Context. Light bridges are convective intrusions in sunspots that often show enhanced chromospheric activity. Aims. We seek to determine the nature of flux emergence in a light bridge and the processes related to its evolution in the solar atmosphere. Methods. We analyse a sequence of high-resolution spectropolarimetric observations of a sunspot taken at the Swedish 1-m Solar Telescope. The data consist of spectral scans of the photospheric Fe i line pair at 630 nm and the chromospheric Ca?ii 854.2 nm line. Bisectors were used to construct Dopplergrams from the Fe?i 630.15 nm measurements. We employed LTE and non-LTE inversions to derive maps of physical parameters in the photosphere and chromosphere, respectively. Results. We observe the onset of blueshifts of about 2 km s-1 near the entrance of a granular light bridge on the limbward side of the spot. The blueshifts lie immediately next to a strongly redshifted patch that appeared six minutes earlier. Both patches can be seen for 25 min until the end of the sequence. The blueshifts coincide with an elongated emerging granule, while the redshifts appear at the end of the granule. In the photosphere, the development of the blueshifts is accompanied by a simultaneous increase in field strength of about 400 G. The field inclination increases by some 25°, becoming nearly horizontal. At the position of the redshifts, the magnetic field is equally horizontal but of opposite polarity. An intense brightening is seen in the Ca?ii filtergrams over the blueshifts and redshifts, about 17 min after their detection in the photosphere. The brightening is due to emission in the blue wing of the Ca ii 854.2 nm line, close to its knee. Non-LTE inversions reveal that this kind of asymmetric emission is caused by a temperature enhancement of ~700 K between ?5.0 ≤ log?τ ≤ ?3.0 and a blueshift of 3 km s-1 at log?τ = ?2.3 that decreases to zero at log?τ = ?6.0 Conclusions. The photospheric blueshifts and redshifts observed in a granular light bridge seem to be caused by the emergence of a small-scale, flat Ω-loop with highly inclined footpoints of opposite polarity that brings new magnetic field to the surface. The gas motions detected in the two footpoints are reminiscent of a siphon flow. The rising loop is probably confined to the lower atmosphere by the overlying sunspot magnetic field and the interaction between the two flux systems may be responsible for temperature enhancements in the upper photosphere/lower chromosphere. This is the first time that magnetic flux is observed to emerge in the strongly magnetised environment of sunspots, pushed upwards by the convective flows of a granular light bridge.
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机译：上下文。光桥是黑子中的对流侵入，通常表现出色球活动增强。目的我们试图确定光桥中通量出现的性质以及与它在太阳大气中的演化有关的过程。方法。我们分析了一系列在瑞典1米太阳望远镜上拍摄的黑子的高分辨率分光偏振观测。数据由光球Fe i线对在630 nm的光谱扫描和色球Ca ii 854.2 nm线的光谱扫描组成。根据Fe？i 630.15 nm的测量结果，平分线用于构造多普勒图。我们分别采用LTE和非LTE反演来得出光球和色球中的物理参数图。结果。我们观察到在该点的拐角处的颗粒状光桥入口附近约2 km s-1的蓝移开始。蓝移紧邻六分钟前出现的强烈红移补丁。可以看到两个补丁25分钟，直到序列结束。蓝移与细长的新兴颗粒相吻合，而红移出现在颗粒的末端。在光球中，蓝移的发展伴随着场强的同时增加，约为400G。场倾角增加了约25°，几乎变为水平。在红移的位置，磁场水平相等，但极性相反。在蓝移和红移后的Ca？ii滤图中，在光球中被检测到大约17分钟后，便会看到强烈的增亮。变亮是由于在靠近其膝盖的Ca ii 854.2 nm线的蓝色翅膀中发射的。非LTE反演结果表明，这种不对称发射是由温度升高〜700 K引起的，在〜5.0≤log？τ≤≤3.0的范围内进行，并且在log？τ=？2.3处的蓝移为3 km s-1，并降低到log =τ=？6.0时为零结论。在颗粒状光桥中观察到的光球蓝移和红移似乎是由小规模，平坦的Ω环的出现引起的，该环具有相反极性的高度倾斜的脚点，从而为表面带来了新的磁场。在两个脚点处检测到的气体运动让人联想到虹吸流。上升的环路可能被上方的太阳黑子磁场限制在较低的大气层中，并且两个通量系统之间的相互作用可能导致较高的光层/较低色度层中的温度升高。这是第一次观察到磁通量在黑子的强磁化环境中出现，并被颗粒状光桥的对流推动向上。
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