COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2235

                                    Konkoly Observatory
                                    Budapest
                                    1982 November 29

                                    HU ISSN 0374-0676

           HD 154973, A NEW SHORT PERIOD
                   VARIABLE STAR



    It is estimated that about a third of the stars in
the instability strip of the HR diagram are pulsators
(Breger, 1979). Keeping this in mind, whenever a known
variable star is going to be observed, systematically an
additional comparison star is chosen with the spectral
characteristics of a Delta Scuti star.
    In the present case, when HR 6391 was observed, three
comparison stars were chosen according to the criteria
stated by Warman et al. (1974) or Baglin et al. (1973),
namely that they must be of approximately the same magnitude
and spectral type of the problem star and that they should
be closer than two degrees to it. It is expected that at
least two of them should behave alike and probably the
third could be variable. The characteristics of the
observed stars are shown in Table I.


                   Table I

STAR                        Mv  Sp. T.     alpha (1982) delta (1982)   Type
                       
V HR 6391(=V620 Her)        6.8  A8V       17h 10m 18s +24deg 16'   Variable
C2 HD 155543                7.0   F2       17h 03m 35s +24deg 17'   Standard
C2 HD 155104                6.8   A0       17h 07m 53s +24deg 31'   Standard
C3 HD 154973(=BD+24deg3124) 8.2   A2       17h 07m 05s +24deg 37' New variable



    The observations were made with the 60-inch reflector
telescope at the Observatorio Nacional, San Pedro Martir,
Mexico, during the nights of May 20, 21, 22 and 23, 1982.
A dry-ice cooled 1P21 photocell was used with the Johnson's
V filter.
    Each observation is the result of at least four
ten-second integrations of every star and two ten-second
integrations of the sky. The sequence C1 sky V sky C2
sky C3 sky was followed uninterruptedly. The photometric
points reported in Figure 1 are the magnitude differences
between HD 154973 and the average of the standard stars C1
and C2 interpolated to the time of the observation. The
average of the points was then subtracted to establish the
zero baseline. Our data points are accurate to 0.005 mag;
the average time span between successive points is 0.008
day and the accuracy in time is of 0.001 day.


                      [FIGURE 1]

 Figure 1.: Photoelectric photometry of HD 154973.
            Ordinate is in magnitudes; to convert
            tome shown to HJD add 2445000.0.




   From Figure 1 it can be seen that the amplitude of
variation changes from night to night from 0.10 mag on May
20, 1972 to basically a constant star on May 22. On one
night (May 20) the calculated standard deviation of the
difference in magnitudes of the comparison stars is about
a third that of the magnitude of the variable star while,
on May 22 is about a half.
   This same behavior has been observed in HR 5005. This
star was first reported by Danziger and Dickens (1967) but
later, Valtier (1971) failed to detect any light variability
on an observing run of almost five hours but the variability
of the star was later confirmed by Jerzykiewicz (1975), and
Pena et al. (1982). This is a behavior one could expect if
more than one pulsation mode is present since at times
destructive interference may occur.
   By now, nothing can be said about the period of this
star, but it is of the order of hours. Due to the fact
that it has a spectral type A2, low amplitude and short
period of variation, it could be said that it is a probable
delta Scuti star. More detailed observations are encouraged
since they are necessary to determine its periodic content.
   The observations reported in this paper have been
submitted to the IAU Archives of Unpublished Observations
of Variable Stars (Breger, at the University of Texas-Austin).
   We would like to thank the staff of the Observatorio
Astronomico Nacional for the assistance provided. One of



us, M.A.H., would also like to acknowledge the University of
Mexico for the observational time provided.





                  MARCO A. HOBART
                  Facultad de Fisica
                  Universidad Veracruzana
                  Apartado Postal 270
                  Jalapa, Ver., Mexico


                  JOSE H. PENA and
                  ROSARIO PENICHE
                  Universidad Nacional Autonoma de Mexico
                  Apdo. Postal 70-264
                  04510 Mexico, D. F.





References:

Baglin, A., Breger, M., Chevalier, C., Hauck, B., Le Contel,
      J. M., Sareyan, J. P., and Valtier, J. C. 1973,
      Astron. and Astrophys. 23, 221. [BIBCODE 1973A&A....23..221B ]
Breger, M., 1979 Pub. Astron. Soc. Pac., 91, 5. [BIBCODE 1979PASP...91....5B ]
Danziger, I. J., and Dickens, R. J. 1967, Ap. J., 149, 55. [BIBCODE 1967ApJ...149...55D ]
Jerzykiewicz, M. 1975, Pub. A.S.P., 87, 817. [BIBCODE 1975PASP...87..817J ]
Pena, J. H., Peniche, R., Gonzalez, S. F., submitted for
      publication, 1982. [BIBCODE 1983A&AS...53...81P ]
Warman, J., Malacara, Z., and Breger, M. 1974, Rev. Mexicana
      Astr. and Astrof., 1, 143. [BIBCODE 1974RMxAA...1..143W ]