Analysis of a Solar Coronal Bright Point Extreme Ultraviolet Spectrum from the EUNIS Sounding Rocket Instrument
We present a well-calibrated EUV spectrum of a solar coronal bright point observed with the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding rocket instrument on 2006 April 12. The coronal bright point brightened around 06:30 UT during a period of emerging magnetic flux and remained bright at least until the rocket flight around 18:12 UT, while the magnetic flux merged and canceled. Density-sensitive line intensity ratios yield mutually consistent coronal electron densities (Ne in cm-3) of log Ne ≈ 9.4. The differential emission measure (DEM, in cm-5 K-1) curve derived from the spectrum yields a peak of log DEM ≈ 20.70 at log T ≈ 6.15 and a local minimum of log DEM ≈ 20.15 at log T ≈ 5.35. Photospheric (not coronal) element abundances are required to achieve equality and consistency in the DEM derived from lines of Mg V, Mg VI, Mg VII, and Ca VII (with a low first ionization potential, or FIP) and lines from Ne IV and Ne V (with a high FIP) formed at transition region temperatures. The bright point's photospheric abundance is likely produced by reconnection-driven chromospheric evaporation, a process that is not only central to existing bright point models, but also consistent with measurements of relative Doppler velocities.