COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2729

                                        Konkoly Observatory
                                        Budapest
                                        24 May 1985

                                        HU ISSN 0374 - 0676



      A CEPHEID-LIKE VARIABLE IN THE ANDROMEDA GALAXY WITH AN
                     EXTREMELY LONG PERIOD



  Hubble (1929) indicated H19 as the brightest variable in M31 with a
period of 5 years and an unstable light curve varying from cycle to cycle.
  The magnitudes of H19 were measured on 16 B plates taken with the 2m RCC
telescope of Rozhen Observatory. Our observations are given in Table I.
Hubble's magnitude scale mpg was transformed into the B system using the
formula mpg + 1.3 = B. (It is supposed that H19 does not change its mean
magnitude). By a computer period-finding programme we obtained a period
P = 1846 d. This value confirms Hubble's period. Figure 1 shows the light
curve of H19. Our observations are drawn by circles and those by Hubble by
dots. The large dispersion of the light curve can be explained in terms of
variations of the light curve from epoch to epoch as one can see in Hubble's
Figure 4 (1929). The absolute magnitude of H19 is MB <= -7.7mag

                 Table I.   Photometry of H 19
JD 2440000+      B          JD 2440000+    B
       4528.43   16.73      5557.6         17.7:
       4530.42   16.82      5622.33        17.65
       4883.42   16.86      5622.34        17.4
       5283.4    17.45      5622.36        17.4
       5287.31   17.5       5623.33        17.4
       5288.33   17.5       5624.33        17.4
       5296.39   17.5       5702.21        17.3
       5297.31   17.45      5998.42        17.35
       5348.31   17.5


  A similar variable in M31 is H42 with P = 176.7d. Ivanov and Kourtev
(1985) obtained the period of H42 to be constant but the light curve was
unstable.
  The flat-topped light curves of H19 and H42 remind of the variable S Vul.
The luminosity of this variable coincides with the value predicted by the
period - luminosity relation. However, there are variations in the light
curve of S Vul (Beyer, 1930) similar to those in H19 and H42.


                           [FIGURE 1]
                           [FIGURE 2]


  H19 is located in a group of stars which is not indicated as an OB
association by Van den Bergh (1964). The location of H42 is at the outer
edge of the arm which consists of older stars [Ivanov, 1985). Neither H19,
nor H42 belong to young star complexes with active process of star formation.
  Both H19 and H42 lie 0.5mag below the straight line of the period - 
luminosity relation (Figure 2). This fact can be explained by the absorption in
the M31 galaxy. A possible cepheid with a period of 75 days and an amplitude
AB~0.5mag is marked by V in Figure 2.



   We suppose that both H19 and H42 are cepheid-like variables. These
stars are similar to the classical cepheids by their luminosity but they
differ from them, as regards the shape and instability of their light curves
and probably their age.




                          G.R. IVANOV

                       Department of Astronomy
                       University of Sofia
                       Sofia, Bulgaria





References:

Baade, W., and Swope, H.H., 1965, Astron. J., 70, 212. [BIBCODE 1965AJ.....70..212B ]
Beyer, M., 1930, Astron. Abh., Erg.-Heft Astr. Nachr., 8, 3, C44.
Hubble, E., 1929, Astrophys. J., 69, 103. [BIBCODE 1929ApJ....69..103H ]
Ivanov, G.R., 1985, Astrophys. Space Sci., in press [BIBCODE 1985Ap&SS.110..357I ]
Ivanov, G.R., and Kourtev, R., 1985, Inf. Bull. Var. Stars, No. 2666.
Van den Bergh, S., 1964, Astrophys. J. Suppl., 9, 65. [BIBCODE 1964ApJS....9...65V ]