COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2300

                                            Konkoly Observatory
                                            Budapest
                                            1983 March 24

                                            HU ISSN 0374-0676

              UBV OBSERVATIONS OF YY Eri

  The 8th magnitude W UMa-type eclipsing binary system YY Eri
appears to be a fairly representative example of the W subgroup
of these stars (Binnendijk, 1965, 1970; Rucinski, 1973; Yamasaki,
1975) - possibly the first to be recognized as such (Struve, 1947).
In keeping with this character is the tendency of period increase
(Yamasaki, op.cit.) noted by Cillie (1951), Huruhata et al. (1953)
and Kwee (1958), and taken to have constant retardation by the
Purgathofers (1960), though Bhattacharyya (1967) indicates that
this need not be the case.


   The star was observed during five nights, over the period
Jan. 22-Feb. 7 1983, at the Black Birch Outstation of Carter
Observatory, using the 41cm Ruth Crisp telescope and optical filters
which have characteristics close to standard UBV. The observations
cover the primary minimum three times and part of the secondary on
one night (see diagrams). Data in the phase range ~ 0.45-0.7 were
obtained on the night of Feb. 6 with less than perfect weather
present (thin cirrus), which deteriorated somewhat during the
observations. This is reflected in the increased scatter of the
given points, and the "normalizing" (averaging) of later data
from that night. The remaining data are individual points
straightforwardly obtained by a standard DC amplifier/chart
recorder system, with a minimum of reductional procedures applied
through the University of Wellington's VAX computer. (The diagrams
shown have been produced as part of the output from this computer).


   The principle comparison and check stars were the same as those
used by Bhattacharyya (op.cit.). The discrepancy between
comparison and check (s.d. 0.022mag in B and U) is rather greater
than one would like; it may be associated with some microvariability 
of the K-type check star.




                             [FIGURE 1]
                             [FIGURE 2]
                             [FIGURE 3]



    A preliminary epoch of minimum is given as HJD 2445356.9456.
This will give an O-C of -0.0086 days when reckoned by the light
elements of the Purgathofers, though this is reduced to -0.0045
days when calculated from Strauss' (1976) more recent light
elements. While the residual is still rather large, it is less
than that given by Strauss when comparing his own observed time of
minimum with that calculated by the ephemeris of the Purgathofers.
Strauss (op.cit.) concluded that the period was nonmonotonically
varying, or that the Purgathofers did not estimate it accurately
(though the error limit specified by the latter is much less than
could explain the discrepancy).


    Perhaps this period variation is related to the "exceptionally
interesting phenomenon" of apparent spectroscopic luminosity
variation emphasized by Struve (op.cit.), which in turn may be
connected with the polarization effects considered by Oshchepkov
(1974), (though the latter's interpretation of the sense of the
supposed "stream" is surely at variance with other effects). In
any case, the system merits close attention as a potentially informative 
member of this enigmatic class of object.




                EDWIN BUDDING
                Carter Observatory
                P.O. Box 2909,
                Wellington, 1,
                NEW ZEALAND.


References:

Bhattacharyya, J.C.: 1967, Kodaikanal Observatory Bull. Ser. A
  No. 181
Binnendijk, L.: 1965, Astron. J. 70, 209 [BIBCODE 1965AJ.....70..209B ]
Binnendijk, L.: 1970, Vistas in Astronomy 12, 217 [BIBCODE 1970VA.....12..217B ]
Cillie, G.G.: 1951, Harv. Bull. No. 920, 41
Huruhata, M., Dambara, T. and Kitamura, M.: 1953, Tokyo Ann.
  3, Sec. Ser. No. 4, 227
Kwee, K.K.: 1958, B.A.N. 14, No. 485, 131 [BIBCODE 1958BAN....14..131K ]
Oshchepkov, V.A.: 1974, Abastumani Bull. 45, 51
Purgathofer A. and Purgathofer, I.: 1960, Mitt. Wien 10, 195
Rucinski, S.M.: 1973, Acta Astron. 23, 79 [BIBCODE 1973AcA....23...79R ]
Strauss, F.M.: 1976, P.A.S.P. 88, 531 [BIBCODE 1976PASP...88..531S ]
Struve, O.: 1947, Astrophys. J. 106, 92 [BIBCODE 1947ApJ...106...92S ]
Yamasaki, A.: 1975, Astrophys. Space Sci. 34, 413 [BIBCODE 1975Ap&SS..34..413Y ]