南冕座R区的厘米偏振测量
Centimeter Polarimetry of the R Coronae Australis Region
摘要：
圆偏振3.5厘米连续辐射被检测到朝向三个射电源在R CrA区域使用甚大阵列。I类原恒星IRS5b在8年内持续显示出螺旋度恒定的极化射电辐射，这表明它的磁层具有稳定的结构。斯托克斯I和斯托克斯V通量之间有很好的相关性，分数偏振度约为0.17。在活跃阶段，分数偏振是一个弱的斯托克斯I通量的递减函数，这表明IRS 5b是现象上类似于其他类型的耀斑星，如RS CVn双星。偏振通量的变化时间尺度约为一个月，IRS5b的磁层一定很大。I类原恒星IRS 7A在圆偏振射电辐射中被探测到一次，尽管IRS 7A驱动着一个热射电喷流。这一发现意味着，年轻原恒星磁层的射电辐射至少偶尔可以逃脱部分电离风的吸收。IRS 7A和IRS 5b的性质表明，I类原恒星具有几千高斯的有组织的星周磁场，磁层发射的可探测性可能取决于原恒星的演化状态。还报告了对可变射电源B5的圆偏振无线电发射的检测。
英文摘要：
Circularly polarized 3.5 cm continuum emission was detected toward three radio sources in the R CrA region using the Very Large Array. The Class I protostar IRS 5b persistently showed polarized radio emission with a constant helicity over 8 yr, which suggests that its magnetosphere has a stable configuration. There is a good correlation between the Stokes I and Stokes V fluxes, and the fractional polarization is about 0.17. During active phases the fractional polarization is a weakly decreasing function of Stokes I flux, which suggests that IRS 5b is phenomenologically similar to other types of flare stars such as RS CVn binaries. The variability timescale of the polarized flux is about a month, and the magnetosphere of IRS 5b must be very large in size. The Class I protostar IRS 7A was detected once in circularly polarized radio emission, even though IRS 7A drives a thermal radio jet. This detection implies that the radio emission from the magnetosphere of a young protostar can escape the absorption by the partially ionized wind at least once in a while. The properties of IRS 7A and IRS 5b suggests that Class I protostars have organized peristellar magnetic fields of a few kilogauss and that the detectability of magnetospheric emission may depend on the evolutionary status of protostar. Also reported is the detection of circularly polarized radio emission toward the variable radio source B5.
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