COMMISSION 27 OF THE I.A.U.
       INFORMATION BULLETIN ON VARIABLE STARS
                    NUMBER 278

                                 Konkoly Observatory
                                 Budapest
                                 1968 Juni 5


   THE SECONDARY PERIOD OF THE RRab STAR TT CANCRI


This variable star off RR Lyrae type was recently investigated by W.S. FITCH,
W.Z. WISNIEWSKI and H.L. JOHNSON (Comm.  Lunar and Planetary Laboratory No
71, Vol. 5, Part 2). Their photoelectric observations suggest the presence of
Blashko-effect.

In order to investigate the nature of the light curve variation and determine
the secondary period 1080 photoelectric observations have been obtained in
yellow, blue and ultraviolet with the 24 inch telescope at the Konkoly
Observatory. From December 1967 to April, 1968 thirteen light maxima were
observed, which shows large variations in height and phase.

The first column of the Table contains the times of the observed maxima, the
second column the O-C values computed by the following elements:

Max.hel.=J.D. 2439944.3670 +0.^d5634494*E

In the third and fourth columns the heights of the maxima relative to the
comparison star are listed in yellow (Delta M_y) and blue (Delta M_b) in the
instrumental system.

J.D.max.hel.       O-C    Delta M_y   Delta M_b
2439826.6074    +0.0013    -0.44      -0.35
    840.707:    +0.0147    -0.56      -0.51
    856.4738    +0.0049    -0.67      -0.66
    865.4749    -0.0092    -0.55      -0.52
    875.6060    -0.0202    -0.41      -0.38
    878.4300    -0.0134    -0.42      -0.37
    905.4841    -0.0049    -0.31      -0.25
    914.5085    +0.0043    -0.35      -0.28
    917.3289    +0.0075    -0.42      -0.38
    935.3642    +0.0124    -0.62:     -0.58
    940.4285    +0.0056    -0.60      -0.57
    944.3670     0.0000    -0.58      -0.53
    966.324:    -0.0175    -0.42      -0.37

In the upper part of the Figure the brightness variations of the light maxima
are plotted against Julian Date. In the lower part the phase oscillations of
the light maxima and the point at Delta m_b=-0^m1 on the rising branch (in
blue) are shown. The maximum retardation in phase is reached when the
amplitude nearly has its mean value and is increasing.


                          [FIGURE 1]

The oscillations both in the height of maxima and in their phase suggest a
secondary period of about 89 days:

Min.ampl.=J.D.2439903+89^d.n

This formula is in good agreement with the observations obtained by FITCH, etc,
as well.

Next year further observations will be carried out in order to determine a more
exact value for the secondary period.


Konkoly Observatory, Budapest
                                          B. SZEIDL