2,254 research outputs found
UV Upturn in Elliptical Galaxies: Theory
The UV upturn is the rising flux with decreasing wavelength between the Lyman
limit and 2500\AA found virtually in all bright spheroidal galaxies. It has
been a mystery ever since it was first detected by the OAO-2 space telescope
(Code & Welch 1979) because such old metal-rich populations were not expected
to contain any substantial number of hot stars. It was confirmed by following
space missions, ANS (de Boer 1982), IUE (Bertola et al. 1982) and HUT (Brown et
al. 1997). The positive correlation between the UV-to-optical colour (i.e., the
strength of the UV upturn) and the Mg2 line strength found by Burstein et al.
(1987) through IUE observations has urged theorists to construct novel
scenarios in which metal-rich () old ( a few Gyr)
stars become UV bright (Greggio & Renzini 1990; Horch et al. 1992). Also
interesting was to find using HUT that, regardless of the UV strength, the UV
spectral slopes at 1000--2000\AA in the six UV bright galaxies were nearly
identical suggesting a very small range of temperatures of the UV sources in
these galaxies (Brown et al. 1997), which corresponds to K. This, together with other evidence, effectively ruled out
young stars as the main driver of the UV upturn. A good review on the
observational side of the story is given in the next article by Tom Brown, as
well as in the recent articles of Greggio & Renzini (1999) and O'Connell
(1999).Comment: 6 figures; belated paper from Keele Conferenc
Explaining the Color Distributions of Globular Cluster Systems in Elliptical Galaxies
The colors of globular clusters in most of large elliptical galaxies are
bimodal. This is generally taken as evidence for the presence of two cluster
subpopulations that have different geneses. However, here we find that, because
of the non-linear nature of the metallicity-to-color transformation, a coeval
group of old clusters with a unimodal metallicity spread can exhibit color
bimodality. The models of cluster colors indicate that the horizontal-branch
stars are the main drivers behind the empirical non-linearity. We show that the
scenario gives simple and cohesive explanations for all the key observations,
and could simplify theories of elliptical galaxy formation.Comment: Science, 311, 1129; Minor changes to text to match the published
version (9 pages, 3 figures
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