COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                    Number 2843

                                   Konkoly Observatory
                                   Budapest
                                   28 December 1985
                                   HU ISSN 0374 - 0676


NEW PHOTOMETRIC OBSERVATIONS OF THE Beta CMa STARS Gamma Peg, 12 Lac 
                    AND Beta Cep



   Recent studies demonstrated the existence of secular changes
in periods and amplitudes in most of Beta CMa stars (Chapellier, 1985,
1986). In these papers the importance of regular observations of
these stars were underlined.

   Three of the classical Beta CMa stars, i.e. Gamma Peg, 12 Lac and
Beta Cep were observed in October 1985, at Pico del Veleta, (Spain),
with the 60 cm telescope of the Nice Observatory. The Geneva type
photometer described in Le Contel et al. (1974) was changed from
analogical to photon counting system. The photomultiplier was a
9816Q EMI tube with a S20 photocathode. Its temperature was regulated
at -13degC +- 0.1. Filters 4 and 5 (respectively UV and blue) described
in Sareyan et al. (1976) were used. For the brightest stars, Gamma Peg
and Gamma Cep, a neutral filter (d = 1.2) was used. One comparison and a
check star were observed in sequence with the variable. In Table I 
we listed for each variable the comparison star, the heliocentric  
dates of observed maxima on the different nights and the corresponding
amplitudes in the two filters. When we were unable to give a precise
determination of a light maximum we only give in column 3 the Julian
day.


    Gamma Pegasi

   The observed maxima are in agreement with the two latest
ephemerides published by Sareyan et al. (1975) and Koubsky et al.
(1981). As the phase lag between radial velocity maxima and light
maxima is different from one study to another, (0.25 P in Sareyan
et al., 0.18 in Koubsky et al.), we reanalysed separately all the
published photoelectric and spectrographic data and derived the
following ephemeris :

   Mvsun = 2426000.1106 + 0.15175022d E
                  +- 26         +- 3

Table I:  Light maxima dates and amplitudes


Star    Filter        Mlsun          Amplitudes   Comparison
                                     (mag)        star
                    (2400000+)
GammaPeg blue        46351            0.025        HR 26
-        uv          46351.367        0.04
-        uv          46351.529         -
-        b           46354.39:        0.02
-        b           46354.560         -
-        uv          46354.409        0.03
-        uv          46354.560         -


12 Lac   b           46348            0.02         HR 8603
  -      uv          46348            0.03
  -      b           46353.420        0.09
  -      uv          46353.424        0.14


BetaCep  b           46349.51:        0.045        HR 8227
  -      uv          46349.501        0.055
  -      b           46352.38:        0.03
  -      uv          46352.379        0.04





  The corresponding mean phase lag is 0.24 +- 0.03 P.

  In conclusion the period and amplitudes of gamma Peg appear to have
remained constant over the last fifty years.


  12 Lacertae

  This multiperiodic variable was observed at two different phases
of the beat period. The amplitude seems to be constant. Only one
maximum could be determined on the night when the amplitude of the
beat period is larger. Its date is in good agreement with the
ephemeris determined by Chapellier (1985) assuming a constant primary
period since 1939. On the contrary it departs (Delta T = 0.0230 d) from
the ephemeris which assumes that the primary period is decreasing
at a rate of 0.21 s/c.




    Beta Cephei


    The amplitude in both filters is almost twice that of our
last observations performed in 1983 (Chapellier, 1983). The cyclic
variation of this parameter pointed out by Chapellier (1986) is
confirmed. The period remains constant.



Acknowledgements: We thank J. Colin and D. Ducatel for technical
          assistance.





                  J.C. VALTIER, E. CHAPELLIER, P.J. MOREL,

                         J.M. LE CONTEL

                  Observatoire de Nice - L.A. 128
                  B.P. 139 - 06003 NICE CEDEX



References:


Chapellier, E. : 1985 Astron. Astrophys. 147, 135 [BIBCODE 1985A&A...147..135C ]
Chapellier, E. : 1986, Astron. Astrophys. Suppl. in press [BIBCODE 1986A&AS...64..275C ]
Koubsky, P., Harmanec, P., Krpata, J., Zdarsky, F. : 1981,
   Workshop on Pulsating B stars, eds. G.E.V.O.N. and C. Sterken,
   p. 161, Nice [BIBCODE 1981pbs..work..161K ]
Le Contel, J.M., Valtier, J.C., Sareyan, J.P., Zribi, G., Baglin, A. :
   1974, Astron. Astrophys. Suppl. 15, 115 [BIBCODE 1974A&AS...15..115L ]
Sareyan, J.P., Le Contel, J.M., Valtier, J.C. : 1976, Astron. Astrophys.
   Suppl. 25, 129 [BIBCODE 1976A&AS...25..129S ]
Sareyan, J.P., Valtier, J.C., Le Contel, J.M. : 1975, Astron.
   Astrophys. 44, 215 [BIBCODE 1975A&A....44..215S ]