COMMISSION 27 OF THE I. A. U.
     INFORMATION BULLETIN ON VARIABLE STARS
                 Number 1801

                               Konkoly Observatory
                               Budapest
                               1980 June 9






   REDISCUSSION OF THE PHOTOMETRIC ELEMENTS OF SW LYN



   The light variation of the eclipsing binary SW Lyn has been the
subject of several photoelectric investigations (Gleim 1967, Vetesnik
1968, Vetesnik 1977).Vetesnik(1977) also obtained a single-lined
radial velocity curve, but the eccentricity reported by him is probably
spurious according to Wilson's (1979) rediscussion of Vetesnik's (1968)
lightcurve in yellow light.
   In view of the appreciably discordant photometric elements computed
by Gleim (1967), Vetesnik (1968), and Wilson (1979), we have reanalyzed
Vetesnik's (1968) two-colour photoelectric observations by using Wood's
(1972; 1973-1978) lightcurve synthesis numerical model. In the table
we list our new photometric elements ( for the explanation of the
symbols see Mardirossian et al.(1980)). The chief variable parameters
are the orbital inclination angle i, the unperturbed radius r_h of the
hotter component, the ratio k=r_c /r_h of the unperturbed radii and the
temperatures T_h and T_c of the two components. The mass ratio q=M_c/M_h
was also taken as a free parameter.
   That no good concordance exists between our two photometric solutions
emphasizes that SW Lyn is a very complicated system; for any formalized
binary model it is probably difficult to represent this binary well.
However, it is likely that SW Lyn is a contact system; its secondary
member (probably around K0 according to our values of T_c ) seems to be
slightly farther from the ZAMS than its F2V companion, whenever a mass
typical of dwarfs of the same spectral type is assumed for this hotter
star.

        Table


lambda    yellow        blue
i         77.7+-0.6     84.7+-0.6
r_h       0.398+-0.005  0.395+-0.003
k         0.747+-0.019  0.642+-0.005
a_h       0.422         0.417
b_h       0.408         0.404
c_h       0.390         0.387
a_c       0.338         0.276
b_c       0.296         0.252
c_c       0.276         0.241
T_h(eq)   6910+-110     6860+-160
T_h(pol)  7200          7130
T_c(eq)   4740+-40      4640+-50
T_c(pol)  4820          4700
u_h       0.59          0.84
u_c       0.75          1.00
beta_h    0.25          0.25
beta_c    0.08          0.08
w_h       1             1
w_c       0.5           0.5
L_h       0.896         0.924
L_c       0.104         0.076
q         0.37+-0.02    0.34+-0.01
          1.59          1.36





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


References:


Gleim,J.K., 1967, Astron.J.72,493. [BIBCODE 1967AJ.....72..493G ]
Mardirossian,F., Mezzetti,M., Predolin,F., and Giuricin,G., 1980,
   Astron.Astrophys.Suppl.40,57. [BIBCODE 1980A&AS...40...57M ]
Vetesnik,M., 1968, Bull.Astron.Inst.Czechosl.19,110. [BIBCODE 1968BAICz..19..110V ]
Vetesnik,M., 1977, Bull.Astron.Inst.Czechosl.28,120. [BIBCODE 1977BAICz..28..120V ]
Wilson,R.E., 1979, Astrophys.J.234,1054. [BIBCODE 1979ApJ...234.1054W ]
Wood,D.B., 1972, A Computer Program for Modeling Non-Spherical
   Eclipsing Binary Systems, Greenbelt, Maryland, U.S.A..
Wood,B.D., 1973-1978, WINK Status Report No.1-9, private communication.