COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                         Number 2591

                                             Konkoly Observatory
                                             Budapest
                                             21 September 1984

                                             HU ISSN 0374 - 0676


       THE PERIOD AND PHOTOELECTRIC LIGHT CURVES OF DM Del

  DM Del = BD+13d 4478 was discovered as an Algol type eclipsing binary by
Hoffmeister (1935). Tsesevich (1954) obtained the following light elements
from his visual observations:

       Hel.Min. JD = 24 30 663.067 + 0.84456dxE.

Perova (1952) gave the corrected light elements as follows:

       Hel.Min. JD = 24 30 663.067 + 0.8446725dxE.

Ishtshenko (1955) confirmed the above Perova's elements and classified the
light curve of the system as beta Lyrae. Schneller (1960) observed DM Del
photoelectrically in one colour and analyzed his light curve. Diethelm
(1976) gave the period of 0.333042d from the visual observations. But several
observers showed that this period was not correct. Berthold (1978) observed
the system visually and photographically and gave the following light
elements:

       Hel.Min. JD = 24 42 685.302 + 0.8446733dxE.

According to his photographic light curve, the depths of the minima are
approximately equal.
  In order to check the period of DM Del, we observed it photoelectrically
during the observational seasons of 1982 and 1983 in 12 different nights.
The observations were made with the 48 cm Cassegrain reflector equipped with
an unrefrigerated EMI 9781A photomultiplier tube and with B,V filters very
close to Johnson's system. BD +14d4379 was used as comparison star. Three
primary and four secondary times of minima were obtained. These minima are
given in Table I where (O-C)1 residuals are computed with the elements in
GCVS (1969). It is seen that all (O-C)1 values are large and positive. Therefore,
using these photoelectric minima given in Table I and the photoelectric
minimum time of Schneller, the new light elements were calculated by the
method of weighted least squares, as follows:

       Hel.Min. JD = 24 45 523.4368 + 0.8446747dxE.
                                +-9         +-3

Table I. The times of minima of DM Del

Hel.Min. JD    Min.   Filter   (O-C)1       (O-C)2
2445194.4394     II    B,V      0.0491       0.0034
    200.345      II    B,V      0.042       -0.004
    219.3558      I    B,V      0.0476       0.0019
    523.4355      I    B,V      0.0452      -0.0013
    605.3694      I    B,V      0.0459      -0.0008
    613.396      II    B,V      0.048        0.001
    619.3059     II    B,V      0.0453      -0.0014


                            [FIGURE 1]

             Figure 1.  Light and colour curves of DM Del


  The light and colour curves are presented in Figure 1 where the individual 
magnitude differences (variable minus comparison) have been plotted
against the phases. The phases in the figure and (O-C)2 values in Table I. were
calculated with the new light elements. The light curves show that DM Del is
a typical Beta Lyrae type eclipsing binary. The system varies about 0.540m and
0.510m at the primary, 0.220m and 0.200m at the secondary minimum in blue and.
yellow light, respectively. The colour curve shows that there is a noticeable 
colour variation at the primary minimum.


                       N. GUDUR, C. SEZER, O. GULMEN
                       Ege University Observatory
                       Bornova, Izmir, Turkey

References:

Berthold, T.: 1978, Mitt. der Bruno-H.-Burgel-Sternwarte, Hartha, 14, 11.
Diethelm, R.: 1976, BBSAG Bull., 29.
Hoffmeister, C.: 1935, Astron. Nachr., 255, Nr. 6118. [BIBCODE 1935AN....255..401H ]
Ishtshenko, I.M.: 1955, Perem. Zvezdy, 10, 403. [BIBCODE 1955PZ.....10..403I ]
Perova, N.B.: 1952, Perem. Zvezdy, 9, 147.
Schneller, H.: 1960, Astron. Nachr., 285, 265. [BIBCODE 1960AN....285..265S ]
Tsesevich, V.P.: 1954, Odessa Izv., 4, 2, p. 16.