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B. E. Schaefer (Louisiana S. U.)
Theoretical models of novae are robust, however the aspect of what triggers the eruption has not been tested observationally. From theory, for a particular white dwarf, the nova should be triggered when a certain amount of matter has accreted, which implies that the inter-eruption time interval (T) should vary inversely with the average accretion rate which should scale as the average B-band intensity, I (or perhaps as a low power of I to account for unknown bolometric corrections). This strong prediction can be tested only on recurrent novae with a complete record with three or more eruptions and without a red giant companion (i.e., only T Pyx and U Sco). I have collected large numbers of B-band magnitudes from the Harvard plate stacks, the UK Schmidt, and the literature over many nights.
For T Pyx, the eruptions were at 1890.4, 1902.3, 1920.3, 1944.9, and 1967.0. The four inter-eruption intervals (with T equal to 11.9, 18.0, 24.6, and 22.1 years) have 13, 7, 68, and 29 nights of observation resulting in average magnitudes of 14.32, 14.74, 14.88, and 14.72 mags (I equal to ==1, 0.73, 0.66, and 0.75) respectively. The products are 11.9, 13.1, 16.2, and 16.6 for T*I and 11.9, 9.6, 10.7, and 12.4 for T*I2.
For U Sco, the last four eruptions were at 1969.1, 1979.5, 1987.4, and 1999.2. The three inter-eruption intervals (with T equal to 10.4, 7.9, and 11.8 years) have 2, 4, and 26 nights of observation resulting in average magnitudes of 18.44, 18.30, and 18.52 mags (I equal to ==1, 1.14, and 0.94) respectively. The products are 10.4, 9.0, and 11.1 for T*I and 10.4, 10.3, and 10.4 for T*I2.
We see that the novae are relatively bright during short inter-eruption intervals and dim during long intervals. The simple (i.e., no bolometric correction) product T*I is constant to 16% for T Pyx and 11% for U Sco. The RMS scatter in the product is minimized for intensities raised to powers of ~ 2 (i.e., T*I2), with 11% scatter for T Pyx and 0.6% scatter for U Sco. I regard this as a confident and critical confirmation of the theory of nova triggers.
Since their last eruptions, T Pyx is nearly constant at 15.49 mag (92 nights, I=0.37) while U Sco is close to 18.47 mag (14 nights, I=1.00). I predict T Pyx will go off next in 2019-2057 and that U Sco will next go off in 2009.5±1.0.
The author(s) of this abstract have provided an email address for comments about the abstract: schaefer@lsu.edu
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.