COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1339

                                    Konkoly Observatory
                                    Budapest
                                    1977 September 16





   POSSIBLE RELATION BETWEEN THE PULSATION CONSTANT AND
         THE PERIOD IN DELTA SCUTI VARIABLES




    Owing to theoretical arguments and observational results
of Delta Scuti stars, the pulsation constant has been considered 
variable with the mode of pulsation but constant for each
mode (Cogan 1970, Chevalier 1971, Petersen and Jorgensen 1972,
Jorgensen and Petersen 1974).
    Nevertheless, the observed Q and P reported by Breger and
Bregman (1975), plotted in Figure 1, seem to show a continuous
relation between Q and P.
    Further, if we consider the two zones of the diagram Mv
vs Te reported by Breger and Bregman (1975) as representative
for "hot" and "cold" variables, pulsating respectively in the
first and fundamental overtone, we can compute the fundamental
period of the "hot" variables multiplying their periods by
P0/P1 = Q0/Q1 = 1.324. Then, from the data by Breger and Bregman
(1975), by least squares, we can obtain
           log Q0 = 0.22 log P0 - 1.30.
             +-.11 +-.08         +-0.9

    This relation could lessen the discrepancy between the
theoretical and the empirical relation Mbol=Mbol(P,Te,M), and
make more acceptable the values of the masses presently adopted
for Delta Scuti stars.
    We believe that it should be useful to take in account the
above mentioned remarks in the theoretical models of Delta Scuti
variables.

                      [FIGURE 1]

  Values of Q (Breger and Bregman, 1975) versus periods for
  Delta Scuti stars: (dot) fundamental mode, Q>= 0.29; 
  (o) first overtone, 0.23 <= Q <= 0.29; (x) second overtone, Q < 0.23.



               E. ANTONELLO, M. FRACASSINI and L.E. PASINETTI
               Osservatorio Astronomico di Milano - Merate
                     Via Brera n. 28, 20121 Milano, Italia




References:
Breger, M. and Bregman, J.N. 1975, Astrophys.J. 200, 343 [BIBCODE 1975ApJ...200..343B ]
Chevalier, C. 1971 Astron. and Astrophys. 14, 24 [BIBCODE 1971A&A....14...24C ]
Cogan, B.C. 1970, Astrophys.J. 162, 139 [BIBCODE 1970ApJ...162..139C ]
Jorgensen, H.E. and Petersen, J.O. Astron. and Astrophys. 35, 215 [BIBCODE 1974A&A....35..215J ]
Petersen, J.O. and Jorgensen, H.E. 1972, Astron.and Astrophys. 17, 367 [BIBCODE 1972A&A....17..367P ]