Suzaku monitoring of the Wolf-Rayet binary WR140 around periastron passage: An approach for quantifying the wind parameters

TL;DR

This study uses Suzaku X-ray observations of WR 140 around periastron to analyze wind-wind collision plasma, revealing changes in absorption, plasma components, and wind interactions that inform wind parameter quantification.

Contribution

It introduces a method to quantify wind parameters in WR 140 by analyzing spectral changes and plasma components during periastron passage.

Findings

Increased absorption near periastron indicates dense W-R wind absorption.

Detection of a cool plasma component suggests a transitional phase in wind collision plasma.

The hot plasma emission measure does not inversely scale with star separation, implying wind acceleration effects.

Abstract

Suzaku observations of the Wolf-Rayet binary WR 140 (WC7pd+O5.5fc) were made at four different times around periastron passage in 2009 January. The spectra changed in shape and flux with the phase. As periastron approached, the column density of the low-energy absorption increased, which indicates that the emission from the wind-wind collision plasma was absorbed by the dense W-R wind. The spectra can be mostly fitted with two different components: a warm component with kT=0.3--0.6 keV and a dominant hot component with kT~3 keV. The emission measure of the dominant, hot component is not inversely proportional to the distance between the two stars. This can be explained by the O star wind colliding before it has reached its terminal velocity, leading to a reduction in its wind momentum flux. At phases closer to periastron, we discovered a cool plasma component in a recombining phase, which is less absorbed. This component may be a relic of the wind-wind collision plasma, which was cooled down by radiation, and may represent a transitional stage in dust formation.