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The FarUltraviolet Spectrum of NGC 4151 as Observed with the Hopkins Ultraviolet Telescope on Astro2

Summary: The Far­Ultraviolet Spectrum of NGC 4151 as Observed with the Hopkins
Ultraviolet Telescope on Astro­2
Gerard A. Kriss, Arthur F. Davidsen, Wei Zheng, Jeffrey W. Kruk and Brian R. Espey
Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD 21218
We observed NGC 4151 on six separate occasions at intervals of one to three
days using the Hopkins Ultraviolet Telescope during the flight of Astro­2 aboard the
space shuttle Endeavour in March 1995. The far­ultraviolet spectra cover the spectral
range from the interstellar cutoff at 912 š A to 1840 š A with a resolution of 2--4 š A. The
mean spectrum, representing 4752 s of integration time, has a S/N of ¸30, and it
shows profound differences compared to that obtained during the flight of Astro­1 in
December 1990. The continuum, 5:3 \Theta 10 \Gamma13 erg cm \Gamma2 s \Gamma1 š A \Gamma1 at 1455 š A, is five
times brighter, the brightest UV flux ever observed for NGC 4151. All high­ionization
absorption lines have strengthened considerably --- S vi ––933; 945, C iii –977, O vi
––1032; 1038, N v ––1239; 1243, Si iv ––1394; 1403, and C iv ––1548; 1551. The
Lyman series absorption lines have also increased in strength, with the bulk of the
absorption requiring a neutral hydrogen column density of 5 \Theta 10 17 cm \Gamma2 covering only
78% of the UV source with an effective Doppler parameter of 350 km s \Gamma1 . However,
up to 5 \Theta 10 20 cm \Gamma2 of neutral hydrogen that fully covers the source could be present
in gas with a thermal Doppler parameter of 20 km s \Gamma1 . Single­zone photoionization


Source: Henry, Richard C.- Department of Physics and Astronomy, Johns Hopkins University


Collections: Physics