Bright Points and Jets in Polar Coronal Holes Observed by the Extreme-Ultraviolet Imaging Spectrometer on Hinode
We present observations of polar coronal hole bright points (BPs) made with the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft. The data consist of raster images of BPs in multiple spectral lines from mostly coronal ions, e.g., Fe X-Fe XV. The BPs are observed for short intervals and thus the data are snapshots of the BPs obtained during their evolution. The images reveal a complex unresolved temperature structure (EIS resolution is about 2''), with the highest temperature being about 2 × 106 K. Some BPs appear as small loops with temperatures that are highest near the top. But others are more point-like with surrounding structures. However, the thermal time evolution of the BPs is an important factor in their appearance. A BP may appear quite different at different times. We discuss one BP with an associated jet that is bright enough to allow statistically meaningful measurements. The jet Doppler speed along the line of sight is about 15-20 km s-1. Electron densities of the BPs and the jet are typically near 109 cm-3, which implies path lengths along the line of sight on the order of a few arcsec. We also construct differential emission measure curves for two of the best observed BPs. High spatial resolution (significantly better than 1'') is required to fully resolve the BP structures.