期刊
ASTROPHYSICAL JOURNAL
卷 763, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/763/2/106
关键词
line: profiles; Sun: corona; techniques: spectroscopic; waves
资金
- NASA Solar Heliospheric Physics program [NNX09AB25G]
- NSF Division of Atmospheric and Geospace Sciences SHINE program [AGS-1060194]
- Directorate For Geosciences
- Div Atmospheric & Geospace Sciences [1060194] Funding Source: National Science Foundation
We present a new diagnostic allowing one to measure the anisotropy of ion temperatures and non-thermal velocities, as well as Doppler shifts with respect to the ambient magnetic field. This method provides new results, as well as an independent test for previous measurements obtained with other techniques. Our spectral data come from observations of a low-latitude, on-disk coronal hole. A potential field source surface model was used to calculate the angle between the magnetic field lines and the line of sight for each spatial bin of the observation. A fit was performed to determine the line widths and Doppler shifts parallel and perpendicular to the magnetic field. For each line width component we derived ion temperatures T-i,T-perpendicular to and T-i,T-parallel to and non-thermal velocities v(nt,perpendicular to) and v(nt,parallel to). T-i,T-perpendicular to was cooler than off-limb polar coronal hole measurements, suggesting increasing collisional cooling with decreasing height. T-i,T-parallel to is consistent with a uniform temperature of (1.8 +/- 0.2) x 10(6) K for each ion. Since parallel ion heating is expected to be weak, this ion temperature should reflect the proton temperature. A comparison between our results and others implies a large proton temperature gradient around 1.02 R-circle dot. The non-thermal velocities are thought to be proportional to the amplitudes of various waves. Our results for v(nt,perpendicular to) agree with Alfven wave amplitudes inferred from off-limb polar coronal hole line width measurements. Our v(nt,parallel to) results are consistent with slow magnetosonic wave amplitudes inferred from Fourier analysis of time-varying intensity fluctuations. Doppler shift measurements yield outflows of approximate to 5 kms(-1) for ions formed over a broad temperature range. This differs from other studies that found a strong Doppler shift dependence on formation temperature.
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