Simultaneous monitoring of the photometric and polarimetric activity of the young star PV Cep in the optical/near-infrared bands

TL;DR

This study presents a two-year simultaneous optical and near-infrared monitoring of the young star PV Cep, revealing an outburst, a time lag between bands, and complex interactions among the star, disk, and nebula affecting its polarization.

Contribution

It provides a detailed multi-component model of PV Cep's activity, challenging its classification as a simple EXor star and highlighting the complexity of young stellar objects in outburst.

Findings

Detected a 120-day outburst decline in all bands.

Measured a ~30-day lag between optical and infrared light curves.

Observed high polarization (~20%) and its fluctuations.

Abstract

We present the results of a simultaneous monitoring, lasting more than 2 years, of the optical and near-infrared photometric and polarimetric activity of the variable protostar PV Cep. During the monitoring period, an outburst has occurred in all the photometric bands, whose declining phase ($\Delta$J $\approx$ 3 mag) lasted about 120 days. A time lag of $\sim$ 30 days between optical and infrared light curves has been measured and interpreted in the framework of an accretion event. This latter is directly recognizable in the significant variations of the near-infrared colors, that appear bluer in the outburst phase, when the star dominates the emission, and redder in declining phase, when the disk emission prevails. All the observational data have been combined to derive a coherent picture of the complex morphology of the whole PV Cep system, that, in addition to the star and the accretion disk, is composed also by a variable biconical nebula. In particular, the mutual interaction between all these components is the cause of the high value of the polarization ($\approx$ 20%) and of its fluctuations. The observational data concur to indicate that PV Cep is not a genuine EXor star, but rather a more complex object; moreover the case of PV Cep leads to argue about the classification of other recently discovered young sources in outburst, that have been considered, maybe over-simplifying, as EXor.