Analysis of Three Fast Oxygen‐Neon‐Magnesium NovaeAuthor(s): Karen M.  VanlandinghamSource: Publications of the Astronomical Society of the Pacific, Vol. 110, No. 749 (July 1998),p. 881Published by: The University of Chicago Press on behalf of the Astronomical Society of the PacificStable URL: http://www.jstor.org/stable/10.1086/316189 .

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Dissertation Summary

Analysis of Three Fast Oxygen-Neon-Magnesium Novae

Karen M. Vanlandingham

Current address: Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504; karenv@suelee.la.asu.eduThesis work conducted at Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504

Ph.D. thesis directed by Sumner Starrfield; Ph.D. degree awarded 1997

Received 1998 February 26; accepted 1998 February 27

Since astronomers have only known about the existence ofoxygen-neon-magnesium (ONeMg) novae for the last decade,little work has been done on them as a group. The purpose ofthis work was to study three fast ONeMg novae: V838 NovaHerculis 1991 (Her 91), V693 Nova Coronae Australis 1981(CrA 81), and Nova LMC 1990 No. 1 (LMC 90a). Each ofthese novae has been studied in detail, and a comparison ofthe results is provided in order to better understand ONeMgnovae as a class. My analyses have provided values of theelemental abundances, ejection velocities, ejected masses,white dwarf (WD) masses, maximum outburst luminosities, andwhite dwarf turn-off times for these novae.

All three novae have abundances enhanced relative to solarvalues, with the oxygen abundance of Her 91 being the ex-ception (see Table 1). They show high N/O ratios, indicatinghigh-mass WD progenitors. We find CrA 81 and LMC 90a tohave almost identical abundances, even though the initial metalabundances for the LMC novae are one-third of solar values.Each of the novae exhibited a super-Eddington luminosityphase at maximum light. Our analysis of the Her 91 spectrumtaken 2 months after outburst, however, required a luminosityalmost 2 orders of magnitude lower than the Eddington limitfor a 1.4 M, WD. The best fits for CrA 81 and LMC 90a, onthe other hand, were consistent with a constant luminosity of∼1038 ergs s21 for at least 2 months after outburst. While wewere unable to accurately determine ejected masses for eitherCrA 81 or LMC 90a owing to the lack of optical data, wefound an ejected mass of ∼1024 M, for Her 91. This is inagreement with the values found by other groups using differentdata and different techniques.

The results of this study can be used in many ways to helpfurther the understanding of novae and stellar evolution. Theelemental abundances that have been determined can be usedas input to theoretical hydrodynamic models. This will providebetter constraints on the models in order to determine the en-

ergetics of the outburst and the mass of the underlying whitedwarf, properties that are difficult to obtain observationally.Knowledge of the abundances will also help determine thecontribution of fast ONeMg novae to the heavy-element contentof the interstellar medium. In particular, with the abundanceresults, the mass fraction of 26Al in the nova ejecta can beestimated. These estimates will help to determine if novae areimportant for Galactic nucleosynthesis. Analysis of LMC 90aprovides the means to compare Galactic with extragalactic no-vae. For example, the LMC novae can be used to calibrate theluminosities of (and therefore distances to) Galactic novae. Thiscalibration will allow a better determination of the fast end ofthe absolute-magnitude decay-rate relationship or perhaps de-velop a separate relationship for this class of novae.

TABLE 1Model Derived Parameters

Parameter Her 91 CrA 81 LMC 90a

Time since discovery (days) . . . . . . 61 72 46L (ergs s21) . . . . . . . . . . . . . . . . . . . . . . . . 5.1 # 1036 1.5 # 1038 1.3 # 1038

Density (cm23) . . . . . . . . . . . . . . . . . . . . 4.2 # 106 1.6 # 108 2.1 # 107

Filling factor . . . . . . . . . . . . . . . . . . . . . . . 0.1 0.01 0.1AMejS (M,) . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 # 1024 6.8 # 1025 1.6 # 1024

Hea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.310.520.2 1.310.6

20.5 1.010.420.2

C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.715.923.5 2.510.9

21.1 81424

N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.3111.4210.9 132155.4

244.9 117140239

O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.310.220.2 14.114.7

26.1 2011129

Ne . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40.0116.0210.7 2471183.6

2105.3 62146235

Mg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ) 7.918.125.9 1018

25

Al . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ) 60.6162.8256.0 2271188

110

Si . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ) 21.9119.0216.0 40117

216

S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.115.625.0 ) )

a Abundances are relative to H relative to solar values, with the followingvalues for log(solar): He 5 21.0, C 5 23.45, N 5 24.03, O 5 23.13, Ne5 23.93, Mg 5 24.42, Al 5 25.53, Si 5 24.45.

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