COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1762

                                 Konkoly Observatory
                                 Budapest
                                 1980 March 26


        PHASE-DEPENDENT MASS FLOW IN UW CMa


Mass flow in the interacting binary system UW CMa, consisting of an O7f primary
and an O7 secondary (Batten, Fletcher and Mann 1978), has been studied using
the Copernicus ultraviolet spectra by McCluskey, Kondo and Morton (1975),
McCluskey and Kondo (1976) and Drechsel, Rahe, Kondo and McCluskey (1980).
Mass loss rate has been estimated to be in the range of 2.3 to 3.0 x 10^-6
solar mass per year.

However, as the Copernicus telescope spectrometer employed a single-channel
detector system (Rogerson, Spitzer et al. 1973), it took a quarter of the
orbital period or longer to complete the spectral scan in the spectral range
1000 to 1550 A. This made a study of the phase-dependence of the absorption
and emission features, many of which were of P Cygni type, quite difficult.
Consequently, the results reported by McCluskey and Kondo (1976) were uncertain
in this respect.

We have performed a preliminary examination of the ultraviolet spectra of UW
CMa obtained with the IUE on 1978 June 2 and 4. The exposures were 80 and 100
seconds; thus, the time-resolution was excellent. The phase of observation was
0.84 and 0.24 for the respective dates.

The radial velocity changes observed in the shifting of the short-wavelength
edge of the emission in the CIII (1175 A), N V (1238 and 1242 A), SiIV (1393
and 1402 A) and CIV (1548 and 1550 A) P Cygni profiles corresponded to a value
in the vicinity of 400 kms^-1) the radial velocity was in the positive sense at
phase 0.84 and negative at phase 0.28. Several absorption lines., e.g. SiIII
(1206 A) and N IV (1718 A), show no emission but are displaced by a constant
value of 500 to 800 kms^-1 with the orbital velocity variation superimposed on
top of this mean displacement. The radial velocity difference for the O7f star
at these two phases was 406 kms^-1 using K_1=222.5 kms^-1 (Batten et al.
1978). The P Cygni absorption components of these lines also show a velocity
change due to orbital motion superimposed on the 800 to 1100 kms^-1 mean
expansion velocity.

We have re-examined the previous Copernicus data. The radial velocity changes,
although not conclusive, are basically not in disagreement with the current
findings.

Incorporating the previous results, we conclude that the mass flow in UW CMa is
primarily from the O7f primary and that the matter is being lost from the
binary system at the rate of 2.3 to 3.0 x 10^-6 solar mass per year. The P
Cygni lines must arise within several stellar radii above the surface of the
primary star in order to show such orbital motion effects.


GEORGE E. McCLUSKEY
Division of Astronomy
Department of Mathematics
Lehigh University
Bethlehem, Pa. 18015, U.S.A.

YOJI KONDO
Code 685, Goddard Space Flight Center,
Greenbelt, Md. 20771
U.S.A.

JURGEN RAHE
Remeis-Sternwarte
Sternwartstrasse 7
D-8600 Bamberg,
Federal Republic of Germany

References:

Batten, A.H., Fletcher, J.M. and Mann, P.J. 1978, Publications of the Dominion
   Astrophysical Observatory, XV, No. 5 [BIBCODE 1978PDAO...15..121B ]
Drechsel, H., Rahe, J., Kondo, Y. and McCluskey, G.E. 1980, Astron. Ap., in
   press [BIBCODE 1980A&A....83..363D ]
McCluskey, G.E., Kondo, Y. and Morton, D.C. 1975, Ap.J., 201, 607 [BIBCODE 1975ApJ...201..607M ]
McCluskey, G.E. and Kondo, Y. 1976, Ap.J. 208, 760 [BIBCODE 1976ApJ...208..760M ]
Rogerson, J,B., Spitzer, L., Drake, J.F., Dressler, K., Jenkins, E.B., Morton,
   D.C. and York, D.G. 1973, Ap.J., 181, L97 [BIBCODE 1973ApJ...181L..97R ]