The secrets of T Pyxidis

Abstract

Aims. We study the UV spectral behavior of the recurrent nova T Pyx during 16 years of IUE observations. Methods. We examined both the IUE line-by-line images and the extracted spectra in order to understand the reality and the origin of the observed spectral variations. We compare different extraction methods and their influence on the spectrum of an extended object. Results. The UV continuum of T Pyx has remained nearly constant in slope and intensity over this time interval, without any indication of long-term trends. The reddening determined from the UV data is E B−V = 0.25 ± 0.02. The best single-curve fit to the dereddened UV continuum is a power-law distribution ∝λ −2.33 . The tail of this curve agrees well with the B, V, and J magnitudes of T Pyx, indicating that the contribution of the secondary star is negligible. One peculiar aspect of T Pyx is that most emission lines (the strongest ones being those of CIV 1550 and HeII 1640) show substantial changes both in intensity and detectability, in contrast to the near constancy of the continuum. Several individual spectra display emission features that are difficult to identify, suggesting a composite spectroscopic system. We tentatively ascribe the origin of these transient emission features either to loops and jets from the irradiated secondary or to moving knots of the surrounding nebula that are (temporarily) projected in front of the system. The inspection of all IUE line-by-line images has led to the detection of emission spikes outside the central strip of the spectrum, which in some cases seem associated to known emission features in the (main) spectrum. A comparison with other ex-novae reveals a surprising similarity to the spectrum of the very-slow nova HR Del, whose white dwarf primary has a mass that is allegedly about one half that of T Pyx.

An archive study of 18 old novae

“…(A linear plot would not show the progressive departure from a power law starting at λ ∼ 4300 since it would compress it within a few per cent of the y-axis.) As in the case of T Pyx, which shows a very similar behavior (Gilmozzi & Selvelli 2007), we interpret this departure as an indication that the contribution of the disk to these wavelengths comes from its outer region, where it becomes optically thin (or reaches a physical edge) and is the superposition of the blackbody tails from the progressively larger and cooler last optically thick outer annuli of the disk. The temperature of this outer region of the disk was estimated at ∼10 000 K for T Pyx, and this seems to the case for V603 Aql as well, since the wavelength at which the departure starts is very similar for the two objects.…”

“…It should also be noted that the near coincidence in wavelength of several of these weak emission features in different objects gives support to their reality: the line near 1280 Å is present in DQ Her and GK Per, the line near 1434 Å in V603 Aql and HR Del (and also in T Pyx, see Gilmozzi & Selvelli 2007), the line near 1590 Å in V603Aql and RR Pic, the line near 1914 Å in V603 Aql and DQ Her, the line near 3124 Å in V603 Aql, DQ Her, and RR Pic. It is tempting to identify this last feature as the strong O iii Bowen line λ 3132 Å, although the wavelength separation is systematically too large.…”

SALT observations of southern post-novae

“…3 and Table 2) The equivalent widths (EW) and the FWHM of the strongest emission lines measured in the target spectra are provided in Table 3. The measurements were done with the  task  Gilmozzi & Selvelli (2007); (2) Shafter (1997); (13) Henize & Liller (1975); (14) Selvelli & Gilmozzi (2013); (15) Zhao & McClintock (1997); (16) Selvelli (2004). fitting Gaussians to the emission lines. The error estimates were computed directly in  by running a number of Monte Carlo simulations based on preset instrumental parameters.…”

The 2011 Eruption of the Recurrent Nova T Pyxidis: The Discovery, the Pre-Eruption Rise, the Pre-Eruption Orbital Period, and the Reason for the Long Delay

“…The C iv line at 1550 Å is significant, and the He ii line at 1640 Å is likely visible but not significant. This spectrum can be compared with the ultraviolet spectrum derived from greatly longer exposures with the IUE satellite that covers a somewhat broader wavelength range (Selvelli et al 2010). variable in the IUE spectrum (Gilmozzi & Selvelli 2007). This spectrum is well fit by a power law, for which we find an index of −2.25 ± 0.03, while the normalization has a formal error of 1.1%.…”