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We show that SBS 1150+599A is most probably a planetary nebula located in the Galactic halo (becoming PN G135.9+55.9). Our photoionization models indicate that its oxygen abundance is lower than 1/100 solar.
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Infrared spectra of NGC 7027 and NGC 6543 ranging from 2.4 μ m to 45 μ m were obtained with the Short Wavelength Spectrometer on board the Infrared Space Observatory. A first analysis of these spectra, with the aid of photo-ionization models, is presented in Beintema et al. (1996).
Infrared astronomy
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We have detected the central star of NGC 7027 by imaging the nebula through a narrow band ‘continuum’ filter onto the IPCS detector at the 2.5m Isaac Newton Telscope. We obtain an apparent visual magnitude for the central star of m v = 17.7 ± 0.5 mags. Assuming that the central star radiates approximately as a blackbody, which is reasonable for the case of a hot star, then Zanstra temperatures for the central star can be calculated. We find T Z (H) = 3.9 × 10 5 K and T z (HeII) = 2.6 × 10 5 K. Using the correction due to Stasinska & Tylenda (1986) we estimate the central star of NGC 7027 to have a temperature, T eff = 3.1 × 10 5 K. The luminosity and radii are found assuming a distance of d=1.2 kpc., giving L = 12,600 L ⊙ and R = 0.039 R ⊙ . Placing the central star on the Log L - Log T diagram and comparing with evolutionary tracks for central stars with various masses from Wood & Faulkner (1986), indicates that the central star of NGC 7027 must have a mass, M ≥ 0.8 M ⊙ . Radio observations of NGC 7027 have been taken using the Westerbork Radio Synthesis Telesocpe at 21cm. Self calibration techniques have been employed to give a radio continuum map of high dynamic range. These observations are being compared with a deep optical H β map to study the nature of the faint halo seen around NGC 7027 (Atherton et al. 1979)
Star (game theory)
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As part of a continuing program to estimate the distances to planetary nebulae (PNe), we have applied an expansion parallax algorithm to four objects: NGC 2392, NGC 3242, NGC 6210, and NGC 6572. The algorithm requires two Epochs of data obtained at the VLA at λ6 cm. With 6 years between Epochs, we have measured the angular expansion rate of three of the above PNe, NGC 6572, NGC 6210, and NGC 3242 with errors of 20, 25, and 40%, respectively. We did not detect the expansion of NGC 2392, but were able to ascertain an upper limit to the expansion rate. By combining the detected angular expansion rate with the Doppler expansion velocity and assuming uniform expansion, we have directly computed the distances to NGC 6572, NGC 6210, and NGC 3242 with accuracies that represent significant improvements over the current estimates in the literature. For most of the nebulae thus surveyed, our expansion parallax distances are all at least as large as recent Shklovsky distances determined by statistical methods.
Hubble sequence
Asymptotic giant branch
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