Investigating X-ray Emission from PPN and PN using numerical simulations

Abstract

The shaping of Pre-planetary nebulae (PPN) and Planetary Nebulae (PN) is believed to result from the interaction of a fast, collimated post-AGB wind (CFW) plowing into the slow, dense wind emitted during the AGB phase, followed by an isotropic tenuous wind during the PN phase (Sahai & Trauger 1998). The expanding shell which forms the PPN and later the PN is expected to produce extended X-ray emission due to the large speed of the fast wind and resulting high temperatures in the shocked gas. X-ray emission was only detected in 3 of 60 PNs observed with ROSAT, followed by a few more from CHANDRA and XMM (e.g. Guerrero et al. 2005). In the case of PPNs, there is so far only one confirmed X-ray detection (Sahai et al. 2003), although many have been observed with CHANDRA. The general problem of understanding the formation and shaping of PNs has been addressed analytically and numerically (see Balick & Frank 2002, and references therein). X-ray emission is one of the most direct probes of the fast wind and the interaction process which drives PN formation. However, this probe has not been fully exploited in previous modeling studies. Very recently, Akashi et al. (2006, hereafter ASB06) used analytical, self-similar, spherically symmetric models to address this problem. We are performing numerical simulations with the hydrodynamics code FLASH varying the basic parameters of the fast and slow wind over an extensive parameter grid and computing the X-ray emission as a function of these parameters and the time history of the fast wind.