COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1548

                                 Konkoly Observatory
                                 Budapest
                                 1979 February 12




   SOME PECULIARITIES OF THE PULSATING STAR DELTA SCUTI


   The pulsating star delta Sct differs in many respects from the
other Delta Scuti stars. Frolov (1972) proposes that delta Sct is
perhaps a dwarf cepheid. For this star Elliott (1974) gives a
series of (especially photometric) peculiarities and discrepancies
of the observational data.
   It is of interest to study other characteristics of delta Sct.
Using observational data of 59 Delta Scuti stars (Breger and
Bregman, 1975) we have estimated their pulsation modes and have
calculated the evolution and pulsation masses (Tsvetkov, 1977 a,
b). Our results have indicated new peculiarities of delta Sct, which
distinguish this star from the remaining Delta Scuti stars.
   1. By comparison of the photometric M_v and "theoretical"
M_bol absolute magnitudes (the latter are derived from theoretical
period - effective temperature - luminosity relations for the
four lowest modes) we have estimated the pulsation modes. The
difference between the two kinds of luminosities for the estimated 
in this manner mode of a given star does not exceed 0.2-0.3mag.
But for delta Sct this difference is about 1 mag: M_v=1.62m M_bol=
0.56m for fundamental mode (for overtones M_bol is still smaller).
   2. The pulsation M_Q and evolution M_e masses of all stars
studied by us are consistent (in the limits of the accuracy of
determination). For delta Sct, however, we have derived a too large
difference: M_Q=0.57 M_Sun, M_e=1.66 M_Sun.
   Using a scanning spectrometer moreover, Doroshenko and
Glushneva (1971) have observed a variable emission at Lambda 4501
in the delta Sct spectrum. The presence of a strong emission during
the larger part of the pulsation period just at lambda 4501 A (if
it would be confirmed by new observations) is perhaps another
peculiarity of this star. We note that a weak emission in the
spectral lines of the hydrogen (Valtier et al., 1975) or calcium
(Dravins et al., 1977) has been observed in certain Delta Scuti
stars.
    The results of the investigations given above confirm
Elliott's conclusion that "in nearly every respect delta Sct is the
exception rather than the rule" for Delta Scuti stars. It is
possible that delta Sct belongs to another type of variable stars,
the mass is not "normal" and the evolution stage is different,
or the ordinary photometric calibrations are not applicable to
this star. Further detailed observations of delta Sct are needed to
clarify these problems. The investigators must pay special attention 
to this star.
    In conclusion we note that only rho Pup of the remaining
stars studied by us has similar but less expressed peculiarities:
M_v=1.82m, M_bol=1.31m for fundamental mode; M_Q=0.98 M_Sun, M_e=1.59 M_Sun.
A chromospheric-type emission has been observed in this star
(Dravins et al., 1977).




                          TS. TSVETKOV
                      Department of Astronomy
                      University of Sofia
                      Anton Ivanov Street 5
                      1126 Sofia, Bulgaria



References:

Breger, M.,and Bregman, J.N., 1975, Ap.J., 200, 343 [BIBCODE 1975ApJ...200..343B ]
Doroshenko, V.T., Glushneva, I.N., 1971, Astron.Circ., No. 652, 3 [BIBCODE 1971ATsir.652....3D ]
Dravins, D., Lind, J., Sarg, K., 1977, Astron.& Astrophys., 54, 381 [BIBCODE 1977A&A....54..381D ]
Elliott, J.E., 1974, A.J., 79, 1082 [BIBCODE 1974AJ.....79.1082E ]
Frolov, M.S., 1972, Astron. Circ., No. 671, 3 [BIBCODE 1972ATsir.671....3F ]
Tsvetkov, Ts., 1977 a, Dissertation, Moscow
Tsvetkov, Ts., 1977 b, Nauchnye Informatsii, 37, 63 [BIBCODE 1977NInfo..37...63T ]
Valtier, J.C., Le Contel., J.M., Sareyan, J.P., Baglin, A., 1975,
       I.A.U. Colloquium, No. 29, Budapest, Part II, 243