Universal Decline Law of Novae

Optical and infrared light-curves of classical novae are approximately homologous among various white dwarf (WD) masses and chemical compositions when free-free emission from optically thin ejecta is spherical and dominates the continuum flux of novae. Such a homologous template light-curve is called “a universal decline law.” Various nova light-curves are approximately reproduced from this universal law by introducing a timescaling factor which stretches or squeezes the template light-curve to match the observation. The timescale of the light curve depends strongly on the WD mass but weakly on the chemical composition, so we are able to roughly estimate the WD mass from the light-curve fitting. We have applied the universal decline law to the old nova GK Persei 1901 and recent novae that outbursted in 2005. The estimated WD mass is 1.15 M⊙ for GK Per, which is consistent with a central value of the WD mass determined from the orbital velocity variations. The other WD masses of 10 novae in 2005 are also estimated to be 1.05 M⊙ (V2361 Cyg), 1.15 M⊙ (V382 Nor), 1.2 M⊙ (V5115 Sgr), 0.7 M⊙ (V378 Ser), 0.9 M⊙ (V5116 Sgr), 1.25 M⊙ (V1188 Sco), 0.7 M⊙ (V1047 Cen), 0.95 M⊙ (V476 Sct), 0.95 M⊙ (V1663 Aql), and 1.30 M⊙ (V477 Sct), within a rough accuracy of ±0.1 M⊙. Four (V382 Nor, V5115 Sgr, V1188 Sco, and V477 Sct) of ten novae in the year 2005 are probably neon novae on an O-Ne-Mg WD. Each WD mass depends weakly on the chemical composition (especially the hydrogen content X in mass weight), i.e., the obtained WD masses increase by +0.5(X − 0.35) M⊙ for the six CO novae and by +0.5(X − 0.55) M⊙ for the four neon novae above. Various nova parameters are discussed in relation to its WD mass. Subject headings: novae, cataclysmic variables — stars: individual (GK Persei) — stars: winds, outflows — white dwarfs