Revealing the Mid‐Infrared Emission Structure of IRAS 16594−4656 and IRAS 07027−7934

Abstract

TIMMI2 diffraction-limited mid-infrared images of a multipolar protoplanetary nebula IRAS 16594−4656 and a young [WC] elliptical planetary nebula IRAS 07027−7934 are presented. Their dust shells are for the first time resolved (only marginally in the case of IRAS 07027−7934) by applying the Lucy-Richardson deconvolution algorithm to the data, taken under exceptionally good seeing conditions (≤0.5 ′′ ). IRAS 16594−4656 exhibits a two-peaked morphology at 8.6, 11.5 and 11.7 µm which is mainly attributed to emission from PAHs. Our observations suggest that the central star is surrounded by a toroidal structure observed edge-on with a radius of 0.4 ′′ (∼640 AU at an assumed distance of 1.6 kpc) with its polar axis at P.A.∼80 • , coincident with the orientation defined by only one of the bipolar outflows identified in the HST optical images. We suggest that the material expelled from the central source is currently being collimated in this direction and that the multiple outflow formation has not been coeval. IRAS 07027−7934 shows a bright, marginally extended emission (FWHM=0.3 ′′ ) in the mid-infrared with a slightly elongated shape along the N-S direction, consistent with the morphology detected by HST in the near-infrared. The mid-infrared emission is interpreted as the result of the combined contribution of small, highly ionized PAHs and relatively hot dust continuum. We propose that IRAS 07027−7934 may have recently experienced a thermal pulse (likely at the end of the AGB) which has produced a radical change in the chemistry of its central star.

A mid-infrared imaging catalogue of post-asymptotic giant branch stars★

“…The Water‐Lily nebula PPN has been observed in the mid‐infrared ( N and Q bands) with T‐Recs on Gemini (Volk et al 2006) and with TIMMI2 on the ESO 3.6‐m telescope (García‐Hernández et al 2006). A bright equatorial torus, seen nearly edge‐on, is clearly resolved in their images.…”

Ionization Structure of Heavy Metals for Planetary Nebulae

“…IRAS 07027 is a very peculiar young PN. It has a central star that was classified by [1,10]. As of Wolf-Rayet Carbon type [WC], there about half a dozen PNe that has been classified as [WC11] [11,12].…”

“…Planetary nebulae (PNe) are the results of the evolution of low to intermediate mass stars (0.8-8Mʘ) [1]. These stars experience a phase of extreme mass loss during the previous asymptotic giant branch (AGB) that causes the ejection of the stellar envelope [2].…”

“…These stars experience a phase of extreme mass loss during the previous asymptotic giant branch (AGB) that causes the ejection of the stellar envelope [2]. When this mass loss ceases the AGB phase ends and the star evolves into a short-lived evolutionary stage called the `post AGB' or `proto-PN' phase just before the star becomes a Planetary Nebulae (PN) [1]. The formation of axisymmetric structures in PNe (ranging from elliptical to bipolar) is believed to be completed by the end of the AGB phase [1,3,4].…”

“…There is different asymmetric morphology from elliptical too bipolar to study the PNe but it is unknown. The first is the interaction of stellar winds, binary systems as central stars [3,5], non-radial pulsation [1,6] or the influence of magnetic fields as it was described in [7,8]. To identify which one (s) of the above is the dominant process, in this morphology as early as possible after the departure from the spherical symmetry takes place in PNe.…”