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Multiwavelength Monitoring of the BL Lacertae Object PKS 2155-304 in 1994 May. III. Probing the Inner Jet through Multiwavelength Correlations
Shull, J. M.; Takahashi, T.; Urry, C. Megan +16 more
In 1994 May, the BL Lac object PKS 2155-304 was observed continuously for ~10 days with the International Ultraviolet Explorer and the Extreme Ultraviolet Explorer and for 2 days with ASCA, as well as with ROSAT and with ground-based radio, infrared, and optical telescopes. The light curves show a well-defined X-ray flare followed by a broader, lo…
The Morphology of Distant Cluster Galaxies. II. HST Observations of Four Rich Clusters at z ~= 0.4
Dressler, Alan; Oemler, Augustus, Jr.; Butcher, Harvey R.
We present Hubble Space Telescope (HST) WF/PC and WFPC2 observations of four rich clusters of galaxies at redshifts z ~ 0.4: CL 1447+2619, CL 0939+4713, CL 0024+1654, and Abell 370. Extensive ground-based observations have shown that all have substantial populations of blue, star-forming, and (in some cases) starbursting galaxies. We find the gala…
Hubble Space Telescope Observations of Planetary Nebulae in the Magellanic Clouds. V. Mass Dependence of Dredge-up and the Chemical History of the Large Magellanic Cloud
Ford, H. C.; Harrington, J. P.; Wood, P. R. +6 more
A photoionization analysis of Hubble Space Telescope UV and ground-based optical spectrophotometry is given for eight more planetary nebulae (PNs) in the Large Magellanic Cloud (LMC). This allows the central stars to be placed accurately on the H-R diagram and permits the determination of the He, C, N, O, Ne, S, and Ar abundances. In some cases, t…
First Hubble Space Telescope Observations of Mira AB Wind-accreting Binary Systems
Raymond, John; Karovska, Margarita; Guinan, Edward +1 more
The Mira AB system belongs to a class of detached binaries in which a compact object accretes mass from the wind of a cool giant or supergiant. This system provides a unique laboratory for detailed study of the characteristics of the wind accretion processes because it can be spatially resolved with the Hubble Space Telescope (HST) and the compone…
Hubble Space Telescope Observations of the Post-Core-Collapse Globular Cluster NGC 6752. II. A Large Main-Sequence Binary Population
Bailyn, Charles D.; Rubenstein, Eric P.
We present a color-magnitude diagram (CMD) of NGC 6752 based on post-refurbishment Planetary Camera 2 observations of its core. The main sequence is broadened and asymmetric, as would be expected if there were large numbers of binary stars. We use artificial star experiments to characterize the broadening of the main sequence that is expected, due…
Evaluating Possible Heating Mechanisms Using the Transition Region Line Profiles of Late-Type Stars
Ayres, Thomas R.; Wood, Brian E.; Linsky, Jeffrey L.
Our analysis of high-resolution Goddard High-Resolution Spectrograph (GHRS) spectra of late-type stars shows that the Si IV and C IV lines formed near 105 K can be decomposed into the sum of two Gaussians, a broad component and a narrow component. We find that the flux contribution of the broad components is correlated with both the C I…
The LINER Nucleus of M87: A Shock-excited Dissipative Accretion Disk
Dopita, Michael A.; Sutherland, Ralph S.; Ford, Holland C. +4 more
We present long-baseline Faint Object Spectrograph (FOS) spectra of the nuclear accretion disk in M87 (NGC 4486), offset from the nucleus by 0.6" (42.7 pc) in order to avoid the nuclear continuum. Even so close to the nucleus, the optical spectrum has the appearance of a normal LINER galaxy. We show that the presence of strong UV emission lines pr…
Origin and Evolution of Coronal Streamer Structure During the 1996 Minimum Activity Phase
Llebaria, A.; Michels, D. J.; Paswaters, S. E. +17 more
We employ coronal extrapolations of solar magnetograph data to interpret observations of the white-light streamer structure made with the LASCO coronagraph in 1996. The topological appearance of the streamer belt during the present minimum activity phase is well described by a model in which the Thomson-scattering electrons are concentrated around…
Detection of Zonal Shear Flows beneath the Sun's Surface from f-Mode Frequency Splitting
Kosovichev, A. G.; Schou, J.
We report on the first successful measure of the zonal variations of the Sun's differential rotation (so-called torsional oscillations) by helioseismology. Using new helioseismic data from the Michelson Doppler Imager on board SOHO, we have detected zonal flow bands with velocity variation of 5 m s-1 at a depth of 2-9 Mm beneath the sur…
SUMER Observations Confirm the Dynamic Nature of the Quiet Solar Outer Atmosphere: The Internetwork Chromosphere
Judge, P. G.; Wilhelm, K.; Carlsson, Mats
On 1996 March 12, during the commissioning phase of the SOHO mission, we obtained observations of the quiet-Sun with the SUMER instrument. The observations were sequences of 15-20 s exposures of ultraviolet emission-line profiles and of the neighboring continua. These data contain signatures of the dynamics of the solar chromosphere that are uniqu…