COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       Number 3350

                                           Konkoly Observatory
                                           Budapest
                                           7 July 1989

                                           HU ISSN 0374 - 0676


PHOTOELECTRIC PHOTOMETRY RESULTS OF THE ALGOL-TYPE ECLIPSING BINARY SYSTEM
                         RS VULPECULAE


RS Vulpeculae is an Algol-type variable consisting of a middle to late B-type
main sequence primary and a slightly larger secondary whose spectrum is
difficult to measure (Payne-Gaposchkin and Gaposchkin, 1938). Previous
investigators (Popper 1957, Hutchings and Hill 1971) have classified the
secondary as early as B9 to as late as G2. The secondary eclipse is slightly
displaced toward primary eclipse (Dugan 1923a) and various relative orbital
eccentricities have been reported, most of them near 0.05 (Plaskett 1922,
Sahade and Struve 1945). Baglow's (1952) solutions of earlier light curves
indicate the primary eclipse is an occultation, with mid-eclipse being only
partial. Dugan (1923b) found the duration of the primary eclipse to be on the
order of 15 hours out of the 4.5 day period.

The observations were made on 43 different nights from 1976 to 1981 using an
uncooled 1P21 photometer, with standard BV filters, mated to the f/15 20-inch
Cassegrain of the Lehigh Valley Astronomical Society, Allentown, PA. Variable
readings were flanked by comparison star and sky readings. Once or twice a
night readings were also taken of the check star. There were no
transformations made to the standard system, so all results are instrumental.
However, they closely match published values of visual magnitudes. The
comparison and check stars used were HD 180889 and HD 180811, respectively.
For the first nine nights HD 180811 was used as the comparison and HD 180889
was used as the check; data reduction methods took into account this switch.

In the plotted light curves the values of the deltas are in the sense of
variable-comparison, taking into account differential extinction and color
corrections. All sky and comparison readings were interpolated in the data
reduction program written by the author. Heliocentric phase was computed using
the epoch (Scarfe, 1973):

             J.D. Hel Min = 24432808.257+4.477635d E

The most obvious feature of the light curves is the large primary and shallow
secondary amplitudes, indicating widely separated components based on current
EA variable theory. In the visual light curve (Figure 1) the primary amplitude
A1 is 0.97 magnitude, and the secondary A2 is 0.05 magnitude. These numbers
are close to the A1=0.965 and A2=0.082 found by Dugan (1923a) but are slightly
less than the A1=1.00 and A2=0.11 obtained by Keskin (1985). Primary and
secondary amplitudes in blue light curve (Figure 2) were measured at A1=1.00
and A2=0.02 magnitude, again less than Keskin's values (A1=1.07, A2=0.10). In
both cases, however, it can be seen that the blue primary amplitude is slightly
greater than the visual primary amplitude.


                              [FIGURE 1]

                      Figure 1   RS Vul visual

                              [FIGURE 2]

                      Figure 2   RS Vul blue

                              [FIGURE 3]

                      Figure 3   RS Vul color index


The observed amplitudes are consistent with the B8 main sequence primary being
the brighter component of the system as reported earlier (Dugan 1923b Lb= .804)
and during primary eclipse most of its radiation being blocked off by the
slightly larger subgiant secondary. This would indicate that primary eclipse
is an occultation. Supporting this is the color index curve (Figure 3);
leading up to primary eclipse (phase=1.0) the color index becomes progressingly
larger, indicating that the radiation from the hotter bluer star is being
blocked by the secondary.

As seen from the visual curve the secondary is slightly displaced toward the
primary by 0.01 in phase, or 1.0746 hours (0.045 days). This value is
comparable to previous measurements of 0.03 to 0.04 days (Baglow 1952). The
displaced secondary implies an elliptical orbit. The length of the primary
eclipse seems to be slightly longer than 15 hours, in agreement with earlier
measurements by Dugan. The rounded minimum implies a partial eclipse,
suggesting a relatively highly inclined orbit. Previous estimates
(Payne-Gaposchkin and Gaposchkin 1938, Baglow 1952) have inclinations of 78 and
79 degrees.


R. WASATONIC
Computer Sciences Corporation
Space Telescope Science Institute
3700 San Martin Drive
Baltimore, MD 21218
U.S.A.

References:

Baglow, R. L. 1952, Pub. David Dunlap II(1) [BIBCODE 1952PDDO....2.....B ]
Dugan, R. S. 1923a, Pop Astr 31, 190 [BIBCODE 1923PA.....31R.190D ]
Dugan, R. S. 1923b, Pr. Cont, No. 6, 33
Hutchings, J. B. and Hill, G. 1971, Ap.J., 166, 382 [BIBCODE 1971ApJ...166..373H ]
Keskin, V. 1985, IBVS 2815
Payne-Gaposhkin, C. and Gaposchkin, S. 1938, Harvard Obs. Monographs, No. 5 [BIBCODE 1938HarMo...5.....P ]
Plaskett, J. S. 1922, Pub. Dominion Astrophysical Obs, Vol. 1, 141 
Popper, D. M. 1957, Ap.J. Supp 29, Vol. III, 139 [BIBCODE 1957ApJS....3..107P ]
Sahade, J. and Struve, O. 1945, Ap.J., 102, 486(3) [BIBCODE 1945ApJ...102..480S ]
Scarfe, C. D., et.al. 1973, IBVS 844