Photometric variability of nitrogen-rich Wolf-Rayet stars in Magellanic Clouds with OGLE

TL;DR

This study analyzes the photometric variability of nitrogen-rich Wolf-Rayet stars in the Magellanic Clouds using OGLE, revealing widespread variability, periodicities, outbursts, and transient behaviors, and comparing results across multiple surveys.

Contribution

It provides the first comprehensive analysis of variability in these stars, identifying new types of outbursts and transient phenomena, and linking variability to wind structures, binaries, and pulsations.

Findings

Approximately 33% of stars show high variability.

11 stars exhibit periodic variations with 2-56 day timescales.

Nine stars display quasi-periodic outbursts.

Abstract

We present a comprehensive analysis of the photometric variability of (presumably single) nitrogen-rich Wolf-Rayet (WN) stars in the Magellanic Clouds, using long-term observations from the OGLE survey. Our sample comprises 47 stars with no nearby Gaia counterparts. We characterize both overall and short-term variabilities, examining data dispersion and identifying periodicities. To validate our findings, we also compare the OGLE light curves with data from the MACHO and TESS missions. Variability is ubiquitous in our WR sample: about one third of stars display high variability, or four fifths if we include cases with moderate variations. The observed changes are found to be periodic in 11 cases, with timescales of 2-56 d. Such periodic variations originate in corotating wind structures, binary effects, or pulsations, thereby increasing the number of systems known to show these phenomena. Surprisingly, nine targets display (quasi-periodic) outbursts, making such changes a new type of WR variability. The variability shows a transient character, in about 30$\%$ of the sample, with changing amplitudes for periodic signals or for outbursts (they even sometimes completely disappear from view). Finally, we identified six long-period variables, four of which have been confirmed by at least two independent surveys.