OBSERVATION OF THE FAR-ULTRAVIOLET CONTINUUM BACKGROUND WITH SPEAR/FIMS
- Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of)
- Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)
- Ritter Astrophysical Research Center, University of Toledo, Toledo, OH 43606 (United States)
- Korea Advanced Institute of Science and Technology, Daejeon 305-701 (Korea, Republic of)
- Korea Intellectual Property Office, Daejeon 302-701 (Korea, Republic of)
We present the general properties of the far-ultraviolet (FUV; 1370-1710 A) continuum background over most of the sky, obtained with the Spectroscopy of Plasma Evolution from Astrophysical Radiation (SPEAR) instrument (also known as FIMS), flown aboard the STSAT-1 satellite mission. We find that the diffuse FUV continuum intensity is well correlated with N{sub HI}, 100 {mu}m, and H{alpha} intensities but anti-correlated with soft X-ray intensity. The correlation of the diffuse background with the direct stellar flux is weaker than the correlation with other parameters. The continuum spectra are relatively flat. However, a weak softening of the FUV spectra toward some sight lines, mostly at high Galactic latitudes, is found not only in direct stellar but also in diffuse background spectra. The diffuse background is relatively softer than the direct stellar spectrum. We also find that the diffuse FUV background averaged over the sky has a bit softer spectrum compared to direct stellar radiation. A map of the ratio of 1370-1520 A to 1560-1710 A band intensity shows that the sky is divided into roughly two parts. However, this map shows a lot of patchy structures on small scales. The spatial variation of the hardness ratio seems to be largely determined by the longitudinal distribution of OB-type stars in the Galactic plane. A correlation of the hardness ratio with the FUV intensity is found at high intensities but an anti-correlation is found at low intensities. We also find evidence that the FUV intensity distribution is log-normal in nature.
- OSTI ID:
- 21560328
- Journal Information:
- Astrophysical Journal, Supplement Series, Vol. 196, Issue 2; Other Information: DOI: 10.1088/0067-0049/196/2/15; ISSN 0067-0049
- Country of Publication:
- United States
- Language:
- English
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