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

                       Number 2825

                                         Konkoly Observatory
                                         Budapest
                                         27 November 1985
                                         HU ISSN 0374 - 0676



                  THE VARIABILITY OF ET And



  The peculiar star ET And (= HD219 749 = HR8861 ) has been observed 
photoelectrically in the National Astronomical Observatory (Bulgaria) in 1981-1984
using the 60 cm telescope and the UBV photoelectric photometer. Our photometric
observations reveal two different types of variability: periodic light
variations with P= 1.61887d, probably resulting from the rotation of the
star, and 0.0994d period light variations (with an amplitude of 0.01 - 0.02
mag) the origin of which is still uncertain. One possible origin of this
variability could be pulsational instability.

  The standard UBV magnitudes obtained in October 1984 are:
V = 6.45, B-V = -0.02, and U-B = -0.25. These values are in good agreement 
with Crawford's (1963) photometry. Using the standard reddening law
E(U-B)/E(B-V) = 0.72 we obtained E(B-V) = 0.06 and E(U-B) = 0.03. The unreddened
colours of ET And therefore are: (B - V)0 =-0.08 and (U- B)0 = -0.28. The UBV
data seem to indicate a location for ET And near or on the main sequence of
B8 but UBV photometry is not well suited for determining the luminosity
class. Crawford's (1963) Hbeta photometry indicates a main sequence position
of ET And, while other spectroscopic criteria (Scholz, 1985, private 
communication) show a position above the main sequence. The luminosity class of
ET And is, therefore, still uncertain. Indirect evidence could be obtained
from the photometric period of 1.6 days. We believe that this variation is
due to the rotation of the star. From the 1.6 day period and the value of
v.sin i= 79 km/s (Barylak and Rakos, 1983) the radius of the star can be
derived: R =~ 3Rsun which is consistent with the main sequence position. In
order to determine the Teff of this star, we used the calibration of peculiar
stars by Stepien and Muthsam (1980). Our photometry gives Teff= 10700-10900 K,
i.e. the star lies clearly outside the instability strip. This finding makes
it difficult to interpret the 0.0994 day light variability as a pulsation
(radial?) of the star. Furthermore, there are indications of rapid light
variability with periods of the order of minutes. Fourier analysis of B and U
data, obtained on four nights in November 1982 shows possible existence of


                              [FIGURE 1]


rapid light oscillations at f= 194 day^-1 , corresponding to 7.4 min period
(amplitudes: 0.002 mag in B, and 0.006 mag in U). In order to account for
atmospheric effects the comparison star HD219 891 was observed alternatively
with ET And. For each star the total monitoring time was 11.5 hours and for
each of them 199 points were obtained (in both E and U filters). We plotted
the Fourier spectra for the frequency interval 100- 200 day^-1 separately
for ET And and the comparison star in Figure 1. The method of Deeming (1975)
was used. Since the comparison star was observed in the same conditions as
ET And, all possible disturbances due to a atmospheric and instrumental effects
should be contained in the "comparison spectra". From Figure 1 another
possible frequency of rapid light oscillations appears at about 13 min.
Considering the small amplitudes of the rapid light oscillations, a 
confirmation of these results is needed. Rapid light oscillations in several Ap
stars have been discovered by Kurtz (1982) and can be interpreted as nonradial 
pulsations at high overtones.




                            K.P. PANOV

                      Department of Astronomy and
                      National Astronomical Observatory
                      Bulgarian Academy of Sciences
                      72 Lenin Blvd, Sofia - 1184
                      Bulgaria




References:

Barylak, M., and Rakos, K.D., 1983, Astron. Astrophys., 127, 366. [BIBCODE 1983A&A...127..366B ]
Crawford, D.L., 1963, Astrophys. J., 137, 530. [BIBCODE 1963ApJ...137..530C ]
Deeming, T.J., 1975, Astrophys. Space Sci., 36, 137. [BIBCODE 1975Ap&SS..36..137D ]
Kurtz, D.W., 1982, Mon. Not. R. astr. Soc., 200, 807. [BIBCODE 1982MNRAS.200..807K ]