Herschelimaging of the dust in the Helix nebula (NGC 7293)

Abstract

Aims. In our series of papers presenting the Herschel imaging of evolved planetary nebulae, we present images of the dust distribution in the Helix nebula (NGC 7293). Methods. Images at 70, 160, 250, 350, and 500 µm were obtained with the PACS and SPIRE instruments on board the Herschel satellite.Results. The broadband maps show the dust distribution over the main Helix nebula to be clumpy and predominantly present in the barrel wall. We determined the spectral energy distribution of the main nebula in a consistent way using Herschel, IRAS, and Planck flux values. The emissivity index of β = 0.99 ± 0.09, in combination with the carbon rich molecular chemistry of the nebula, indicates that the dust consists mainly of amorphous carbon. The dust excess emission from the central star disk is detected at 70 µm and the flux measurement agrees with previous measurement. We present the temperature and dust column density maps. The total dust mass across the Helix nebula (without its halo) is determined to be 3.5 × 10 −3 M at a distance of 216 pc. The temperature map shows dust temperatures between 22 K and 42 K, which is similar to the kinetic temperature of the molecular gas, confirming that the dust and gas co-exist in high density clumps. Archived images are used to compare the location of the dust emission in the far infrared (Herschel) with the ionized (GALEX and Hβ) and molecular (H 2 ) component. The different emission components are consistent with the Helix consisting of a thick walled barrel-like structure inclined to the line of sight. The radiation field decreases rapidly through the barrel wall.

CO in the C1 globule of the Helix nebula with ALMA

“…The C 18 O detection shows that the progenitor mass must be below this range. The second constraint comes from the suggestion that the dust in the helix is carbonaceous (Van de Steene et al 2015).…”

“…In recent studies (e.g. Van de Steene et al 2015), the Helix nebula is treated as a carbon-rich nebula based on the emissivity index of the dust emission. Carbonaceous dust requires that C/O > 1.…”

“…We calculate the gas mass of the globule using the measured dust emission. On the assumption that grains in the nebula are mainly amorphous carbon, Van de Steene et al (2015) found that the temperature of the dust in the Helix nebula varies from 22 to 42 K with a mean value of 30.8 ± 1.4 K. We use…”

Planetary nebulae seen with TESS: Discovery of new binary central star candidates from Cycle 1

“…It has been well-characterized thanks to numerous observations from a wide range of wavelengths and telescopes. It is a double ring PN, with an inner thick disk and multitude of cometary knots present in the nebular centre (see, e.g., Meaburn et al 1998;Henry et al 1999;O'Dell et al 2005;Van de Steene et al 2015, and references therein). In addition, the whole nebula is surrounded by a massive molecular envelope (Young et al 1999).…”

On the Origin of Morphological Structures of Planetary Nebulae

“…Current mid-infrared imaging of PNe mainly reveals dust in the torus or in the bipolar lobes [29,30]. Although efforts have been made to map the cold dust component by Spitzer [31,32], AKARI [33], and Herschel [34][35][36], the extended cold dust component be truly revealed with high angular resolution, high sensitivity, far infrared imaging with facilities such as SOFIA.…”