COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2794
                                      Konkoly Observatory
                                      Budapest
                                      18 September 1985

                                      HU ISSN 0374 - 0676


        BD-7deg1108, A NEW DELTA SCUTI VARIABLE
             


   The star BD-7deg1108 in the Orion OB1 association was measured 
in the Geneva photometric system as part of a photometric
program for all stars belonging to the Curchod and Hauck (1979)
catalogue of Am stars. This 10th mag. star appeared to vary 
significantly within one observation requiring 12 minutes of 
integration time. Consequently, we have observed this star frequently 
during 14 nights in late 1984 at the Swiss station at La Silla
Observatory, Chile. Between JD 2445738. and JD 2446043. we have
gathered 128 measurements showing a standard deviation of 0.066
mag. In the subsequent analysis an early observation obtained on
JD 2445347. is also included.


   We have used a Fourier method (Deeming, 1975) and a phase
dispersion minimization technique (Stellingwerf, 1978) to determine 
the frequency of 12.7087 +/- 0.0003 c/d, with a corresponding
period of 0.078686 +/- 0.000002 days. The error in frequency 
represents (1/10T) c/d, T being the time base of the data. The phase
diagram of all but two observations is presented (Figure 1). Those
two observations deviate by more than 0.04 mag from the fitted
light curve, shown as a continuous curve in Figure 1. The fit
includes the first harmonic of 12.7087 c/d in order to reduce the
residual scatter to 0.010 mag in the V-filter and 0.009 mag. in
the Geneva [B-V] colour index. Such a residual scatter is 
representative of the noise level expected in the observations of a
10th mag. star in the system as indicated by Figure 8 in the Third
Catalogue of Stars measured in the Geneva Observatory Photometric
System (Rufener, 1981). The observed full amplitudes are 0.18 mag.
in V and 0.26 mag. in B. Colour variations are in antiphase with
the light variations (Figure 2).


                        [FIGURE 1]

 Figure 1: Phase diagram of the 127 V-magnitudes.
           The fit represents: 
            f(t) = 9.878m + 0.092m cos(2pi 12.7087(t-t0)+0.70)
                          + 0.013m cos(2pi 25.4174(t-t0)+0.40)
                          with t0 equal to JD 2445347.0.

                        [FIGURE 2]

 Figure 2: Phase diagram of the 129 [B-V] Geneva colours. The
           crosses represent the two observations not plotted in Figure 1.
           The fit here is: 
            f(t) = -0.570m + 0.038m cos(2pi 12.7087(t-t0)+0.80)
                           + 0.005m cos(2pi 25.4174(t-t0)-0.95)



    In conclusion, we report the Delta Scuti type variability
of BD-7deg1108 with a period of 1h 53min and a V-amplitude of
0.18 mag. The photometric parameters d=1.193 and B2-V1 = 0.120
locate this star inside the instability strip of the observational 
HR-diagram for A and F type stars in the Geneva system.


    Smith (1972) classified this star as metallic lined with
SP(K) = A6, SP(H) = A9 and SP(ML) = F2. From the photometric
point of view we cannot confirm the metallicity character as
both, the Delta m2-parameter (= -0.027) and the m-parameter (= -0.042)
have values resembling those of the normal A stars. Hauck (1978)
derived a mean Delta m2 = -0.009 for normal A stars versus Delta m2 = +0.013
for classical Am stars, while Nicolet and Cramer (1983) found
that Am stars tend to have 0.035< m < 0.120. The metallicity 
character of BD-7deg1108 has already been questioned by Hesser,
Mc Clintock and Henry (1977).


    A more detailed study of the observations of BD-7.1108 is
presently being undertaken. The individual observations will be
published at a later stage.


    We gratefully acknowledge Dr. Ir. M. Burnet for observing
some fine light curves of BD-7deg1108 at La Silla, Dr. G. Burki
for kindly putting his computer programs at our disposal and
Prof. F. Rufener to have pointed out the variable character of
BD-7deg1108 and to have provided for observing facilities with the
instruments of the Observatoire de Geneve.



                       PATRICIA LAMPENS

                       Observatoire de Geneve
                       CH-1290 SAUVERNY/SUISSE


                       on leave of absence from the:

                       Astronomisch Instituet
                       Katholieke Universiteit Leuven
                       Celestijnenlaan 200 B
                       B-3030 HEVERLEE/BELGIUM





References :


Curchod, A. and Hauck, B.: 1979, Astron. Astrophys. Suppl. Ser.
   38, 449. [BIBCODE 1979A&AS...38..449C ]
Deeming, T.J: 1975, Astrophys. Space Sci. 36, 137. [BIBCODE 1975Ap&SS..36..137D ]
Hauck, B.: 1978, Astron. Astrophys. 69, 285. [BIBCODE 1978A&A....69..285H ]
Hesser, J.E., Mc Clintock, W. and Henry, R.C.: 1977, Astrophys.J.
   213, 100. [BIBCODE 1977ApJ...213..100H ]
Nicolet, B. and Cramer, N.: 1983, Astron. Astrophys. 117, 248. [BIBCODE 1983A&A...117..248N ]
Rufener, F.: 1981, Astron. Astrophys. Suppl. Ser. 45, 207. [BIBCODE 1981A&AS...45..207R ]
Smith, M.A.: 1972, Astrophys. J. 175, 765. [BIBCODE 1972ApJ...175..765S ]
Stellingwerf, R.F.: 1978, Astrophys. J. 224, 953. [BIBCODE 1978ApJ...224..953S ]