Maitzen, H.M., Catalano, F.A., Renson, P., Weiss, W.W., Floquet, M., 1984, Astron.Astrophys., 132, 291 [BIBCODE 1984A&A...132..291H ] Krause, F., Scholz, G., 1981, in Upper Main Sequence CP stars, 23 Liege Coll. p. 323 [BIBCODE 1981LIACo..23..323K ] Kurtz, D., 1983, Monthly Not. RAS 202, 1 [BIBCODE 1983MNRAS.202....1K ] Wesselius, P.R., van Duinen, R.J., DeJong, A.R.W., Aalders, J.W.G., Luinge, W., Wildeman, K.J., 1982, Astron.Astrophys.Suppl., 49, 427 [BIBCODE 1982A&AS...49..427W ]