  We investigated the optical lightcurve of T Pyx during its 2011 outburst by
compiling a database of SMEI and AAVSO observations. The SMEI lightcurve,
providing unprecedented detail covering 1.5-49d post-discovery, was divided
into four phases based on the idealised CN optical lightcurve; the initial rise
(1.5-3.3d), the pre-maximum halt (3.3-13.3d), the final rise (14.7-27.9d), and
the early decline (27.9d-). The SMEI lightcurve contains a strongly detected
period of 1.44+/-0.05d during the pre-maximum phase. These oscillations
resemble those found in TNR models arising from instabilities in the expanding
envelope. No spectral variation mirroring the lightcurve periodicity was found.
A marked dip at 22-24d just before maximum light (27.9d) may represent the same
phenomenon seen in novae observed by SMEI. Spectra from the Liverpool Telescope
and SMARTS 1.5m were obtained from 0.8-80.7 and 155.1-249.9d, covering the
major phases of development. A distinct high velocity ejection phase was
evident during the early rise (V~4000 km/s). A marked drop at 5.7d, and then a
gradual increase occurred in the ejection velocity which stabilised at ~1500
km/s at the pre-maximum halt. Here we propose two stages of mass loss, a
short-lived phase occurring immediately after outburst, lasting ~6d, followed
by a steadily evolving and higher mass loss phase. The overall spectral
development follows that typical of a CN and comparison with the photometric
behaviour reveals consistencies with the evolving pseudo-photosphere model of a
CN outburst. Comparing optical spectra to X-ray and radio lightcurves, weak [Fe
X] 6375 Angstrom emission was marginally detected before the X-ray rise and was
clearly present during the brightest phase of X-ray emission. If the onset of
the X-ray phase and the start of the optical final decline are related to the
cessation of significant mass loss, then this occurred at 90-110d.
