13 Years of P Cygni Spectropolarimetry: Investigating Mass-loss Through H$\alpha$, Periodicity, and Ellipticity

TL;DR

This 13-year spectropolarimetric study of P Cygni reveals insights into LBV mass-loss, circumstellar geometry, and uncovers new periodicities and polarization structures, enhancing understanding of massive star evolution.

Contribution

The paper introduces a novel statistical method to detect preferred polarization angles and provides long-term observational data on LBV mass-loss mechanisms.

Findings

Consistent with free-electron scattering off clumps around P Cygni.

Detection of previously unknown periodicities in polarization data.

Identification of complex polarization structures in Hα line.

Abstract

We report on over 13 years of optical and near-ultraviolet spectropolarimetric observations of the famous Luminous Blue Variable (LBV), P Cygni. LBVs are a critical transitional phase in the lives of the most massive stars, and achieve the largest mass-loss rates of any group of stars. Using spectropolarimetry, we are able to learn about the geometry of the near circumstellar environment surrounding P Cygni and gain insights into LBV mass-loss. Using data from the HPOL and WUPPE spectropolarimeters, we estimate the interstellar polarization contribution to P Cygni's spectropolarimetric signal, analyze the variability of the polarization across the H$\alpha$ emission line, search for periodic signals in the data, and introduce a statistical method to search for preferred position angles in deviations from spherical symmetry which is novel to astronomy. Our data are consistent with previous findings, showing free-electron scattering off of clumps uniformly distributed around the star. This is complicated, however, by structure in the percent-polarization of the H$\alpha$ line and a series of previously undetected periodicities.