COMMISSIONS 27 AND 42 OF THE IAU
             INFORMATION BULLETIN ON VARIABLE STARS
                          Number 3894

                                           Konkoly Observatory
                                           Budapest
                                           10 June 1993

                                           HU ISSN 0374 - 0676


            V577 OPHIUCHI: AN ECLIPSING BINARY WITH A
           NON-CIRCULAR ORBIT AND A PULSATING COMPONENT


During the course of an observing run aimed at determining the times of minima
of eclipsing binaries with non-circular orbits, the results of which will be
published elsewhere (Diethelm, 1993), a secondary minimum of V577 Ophiuchi was
followed with a photoelectric photometer at the 76 cm reflector of the
Rosemary Hill Observatory of the University of Florida.  Since the results of
this investigation were rather surprising, and since they might be of
considerable physical implication, we decided to publish them separately.

The observational history of V577 Ophiuchi=BD+06d 3679 has been summarized by
Meinunger (1981) and by Shugarov (1984).  Shugarov's UBV photometry showed,
that the orbit V577 Oph is non-circular (e=0.22+-0.08).  He determined its
colours to be B-V=+0.51 and U-B=+0.22 mag, respectively.  From an
estimate of the interstellar reddening E_B-V=0.2-0.3, a spectral type of ~~A8
was inferred.  A remarkable feature of Shugarov's light curve lies in the
fact, that his photoelectric observations at maximum light show a scatter in
excess of 0.1 mag, much larger than could be expected.  Our observations will
present an explanation for this.

The secondary minimum of V577 Oph at JD 2449105 was observed by us with the
photoelectric photometer at the 76 cm reflector of the Rosemary Hill
Observatory of the University of Florida.  The details of the observing
procedure will be published separately (Diethelm, 1993).  Because we were
primarily interested in the determination of the time of minimum, no filter was
used, in order to get the best signal to noise ratio possible, although the
night of JD 2449105 was of exceptional photometric quality.  The nearby star
BD+06d 3680 served as comparison star, while the UBV standard HR6629=gamma Oph
was used as check star.  In Figure 1, we present the differential photometry in
the sense variable minus comparison.

Evidently, some sort of pulsational variation is superimposed on the eclipse
light curve.  For reasons given below, this variation is intrinsic to V577 Oph,
and since it is observable throughout the secondary minimum, it is very likely
connected to the component not eclipsed in this minimum.  In order to give a
better representation of this secondary variation, we have subtracted the best
quadratic fit to the observations, simulating the eclipse light curve, from the
measurements.  Figure 2 shows these residuals.  We conclude, that the primary
component of V577 Oph not eclipsed at secondary minimum is a delta Scuti
variable with a period of about 0.07 days.  The spectral type found by Shugarov
supports this conclusion.


                              [FIGURE 1]

 Figure 1. Unfiltered differential photometry of the secondary minimum
          of V577 Oph relative to BD+06d3680 on JD 2449105.


As a measure to check this conclusion, we decided to observe V577 Oph outside
eclipse during the night of JD 2449122 (phase 0.357 to 0.372 according to the
elements of, Shugarov, 1984).  The night was again of good photometric
quality.  This time, we used a filter which together with the EMI 62565
photomultiplier tube yields magnitudes very close to the standard Johnson B
system at the Rosemary Hill Observatory.  In Figure 3 we depict the resulting
light curve, using the same scales as in Figure 2.  As special care was taken
to ensure that the variation was not due to the comparison star, these data
serve to prove the conclusion reached above.


                              [FIGURE 2]

 Figure 2. Residual variation after subtracting the eclipse light curve.

                              [FIGURE 3]

 Figure 3. Differential observations of V577 Oph in the instrumental
          b system at maximum light (JD 2449122).


The physical implication of our finding makes V577 Oph worthy of more thorough
investigation.  Especially the question, to what extent the variable
gravitational field due to the non-circular orbit in this binary has an
influence on the characteristics of the pulsation should yield some further
insight into the reliability of the models of stellar pulsation.

Acknowledgements:  We would like to thank the staff of the Dept. of Astronomy
of the University of Florida for their hospitality and for the allocation of
observing time at Rosemary Hill Observatory.  The continuing technical
assistance by J. Baker is especially acknowledged.  This research is supported
by a grant from the Emilia Guggenheim-Schnurr foundation.


                         R. DIETHELM
                         BBSAG
                         Rennweg 1
                         CH-4118 Rodersdorf
                         Switzerland

References:

Diethelm, R., 1993, in preparation
Meinunger, L., 1981, MVS, 9, 73
Shugarov, S. Yu., 1984, Astr. Circ., No. 1359, 4 [BIBCODE 1985ATsir1359....4S ]