A Theoretical Light-Curve Model for the 1999 Outburst of U Scorpii

Abstract

A theoretical light curve for the 1999 outburst of U Scorpii is presented in order to obtain various physical parameters of the recurrent nova. Our U Sco model consists of a very massive white dwarf (WD) with an accretion disk and a lobe-filling, slightly evolved, main-sequence star (MS). The model includes a reflection effect by the companion and the accretion disk together with a shadowing effect on the companion by the accretion disk. The early visual light curve (with a linear phase of t approximately 1-15 days after maximum) is well reproduced by a thermonuclear runaway model on a very massive WD close to the Chandrasekhar limit (MWD=1.37+/-0.01 M middle dot in circle), in which optically thick winds blowing from the WD play a key role in determining the nova duration. The ensuing plateau phase (t approximately 15-30 days) is also reproduced by the combination of a slightly irradiated MS and a fully irradiated flaring-up disk with a radius approximately 1.4 times the Roche lobe size. The cooling phase (t approximately 30-40 days) is consistent with a low-hydrogen content of X approximately 0.05 of the envelope for the 1.37 M middle dot in circle WD. The best-fit parameters are the WD mass of MWD approximately 1.37 M middle dot in circle, the companion mass of MMS approximately 1.5 M middle dot in circle (0.8-2.0 M middle dot in circle is acceptable), the inclination angle of the orbit (i approximately 80&j0;), and the flaring-up edge, the vertical height of which is approximately 0.30 times the accretion disk radius. The duration of the strong wind phase (t approximately 0-17 days) is very consistent with the BeppoSAX supersoft X-ray detection at t approximately 19-20 days because supersoft X-rays are self-absorbed by the massive wind. The envelope mass at the peak is estimated to be approximately 3x10-6 M middle dot in circle, which is indicates an average mass accretion rate of approximately 2.5x10-7 M middle dot in circle yr-1 during the quiescent phase between 1987 and 1999. These quantities are exactly the same as those predicted in a new progenitor model of Type Ia supernovae.

Rotation of surviving companion stars after type Ia supernova explosions in the WD+MS scenario

“…This model is named "MS_110", the "MS" indicating a CO WD+MS binary system, the "110" means the rotational velocity of the companion star of v SN rot ∼ 110 km s −1 at the moment of the explosion. U Scorpii is one of the bestobserved recurrent novae, and it has been suggested as a progenitor of an SN Ia because its white dwarf mass is close to the Chandrasekhar mass (Hachisu et al 2000;Thoroughgood et al 2001;Podsiadlowski 2003). To investigate the physical parameters of the recurrent nova, Hachisu et al (2000) have successfully modeled the theoretical light curve for the outburst of the U Scorpii system with a model consisting of a WD mass of A109, page 3 of 12 A&A 554, A109 (2013) are the mass, the orbital period, the radius, the spin velocity, and the angular momentum of the companion star at the moment of the explosion.…”

[ITAL]Chandra[/ITAL] Observations of the Recurrent Nova CI Aquilae after Its 2000 April Outburst

“…Since the M , ejecta of RNe typically are not metal-enriched, the white dwarfs in RNe are not significantly eroded but may grow in mass (Starrfield, Sparks, & Truran 1985). The fitting of RN optical light curves suggests that the white dwarf masses are high, near the Chandrasekhar limit (e.g., Hachisu & Kato 1999;Hachisu et al 2000), suggesting that RNe may be progenitors of Type Ia supernovae (SNe Ia).…”

High-Velocity Jets in Recurrent Nova Outbursts

“…In the case of U Sco, however, most of these mechanisms do not work, at least in the early phase of the outburst, because the accretion disk and the companion star are completely engulfed by the expanded envelope (Hachisu et al 2000a). In addition, no indication of strong magnetic field or surrounding asymmetric medium is reported for U Sco.…”

“…Therefore, a light curve fitting of U Sco (Kato 1999;Hachisu et al 2000aHachisu et al , 2000b gives us a WD mass of ∼1.37 M , . Even in such a massive WD, large expansion velocities observed cannot be reproduced by theories presented so far.…”