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Solar and Heliospheric ObservatoryUltraviolet Coronagraph Spectrometer andYohkohSoft X‐Ray Telescope Observations of the High‐Temperature Corona above an Active Region Complex
Author(s) -
YuanKuen Ko,
J. C. Raymond,
Jing Li,
A. Ciaravella,
J. Michels,
Silvano Fineschi,
Rai Wu
Publication year - 2002
Publication title -
the astrophysical journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.376
H-Index - 489
eISSN - 1538-4357
pISSN - 0004-637X
DOI - 10.1086/342616
Subject(s) - physics , coronagraph , astrophysics , astronomy , corona (planetary geology) , telescope , observatory , extreme ultraviolet , spectrometer , coronal hole , imaging spectrometer , coronal mass ejection , solar wind , plasma , optics , stars , exoplanet , laser , quantum mechanics , astrobiology , venus
We present the results of Solar and Heliospheric Observatory Ultraviolet Coronagraph Spectrometer (SOHO/UVCS) and Yohkoh Soft X-Ray Telescope (SXT) observations above an active region complex (AR 8194, 8195, and 8198) at the southeast limb on 1998 April 6-7. This active region complex appears to be the base of a small streamer seen by the Large Angle and Spectrometric Coronagraph Experiment (LASCO/C2) at the southeast limb. The UVCS was offset-pointed to observe low in the corona from 1.22 up to 1.6 R☉ with normal pointing. High-temperature lines such as [Fe XVIII] λ974 and Ne IX λ1248 were present in this region, implying that the electron temperature is higher than that in the quiet-Sun corona. This region of the corona is also seen as particularly bright in the Yohkoh/SXT, SOHO EUV Imaging Telescope high-temperature filter (Fe XV λ284) and SOHO/LASCO C1. The electron temperature analysis indicates a two-temperature structure, one of ~1.5 × 106 K, which is similar to that observed in quiet-Sun streamers, and the other at a high temperature of ~3.0 × 106 K. This two-temperature region likely corresponds to two distinct coronal regions overlapping in the line of sight. We compare the electron temperature and emission measure results from the SOHO/UVCS data with those from the Yohkoh/SXT data. The absolute elemental abundances show a general first ionization potential effect and decrease with height for all the elements. This is consistent with the effect of gravitational settling, which, however, cannot totally account for the observed elemental abundances. Other mechanisms that are likely to affect the coronal elemental abundance are discussed.

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