  The outburst of Nova Sgr 2011 N.2 (=V5588 Sgr) was followed with optical and
near-IR photometric and spectroscopic observations for 3.5 years, beginning
shortly before the maximum. V5588 Sgr is located close to Galactic center,
suffering from E(B-V)=1.56 (+/-0.1) extinction. The primary maximum was reached
at V=12.37 on UT 2011 April 2.5 (+/-0.2), and the underlying smooth decline was
moderately fast with t(2,V)=38 and t(3,V)=77 days. On top of an otherwise
normal decline, six self-similar, fast evolving and bright secondary maxima
(SdM) appeared in succession. Only very few other novae have presented so clear
secondary maxima. Both the primary maximum and all SdM occurred at later times
with increasing wavelengths, by amounts in agreement with expectations from
fireball expansions. The radiative energy released during SdM declined
following an exponential pattern, while the breadth of individual SdM and the
time interval between them widened. Emission lines remained sharp (FWHM~1000
km/s) throughout the whole nova evolution, with the exception of a broad
pedestal with a trapezoidal shape (extending for 3600 km/sec at the top and
4500 km/sec at the bottom) which was only seen during the advanced decline from
SdM maxima and was absent in between SdM. V5588 Sgr at maximum light displayed
a typical FeII-class spectrum which did not evolve into a nebular stage. About
10 days into the decline from primary maximum, a typical high-ionization
He/N-class spectrum appeared and remained visible simultaneously with the
FeII-class spectrum, qualifying V5588 Sgr as a rare "hybrid" nova. While the
FeII-class spectrum faded into oblivion, the He/N-class spectrum developed
strong [FeX] coronal lines.
