COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1872

                                 Konkoly Observatory
                                 Budapest
                                 1980 November 24

                                 HU ISSN 0374-0676




        ON THE PHOTOMETRIC ELEMENTS OF RX Her




   In Popper's (1980) excellent review on the stellar
masses proper emphasis has been placed on the importance
of considering the spectroscopic estimates of the ratio
of the light of binary components in order to avoid giving
misleading solutions of eclipsing binary lightcurves. In
particular, Popper (1980) considered the double-lined
spectrum eclipsing binary RX Her (=HD170757; for the history 
of this star see, e.g., Popper (1980) and references
cited therein) as an illustrative example of these kinds
of problems ccnnected with binary lightcurve analyses. He
stated that Cester et al.'s (1978) reanalysis of Wood's
(1948) lightcurve of RX Her is very questionable, since
it leads to a too large light ratio ( L_h /L_c =2.44) as compared 
with Petrie's (1950) spectroscopic estimate ( L_h/L_c=
=1.44). But this conclusion is due to an unfortunate
misunderstanding concerning the meaning of the entries L_h
and L_c given in Table 2 of the paper by Cester et al. (we
recognize that this point is somewat unclear in the text):
in fact, these entries are the normalized fractional luminosities 
integrated over 4 pi steradians and not the monochromatic 
(i.e. blue) fractional luminosities. For RX Her,
the light ratio (in blue) computed by Cester et al. is
indeed 2.12, whereas the surface flux ratio is J_h/J_c= 1.18
(the ratio of the observed depths of minima is equal to
1.22). As a consequence, in view of the large uncertainties
affecting Petrie's estimate for the light ratio, Cester et
al.'s photometric solution appears to be consistent with
the available spectroscopic results.


              G. GIURICIN and F. MARDIROSSIAN
              Osservatorio Astronomico di Trieste
              via G.B. Tiepolo 11
              I-34131 Trieste, Italy












References:
Cester,B., Fedel,B., Giuricin,G., Mardirossian,F., Mezzetti,
    M.: 1978, Astron. Astrophys. Suppl. 33,91 [BIBCODE 1978A&AS...33...91C ]
Petrie,R.M.: 1950, Publ. Dom. Astrophys. Obs. Victoria 8,319 [BIBCODE 1950PDAO....8..319P ]
Popper,C.M.: 1980, Ann. Rev. Astron. Astrophys. 18,115 [BIBCODE 1980ARA&A..18..115P ]
Wood,F.B.: 1948, Astrophys.J. 110,465 [BIBCODE 1949ApJ...110..465B ]