COMMISSION 27 OF THE I. A. U.
                INFORMATION BULLETIN ON VARIABLE STARS
                             Number 2297

                                                        Konkoly Observatory
                                                        Budapest
                                                        1983 March 18

                                                        HU ISSN 0374-0676


    ON THE CONSTANCY OF THE PERIOD OF THE MAGNETIC Ap STAR HD 215441



  Rakosch (1968) suggested variable periods for some Ap stars. From the point
of view of the interpretation of the light variability of magnetic Ap stars
as an effect of rotation it is an important question whether the period is
constant or not. Therefore many authors investigated this problem. In the
course of time it becomes more and more clear that all observations can be
explained with constant periods.
  Only HD 215441 remains, for which Rakosch (1968) and later Stift (1973)
discussed a variable period. Renson (1972) could not find any change in the
period of this star, but Panov and Schoneich (1975) showed that, at some
epochs, small changes could not be excluded. All these investigations,
carried out with O-C-diagrams, use a small number of observations around the
extreme values of the light curves only. The accuracy of the obtained phases
will be higher if all points of the light curve are used.
  Hempelmann and Schoneich (in preparation) developed a method for the
determination of the brightness distribution over the star's surface from the
light curve. This method permits also derivation of the phase angle Theta, at
which the centre of the peculiar region passes by the line of sight. It has
to be underlined that, among all parameters, Theta can be obtained with the highest
degree of accuracy and is especially for a star like HD 215441 with a single
peculiar region, independent from the accuracy of other parameters.
  We investigated the wavelength dependence of Theta. The values of Theta were
computed for the light curves of the ten colour photometry by Schoneich et
al. (1976) and the UV photometry by Leckrone (1974), provided that the 
observations are carried out at nearly the same time. Figure 1, presenting Theta
as a function of the wavelength, shows a constancy of Theta in the range greater
than 200 nm. For this reason one can compare the light curves from all other
authors in different colours.

  For all available observations by Jarzebowski (1960), Cameron (1966),
Stepien (1968), Schoneich et al. (1976), Leckrone (1974), Hildebrandt et al.
(in preparation) and Panov (private communication) the angle Theta was computed



                                  [FIGURE 1]

 Figure 1   The wavelength dependence of the phase angle Theta. Open circles
 denote Theta from measurements by Leckrone (1974), filled circles are 
 for the ten-colour-photometry.

                                  [FIGURE 2]

             Figure 2   The time dependence of Theta.


with the elements by Panov (private communication).


            JD0 = 2441902.49 + 9.4875 E
             


Figure 2 presents the computed Theta as a function of time. There is no significant 
difference of a single Theta from the averaged ones and therefore we
conclude that in the last 22 years there has been no observational evidence
for any change in the period of HD 215441.





          A. HEMPELMANN, W. SCHONEICH

          Zentralinetitut fur Astrophysik
          Astrophysikalisches Observatorium Potsdam
          DDR-1500 Potsdam
          Telegrafenberg





References:

Cameron, R.C. (1966), Georgetown Obs. Monograph No. 21 [BIBCODE 1966GeoOM..21....0C ]
Jarzebowski, T. (1960), Acta Astronomica 10, 119 [BIBCODE 1960AcA....10..119J ]
Leckrone, D.S. (1974), Astrophys. J. 190, 319 [BIBCODE 1974ApJ...190..319L ]
Panov, K., Schoneich, W. (1975), Magnetic Ap Stars, Baku 1975, p.16. [BIBCODE 1975mazb.conf...16P ]
Rakosch, K.D. (1968), Astronom. J. 73, 114
Renson, P. (1972), Astron. and Astrophys. 18, 159 [BIBCODE 1972A&A....18..159R ]
Schoneich, W., Hildebrandt, G., Furtig, W. (1976), Astron. Nachr. 297, 39 [BIBCODE 1976AN....297...39S ]
Stepien, K. (1968), Contrib. Lick Obs. No. 267
Stift, M.J. (1973), Astron. and Astrophys. 22, 209 [BIBCODE 1973A&A....22..209S ]