COMMISSION 27 OF THE I. A. U.
       INFORMATION BULLETIN ON VARIABLE STARS
                   Number 1790

                               Konkoly Observatory
                               Budapest
                               1980 May 26


           REVISED PHOTOMETRIC ELEMENTS OF ST Aqr


The eclipsing binary system ST Aqr is believed to consist of an A7 primary
(brighter) star accompanied by a G8IV secondary companion (see Roman 1956).
The light variation of this binary has been studied photoelectrically by Knipe
(1971) in yellow light and later by Gleim (1973) in yellow, blue and
ultraviolet light. As a follow-up to a series of works, which systematically
rediscuss the photometric elements of numerous eclipsing binaries (see, e.g.,
Mardirossian et al. 1980), we have reanalyzed Gleim's (1973) three-colour
observations by means of Wood's (1972, 1973-1978) lightcurve synthesis computer
model. Our photometric solutions are listed in the table (for the explanation
of the symbols the reader is referred to the paper by 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 of the unperturbed
radii k=r_c/r_h, and the temperatures T_h and T_c of the two components.  The
mass ratio q=M_c/M_h was also treated as a free parameter. Proximity effects
probably give rise to some discordance among the temperatures T_h an T_c we
have deduced for different lightcurves. However, no doubt the primary minimum
is due to a transit and both components can be considered to be in contact with
their Roche lobes, in substantial agreement with the results computed by Gleim
(1973) by means of Russell and Merrill's (1952) method. It is remarkable that
for our ratio of the radii k~=0.5 both components of ST Aqr may belong to the
main sequence. Further spectrographic observations are needed for checking
this possible view.

Table

lambda        yellow         blue           ultraviolet
i           76.6+-0.9      76.5+-0.8       76.1+-1.1
r_h        0.494+-0.004   0.496+-0.005    0.501+-0.004
k          0.552+-0.014   0.526+-0.003    0.548+-0.010
a_h        0.549+-0.007   0.553+-0.010    0.559+-0.009
b_h        0.516+-0.005   0.519+-0.006    0.523+-0.005
c_h        0.475+-0.003   0.477+-0.003    0.481+-0.003
a_c        0.302+-0.011   0.286+-0.005    0.305+-0.008
b_c        0.271+-0.007   0.260+-0.003    0.273+-0.005
c_c        0.257+-0.005   0.248+-0.002    0.258+-0.004
T_c(eq)    8100+-200      7000+-200       7000+-300
T_h(pol)   8700           7500            7500
T_c(eq)    5200+-100      4000+-300       4500+-200
T_c(pol)   5200           4100            4600
u_h        0.58           0.73            0.67
u_c        0.70           0.84            0.90
beta_h     0.25           0.25            0.25
beta_c     0.08           0.08            0.08
w_h        1              1               1
w_c        0.5            0.5             0.5
L_h        0.957          0.975           0.955
L_c        0.043          0.025           0.045
q          0.4+-0.1       0.4+-0.1        0.4+-0.1


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

References:

Gleim, J.K., 1973, Astron. J. 78, 662. [BIBCODE 1973AJ.....78..622G ]
Knipe, G.F.G., 1971, Mon. Not. Astron. Soc. South Africa 30, 157. [BIBCODE 1971MNSSA..30..157K ]
Mardirossian, F., Mezzetti, M., Predolin, F., and Giuricin, G., 1980, Astron.
   Astrophys. Suppl. 40, 57. [BIBCODE 1980A&AS...40...57M ]
Roman, N.G., 1956, Astrophys. J. 123, 247. [BIBCODE 1956ApJ...123..246R ]
Russell, H.N., and Merrill, J.E., 1952, Princeton Contrib. No. 26. [BIBCODE 1952deeb.book.....R ]
Wood, D.B., 1972, A Computer Program for Modeling Non-Spherical Eclipsing
   Binary Systems, Greenbelt, Maryland, U.S.A.
Wood, D.B., 1973-1978, WINK Status Report No. 1-9, private communications.