COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2441

                                       Konkoly Observatory
                                       Budapest
                                       5 December 1983

                                       HU ISSN 0374-0676



       PHOTOMETRIC VARIATIONS IN THE Ap STAR HD 215441


  Photometric variations of the peculiar class A (Ap) magnetic stars have
been theorized to occur due to the rotational modulation of an inhomogeneous
distribution of emmittant flux, as opposed to effective temperature variations
of the stars as a whole. This process has been shown to occur in the
one Ap star alpha^2 CVn by Cohen (1970) and Molnar (1973). However, calculations
of the effective temperature variation of the other highly magnetic (maximum
field strength =~ +32 kilogauss) Ap star HD 215441 (Babcock's star) have left
uncertainties as to the applicability of the flux redistribution theory to
it. Stepien (1968) calculated a variation of 1300 K in effective temperature,
while far-ultraviolet photometry by Leckrone (1974) indicated a variation of
no more than 100 K, indicating the existence of a flux redistribution mechanism.
  The lack of agreement in these values indicated that, as for alpha^2 CVn, 
spectrophotometric observations of the star over its period and consequent 
effective temperature determinations would be of interest. No basis of data has
yet been obtained in support of Leckrone's conclusion that the star undergoes
flux redistribution, in terms of observations of the star's continuum over
its period.
  Observations of HD 215441 over half its period were made in the
region from Lambda7650 to Lambda8950 using the 256 photodiode array direct
mode Reticon spectrometer system developed by the University of California
at Los Angeles Department of Astronomy. The instrument was mounted at the
cassegrain foci of the 16 inch reflector of the University and the 24 inch
reflector of the Table Mountain Observatory facility of the Jet Propulsion
Laboratory.
  Figure 1 shows a composite of the scans obtained (non-flux calibrated)
from phase 0.0 at the top to phase 0.5 at bottom. Phases were calculated
using the ephemeris of Preston (1969).
  Following the full reduction and sky subtractions for the individual scans,
the count per channel values of each scan were divided into those of the scan
for phase 0.0 across the entire scan range in an effort to detect any slope
variation of the continuum as a function of phase. Figure 2 shows the results


                             [FIGURE 1]
                             [FIGURE 2]


of the divisions where the zero point of the abscissa is arbitrary.
  For the wavelength region Lambda8100 - Lambda8800 the flat nature of the scan 
divisions is indicative of negligible slope variations and consequent effective
temperature variations over the phases covered in this study. It thus appears
that some form of flux redistribution is responsible for the photometric
variations of the star, as no form of large temperature variation is indicated
by the data obtained here.
  The author wishes to thank the University of California at Los Angeles
Department of Astronomy and the staff of Table Mountain Observatory for their
assistance and provision of facilities. In particular, the assistance of
Dr. Roger Ulrich, Mr. Steven Tomczyk, and Mr. Bradley Wood of UCLA is 
gratefully acknowledged. This work was supported by a grant from U.S. Army Research
Office.





                  M. CORBIN

          Undergraduate, Department of Astronomy,
          Columbia University
          New York, N.Y. 10027
          U.S.A.





References:

Cohen, J.G., 1970, Ap.J., 159, 473 [BIBCODE 1970ApJ...159..473C ]
Krautter, A.H., 1977, Ap.J., 216, 33 [BIBCODE 1977ApJ...216...33K ]
Leckrone, D.S., 1974, Ap.J., 190, 319 [BIBCODE 1974ApJ...190..319L ]
Molnar, M., 1973, Ap.J., 179, 527 [BIBCODE 1973ApJ...179..527M ]
Peterson, D.M., 1970, Ap.J., 161, 685 [BIBCODE 1970ApJ...161..685P ]
Preston, G.W., 1969, Ap.J., 156, 967 [BIBCODE 1969ApJ...156..967P ]
Stepien, K., 1968, Ap.J., 154, 945 [BIBCODE 1968ApJ...154..945S ]