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Astron. Astrophys. 322, 807-816 (1997)

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Appendix A: the period-amplitude relation of novae

In order to study the period-amplitude relation of novae, the amplitudes of all novae with known period were calculated from the maximum and minimum magnitudes quoted in the catalogue of Duerbeck (1987). The only system excluded from this investigation is GK Per because due to its evolved secondary its period is much longer than that of any other nova.

The outburst amplitudes are plotted against orbital period P in Fig. 7. It is obvious that there is a definite trend in the sense that the amplitude is lower if the period is longer. The most deviating points are V1500 Cyg which has an unusually high amplitude, and DO Aql and HR Del which have low amplitudes. Note that the latter is intrinsically extraordinarily bright in quiescence (Bruch 1982a) and that the observed outburst amplitude is therefore lower than that of nova with mean quiescent brightness and the same intrinsic strength of the outburst.

[FIGURE] Fig. 7. Orbital period - outburst amplitude relation for classical novae together with the best fit straight line

A linear least squares fit to the data yields a formal period-amplitude relation (shown as a solid line in Fig. 7) with an inclination of [FORMULA]. The correlation coefficient is [FORMULA]. The significance level at which the null hypothesis of zero correlation is disproved (see e.g. Press et al. 1986) is [FORMULA]. (Excluding V1500 Cyg, DO Aql and HR Del leads to [FORMULA], [FORMULA] and [FORMULA].)

Since the observed amplitude of the outburst depends on the intrinsic strength of the eruption and the quiescent absolute magnitude of the system, i.e. on the background before which the outburst is seen, any relation between period and absolute magnitude of novae in quiescence will influence the period-amplitude relation. No such relation is known for nova, but Warner (1987) found that the absolute magnitude of dwarf novae in outburst depends linearily on the orbital period (if a correction is made to reduce all systems to the same orbital inclination). The accretion disks of outbursting dwarf novae are expected to behave similar to steady state disks, and so are the disks of novae in quiescence. Therefore, it may be assumed that the period-magnitude relation found by Warner is also valid for classical novae.

Warner's relation indicates that the absolute magnitude increases (i.e. its numerical value decreases!) with the period by [FORMULA] mag/hour. Within the error limits this is identical to the decrease of the observed outburst amplitude of novae found above.

In conclusion we can state that the intrinsic strength of a nova outburst does not depend on the orbital period of the system.

Nova theory predicts that the outburst amplitude should increase with the white dwarf mass. The independence of intrinsic outburst amplitude and period therefore also indicates that the mass distribution of the white dwarfs in novae does not depend noticeably on the period.

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© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998