The secrets of T Pyxidis

Abstract

Aims. We compare the observed and theoretical parameters for the quiescent and outburst phases of the recurring nova T Pyx. Methods. IUE data were used to derive the disk luminosity and the mass accretion rate, and to exclude the presence of quasi-steady burning at the WD surface. XMM-NEWTON data were used to verify this conclusion.. These values were about twice as high in the pre-1966-outburst epoch. This allowed the first direct estimate of the total mass accreted before outburst, M accr =Ṁ pre−OB ·Δt, and its comparison with the critical ignition mass M ign . We found M accr and M ign to be in perfect agreement (with a value close to 5 × 10 −7 M ) for M 1 ∼ 1.37 M , which provides a confirmation of the thermonuclear runaway theory. The comparison of the observed parameters of the eruption phase, with the corresponding values in the grid of models by Yaron and collaborators, provides satisfactory agreement for values of M 1 close to 1.35 M and logṀ between −8.0 and −7.0, but the observed value of the decay time t 3 is higher than expected. The long duration of the optically thick phase during the recorded outbursts of T Pyx, a spectroscopic behavior typical of classical novae, and the persistence of P Cyg profiles, constrains the ejected mass M ign to within 10 −5 −10 −4 M . Therefore, T Pyx ejects far more material than it has accreted, and the mass of the white dwarf will not increase to the Chandrasekhar limit as generally believed in recurrent novae. A detailed study based on the UV data excludes the possibility that T Pyx belongs to the class of the supersoft X-ray sources, as has been postulated. XMM-NEWTON observations have revealed a weak, hard source and confirmed this interpretation.

The spectroscopic evolution of the recurrent nova T Pyxidis during its 2011 outburst

“…Selvelli et al (2008) and Schaefer (2010) provide the most recent compilations of the estimates for T Pyx, giving a distance of 3.5±1 kpc and E(B−V) = 0.25±0.02 and, for the purposes of this Letter we refer the reader to Tables 26 and 29 of Schaefer (2010) for details. Although some spectroscopy during the extended minimum was included in these previous studies, with inconclusive results, almost all estimates of both distance and reddening were based on photometry.…”

“…1 along with the interstellar absorption lines listed in Table 2. The effect of this revision on the luminosity, in both quiescence and outburst is obvious, but the larger extinction also affects the derived properties of the WD based on the continuum from 1200-3000 Å (Selvelli et al 2008). The increase in E(B − V) in turn steepens the UV spectral gradient with wavelength such that the effective temperature of the WD is lower than earlier determinations (but we will discuss how much this change depends on a model atmosphere analysis in the next paper in this series).…”

Pre-outburstChandraobservations of the recurrent nova T Pyxidis

“…Since there are no current models that describe Comptonized plasmas for nonmagnetic CVs (and WDs), no further elaboration will be included, but there is consistency with the existing Comptonized plasma emission models. Selvelli et al (2008) and Balman (2010) discuss how the blackbody model of emission is inconsistent with the data. A 2σ upper limit on the soft X-ray emission from T Pyx calculated from the spectral fits to the Chandra data using the blackbody model is a of kT BB < 25 eV and f BB < 1.5 × 10 −12 erg s −1 cm −2 in the 0.1−10.0 keV range.…”

“…Hubble Space Telescope (HST;1994 observations of the shell show thousands of knots in Hα and [NII] with expansion velocities of 500−715 km s −1 that have not decelerated and the main emission is within a radius of 5 −6 (Shara et al 1997;Schaefer et al 2010). The spectral energy distribution (SED) is dominated by an accretion disk in the UV+opt+IR ranges, with a distribution (after correction for reddening) that is described by a power law F λ = 4.28 × 10 −6 λ −2.33 erg s −1 cm −2 Å −1 , while the continuum in the UV range can also be represented by a single blackbody of T ∼ 34 000 K withṀ ∼ (1−4) × 10 −8 M yr −1 (Gilmozzi & Selvelli 2007;Selvelli et al 2008). Therefore, T Pyx is believed to be a nonmagnetic CV accreting at high rates as expected from RN precursers with a distance estimate of 3.50 ± 0.35 kpc (Selvelli et al 2008).…”

“…The spectral energy distribution (SED) is dominated by an accretion disk in the UV+opt+IR ranges, with a distribution (after correction for reddening) that is described by a power law F λ = 4.28 × 10 −6 λ −2.33 erg s −1 cm −2 Å −1 , while the continuum in the UV range can also be represented by a single blackbody of T ∼ 34 000 K withṀ ∼ (1−4) × 10 −8 M yr −1 (Gilmozzi & Selvelli 2007;Selvelli et al 2008). Therefore, T Pyx is believed to be a nonmagnetic CV accreting at high rates as expected from RN precursers with a distance estimate of 3.50 ± 0.35 kpc (Selvelli et al 2008). Recently, the ultravioletoptical-infrared SED is found to be fitted by a power law ( f ν ∝ ν 1 ) which suggests that most of the T Pyx light in quiescence may not originate from a standard accretion disk, or any superposition of blackbodies, but rather comes from some nonthermal source (Schaefer et al 2013).…”