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We continue our study of the physical properties of the recurrent nova T Pyx,focussing on the structure of the ejecta in the nebular stage of expansionduring the 2011 outburst. The nova was observed contemporaneously with theNordic Optical Telescope (NOT), at high resolution spectroscopic resolution (R~ 65000) on 2011 Oct. 11 and 2012 Apr. 8 (without absolute flux calibration),and with the Space Telescope Imaging Spectrograph (STIS) aboard the HubbleSpace Telescope, at high resolution (R ~ 30000) on 2011 Oct. 10 and 2012 Mar.28 (absolute fluxes). We use standard plasma diagnostics (e.g. [O III] and [NII] line ratios and the H$\beta$ line fluxes) to constrain electron densitiesand temperatures. Using Monte Carlo modeling of the ejecta, we derive thestructure and filling factor from comparisons to the optical and ultravioletline profiles. The ejecta can be modeled using an axisymmetric conical --bipolar -- geometry with a low inclination of the axis to the line of sight,i=15+/-5 degrees, compatible with published results from high angularresolution optical spectro-interferometry. The structure is similar to thatobserved in the other short orbital period recurrent novae during their nebularstages. We show that the electron density scales as $t^{-3}$ as expected from aballistically ejected constant mass shell; there is no need to invoke acontinuing mass outflow following the eruption. The derived mass for the ejectawith filling factor f ~ 3%, M_ej ~ 2E-6$M_sun is similar to that obtained forother recurrent nova ejecta but inconsistent with the previously reportedextended optically thick epoch of the explosion. We suggest that the systemunderwent a common envelope phase following the explosion that produced therecombination event. Implications for the dynamics of the recurrent novae arediscussed. (truncated)

astronomy and astrophysics

The spectroscopic evolution of the recurrent nova T Pyxidis during its  2011 outburst. II.The optically thin phase and the structure of the ejecta in  recurrent novae