Other
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aas...207.0802s&link_type=abstract
American Astronomical Society Meeting 207, #08.02; Bulletin of the American Astronomical Society, Vol. 37, p.1161
Other
Scientific paper
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 plowing into the slow, dense wind emitted during the AGB phase, followed by an isotropic tenuous wind during the PN phase (Sahai and Trauger 1998). These interacting winds result in an expanding shell of shocked matter which forms the PPN and later the PN. Due to the large speed of the fast wind (from few x 100 km s-1 up to 2000 km s-1), one expects extended X-ray emission to be produced in PPNs (where the shaping mainly occurs) and PNs. However, X-ray emission was only detected in 3 of 60 PNs observed with ROSAT, followed by a few others from CHANDRA and XMM (e.g. Guerrero et al. 2004). Up to now, there is only one confirmed X-ray detection in PPNs (Sahai et al. 2003), although many have been observed with Chandra (Sahai et al. 2006, in prep.). X-ray emission should be present in principle in all of these systems -- hence the low detection rate implies that it is obviously below the detection limit.
Several questions then arise: most importantly, what constraints can be set on the physical quantities of the fast wind (speed, mass-flux, opening angle) in order to produce the observed X-ray emission properties of PPNs and PNs, and, which nebular regions are mainly responsible for the X-ray emission. To find answers, one has to solve the equations of hydrodynamics including radiative cooling effects in the case of interacting winds. This has been done analytically using self-similar, spherically symmetric models (Akashi et al. 2005). Here we report preliminary results from two-dimensional numerical simulations (using the NIRVANA code) in which we vary the basic parameters of the fast wind over an extensive parameter grid, to simulate the evolution from the PPN phase to the PN phase. We have calculated the expected X-ray flux using data from the atomic database ATOMDB. We present X-ray emission spectra and images from our models, including the inclination-dependent effect of circumstellar extinction.
Sahai Raghvendra
Stute Matthias
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