A Study of the Stochastic Photometric Variability in the Winds of Galactic Wolf–Rayet Stars
Guillaume Lenoir-Craig, Nicole St‐Louis, A. F. J. Moffat, H. Pablo, G. Handler, R. Kuschnig, Adam Popowicz, G. A. Wade, K. Zwintz
Abstract
Abstract In order to explore how the ubiquitous short-term stochastic variability in the photometric observations of Wolf–Rayet (WR) stars is related to various stellar characteristics, we examined a sample of 50 Galactic WR stars using 122 lightcurves obtained by the BRIght Target Explorer-Constellation, Transiting Exoplanet Survey Satellite and Microvariability and Oscillations of Stars satellites. We found that the periodograms resulting from a discrete Fourier transform of all our detrended lightcurves are characterized by a forest of random peaks showing an increase in power starting from ∼0.5 day −1 down to ∼0.1 day −1 . After fitting the periodograms with a semi-Lorentzian function representing a combination of white and red noise, we investigated possible correlations between the fitted parameters and various stellar and wind characteristics. Seven correlations were observed, the strongest and only significant one being between the amplitude of variability, α 0 , observed for hydrogen-free WR stars, while WNh stars exhibit correlations between α 0 and the stellar temperature, T * , and also between the characteristic frequency of the variations, ν char , and both T * and v ∞ . We report that stars observed more than once show significantly different variability parameters, indicating an epoch-dependent measurement. We also find that the observed characteristic frequencies for the variations generally lie between <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:mn>0.5</mml:mn> <mml:mo><</mml:mo> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>char</mml:mi> </mml:mrow> </mml:msub> <mml:mo><</mml:mo> <mml:mn>0.5</mml:mn> </mml:math> , and that the values of the steepness of the amplitude spectrum are typically found in the range <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:mn>0.1</mml:mn> <mml:mo><</mml:mo> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mi>γ</mml:mi> <mml:mo><</mml:mo> <mml:mn>0.5</mml:mn> </mml:math> . We discuss various physical processes that can lead to this correlation.