Showing papers by "Christopher J. Wareing published in 2006"

The shaping of planetary nebula Sh 2-188 through interaction with the interstellar medium

Abstract: Sh2-188 is an example of strong interaction between a planetary nebula (PN) and the interstellar medium (ISM). It shows a single arc-like structure, consisting of several filaments, which is postulated to be the result of motion through the ISM. We present new Hα images from the Isaac Newton Telescope Photometric Hα Survey of the Northern Galactic Plane (IPHAS) which reveal structure behind the filamentary limb. A faint, thin arc is seen opposite the bright limb, in combination forming a closed ring. Behind the faint arc a long wide tail is detected, doubling the size of the nebula. The nebula extends 15 arcmin on the sky in total. We have developed a ‘triplewind’ hydrodynamical model, comprising of the initial ‘slow’ asymptotic giant branch (AGB) wind and the later ‘fast’ stellar wind (the interacting stellar wind model), plus a third wind reflecting the motion through the ISM. Simulations at various velocities of the central star relative to the ISM indicate that a high velocity of 125 kms 1 is required to reproduce the observed structure. We find that the bright limb and the tail already formed during the AGB phase, prior to the formation of the PN. The closure of the ring arises from the slow–fast wind interaction. Most of the mass lost on the AGB has been swept downstream, providing a potential explanation of the missing mass problem in PNe. We report a proper motion for the central star of 30± 10 masyr 1 in the direction of the bright limb. Assuming the central star is moving at 125± 25 kms 1 , the distance to the nebula is estimated to be 850 +500 420 pc, consistent with a spectroscopic distance to the star. Expansion velocities measured from spectroscopic data of the bright filaments are consistent with velocities measured from the simulation. Sh2-188 is one of the largest PNe known, with an extent of 2.8 pc. The model shows that this size was already set during the AGB phase.

Detached shells as tracers of asymptotic giant branch-interstellar medium bow shocks

Abstract: New Spitzer imaging observations have revealed the structure around the Mira variable star R Hya to be a one-sided parabolic arc 100 arcsec to the west, stretching from north to south. We successfully model R Hya and its surroundings in terms of an interaction of the stellar wind from an asymptotic giant branch (AGB) star with the interstellar medium (ISM) the star moves through. Our three-dimensional hydrodynamic simulation reproduces the structure as a bow shock into the oncoming ISM. We propose this as another explanation of detached shells around such stars, which should be considered alongside current theories of internal origin. The simulation predicts the existence of a tail of ram-pressure-stripped AGB material stretching downstream. Indications for such a tail behind R Hya are seen in IRAS maps.

Detached shells as tracers of AGB-ISM bow shocks

Abstract: New Spitzer imaging observations have revealed the structure around the Mira variable star R Hya to be a one-sided parabolic arc 100 arcsec to the West stretching from North to South. We successfully model R Hya and its surroundings in terms of an interaction of the stellar wind from an asymptotic giant branch (AGB) star with the interstellar medium (ISM) the star moves through. Our three-dimensional hydrodynamic simulation reproduces the structure as a bow shock into the oncoming ISM. We propose this as another explanation of detached shells around such stars which should be considered alongside current theories of internal origin. The simulation predicts the existence of a tail of ram-pressure-stripped AGB material stretching downstream. Indications for such a tail behind R Hya are seen in IRAS maps.

The shaping of planetary nebulae through interaction with the interstellar medium

Abstract: References Introduction The accepted theory of planetary nebula (PN) formation is the interacting stellar winds model (ISW) (Kwok 1982, Balick 1987) where a fast wind (~1000 kms-1) from the hot central star of a PN sweeps up the slow wind (~15 km s-1) produced during the preceding asymptotic giant branch (AGB) phase. The swept-up dense shell is ionised by the energetic UV radiation of the central star, producing the familiar ring-like appearance of PNe.