MASS-LOSS RATES AND STELLAR WIND MOMENTA OF A-SUPERGIANTS IN M31 - FIRST RESULTS FROM THE KECK HIRES SPECTROGRAPH

High-quality Keck HIRES echelle spectra of two A-supergiants in M31, d esignated 41-3654 (spectral type A2 Ia-O) and 41-3712 (A3 Ia-O), at 10 .2 kpc galactocentric distance are analyzed by means of NLTE unified m odel atmospheres to determine the properties of their stellar winds, i n Particular the wind momenta. We obtain mass-loss rates of 1.9 x 10(- 6) and 1.1 x 10(-6) M. yr(-1) for 41-3654 and 41-3712, respectively, w ith an accuracy of 15% from the fit of the Ha profiles. The terminal v elocities are 200 +/- 25 km s(-1). In addition, the exponents of the w ind velocity fields are determined (beta = 2 and 3, respectively) and microturbulent velocities of the order of 20 km s(-1) are found. The w ind momenta of the two targets are in excellent agreement with the win d momentum-luminosity relation (WLR) for galactic A- and B-supergiants . We discuss the potential of the WLR for extragalactic distance deter minations and conclude that it may allow independent distance moduli t o be obtained with an accuracy of 10%.