High-precision broadband linear polarimetry of early-type binaries. V. The Binary System HD 165052 in Open Cluster NGC 6530

TL;DR

This paper presents high-precision broadband polarimetry of the early-type binary HD 165052, determining its orbital parameters, polarization characteristics, and wind interaction effects, while also exploring interstellar polarization in NGC 6530.

Contribution

It provides the first detailed polarization analysis of HD 165052, including orbital inclination, orientation, and wind scattering geometry, using high-precision measurements and period analysis.

Findings

Orbital period of about 2.96 days identified from polarization data.

Estimated orbital inclination around 55 degrees with significant uncertainty.

Detected symmetric scattering likely due to electron scattering in stellar winds.

Abstract

This study continues our investigation of early-type binaries using high-precision broad-band polarimetry, focusing on HD 165052, a massive O+O-type binary in the young cluster NGC 6530. Our aim was to monitor linear polarization variations and independently determine the orbital period through polarization data analysis. By examining the phase-locked Stokes parameters, we estimated the orbital inclination at about 55+5/-55 deg, and the orientation at 148+20/-22 deg. The binary's rotation direction is clockwise. Using the Dipol-2 polarimeter with the 60 cm KVA and Tohoku T60 telescopes, we achieved polarization measurement accuracy around 0.01 percent in the B, V, and R passbands. Period analysis identified a strong periodic signal with a cycle of about 1.48 days, corresponding to half of the orbital period of about 2.96 days. The second Fourier harmonics suggest a symmetric scattering geometry, likely due to electron scattering in interacting stellar winds. Our estimates indicate a mass-loss rate of approximately 3.5 x 10^(-7) solar masses per year. Observations of neighboring stars in NGC 6530 revealed complex interstellar polarization behaviors within the cluster, enhancing our understanding of its polarimetric environment.