اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSpectroscopic Study of the Envelope of the Hybrid Nova V458 Vul and Surrounding Nebula
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تأليف
T. N. Tarasova
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Spectroscopic observations of the hybrid V458 Vul obtained between days 9 and 778 after the brightness maximum are analyzed. Short-period, daily profile variations of forbidden [FeVII] iron lines were detected in the nebular phase, as well as a long-period (about 60-day) cyclic variation that was correlated with the photometric and X-ray cycles. The abundances of helium, neon, and iron in the novas envelope have been estimated. The helium, neon, and iron abundances exceed the solar values by factors of 4.4, 4.8, and 3.7. The envelope mass is 1.4$times$ 10$^{-5}$M$_{odot}$. The electron temperatures and number densities have been calculated for the Northwestern and Southeastern knots of the planetary nebula. The temperature derived for the Northwestern knot is Te = 10 000 K and the electron number density, n$_{e}$ = 600 cm $^{-3}$ for the Southeastern knot, Te = 13 000 K and n$_{e}$ = 750 cm$^{-3}$.
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We describe the highly variable X-ray and UV emission of V458 Vul (Nova Vul 2007), observed by Swift between 1 and 422 days after outburst. Initially bright only in the UV, V458 Vul became a variable hard X-ray source due to optically thin thermal em
ission at kT=0.64 keV with an X-ray band unabsorbed luminosity of 2.3x10^{34} erg s^{-1} during days 71-140. The X-ray spectrum at this time requires a low Fe abundance (0.2^{+0.3}_{-0.1} solar), consistent with a Suzaku measurement around the same time. On day 315 we find a new X-ray spectral component which can be described by a blackbody with temperature of kT=23^{+9}_{-5} eV, while the previous hard X-ray component has declined by a factor of 3.8. The spectrum of this soft X-ray component resembles those typically seen in the class of supersoft sources (SSS) which suggests that the nova ejecta were starting to clear and/or that the WD photosphere is shrinking to the point at which its thermal emission reaches into the X-ray band. We find a high degree of variability in the soft component with a flare rising by an order of magnitude in count rate in 0.2 days. In the following observations on days 342.4-383.6, the soft component was not seen, only to emerge again on day 397. The hard component continued to evolve, and we found an anticorrelation between the hard X-ray emission and the UV emission, yielding a Spearman rank probability of 97%. After day 397, the hard component was still present, was variable, and continued to fade at an extremely slow rate but could not be analysed owing to pile up contamination from the bright SSS component.
We present time-resolved optical spectroscopy of V458 Vulpeculae (Nova Vul 2007 No. 1) spread over a period of 15 months starting 301 days after its discovery. Our data reveal radial velocity variations in the HeII {lambda}5412 and HeII {lambda}4686
emission lines. A period analysis of the radial velocity curves resulted in a period of 98.09647 pm 0.00025 min (0.06812255 pm 0.00000017 d) which we identify with the orbital period of the binary system. V458 Vul is therefore the planetary nebula central binary star with the shortest period known. We explore the possibility of the system being composed of a relatively massive white dwarf (M1 gsim 1.0 Msun) accreting matter from a post-asymptotic giant branch star which produced the planetary nebula observed. In this scenario, the central binary system therefore underwent two common-envelope episodes. A combination of previous photoionisation modelling of the nebular spectra, post-asymptotic giant branch evolutionary tracks and the orbital period favour a mass of M2 sim 0.6 Msun for the donor star. Therefore, the total mass of the system may exceed the Chandrasekhar mass, which makes V458 Vul a Type Ia supernova progenitor candidate.
CK Vulpeculae was observed in outburst in 1670-16721, but no counterpart was seen until 1982, when a bipolar nebula was found at its location. Historically, CK Vul has been considered to be a nova (Nova Vul 1670), but a similarity to red transients,
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