On the status of the star Schulte 12 in the association Cyg OB2

TL;DR

This study analyzes high-resolution spectra of the LBV candidate Schulte 12 over two decades, revealing spectral variability, potential binarity, and estimating its interstellar extinction, luminosity, and position relative to the Humphreys-Davidson limit.

Contribution

It provides new long-term spectroscopic observations of Schulte 12, detecting radial velocity variability suggestive of a companion and refining its physical parameters.

Findings

Detected spectral variability in Hα, HeI, SiII lines.

Found radial velocity variability indicating a possible companion.

Estimated interstellar extinction and luminosity, placing Schulte 12 below the Humphreys-Davidson limit.

Abstract

High-resolution spectra of the LBV candidate Schulte 12 in the Cyg OB2 association were obtained at the 6-meter BTA telescope with the NES echelle spectrograph on the arbitrary dates in 2001-2022. Variability of the emission profile of H$\alpha$ and absorptions of HeI, SiII with time was found. Based on the radial velocity measurements at 10 observation dates, radial velocity variability with an amplitude of $\Delta$Vr$\approx$8 km/s relative to the average value of the heliocentric velocity Vr=$-15.6\pm2.6$ km/s was revealed. This indicates the presence of a companion in the system. Based on the reliable intensity measurements of a sample of DIBs, color excess E(B-V)=1.74$\pm0.03^{m}$ was determined. This results in the interstellar extinction value Av$\approx 5.6^m$ that is only about half of the total extinction. Taking current Schulte 12 parameters, including Gaia~EDR3 parallax, we estimated its absolute magnitude as Mv$\approx -9.2^m$ and luminosity log$(L/L_{\odot})\approx$5.5, which does not exceed the Humphreys-Davidson limit.