Low Transition-Region Outflow: Solar He I 1083 nm Asymmetry in a Disk-Center Coronal Hole

Details Low Transition-Region Outflow: Solar He I 1083 nm Asymmetry in a Disk-Center Coronal Hole Low Transition-Region Outflow: Solar He I 1083 nm Asymmetry in a Disk-Center Coronal Hole

Dec 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...19510703j&link_type=abstract

American Astronomical Society, 195th AAS Meeting, #107.03; Bulletin of the American Astronomical Society, Vol. 31, p.1531

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Scientific paper

We analyze imaging spectroscopy in the He I 1083 nm line of a solar coronal hole observed near disk center on 26 Feb 1999 with the NASA/NSO Spectromagnetograph at the NSO/Kitt Peak Vacuum Telescope. For this study we examine the equivalent width of the He I absorption feature along with its wing asymmetry as determined by the difference in the wavelength position of the line bisector at 30% of central line depth from line center. Dupree, Penn, and Jones (1996, ApJ 467, L121) previously used a similar measure to show that excess blue absorption, indicative of line-of-sight motion towards the observer, is found preferentially in some polar coronal holes where the line is weakest. They suggested on the basis of the variation of this asymmetry with heliocentric angle over the limited domain spanned by their observations that these motions are vertical and are candidates for source regions of high-speed solar wind. Our data confirm that this phenomenon can be observed in coronal holes at disk center with about the magnitude (7-9 km/s) suggested from extrapolating the results of Dupree et al. Motions parallel to the solar surface cannot explain our observations, and these areas may indeed point to low-lying origins of the solar wind. We compare our results to observations on other days of quiet Sun outside of coronal holes near disk center as well as to other polar coronal holes. CFB participated in this research as an NSO Student Research Assistant supported by NASA task 344-12-19-01 (NRA 96-OSS-09). NSO/Kitt Peak data used here are produced cooperatively by NSF/NOAO, NASA/GSFC, and NOAA/SEL.

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