The structure of NGC 7027

Atherton, P. D.; Hicks, T. R.; Reay, N. K.; Robinson, G. J.; Worswick, S. P.; Phillips, J. P.

doi:10.1086/157339

Cited by 38 publications

(36 citation statements)

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“…The intensity of the extended Hα outside the main nebula, varies as ∼r −3 -r −4 , consistent with optically thin scattering of nebula light by the dust envelope, as first discussed by Atherton et al (1979); see also Latter et al (2000). Scattering by the envelope has been directly confirmed by high levels of polarization seen in [O] and Hα outside the main nebula by Walsh & Clegg (1994).…”

Section: Ngc 7027supporting

confidence: 78%

Small scale structure in circumstellar envelopes and the origin of globules in planetary nebulae

Huggins

Mauron

2002

A&A

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Abstract. We analyze the small scale structure in the circumstellar envelopes of NGC 7027 and IRC+10216, using high resolution optical images in dust scattered light. We use the observations to test the proposal that globules in planetary nebulae, typified by globules in the Helix nebula, originate in high density contrast proto-globules in the atmosphere of the progenitor AGB star and are carried out in the circumstellar wind (Dyson et al. 1989). We find no evidence for the presence of protoglobules in the extended envelopes of NGC 7027 and IRC+10216 with the expected sizes and masses > ∼ 10 −5 M which are needed to produce globules like those in the Helix nebula. We do find azimuthal structure in the envelopes on size scales of l > ∼ 0.1d where d is the radial distance, consistent with the smoothing out of small scale structure by thermal motions in the wind acceleration region. Unless globules require special conditions not found in NGC 7027 or IRC+10216, which are among the most likely precursors of Helix-like nebulae, our results argue against their origin in the atmosphere of the central star. We suggest alternative scenarios for globule formation, including the fragmentation of the neutral circumstellar gas at the transition phase by directed outflows or jets.

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Section: Ngc 7027supporting

confidence: 78%

Small scale structure in circumstellar envelopes and the origin of globules in planetary nebulae

Huggins

Mauron

2002

A&A

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“…It is the brightest planetary nebula in the radio sky due to its proximity and youth. It is a compact nebula of 10 × 13.5 arcsec (Atherton et al 1979) observed regularly at the VLA for 25 years and can be taken to be unresolved when observed with the 1.2 arcmin beam of the 32 m telescope. Those features make NGC 7027 a good prime calibrator over a wide frequency range.…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Survey of planetary nebulae at 30 GHz with OCRA-p

Pazderska¹,

Gawroński²,

Feiler³

et al. 2009

A&A

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Aims. We report the results of a survey of 442 planetary nebulae at 30 GHz. The purpose of the survey is to develop a list of planetary nebulae as calibration sources that could be used for high frequency calibration in future. For 41 PNe with sufficient data, we test the emission mechanisms in order to evaluate whether or not spinning dust plays an important role in their spectra at 30 GHz. Methods. The 30-GHz data were obtained with a twin-beam differencing radiometer, OCRA-p, which is in operation on the Toruń 32-m telescope. Sources were scanned both in right ascension and declination. We estimated flux densities at 30 GHz using a free-free emission model and compared it with our data. Results. The primary result is a catalogue containing the flux densities of 93 planetary nebulae at 30 GHz. Sources with sufficient data were compared with a spectral model of free-free emission. The model shows that free-free emission can generally explain the observed flux densities at 30 GHz thus no other emission mechanism is needed to account for the high-frequency spectra.

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“…The major axis is tilted by about 26°-39°with respect to the line of sight to the observer. The faint extended Ha emission observed out to a distance of 30" is probably produced by reflection from the dust ejected during the red-giant phase (3). This bright, ionized shell, which produces the optical spectrum discussed below, is expanding into a vast, cool, molecular cloud of at least two solar masses.…”

mentioning

confidence: 95%

“…The rich IR spectrum shows not only numerous atomic and molecular lines but also many broad structures presumably produced in carbon-rich grains, although specific identifications are not yet established (17)(18)(19)(20) (9) found a Zanstra temperature of 180,000 K. Atherton et al (3) suggest a temperature in excess of 200,000 K. If the residual stellar core is massive, it may be fading rapidly, but the density of the HII zone is so great that its spectrum would quickly respond to these changes. No such variations have been found.…”

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confidence: 99%