Intensity interferometry of P Cygni in the H$\alpha$ emission line: towards distance calibration of LBV supergiant stars

TL;DR

This study uses intensity interferometry and physical modeling to measure the distance to P Cygni, a luminous blue variable star, providing a new calibration method that could enhance cosmic distance measurements.

Contribution

It introduces a novel approach combining interferometry and spectral modeling to estimate stellar distances, applicable to massive stars in various galaxies.

Findings

Estimated P Cygni's distance as 1.56±0.25 kpc, consistent with Gaia data.

Demonstrated method's potential for calibrating distances of luminous stars.

Results suggest smaller distances than traditional literature values.

Abstract

We present intensity interferometry of the luminous blue variable P Cyg in the light of its H$\alpha$ emission performed with 1\,m-class telescopes. We compare the measured visibility points to synthesized interferometric data based on the CMFGEN physical modeling of a high-resolution spectrum of P Cyg recorded almost simultaneously with our interferometry data. Tuning the stellar parameters of P Cyg and its H$\alpha$ linear diameter we estimate the distance of P Cyg as $1.56\pm0.25$~kpc, which is compatible within $1\sigma$ with $1.36\pm0.24$~kpc reported by the Gaia DR2 catalogue of parallaxes recently published. Both values are significantly smaller than the canonic value of $1.80\pm0.10$~kpc usually adopted in literature. Our method used to calibrate the distance of P Cyg can apply to very massive and luminous stars both in our galaxy and neighbour galaxies and can improve the so-called Wind-Momentum Luminosity relation that potentially applies to calibrate cosmological candles in the local Universe.