EIS/Hinode observations of Doppler flow seen through the 40 arcsec wide slit

TL;DR

This study uses Hinode's EIS to observe Doppler flows in the Sun's transition region and corona through wide slit spectral imaging, revealing dynamic events and their association with small-scale solar structures.

Contribution

First to utilize wide slit spectral images from Hinode/EIS for detecting and analyzing Doppler flows in the solar transition region and corona.

Findings

Detected Doppler shifts as horizontal brightenings in spectral images.

Identified explosive event-like Doppler shifts at the footpoints of small X-ray loops.

Observed high-velocity flows up to 220 km/s in transition region and coronal lines.

Abstract

The Extreme ultraviolet Imaging Spectrometer (EIS) on board Hinode is the first solar telescope to obtain wide slit spectral images that can be used for detecting Doppler flows in transition region and coronal lines on the Sun and to relate them to their surrounding small scale dynamics. We select EIS lines covering the temperature range 6x10^4 K to 2x10^6 K that give spectrally pure images of the Sun with the 40 arcsec slit. In these images Doppler shifts are seen as horizontal brightenings. Inside the image it is difficult to distinguish shifts from horizontal structures but emission beyond the image edge can be unambiguously identified as a line shift in several lines separated from others on their blue or red side by more than the width of the spectrometer slit (40 pixels). In the blue wing of He II, we find a large number of events with properties (size and lifetime) similar to the well-studied explosive events seen in the ultraviolet spectral range. Comparison with X-Ray Telescope (XRT) images shows many Doppler shift events at the footpoints of small X-ray loops. The most spectacular event observed showed a strong blue shift in transition region and lower corona lines from a small X-ray spot that lasted less than 7 min. The emission appears to be near a cool coronal loop connecting an X-ray bright point to an adjacent region of quiet Sun. The width of the emission implies a line-of-sight velocity of 220 km/s. In addition, we show an example of an Fe XV shift with a velocity about 120 km/s, coming from what looks like a narrow loop leg connecting a small X-ray brightening to a larger region of X-ray emission.