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تسجيل مستخدم جديدThe Recurrent Nova U Scorpii - A Type Ia Supernova Progenitor
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T. D. Thoroughgood
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We derive the mass of the white dwarf in the eclipsing recurrent nova U Sco from the radial velocity semi-amplitudes of the primary and secondary stars. Our results give a high white dwarf mass of M_1 = 1.55 pm 0.24M_odot, consistent with the thermonuclear runaway model of recurrent nova outbursts. We confirm that U Sco is the best Type Ia supernova progenitor known, and predict that the time to explosion is within ~700,000 years.
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There is a consensus that Type-Ia supernovae (SNe Ia) arise from the thermonuclear explosion of white dwarf stars that accrete matter from a binary companion. However, direct observation of SN Ia progenitors is lacking, and the precise nature of the
binary companion remains uncertain. A temporal series of high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex circumstellar environment that provides an unprecedentedly detailed view of the progenitor system. Multiple shells of circumsteller are detected and the SN ejecta are seen to interact with circumstellar material (CSM) starting 59 days after the explosion. These features are best described by a symbiotic nova progenitor, similar to RS Ophiuchi.
VLT and SALT spectroscopy of U Sco were obtained $sim$18 and $sim$30 months after the 2010 outburst. From these spectra the accretion disc is shown to take at least 18 months to become fully reformed. The spectral class of the companion is constraine
d to be F8$^{+5}_{-6}$,IV-V at the 95% confidence level when the irradiated face of the companion is visible.
The eruption of the recurrent nova U Scorpii on 28 January 2010 is now the all-time best observed nova event. We report 36,776 magnitudes throughout its 67 day eruption, for an average of one measure every 2.6 minutes. This unique and unprecedented c
overage is the first time that a nova has any substantial amount of fast photometry. With this, two new phenomena have been discovered: the fast flares in the early light curve seen from days 9-15 (which have no proposed explanation) and the optical dips seen out of eclipse from days 41-61 (likely caused by raised rims of the accretion disk occulting the bright inner regions of the disk as seen over specific orbital phases). The expanding shell and wind cleared enough from days 12-15 so that the inner binary system became visible, resulting in the sudden onset of eclipses and the turn-on of the supersoft X-ray source. On day 15, a strong asymmetry in the out-of-eclipse light points to the existence of the accretion stream. The normal optical flickering restarts on day 24.5. For days 15-26, eclipse mapping shows that the optical source is spherically symmetric with a radius of 4.1 R_sun. For days 26-41, the optical light is coming from a rim-bright disk of radius 3.4 R_sun. For days 41-67, the optical source is a center-bright disk of radius 2.2 R_sun. Throughout the eruption, the colors remain essentially constant. We present 12 eclipse times during eruption plus five just after the eruption.
We present spectroscopy of the eclipsing recurrent nova U Sco. The radial velocity semi-amplitude of the primary star was found to be K_W = 93 pm 10 kms^{-1} from the motion of the wings of the HeIIlambda4686AA emission line. By detecting weak absorp
tion features from the secondary star, we find its radial velocity semi-amplitude to be K_R = 170 pm 10 kms^{-1}. From these parameters, we obtain a mass of M_1 = 1.55 pm 0.24M_odot for the white dwarf primary star and a mass of M_2 = 0.88 pm 0.17M_odot for the secondary star. The radius of the secondary is calculated to be R_2 = 2.1pm0.2R_odot, confirming that it is evolved. The inclination of the system is calculated to be i = 82.7^circpm2.9^circ, consistent with the deep eclipse seen in the lightcurves. The helium emission lines are double-peaked, with the blue-shifted regions of the disc being eclipsed prior to the red-shifted regions, clearly indicating the presence of an accretion disc. The high mass of the white dwarf is consistent with the thermonuclear runaway model of recurrent nova outbursts, and confirms that U Sco is the best Type Ia supernova progenitor currently known. We predict that U Sco is likely to explode within sim 700,000 years.
We present near-IR observations of the 2010 outburst of U Sco. JHK photometry is presented on ten consecutive days starting from 0.59 days after outburst. Such photometry can gainfully be integrated into a larger database of other multi-wavelength da
ta which aim to comprehensively study the evolution of U Sco. Early near-IR spectra, starting from 0.56 days after outburst, are presented and their general characteristics discussed. Early in the eruption, we see very broad wings in several spectral lines, with tails extending up to ~10000km/s along the line of sight; it is unexpected to have a nova with ejection velocities equal to those usually thought to be exclusive to supernovae. From recombination analysis, we estimate an upper limit of 10^-4.64[+0.92.-0.74]Msun for the ejected mass.
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