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2006ApJS..167...59H - Astrophys. J., Suppl. Ser., 167, 59-80 (2006/November-0)

A universal decline law of classical novae.


Abstract (from CDS):

We calculate many different nova light curves for a variety of white dwarf masses and chemical compositions, with the assumption that free-free emission from optically thin ejecta dominates the continuum flux. We show that all these light curves are homologous and a universal law can be derived by introducing a ``time scaling factor.'' The template light curve for the universal law has a slope of flux F∝t–1.75 in the middle part (from ∼2 to ∼6 mag below the optical maximum), but it declines more steeply, F∝t–3.5, in the later part (from ∼6 to ∼10 mag), where t is the time from the outburst in units of days. This break on the light curve is due to a quick decrease in the wind mass-loss rate. The nova evolutions are approximately scaled by the time of break. Once the time of break is observationally determined, we can derive the period of a UV burst phase, the duration of optically thick wind phase, and the turnoff date of hydrogen shell-burning. An empirical observational formula, t3=(1.68±0.08) t2+(1.9±1.5) days, is derived from the relation of F∝t–1.75, where t2and t3are the times in days during which a nova decays by 2 and 3 mag from the optical maximum, respectively. We have applied our template light curve model to the three well-observed novae, V1500 Cyg, V1668 Cyg, and V1974 Cyg. Our theoretical light curves show excellent agreement with the optical y and infrared J, H, K light curves. The continuum UV 1455 Å light curves observed with IUE are well reproduced. The turn-on and turn-off of supersoft X-ray observed with ROSAT are also explained simultaneously by our model. The WD mass is estimated, from the light curve fitting, to be MWD~1.15 Mfor V1500 Cyg, MWD~0.95 Mfor V1668 Cyg, and MWD~0.95-1.05 Mfor V1974 Cyg, together with the appropriate chemical compositions of the ejecta.

Abstract Copyright:

Journal keyword(s): Stars: Novae, Cataclysmic Variables - Stars: Individual: Constellation Name: V1500 Cygni - stars: individual (V1668 Cygni) - Stars: Individual: Constellation Name: V1974 Cygni - Stars: White Dwarfs - X-Rays: Stars

Simbad objects: 27

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