NEW HST OBSERVATIONS OF THE CORE OF R-AQUARII .1. IMAGING

The inner region of the symbiotic system R Aquarii was imaged with the Faint Object Camera on the Hubble Space Telescope (HST) in order to d etermine the source and structure of the highly collimated bipolar jet near the central Mira variable. Coverage over both a wide wavelength and temporal range was ensured by exposures through narrow and medium band filters containing the [OIII] lambda5007, Hbeta lambda4861, [OII] lambda3727, MgII lambda2800, [OII] lambda2470, CII] lambda2326, and C III] lambda1909 emission lines taken approximately a pulsation period apart on October 1991 and December 1992. The jet can be clearly detect ed in the UV down to at least 15 AU of the Mira, placing its source we ll within the expected binary orbit. From there, it flows towards the NE (position angle PA=40-degrees) in a narrow collimated stream with a width < 15 AU for about 50 AU where it encounters a dense clump N2 th at it shocks into emission and that deviates it in the direction of PA =55-degrees. N2's observed position is coincident with the center of t he C1 radio continuum feature and it is, by far, the brightest object in the R Aqr core in the UV. Beyond N2, the flow manifests itself in a series of 3-4 prominent parallel features lying transverse to the flo w direction at 170-250 AU from the Mira. The jet itself, however, proc eeds beyond this area in a continuous and extremely well collimated fl ow with a length to width ratio of over 50 until it reaches a bright l oop located at about 750 AU where it breaks up into separate pieces ar cing out to several thousand AU towards the North. The counter jet see ms more discontinuous and made up of separate knots roughly aligned in the SW direction. Line emission flux ratios in the most prominent fea tures of the jet are all consistent with most, if not all, of the emis sion being due to a shock driven through material left over from an ea rlier episode of mass ejection and pre-ionized by the hot companion an d/or an accretion disk. The observed intensity variations in the regio n within r<90 AU of the Mira may be due to the Mira modulating the spe ed or direction of the jet thereby indicating that the source and coll imation mechanisms are both intimately connected to the condition of t he Mira wind. This favors the wind collision and nozzle theories for t he origin of the jet in R Aqr.