NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
First spectral observations of the diffuse background with the Extreme Ultraviolet ExplorerWe present the first results from the analysis of the spectroscopic observations of diffuse extreme ultraviolet (EUV) emission taken with the Extreme Ultraviolet Explorer (EUVE) spectrometers in the wavelength range 160-740 A. Although not designed or optimized for diffuse observation, the EUVE spectrometers are the most sensitive diffuse EUV spectrometer in orbit. The spectral resolution for diffuse emission of the medium and long-wavelength spectrometers are 17 and 34 A FWHM, respectively. During the period from 1992 July 25 to 1992 August 19, the spectrometers surveyed a 2 x 20 deg field scanned from (l, b) = (24 deg, -28 deg) to (44 deg, -74 deg) with a total effective exposure time of 575,232 s. The only emission lines detected were those of He I and He II (584, 537, 304 A) with intensities consistent with local geocoronal and/or interplanetary scattering of solar radiation (584 A = 1.30 rayleighs; 537 A = 0.040 R; and 304 A = 0.029 R). Models of the soft X-ray background, which results from a 10(exp 6) K plasma (Local Bubble) surrounding the neutral gas near the Sun (Local Cloud), predict that most of the flux from the hot plasma appears as emission lines in the EUV. We have compared these spectral predictions with our observations to place limits on the emission measure versus temperature of the proposed hot plasma. Using the same plasma model, we derived emissions measures for our data and the C and B soft X-ray bands of the Wisconsin rocket survey. We find that our limits for the plasma emission measure are a factor of 5-10 below the C- and B-band emission measures over the temperature range from 10(exp 5.7) to 10(exp 6.4) K. We explore possible scenarios that could reconcile our results with the X-ray surveys and conclude that depletion or a nonequilibrium plasma state rather than absorption are the more likely explanations of the discrepancy. We also show that our spectrum is inconsistent with the spectrum from the approximately 10(exp 5) K gas at the conductive interface between the hot Local Bubble and the cooler Local Cloud given by Slavin (1989). In addition, we place new limits on the helium ionization parameter in the Sun's vicinity caused by the 10(exp 6) K plasma in the Local Bubble.
Document ID
19950046443
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Jelinksy, P.
(Univ. of California, Berkeley, CA United States)
Vallerga, J. V.
(Univ. of California, Berkeley, CA United States)
Edelstein, J.
(Univ. of California, Berkeley, CA United States)
Date Acquired
August 16, 2013
Publication Date
April 1, 1995
Publication Information
Publication: Astrophysical Journal
Volume: 442
Issue: 2 Pa
ISSN: 0004-637X
Subject Category
Astronomy
Accession Number
95A78042
Funding Number(s)
CONTRACT_GRANT: NAS5-29298
CONTRACT_GRANT: NAS5-30180
Distribution Limits
Public
Copyright
Other

Available Downloads

There are no available downloads for this record.
No Preview Available