2002ApJ...573L.123S

Using second-epoch Hubble Space Telescope imaging of the unusual, bipolar jet source He 2-90, we have discovered proper motions of 0".03 yr^–1 in the jet knots. Combining the proper motion with the knots' radial velocity measured from ground-based long-slit data, we find that the jet speed is roughly 150-360 km.s^–1, the source distance is 1-2.5 kpc, and the inclination (to the sky plane) of the jet axis is θ=10°-4°, although smaller values of θ and larger values of the jet speed and distance are not ruled out. A comparison of the [O III] and [N II] images shows the central obscuring disk structure directly. The disk, seen nearly edge-on, is embedded within a low-excitation circumstellar region extending from the equator up to a latitudinal angle of about ±62°, with the remaining latitudinal angular space being occupied by a biconical high-excitation region whose symmetry axis is aligned along the jet. The jet is at least 1400 yr old; the knots are being ejected at the rate of one pair roughly every 35-45 yr (independent of the tilt angle and distance to He 2-90), and accretion is still occurring since the youngest jet material is only ∼10 yr old. The jet can be plausibly driven by an accretion disk around a low-mass companion in an eccentric orbit with a period of ∼40 yr, with increased accretion during periastron passage producing the jet knots.