9,690 research outputs found
A continuous population of variable stars up to about 1.5 mag above the horizontal branch?
Increasing samples of pulsating variable stars populating the classical
instability strip from the horizontal branch to a few magnitudes brighter are
being found in several Local Group galaxies, irrespective of the galaxy
morphological type. We will review the observational scenario focusing in
particular on the Anomalous Cepheids and related objects.Comment: 5 pages, 2 figures, invited review in JENAM 2003, "Minisymposium:
Asteroseismology and Stellar Evolution", Communications in Asteroseismology,
in pres
Spacetime geometries and light trapping in travelling refractive index perturbations
In the framework of transformation optics, we show that the propagation of a
locally superluminal refractive index perturbation (RIP) in a Kerr medium can
be described, in the eikonal approximation, by means of a stationary metric,
which we prove to be of Gordon type. Under suitable hypotheses on the RIP, we
obtain a stationary but not static metric, which is characterized by an
ergosphere and by a peculiar behaviour of the geodesics, which are studied
numerically, also accounting for material dispersion. Finally, the equation to
be satisfied by an event horizon is also displayed and briefly discussed.Comment: 14 pages, 7 figure
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