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Session 51 - Active Galactic Nuclei & Quasars.
Oral session, Thursday, June 12
North Main Hall A,

[51.04] Far-UV observations of NGC4151 during the Orfeus-II mission

B. R. Espey, G. A. Kriss, Z. Tsvetanov, J. Krolik, A. F. Davidsen, W. Zheng (Center for Astrophysical Sciences, JHU)

We present preliminary results from our far-UV spectroscopic monitoring campaign of NGC4151 during the 14 day ORFEUS-SPAS II astronomy mission. Our spectra were obtained with the Berkeley spectrometer aboard the Astro-SPAS free-flying platform during the space shuttle mission STS-80 in November and December 1995. The data cover a 12 day period with a relative spacing of \sim 2\ hours to \sim 3\ days. During this period NGC4151 was almost as bright as during the Astro-2 observations which covered the period of brightest UV flux ever observed (Kriss et al. 1995, ApJ 454, L7).

Our observations cover the wavelength range of 912 -- 1220Å\ in the observed frame at 95 km/s resolution and show a variability of nearly a factor of 2 in UV continuum flux during the course of the mission. Smaller changes are also seen in the far-UV absorption lines and we discuss the relative changes in the context of the location and nature of the absorbing gas. Variations in the strength of the OVI emission line will also be discussed.

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Program listing for Thursday