Expansion of Hydrogen-Poor Knots in the Born-Again Planetary Nebulae A30 and A78

Abstract

We analyze the expansion of hydrogen-poor knots and filaments in the born-again planetary nebulae A30 and A78 based on Hubble Space Telescope (HST ) images obtained almost 20 yr apart. The proper motion of these features generally increases with distance to the central star, but the fractional expansion decreases, i.e., the expansion is not homologous. As a result, there is not a unique expansion age, which is estimated to be 610-950 yr for A30 and 600-1140 yr for A78. The knots and filaments have experienced complex dynamical processes: the current fast stellar wind is mass loaded by the material ablated from the inner knots; the ablated material is then swept up until it shocks the inner edges of the outer, hydrogen-rich nebula. The angular expansion of the outer filaments shows a clear dependence on position angle, indicating that the interaction of the stellar wind with the innermost knots channels the wind along preferred directions. The apparent angular expansion of the innermost knots seems to be dominated by the rocket effect of evaporating gas and by the propagation of the ionization front inside them. Radiation-hydrodynamical simulations show that a single ejection of material followed by a rapid onset of the stellar wind and ionizing flux can reproduce the variety of clumps and filaments at different distances from the central star found in A30 and A78. Subject headings: ISM: kinematics and dynamics -planetary nebulae: individual (A30 and A78) 2. OBSERVATIONS AND DATA ANALYSIS New HST WFC3 F502N narrowband images of A30 and A78 (PI: M.A. Guerrero, Prop. ID 12935) were obtained on 2013 March 21 and 2012 November 22, respectively. The images were reduced following stan-arXiv:1410.3872v1 [astro-ph.SR]

Forming equatorial rings around dying stars

“…Both PNe show in their inner region an equatorial ring of knots and faster polar outflows, that Fang et al (2014) claim to have been ejected in one event in each PN. The polar knots can reach velocities of 100 km s −1 .…”

“…The polar knots can reach velocities of 100 km s −1 . A fast wind (> 1000 km s −1 ) blown after the ejection of the ring and polar outflows interacted with the knots (Fang et al 2014). A late fast wind is common to SN 1987A and the Necklace as well.…”

On the X-ray temperature of hot gas in diffuse nebulae

“…A 30 and A 78 are part of the selected small number of PNe classified as born-again PNe in which the central star has experienced a very late thermal pulse (e.g., Herwig et al 1999). These ob-jects represent the coolest among all diffuse X-ray-emitters with plasma temperatures of TX 10 6 K. In these cases the carbon-rich fast wind (v∞ 3000 km s −1 ) from the central star slams into the hydrogen-poor material ejected from the very late thermal pulse producing a variety of complex dynamical processes (mass-loading, ablation, hydrodynamical mixing, etc) along with photoevaporation caused by the strong ionizing UV flux from the central star (Fang et al 2014). These processes mix the metal-rich material creating pockets of X-ray-emitting gas, which will have an emission coefficient similar to that of BD+30 • 3639 (see Fig.…”

HST STIS UV Spectroscopic Observations of the Protoplanetary Nebula Hen3-1475∗ †

“…050 pixel −1 ) image was aligned, rebinned and scaled to WFC3 (0. 0396 pixel −1 ) following the procedure described in Fang et al (2014). The two images displayed together show obvious proper motion of the outer knots (NW2/SE2 and NW3/SE3), but it is not obvious in NW1/SE1 whose outer parts are much brighter in 2009 than in 1999 (Figure 1 top).…”