Evolution of the spectrum of Nova Andromedae 1986 during its early light decline

Chang-chun, Huang; Chen, Ya‐Feng; Chen, Ling

doi:10.1016/0083-6656(88)90211-5

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“…The Hβ lines showed a blue shifted absorption component with a mean radial velocity increasing from 1190 km s −1 on December 15 to 1270 km s −1 on December 21. This is in agreement with values obtained by Changchun et al (1988). Based on the strong optical Fe ii lines, OS And 86 was a standard Fe ii (Williams 1992), or CO type nova, suggesting that the nova occurred on the surface of a white dwarf composed of carbon and oxygen.…”

Section: Determination Of the Basic Parameters Of Os And 1986supporting

confidence: 91%

Non-LTE model atmosphere analysis of the early ultraviolet spectra of Nova OS Andromedae 1986

Schwarz

Hauschildt

Starrfield

et al. 1997

Monthly Notices of the Royal Astronomical Society

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We have analyzed the early optically thick ultraviolet spectra of Nova OS And 1986 using a grid of spherically symmetric, non-LTE, line-blanketed, expanding model atmospheres and synthetic spectra with the following set of parameters: 5, 000 ≤ T model ≤ 60, 000K, solar abundances, ρ ∝ r −3 , v max = 2000 km s −1 , L = 6 × 10 4 L ⊙ , and a statistical or microturbulent velocity of 50 km s −1 . We used the synthetic spectra to estimate the model parameters corresponding to the observed IUE spectra. The fits to the observations were then iteratively improved by changing the parameters of the model atmospheres, in particular T model and the abundances, to arrive at the best fits to the optically thick pseudo-continuum and the features found in the IUE spectra.The IUE spectra show two different optically thick subphases. The earliest spectra, taken a few days after maximum optical light, show a pseudo-continuum created by overlapping absorption lines. The later observations, taken approximately 3 weeks after maximum light, show the simultaneous presence of allowed, semi-forbidden, and forbidden lines in the observed spectra.Analysis of these phases indicate that OS And 86 had solar metallicities except for Mg which showed evidence of being underabundant by as much as a factor of 10. We determine a distance of 5.1 kpc to OS And 86 and derive a peak bolometric luminosity of ∼ 5 × 10 4 L ⊙ . The computed nova parameters provide insights into the physics of the early outburst and explain the spectra seen by IUE. Lastly, we find evidence in the later observations for large non-LTE effects of Fe ii which, when included, lead to much better agreement with the observations.

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Section: Determination Of the Basic Parameters Of Os And 1986supporting

confidence: 91%