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Session 47 - Novae.
Display session, Tuesday, January 14
We have begun a study of the subclass of novae known as `neon' or ONeMg novae (Starrfield, Sparks amp; Truran 1986). Novae of this type are characterized by strong neon emission lines in their spectra and high ejecta velocities. These novae are thought to occur on ONeMg white dwarfs with masses near the Chandrasekhar limit. Our study includes Nova Herculis 1991, Nova Corona Austrinae 1981, and Nova LMC 1990 #1. Analysis of Her 91 (Vanlandingham et al. 1996 MNRAS 282 563) is complete and we are currently working on LMC 90 #1. Here we present our recent results for Corona Austrinae 1981.
Nova V693 Corona Austrinae (CrA81) was discovered on April 2.75 UT 1981. Observations with IUE began on 1981 April 10 and continued through 1981 November 14. CrA81 was a fast ONeMg nova, with t_2\simeq8 days and t_3\simeq14 days. By matching the SWP and LWR spectra together at 2000Å\ and adjusting the value of the reddening until the continuum had a roughly constant slope we find E(B-V)\simeq 0.2\pm0.1 for the nova. Using maximum magnitude-decay rate relationships (Della Valle 1995; Livio 1992) we find the distance to CrA81 to be 14.3\pm0.2 kpc. We used the photoionization code CLOUDY 84 and the minimization routine MINUIT to determine elemental abundances for the nova. Our results show all of the elements to be enhanced relative to solar material. While helium, carbon, and magnesium are only marginally enhanced, oxygen and silicon are about 20 times solar, and nitrogen and neon are 140 and 287 times solar, respectively. The high neon abundance supports the fact that CrA81 is an ONeMg nova. These results are based on independent fits to three different observations, spanning over six months. Williams et al (1985) and Andreä et al (1994) also performed abundance analyses on CrA81. Andreä's values are 2 to 5 times larger than those of Williams. Our abundance values are lower than both Williams and Andreä for He, C, O, Mg, and Al, with our values being closer to Williams for N, Ne, and Si. Comparing the abundance results for CrA81 with those of Her 91 we find them to be very similar. Both show most elements to be enhanced relative to solar material, with neon being the most abundant, however Her 91 had helium and oxygen abundances that were less than solar (\approx0.3 times solar). The high N/O ratios of these novae are indicative of outbursts on massive white dwarfs (Starrfield et al 1993).
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