Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1981
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981apj...244.1022f&link_type=abstract
Astrophysical Journal, Part 1, vol. 244, Mar. 15, 1981, p. 1022-1032.
Astronomy and Astrophysics
Astronomy
59
Astronomical Models, Dwarf Stars, Nebulae, Novae, X Ray Sources, X Ray Spectra, Emission Spectra, Line Spectra, Photoionization, Stellar Mass Accretion, Ultraviolet Astronomy, Ultraviolet Spectra
Scientific paper
A model for the nebula of DQ Her is presented which is built upon the assumption that the power is provided by an X-ray source. The X-ray and UV energy spectra recently calculated by Kylafis and Lamb for the case of spherical accretion onto degenerate dwarfs are modified to take account of the geometry of the system. The influence of a low frequency cutoff is considered: the column density we find to be consistent with our model falls nicely in the range inferred for nova systems by recent observations of Cordova, Mason, and Nelson. The effects of the radiation field upon the envelope ejected in the 1934 outburst were determined with a photoionization program which includes all X-ray heating and ionization processes known to be important (Compton recoil by both bound and free electrons, the Auger effects, and secondary ionization by suprathermal electrons). Our calculations show that many observed features of the nebula follow as a very natural consequence of this model. Specifically, the nebula is expected to be very cool, ∼300 K, and to show extremely strong recombination lines of ionized carbon, nitrogen, and oxygen, as previously reported by Williams et al. Time variations of the inferred nebular composition are to be expected, as the reestablishment of accretion flows, formation of a disk, and the ensuing emergence of an X-ray flux must follow upon the turnoff of the underlying white-dwarf nova remnant. Scrutiny of the spectroscopic data for DQ Her suggests that this turnoff occurred in the late 1940s, and that the nebula cooled rapidly in this stage. The relevance of our results to studies of other nova nebular remnants is briefly examined.
Ferland Gary J.
Truran Jame. W.
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