RW Aur A, a close binary?

We have discovered periodic changes in velocity and equivalent width of a n umber of different spectral features of RW Aur A, a T Tauri star with a jet , broad emission lines and substantial excess continuous emission. In parti cular, the photospheric lines vary in radial velocity with an amplitude of 5.7 km s(-1) over a period of 2.77 days, which appears to have been stable over at least 18 years. The present Letter focusses solely on one straightforward interpretation, n amely that RW Am A is a single-lined spectroscopic binary. However, other s pectral features vary in or out of phase with the same or the double period . Interpretations, other than a binary model, should be considered but must await the more extended report on our large observational material. In the binary case, the small amplitude leads to a mass function of only 5. 10(-5) M., by far the smallest observed for young binaries. The jet velocit y and extent restrict the range of inclinations (if the orbital axis is ali gned with the jet), implying a close binary with a secondary at the brown d warf limit. Further restrictions follow if the primary rotates synchronousl y. Narrow emission components of HeI and HeII vary in antiphase with the photo spheric absorption lines. We show that it is unlikely that these lines refl ect the motion of the secondary.