Nova Aquilae 1982

Abstract

The paper gives results obtained from observations of Nova Aquilae 1982 made with the International Ultraviolet Explorer satellite, the Anglo–Australian Telescope and the Westerbork Synthesis Radio Telescope, and it discusses the interpretation of these results together with those obtained by other observers. Dates are given as day number, D, with D=1.0 for 1982 January 27.0. Light curves are given for B, V and continuum fluxes at 2800 and 1300 Å. An initial rapid decline for |$D\leqslant12$| was followed by a ‘shoulder’ region of slower decline for D=14–26. Dips which occurred in the light curves between D=28 and D=160 are interpreted as being due to absorption by internal dust and estimates of the amounts of absorption are obtained. The light curves for D>160 are smooth continuations of those for the ‘shoulder’ region. Line profiles give velocities V which show the presence of three main gaseous components: (i) high-velocity gas, hvg, with |$V\leqslant10\enspace 000\enspace \text {km}\enspace \text s^{-1}$|⁠; (ii) medium-velocity gas, mvg, with |$V\leqslant3000\enspace \text {km}\enspace \text s^{-1}$|⁠; (iii) low-velocity gas, lvg, with |$\text {FWHM}\simeq 200\enspace \text {km}\enspace \text s^{-1}$|⁠. The hvg was detected only in absorption lines, on D=29 and 35. The mvg and lvg were detected in emission lines and, for the mvg, in Na ID-line absorption. Strong [Ne III] and [Ne V] emission was observed from the mvg. Abundances for H, He, C, N, O, Ne, Mg, Si, S and Fe are obtained for the mvg on D=156. Best estimates for the electron temperature and electron density are Te=10 000 K and Ne=2.5 108 cm−3. The deduced He/H abundance ratio of 0.45 is insensitive to the values adopted for Te and Ne. The heavier elements have abundances amongst themselves which are also insensitive but abundances relative to H which arc much more sensitive. The following remarkably large abundance ratios are obtained: N/H=0.21, Ne/H=0.53 and S/H=0.064. The gas-phase abundances for C, O, Mg, Si and Fe appear to be depleted in consequence of grain formation. The mvg is estimated to have had a mass of |$7\times10^{-6}\enspace M_\odot$|⁠, a filling factor of ε=2.5 10−5 and a kinetic energy of 6×1044 erg. Radio fluxes were obtained at 0.6085 GHz on D=60, at 4.995 GHz on D=73 and at 1.412 GHz on a number of dates with |$D\geqslant142$|⁠. The fluxes are too large for thermal emission from the mvg. A model is considered for thermal emission from the hvg. It requires that the hvg had high values for mass and kinetic energy (⁠|$D\geqslant142$|⁠) and a high temperature (2×106 K). Non-detection of lines such as [Fe XIV] λ 5303 from the hvg make this model implausible if the hvg had the same chemical composition as the medium-velocity material. Synchrotron mechanisms arc also discussed. Ionization in the mvg was probably maintained by photoionization. The required photon flux from a hot stellar remnant is considered and it is estimated that the remnant may have had a temperature of 250 000 K and radius of 0.05 R⊙ on D=156. Properties of the dust grains arc discussed using data from absorption in the optical and UV and from emission in the IR. Spherical silicate grains with a radius of 0.1 μm, a temperature of 300 K and total mass of 1.6×10−6M⊙ are able to explain the absorption and an emission feature at 10 μm. The emission in the near IR is interpreted as being due to metallic grains with a total mass of 2.4×10−6M⊙, and an absorption feature peaking at 2500 Å as being due to absorption by amorphous carbon smoke in the nova shell. The assumed masses and compositions for the grains are consistent with estimated gas-phase depletions. Nova Aquilae had a high mass-fraction, Z, for the elements other than H and He. The value obtained for Z is sensitive to the spectroscopic diagnostics used. The best estimate is Z=0.97, and an approximate lower limit is Z=0.3.