An Investigation of Solar Coronal Bright Points Based on EUV Spectra Obtained with EUNIS-07

The EUNIS sounding rocket instrument is a two-channel imaging spectrograph that observes the solar corona with a rapid cadence made possible by unprecedented sensitivity. The instrument was successfully flown on 2006 April 12 (EUNIS-06) and 2007 November 6 (EUNIS-07), providing hundreds of spectra in the wavelength ranges 170-205 A and 300-370 A with sustained cadences as fast as 1.3 s. The EUNIS-07 data have provided the first on-orbit radiometric calibration of Hinode's EIS and STEREO's SECCHI/EUVI. Although there were no active regions on the solar disk during this flight, EUNIS-07 repeatedly scanned across several small coronal bright points within a large area of quiet Sun near disk center. We fitted Gaussian profiles to emission lines formed at temperatures ranging from 0.05 MK to 2 MK (with particular attention to He II 304 A, Mg IX 368 A, and Fe XIV 334 A) in the spatially resolved EUV spectra. The resulting line profile fits are used to derive a series of bright point images that we investigate for brightness variations on time scales of one minute, as well as relative Doppler velocities. Evolution of the bright points on time scales of hours are investigated with magnetograms from SOHO's MDI. EUNIS is supported by the NASA Heliophysics Division through its Low Cost Access to Space Program in Solar and Heliospheric Physics, and is scheduled to fly again in 2011. EUNIS data are freely available to the solar physics community. RS acknowledges support under NSF/REU grant ATM-00552671 to CUA. JWB is supported by NASA grant NNX10AK45G.