Simultaneous SOHO andYohkoh Observations of a Small Solar Active Region

Journal Article · Sat Jul 01 04:00:00 EDT 2000 · Astrophysical Journal

DOI:https://doi.org/10.1086/309005· OSTI ID:20217426

Griffiths, N W; Fisher, G H; Woods, D T; Acton, L W; Siegmund, O H. W.

We present new results from observations of a small active region taken with the SUMER spectrograph and Extreme Ultraviolet Imaging Telescope (EIT) on SOHO and with the Soft X-Ray Telescope (SXT) on Yohkoh. The SUMER study features line and continuum emission covering a wide range of temperatures and includes the density-sensitive O iv] {lambda}1400 multiplet. A more extensive analysis of quiet Sun data presented in a previous paper is also included. The presence of a power-law relationship between emission-line power and electron density is confirmed, although the exponents in the active region are slightly higher than those found in the quiet Sun. These power-law relationships suggest that the volume filling factor decreases with increasing density and indicate possible differences between emitting material in active regions and the quiet Sun. We study active-region emission measures from both the SUMER and SXT data sets. For the active region as a whole, SXT temperatures and emission measures appear to fit smoothly onto the emission-measure distribution determined from cooler transition region and coronal lines in the SUMER spectra. We find no significant variation in the shape of the lower transition region emission-measure distribution for different subregions of the data set. This reinforces the conclusion from the original quiet Sun paper that ensembles of ''cool loops'' are unlikely to be the source of this emission unless the structures are considerably smaller than the 1'' spatial resolution of SUMER. (c) 2000 The American Astronomical Society.

• OSTI ID: 20217426
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 537; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
EMISSION SPECTRA
EXPERIMENTAL DATA
SOLAR ACTIVITY
SOLAR ATMOSPHERE
SOLAR RADIATION
SUN
ULTRAVIOLET SPECTRA