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LBT/LUCIFER near-infrared spectroscopy of PV Cephei. An outbursting young stellar object with an asymmetric jet

We present a detailed spectroscopic investigation of the young eruptive star PV Cep, to improve our understanding of its nature and characterise its circumstellar environment after its last outburst in 2004. The analysis of our medium-resolution spectroscopy in the near-IR (0.9-2.35 um), collected in 2012 at the Large Binocular Telescope with the IR spectrograph LUCIFER, allows us to infer the main stellar parameters (visual extinction, accretion luminosity, mass accretion and ejection rates), and model the inner disc, jet, and wind. The NIR spectrum displays several strong emission lines associated with accretion/ejection activity and circumstellar environment. Our analysis shows that the brightness of PV Cep is fading, as well as the mass accretion rate (2x10^-7 Msun/yr^-1 in 2012 vs ~5x10^-6 Msun/yr^-1 in 2004), which is more than one order of magnitude lower than in the outburst phase. Among the several emission lines, only the [FeII] intensity increased after the outburst. The observed [FeII] emission delineates blue- and red-shifted lobes, both with high- and low-velocity components, which trace an asymmetric jet and wind, respectively. The observed emission in the jet has a dynamical age of ~8 years, indicating that it was produced during the last outburst. The mass ejection rate in both lobes is 1.5x10^-7 Msun/yr^-1, approximately matching the high accretion rate observed during and immediately after the outburst . The observed jet/outflow asymmetries are consistent with an inhomogeneous medium. Our modelling of the CO emission hints at a small-scale gaseous disc ring, extending from ~0.2-0.4 AU to ~3 AU from the source, with an inner temperature of ~3000 K. Our HI lines modelling indicates that most of the observed emission comes from an expanding disc wind at Te=10000 K. The line profiles are strongly affected by scattering, disc screening, and outflow self-absorption.