COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1992

                                   Konkoly Observatory
                                   Budapest
                                   1981 July 18

                                   HU ISSN 0374-0676


         PHOTOMETRIC VARIABILITY OF 10 LACERTAE


     The star 10 Lac has been reported several times as a
spectroscopic variable. Smith (1977), who included the star in
the group of the so-called 53 Persei variables (see Sareyan et
al, 1980, for the observational definition), tried to calculate
a period for the variation of the line Si IV lambda 4654.1 on the
basis of non-radial pulsations. He obtained two possible values,
14.2 and 8 hours, the second being the most probable one. Otherwise, 
the star has never been detected as photometric variable.
     We observed 10 Lac during the nights of September 24th
and 25th, 1980. 2 And was used as comparison star. In view of
the considerable difference in spectral type between 10 Lac and
2 And - O9 and A3, respectively - the atmospheric extinction is
espected to be larger for the bluer star; by considering the
part of the spectrum in which we observe - U and B filters of
Johnson - this difference is not negligible. We estimate the
corrections upon the light curve by assuming the extinction
coefficient to depend on the wavelength in the form E=exp(-A lambda^-4)
E being the ratio of the fluxes inside and outside the atmosphere 
and A a constant (Rayleigh scattering).
     In Figures 1 and 2 are represented the light curves for
the two days of observation. Crosses correspond to 2 And and
circles to the magnitude difference 10 Lac - 2 And. Vertical
bars represent the above mentioned corrections relative to
the value, corresponding to which the star crosses the meridian.
As we can see, the correction goes in the sense of increasing
the amplitude of the variation. In other words, the variability
found is real.
     As we dispose of very few data, it is difficult to perform 
a period analysis with a certain confidence. We tried such
an analysis and got a most probable period of 6.4 hours for

                     [FIGURE 1]

both U and B filters, using the original and the corrected data.
The amplitude should lie between 0.02m and 0.03m. However, only
an intensive photometric monitoring of the star will allow a
more reliable determination of its characteristics.




                   ANTONIO J. DELGADO
                   RAFAEL GARRIDO
                   Instituto de Astrofisica de Andalucia
                   Apdo. 2144, Granada, Spain

References:
Saryean J.P., Le Contel J.M., Valtier J.C., Ducatel D. 1980:
      Space Sci. Rev. 27, 353. [BIBCODE 1980SSRv...27..353S ]
Smith M. 1977: Astrophys. J. 215, 574. [BIBCODE 1977ApJ...215..574S ]