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Measurements of Far-UV Emission from Elliptical Galaxies at Z = 0.375
Ferguson, Henry C.; Brown, Thomas M.; Deharveng, Jean-Michel +1 more
The ``UV upturn'' is a sharp rise in spectra of elliptical galaxies shortward of rest-frame 2500 Å. It is a ubiquitous phenomenon in nearby giant elliptical galaxies and is thought to arise primarily from low-mass evolved stars on the extreme horizontal branch and beyond. Models suggest that the UV upturn is a very strong function of age for these…
Mass-Loss Rate and He/H Abundance of the Erupting Component in the Small Magellanic Cloud System HD 5980
Schmutz, W.; Koenigsberger, G.; Peña, M. +1 more
The binary Wolf-Rayet system HD 5980 in the Small Magellanic Cloud underwent a major luminous blue variable-type eruptive event in 1994. It is the first such recorded event in which the apparent precursor transits from WNE to WNL spectral types prior to the eruption. In this paper we analyze the spectrum of the system obtained when the outburst wa…
Abundance analysis of the lambda Bootis stars HD 192640, HD 183324, and HD 84123
Heiter, U.; Paunzen, E.; Weiss, W. W. +2 more
The classification of lambda Bootis stars based on photometric indices or low resolution spectra is not sufficient for a final decision concerning a membership to this group. A detailed spectroscopic investigation is necessary to rule out stars with similar classification spectra but different abundance patterns. Therefore a program on abundance a…
Atomic Physics with the Goddard High Resolution Spectrograph on the Hubble Space Telescope. IV. Relative Oscillator Strengths for Singly Ionized Nickel
Federman, S. R.; Zsargó, J.
Absorption lines of trace metals like nickel are often used to measure the metallicity and depletion in H I regions within our Galaxy and others. Ultraviolet absorption lines from the dominant ion, Ni II, are generally weak, making them a convenient tool to study metallicity and depletion in these environments. As an aid for studies of dust evolut…
Star formation triggered by galaxy collisions
Lutz, Dieter; Genzel, Reinhard; Tacconi, Linda
It is becoming increasingly clear that collisions between galaxies play an important role in galaxy evolution. The ultraluminous infrared galaxies are predominantly powered by enormous star-formation events that are triggered in the last phases of such collisions. These bursts occur just before the galaxies merge to form single elliptical galaxies.
General relativistic satellite astrometry. I. A non-perturbative approach to data reduction
Lattanzi, M. G.; Vecchiato, A.; de Felice, F. +1 more
A general relativistic scenario is utilized to build a non-perturbative model, in Schwarzschild metric, for the representation of observed angles among star pairs. This model is then applied to an end-to-end simulation of the GAIA satellite, a concept for global astrometry within the 2000+ scientific program of the European Space Agency. GAIA is e…
Infrared standards for ISO. I. A new calibration of mid infrared photometry
Kessler, M. F.; Bouchet, P.; Metcalfe, L. +5 more
We present N, 8.7 mu m, 9.8 mu m 12.5 mu m and Q bolometry of 26 stars which were observed on the IRTF. These are primarily K giants which have been well measured at other wavelengths and are chosen to be single and non-variable. Hence the data presented provides a new homogeneous set of mid IR standards. As a test of part of the calibration strat…
Systematics of RR Lyrae Statistical Parallax. II. Proper Motions and Radial Velocities
Gould, Andrew; Popowski, Piotr
We investigate whether a misestimate of proper motions or radial velocities could have been a source of substantial systematic errors in the statistical parallax determination of the absolute magnitude of RR Lyrae stars. In an earlier paper, we showed that the statistical parallax method is extremely robust and rather insensitive to various system…
Do coronal mass ejections implode in the solar wind?
Riley, Pete; Gosling, J. T.
Ulysses observations show that many coronal mass ejections observed at high heliographic latitudes expand because they initially have higher internal pressures than that of the surrounding solar wind. This expansion commonly drives a shock wave into the ambient wind in all directions. In the analogous process of an explosion in the Earth's atmosph…
Discovery of an Optical Synchrotron Jet in 3C 15
Baum, Stefi A.; McCarthy, Patrick J.; Sparks, William B. +6 more
We report the discovery of a new optical synchrotron jet in the radio galaxy 3C 15. This brings to nine the number of known optical synchrotron jets in nearby radio galaxies. The jet is well resolved in both length and width and extends to a projected metric distance of ~5 kpc from the galaxy nucleus. The host galaxy shows complex inner structure,…