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Nova Theory

Nova studies in external galaxies were mainly undertaken after astronomers realized their potential use as distance indicators (e.g. Della Valle and Livio 1995, ApJ, 452, 704; van den Bergh and Pritchet 1986, PASP98, 110). Unfortunately, with the exception of some galaxies belonging to the Local Group (M31, LMC and M33), the studies of novae in external galaxies are very sporadic. Novae are, indeed, unpredictable events, and to collect a statistically significant sample of objects one needs to observe as many galaxies as possible (possibly belonging to the same cluster). Therefore, the large field coupled with a 8-m class telescope, will allow us to start systematic programs to study extragalactic novae, even beyond the Virgo Circle. We sketch out the impact that surveys of extragalactic novae could have on the current framework of nova theory, particularly on the properties of the progenitors. Indeed the distribution of the rates of decline (derived from the lightcurves of the novae) can give us information on the mass spectrum of the underlying white dwarfs, since the strength of the nova outburst mainly depends on the mass of the white dwarf through: M $_B=10\times {\rm log} M_{WD}-8.3$ (Livio 1992, ApJ, 393, 516). In addition the rate of nova outbursts, Nout, is related to the number of nova progenitors: N $_{prog}=N_{out}
\times T_R$, where TR is the recurrence time between outbursts. Finally, a close examination of the sites of nova explosions can give us useful piece of information on the stellar population to which the progenitors belong. Indeed, the study of the sites of the nova explosions in M31 led Ciardullo et al. (1987, ApJ, 318, 520) and Capaccioli et al. (1989, AJ, 97, 1622) to conclude that the bulk of novae in the Andromeda galaxy originates in the bulge. On the other hand, Graham (1979, PASP, 91, 79) and Capaccioli et al. (1990, AJ, 97, 1622) found a nova rate of $\geq 2$ novae/yr for the LMC, and Della Valle et al. (1994, A&A, 287, 403) derived a nova rate for M33 of $\sim 5$ novae/yr. Since both the LMC and M33 are bulgeless, their nova production has to be maintained in the disk.


next up previous contents
Next: Nova Rate Up: Extragalactic Novae Previous: Extragalactic Novae
Guido Buscema
1999-01-29