G. H. Herbig, Lick Observatory, writes: "The arcs of emission nebulosity extending to ~ 70" from the symbiotic long-period variable R Aqr are, according to a 1944 note by Baade, in slow expansion at a rate suggesting ejection from the star ~ 600 years before that time. There is also complex emission nebulosity within ~ 15" of the star. On Lick 3-m direct plates of 1960 and 1970 its brightest features are two semistellar knots at separation 8", p.a. 23o (Knot A) and 13", 22o (Knot B) and a remarkable loop of nebulosity 4" in diameter at ~ 8", 177o. Plates taken last month, when the variable was near minimum, show that a striking change has taken place in this inner nebulosity since 1970: a brilliant emission jet or spike [so called by Wallerstein and Greenstein (1980, P.A.S.P. 92, 275), who in 1977 saw what must be the same feature] now extends from very near the star image to ~ 10" in p.a. 22o and has obliterated Knot A. In H-alpha the surface brightness of this spike is now ~ 8 times that of Knot B, the next brightest point in the nebula. In fact, the spike is quite conspicuous visually at the 3-m. Lines of [O I], [N II), He I, [S II], [S III] and H-alpha in the spike give a radial velocity of -64 to -75 km/s, depending on the ion, while Knot B is at ~ -25 km/s, near the stellar velocity. The 1960-1980 direct plates confirm the slow enlargement of the outer structure. Provisional measurements show that the loop and Knot B are moving away from the star at 0".05 to 0".08 per year, corresponding to cross velocities of 50 to 80 km/s at 200 pc. At these velocities, the loop and Knot B would have left the star about the year 1800. The present position of the spike and its absence on the 1970 plate can be reconciled with uniform radial motion (rather than by appearance in place) by assuming a more recent ejection, but with a tangential velocity of at least 300 km/s."
International Astronomical Union Circular
- Pub Date:
- November 1980