Intercombination and allowed transitions in OIV

Journal Article · Sat Jun 01 04:00:00 EDT 1996 · Astrophysical Journal

DOI:https://doi.org/10.1086/177390· OSTI ID:288897

Brage, T ^[1]; Judge, P G ^[2]; Brekke, P ^[3]

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1. Code 681, NRC/Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States)
2. High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder , Colorado 80307-3000 (United States)
3. Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, N-0315 Oslo 3 (Norway)

We report on large-scale {ital ab} {ital initio} multiconfiguration Hartree-Fock calculations for important multiplets including the UV 0.01 multiplet, 2{ital s}{sup 2}2{ital p}{sup 2}{ital P}{sub {ital J}}{minus}2{ital s}2{ital p}{sup 2}{sup 4}{ital P}{sub {ital J}{prime}}, in OIV. The resulting transition probabilities should be accurate to {+-}5%-10% for intersystem lines and 1% or better for permitted lines. We present new calculations of line emission coefficients using these transition probabilities and collisional rate coefficients published by Zhang, Graziani, & Pradhan in 1994. We readdress the use of these lines as diagnostics of electron densities, paying particular attention to uncertainties in density determinations. We find (1) the absolute uncertainties in derived densities are difficult to assess, but are at least {+-}40%, controlled by uncertainties in collision strengths; (2) our new calculations bring observed and computed line ratios into better agreement (earlier papers yielding systematically different densities make the agreement worse); (3) there is additional evidence for strong blends in the 1404.8 emission feature, as argued by other authors, and/or evidence for inaccurate laboratory wavelengths; and (4) the computed branching ratios are in good agreement with observed ratios to within observational uncertainties of {+-}7%. We determine electron densities in a variety of solar features from HRTS data from the first and second flights of this instrument. The derived electron densities vary remarkably little between quiet Sun network and active regions, but resonance line intensities vary dramatically, and we discuss reasons for this. We discuss how new high-quality data from the SUMER instrument to be flown on {ital Solar and Heliosphereic Observatory} (SOHO) could be used to address outstanding problems concerning blends and heating of the solar transition region. {copyright} {ital 1996 The American Astronomical Society.}

• OSTI ID: 288897
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 464; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
AB INITIO CALCULATIONS
ELECTRON DENSITY
ENERGY-LEVEL TRANSITIONS
EXCITATION
LINE INTENSITY
OXYGEN IONS
SOLAR FLARES
SPECTRAL ANALYSIS
SUN
TRANSITION PROBABILITIES
ULTRAVIOLET SPECTRA