A photoionization model study of the old nova shell DQ Herculis 1934

Details A photoionization model study of the old nova shell DQ Herculis 1934 A photoionization model study of the old nova shell DQ Herculis 1934

Dec 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990a%26a...240..433p&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 240, no. 2, Dec. 1990, p. 433-452.

Astronomy and Astrophysics

Astrophysics

31

Accretion Disks, Novae, Photoionization, Stellar Envelopes, Stellar Models, Abundance, Balmer Series, Emission Spectra, Far Infrared Radiation, Stellar Composition, Stellar Luminosity, Atomic Processes, Interstellar Medium: Abundances, Interstellar Medium: Nebulae, Stars: Accretion Disks, Stars: Novae: Dq Her 1934

Scientific paper

It is demonstrated that stationary photoionization by a black body source is very successful at explaining quantitatively the unusual emission-line spectrum of the DQ Her elliptical shell. A complete understanding of the optical forbidden lines involves radiative and dielectronic recombinations, charge exchanges, photoionization to excited states and thermal electron collisional excitation, in spite of the very low temperature indicated by the Balmer continuum. The intriguingly flat Balmer decrement observed by Williams et al. (1978) is shown to mainly result from blends with 0 II multiplets, but the anomalously weak Hα reported by Ferland et al. (1984) remains as the only strong unexplained feature of the spectrum. Fine structure line emission accounts for the 60 m IRAS flux.
The effective temperature of the source is about 10 K and its power 1.7 1034 erg s-1 for a distance of 420 pc. The shell is denser and therefore geometrically thinner than previously believed. The nitrogen abundance relative to hydrogen is nearly one thousand times larger than its cosmic value and the CNO gaseous mass is more than twice the hydrogen mass. Chemical inhomogeneities are unnecessary to explain the marked spectral differences observed between the shell axes.
The illumination of the minor axis of the shell by the central source of ionizing radiation must be about one fourth that of the major axis. We suggest that the so-called "equatorial belt" of the shell, coincident with the minor axis, be identified with the "shadow" of a thickened accretion disk, seen almost edge-on.

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