THE ELECTRON TEMPERATURE OF THE SOLAR TRANSITION REGION AS DERIVED FROM EIS AND SUMER

Journal Article · Fri Jan 01 04:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/708/1/550· OSTI ID:21392456

Muglach, K; Landi, E ^[1]; Doschek, G A ^[2]

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1. Also at Artep Inc., Ellicott City, MD 21042 (United States)
2. Naval Research Laboratory, Washington, DC 20375 (United States)

We use UV and extreme-UV emission lines observed in quiet regions on the solar disk with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instrument and the Extreme Ultraviolet Imaging Spectrometer (EIS) to determine the electron temperature in solar transition region plasmas. Prominent emission lines of O IV and O VI are present in the solar spectrum, and the measured intensity line ratios provide electron temperatures in the range of log T = 5.6-6.1. We find that the theoretical O IV and O VI ion formation temperatures are considerably lower than our derived temperatures. The line ratios expected from a plasma in ionization equilibrium are larger by a factor of about 2-5 than the measured line ratios. A careful cross-calibration of SUMER and EIS has been carried out, which excludes errors in the relative calibration of the two instruments. We checked for other instrumental and observational effects, as well as line blending, and can exclude them as a possible source of the discrepancy between theoretical and observed line ratios. Using a multi-thermal quiet-Sun differential emission measure changes the theoretical line ratio by up to 28% which is not sufficient as an explanation. We also explored additional excitation mechanisms. Photoexcitation from photospheric blackbody radiation, self-absorption, and recombination into excited levels cannot be a possible solution. Adding a second Maxwellian to simulate the presence of non-thermal, high-energy electrons in the plasma distribution of velocities also did not solve the discrepancy.

• OSTI ID: 21392456
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 708; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION
BLACKBODY RADIATION
CALIBRATION
ELECTROMAGNETIC RADIATION
ELECTRON TEMPERATURE
ELECTRONS
ELEMENTARY PARTICLES
EMISSION
ENERGY LEVELS
ENERGY-LEVEL TRANSITIONS
EXCITATION
EXCITED STATES
EXTREME ULTRAVIOLET RADIATION
FERMIONS
IONIZATION
LEPTONS
MAIN SEQUENCE STARS
MEASURING INSTRUMENTS
PLASMA
RADIATIONS
RECOMBINATION
SELF-ABSORPTION
SORPTION
SPECTRA
SPECTROMETERS
STARS
SUN
ULTRAVIOLET RADIATION