Massive, early-type stars have been detected as radio sources for many decades. Their thermal winds radiate free–free continuum and in binary systems hosting a colliding-wind region, non-thermal emission has also been detected. To date, the most abundant data have been collected from frequencies higher than 1 GHz. We present here the results obtained from observations at 325 and 610 MHz, carried out with the Giant Metrewave Radio Telescope, of all known Wolf-Rayet and O-type stars encompassed in area of $\sim$ 15 sq degrees centred on the Cygnus region. We report on the detection of 11 massive stars, including both Wolf-Rayet and O-type systems. The measured flux densities at decimeter wavelengths allowed us to study the radio spectrum of the binary systems and to propose a consistent interpretation in terms of physical processes affecting the wide-band radio emission from these objects. WR 140 was detected at 610 MHz, but not at 325 MHz, very likely because of the strong impact of free–free absorption (FFA). We also report—for the first time—on the detection of a colliding-wind binary system down to 150 MHz, pertaining to the system of WR 146, making use of complementary information extracted from the Tata Institute of Fundamental Research GMRT Sky Survey. Its spectral energy distribution clearly shows the turnover at a frequency of about 600 MHz, that we interpret to be due to FFA. Finally, we report on the identification of two additional particle-accelerating colliding-wind binaries, namely Cyg OB2 12 and ALS 15108 AB.

中文翻译：

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天鹅座地区大质量早期型恒星的兆赫发射

几十年来，大量早期型恒星已被检测为无线电源。它们的热风辐射自由-自由连续体，在包含碰撞风区域的双星系统中，也检测到了非热辐射。迄今为止，已从高于 1 GHz 的频率收集到最丰富的数据。我们在此展示使用巨型米波射电望远镜在 325 和 610 MHz 上观测到的所有已知沃尔夫-拉叶星和 O 型星的结果，这些星 $\sim$ 以天鹅座区域为中心的 15 平方度。我们报告了对 11 颗大质量恒星的探测，包括 Wolf-Rayet 和 O 型系统。在分米波长处测量的通量密度使我们能够研究双星系统的无线电频谱，并就影响这些物体的宽带无线电发射的物理过程提出一致的解释。WR 140 在 610 MHz 时被检测到，但在 325 MHz 时未检测到，这很可能是因为游离 - 游离吸收 (FFA) 的强烈影响。我们还首次报告了对 WR 146 系统的低至 150 MHz 的碰撞风双星系统的检测，该系统利用了从塔塔基础研究所 GMRT 天空调查中提取的补充信息。它的光谱能量分布清楚地显示了频率约为 600 MHz 的转换，我们解释为由于 FFA。最后，我们报告了两个额外的粒子加速碰撞风双星的识别，即 Cyg OB2 12 和 ALS 15108 AB。