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标题：Variable millimetre radiation from the colliding-wind binary Cygnus OB2 #8A
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作者：R. Blomme ; D. M. Fenech ; R. K. Prinja 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2017
卷号：608
页码：1-9
DOI：10.1051/0004-6361/201731403
语种：English
出版社：EDP Sciences
摘要：Context.Massive binaries have stellar winds that collide. In the colliding-wind region, various physically interesting processes occur, leading to enhanced X-ray emission, non-thermal radio emission, as well as non-thermal X-rays and gamma-rays. Non-thermal radio emission (due to synchrotron radiation) has so far been observed at centimetre wavelengths. At millimetre wavelengths, the stellar winds and the colliding-wind region emit more thermal free-free radiation, and it is expected that any non-thermal contribution will be difficult or impossible to detect.Aims.We aim to determine if the material in the colliding-wind region contributes substantially to the observed millimetre fluxes of a colliding-wind binary. We also try to distinguish the synchrotron emission from the free-free emission.Methods.We monitored the massive binaryCyg OB2 #8Aat 3 mm with the NOrthern Extended Millimeter Array (NOEMA) interferometer of the Institut de Radioastronomie Millimétrique (IRAM). The data were collected in 14 separate observing runs (in 2014 and 2016), and provide good coverage of the orbital period.Results.The observed millimetre fluxes range between 1.1 and 2.3 mJy, and show phase-locked variability, clearly indicating that a large part of the emission is due to the colliding-wind region. A simple synchrotron model gives fluxes with the correct order of magnitude, but with a maximum that is phase-shifted with respect to the observations. Qualitatively this phase shift can be explained by our neglect of orbital motion on the shape of the colliding-wind region. A model using only free-free emission results in only a slightly worse explanation of the observations. Additionally, on the map of our observations we also detect the O6.5 III starCyg OB2 #8B, for which we determine a 3 mm flux of 0.21±0.033 mJy.Conclusions.The question of whether synchrotron radiation or free-free emission dominates the millimetre fluxes ofCyg OB2 #8Aremains open. More detailed modelling of this system, based on solving the hydrodynamical equations, is required to give a definite answer.
关键词：enbinaries: spectroscopicstars: winds, outflowsstars: individual: Cyg OB2 #8Astars: individual: Cyg OB2 #8Bstars: massiveradio continuum: stars