COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1745

                                    Konkoly Observatory
                                    Budapest
                                    1980 February 25


                 PHOTOMETRY OF HR 5110


The RS CVn binary HR 5110 (HD 118616, V=+4.97) was observed on a total of nine
nights in June and July 1979 at Biruni Observatory and at Villanova University
Observatory, prompted by the observations of large radio outbursts from the
system in late May and June 1979 (Feldman, 1979; Viner, 1979). The Biruni
observations were obtained using the 51-cm, f/13.5 Cassegrain reflector
equipped with an unrefrigerated RCA 4509 multiplier photocell. A Leeds and
Northrup Speedomax chart recorder was used to record the amplified
photomultiplier output. The Villanova observations were made using a
thermoelectrically cooled (-10degC) RCA C31034 Gallium Arsenide photocell
attached to the 38-cm reflector. A microprocessor-controlled integrating
system recorded the observations (McCook and Maloney, 1979). The comparison
star was 25 CVn (HR 5127, V=+4.84, A7 III). Matched pairs of intermediate and
narrow-band interference filters centered near the Balmer H_alpha line were
used at the two stations. The bandpass of the intermediate-band H_alpha filter
(H_alpha w) is sufficiently broad (HWFH~280 A) to be little affected by the
presence of the line feature. The filter characteristics are given in Guinan
et al. (1979) and Guinan and McCook (1974) for Biruni and Villanova,
respectively. Additional observations were obtained at Biruni using Stromgren
y and u filters.

The observing sequence was the usual pattern of sky-comparison-
variable-comparison-sky, with each observation typically consisting of a 50 sec
deflection. The effects of differential atmospheric extinction were removed.
The differential H_alpha w, y and u magnitudes in the sense (V-C) are given in
Fig.1 as a function of orbital phase, computed from the ephemeris of Burke et
al. (1979):

JD Hel. 2443639.52+2.6131738d*E


                            [FIGURE 1]

        Fig. 1. H alpha w, y and u light curves of HR 5110

where zero phase corresponds to the conjunction in which the F-star is farthest
from the observer (superior conjunction). H_alpha indices were calculated in
the usual manner:

                                 flux through narrow-band filter
alpha-index=constant -2.5 x log --------------------------------
                                 flux through broader-band filter

The mean, standardized alpha-index of the variable is typical for its assumed
spectral type of F2 IV (Conti, 1967) so that there is no evidence for H_alpha
emission. Bopp and Talcott (1980) have also reported an absence of H_alpha
emission. The alpha index of the comparison is also nominal for its assumed
spectral type. Furthermore, a transformation of the y observations indicates
no significant change in the V-magnitude of the system since 1977. As can be
seen from Fig. 1 the amplitude of the light variation is small, ~0.13 mag in
H_alpha, with slightly smaller variations in the other two bandpasses, and is
about the same as reported by Hall et al. (1978) during 1977-1978. The
occurence of minimum light and maximum light at the superior and inferior
conjunctions, respectively, of the F-star are in accord with the light
variation expected from the reflection effect in a system seen at low
inclination. A full discussion will be published later.


J.D. DORREN
and
N. RIAZI
Biruni Observatory
Shiraz, Iran

E.F. GUINAN
and
M.K. HART
Department of Astronomy
Villanova University
Villanova,
Pennsylvania 19085

References:

Bopp, B.W., and Talcott, J.C. (1980) Astron. J. 85, 55 [BIBCODE 1980AJ.....85...55B ]
Burke, E.W., Eaton, J.A., Fisher, G.F., Hall, D.S., Louth, H., Sabria, J.D.,
   Skillman, D.R. (1980) preprint (to be submitted to the Astron, J.) [BIBCODE 1980AJ.....85..744B ]
Conti, P.S. (1967) Astrophys. J. 149, 629 [BIBCODE 1967ApJ...149..629C ]
Feldman, P.A. (1979) I. A. U. Circ. No. 3366 [BIBCODE 1979IAUC.3366....1F ]
Guinan, E.F. and McCook, G.P. (1974) Pub. Astron. Soc. Pac. 86, 947 [BIBCODE 1974PASP...86..947G ]
Guinan, E.F., Dorren, J.D., Siah, M.J. and Koch, R.H. (1979) Astrophys. J. 229,
   296 [BIBCODE 1979ApJ...229..296G ]
Hall, D.S., Henry G.W., Vaucher, C.A., Louth, H., Lovell, L.P., Landlis, H.J.,
   Brooks, P., Schlegel, R. and Wasatonic, R. (1978) 
   Inf. Bull. Var. Stars No. 1459
McCook, G.P. and Maloney, F.P. (1979) Bull. Am. Astron. Soc. 11, 649 [BIBCODE 1979BAAS...11..649M ]
Viner, M.R. (1979) I. A. U. Circ. No. 3368 [BIBCODE 1979IAUC.3368....3V ]