The spectroscopic evolution of the recurrent nova T Pyxidis during its 2011 outburst I. The optically thick phase and the origin of moving lines in novae

TL;DR

This study provides detailed spectroscopic observations of T Pyxidis during its 2011 outburst, analyzing the ejecta's evolution, determining a revised distance and extinction, and explaining the origin of moving absorption lines.

Contribution

It offers the first high-resolution spectroscopic analysis of T Pyxidis's outburst, proposing a new distance estimate and explaining the moving lines through recombination fronts in the ejecta.

Findings

Distance to T Pyx ≥ 4.5 kpc, with a lower limit of 3.5 kpc

Extinction E(B-V) ≈ 0.5, higher than previous estimates

Ejecta mass estimated at 10^{-5} solar masses

Abstract

The nova T Pyx was observed with high resolution spectroscopy (R ~ 65000) spectroscopy, beginning 1 day after discovery of the outburst and continuing through the last visibility of the star at the end of May 2011. The interstellar absorption lines of Na I, Ca II, CH, CH$^+$, and archival H I 21 cm emission line observations have been used to determine a kinematic distance. Interstellar diffuse absorption features have been used to determine the extinction independent of previous assumptions. Sample Fe-peak line profiles show the optical depth and radial velocity evolution of the discrete components. We propose a distance to T Pyx $\geq$4.5kpc, with a strict lower limit of 3.5 kpc (the previously accepted distance). We derive an extinction, E(B-V)$\approx0.5\pm$0.1, that is higher than previous estimates. The first observation, Apr. 15, displayed He I, He II, C III, and N III emission lines and a maximum velocity on P Cyg profiles of the Balmer and He I lines of $\approx$2500 km s$^{-1}$ characteristic of the fireball stage. These ions were undetectable in the second spectrum, Apr. 23, and we use the recombination time to estimate the mass of the ejecta, $10^{-5}f$M$_\odot$ for a filling factor $f$. Numerous absorption line systems were detected on the Balmer, Fe-peak, Ca II, and Na I lines, mirrored in broader emission line components, that showed an "accelerated" displacement in velocity. We also show that the time sequence of these absorptions, which are common to all lines and arise only in the ejecta, can be described by recombination front moving outward in the expanding gas without either a stellar wind or circumstellar collisions.