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
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.