A high-speed bipolar outflow from the archetypical pulsating star Mira A

Abstract

Optical images and high-dispersion spectra have been obtained of the ejected material surrounding the pulsating AGB star Mira A. The two streams of knots on either side of the star, found in far-ultraviolet (FUV) GALEX images, have now been imaged clearly in the light of Ha. Spatially resolved profiles of the same line reveal, that the bulk, of these knots form a bipolar outflow with radial velocity extremes of ±150 km s-1 with respect to the central star. The south stream is approaching and the north stream receding from, the observer. A displacement away from Mira A between the position of one of the south-stream knots in the new Ha- image and its position in the previous Palomar Observatory Sky Survey (POSS I) red plate was noted. If interpreted as a consequence of expansion proper motions, the bipolar outflow is tilted at 69° ± 15° to the plane of the sky, has an outflow velocity of 1.60 ± 10 kms-1 and is ≈1000 y old. ©ESO 2009.