7,458 research outputs found
Age and Metallicity Estimations in Old Stellar Populations from Stromgren Photometry
We present a new technique to determine age and metallicity of old stellar
populations (globular clusters and elliptical galaxies) using an iterative
principal component analysis on narrow band (Str\"omgren) colors. Our technique
is capable of reproducing globular cluster [Fe/H] values to 0.02 dex and CMD
ages to 1.0 Gyrs. We also present preliminary results on the application of our
technique to a sample of high mass, field ellipticals and low mass, cluster
dwarf ellipticals. We confirm the results of earlier studies which find that
globular clusters increase in metallicity with age and that age and metallicity
increase with galaxy mass. However, we find that dwarf ellipticals deviate from
the elliptical sequence by having little to no correlation between age and
metallicity.Comment: 8 pages IAU LaTeX, 5 figures, contributing talk IAU #198 Near-Field
Cosmology with Dwarf Elliptical Galaxie
The tails in the Helix Nebula NGC 7293
We have examined a stream-source model for the production of the cometary
tails observed in the Helix Nebula NGC 7293 in which a transonic or moderately
supersonic stream of ionized gas overruns a source of ionized gas. Hydrodynamic
calculations reveal velocity structures which are in good agreement with the
observational data on tail velocities and are consistent with observations of
the nebular structure. The results also are indicative of a stellar atmosphere
origin for the cometary globules. Tail remnants persist for timescales long
enough for their identification with faint striations visible in the nebula gas
to be plausible.Comment: 7 pages, 6 figures, accepted for publication in A&
The Space Telescope Observatory
A convenient guide to the expected characteristics of the Space Telescope Observatory for astronomers and physicists is presented. An attempt is made to provide enough detail so that a professional scientist, observer or theorist, can plan how the observatory may be used to further his observing programs or to test theoretical models
Impact for Agents
Impact for agents. Most of the agent research community has been predicting greater impact for years and many of us have been working to help the process along. Yet the tremendous growth on the research front has not been met with
Renorming spaces with greedy bases
We study the problem of improving the greedy constant or the democracy
constant of a basis of a Banach space by renorming. We prove that every Banach
space with a greedy basis can be renormed, for a given \vare>0, so that the
basis becomes (1+\vare)-democratic, and hence (2+\vare)-greedy, with
respect to the new norm. If in addition the basis is bidemocratic, then there
is a renorming so that in the new norm the basis is (1+\vare)-greedy. We also
prove that in the latter result the additional assumption of the basis being
bidemocratic can be removed for a large class of bases. Applications include
the Haar systems in , , and in dyadic Hardy space ,
as well as the unit vector basis of Tsirelson space
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