37,983 research outputs found
The specific entropy of elliptical galaxies: an explanation for profile-shape distance indicators?
Dynamical systems in equilibrium have a stationary entropy; we suggest that
elliptical galaxies, as stellar systems in a stage of quasi-equilibrium, may
have a unique specific entropy. This uniqueness, a priori unknown, should be
reflected in correlations between the parameters describing the mass (light)
distribution in galaxies. Following recent photometrical work (Caon et al.
1993; Graham & Colless 1997; Prugniel & Simien 1997), we use the Sersic law to
describe the light profile of elliptical galaxies and an analytical
approximation to its three dimensional deprojection. The specific entropy is
calculated supposing that the galaxy behaves as a spherical, isotropic,
one-component system in hydrostatic equilibrium, obeying the ideal gas state
equations. We predict a relation between the 3 parameters of the Sersic,
defining a surface in the parameter space, an `Entropic Plane', by analogy with
the well-known Fundamental Plane. We have analysed elliptical galaxies in Coma
and ABCG 85 clusters and a group of galaxies (associated with NGC 4839). We
show that the galaxies in clusters follow closely a relation predicted by the
constant specific entropy hypothesis with a one-sigma dispersion of 9.5% around
the mean value of the specific entropy. Assuming that the specific entropy is
also the same for galaxies of different clusters, we are able to derive
relative distances between the studied clusters. If the errors are only due to
the determination of the specific entropy (about 10%), then the error in the
relative distance determination should be less than 20% for rich clusters. We
suggest that the unique specific entropy may provide a physical explanation for
the distance indicators based on the Sersic profile put forward by Young &
Currie (1994, 1995) and discussed by Binggeli & Jerjen (1998).Comment: Submitted to MNRAS (05/05/99), 15 pages, 10 figure
Experimental Bell inequality violation without the postselection loophole
We report on an experimental violation of the Bell-Clauser-Horne-Shimony-Holt
(Bell-CHSH) inequality using energy-time entangled photons. The experiment is
not free of the locality and detection loopholes, but is the first violation of
the Bell-CHSH inequality using energy-time entangled photons which is free of
the postselection loophole described by Aerts et al. [Phys. Rev. Lett. 83, 2872
(1999)].Comment: 4 pages, 3 figures, v2 minor correction
Asteroseismology and Magnetic Cycles
Small cyclic variations in the frequencies of acoustic modes are expected to
be a common phenomenon in solar-like pulsators, as a result of stellar magnetic
activity cycles. The frequency variations observed throughout the solar and
stellar cycles contain information about structural changes that take place
inside the stars as well as about variations in magnetic field structure and
intensity. The task of inferring and disentangling that information is,
however, not a trivial one. In the sun and solar-like pulsators, the direct
effect of the magnetic field on the oscillations might be significantly
important in regions of strong magnetic field (such as solar- / stellar-spots),
where the Lorentz force can be comparable to the gas-pressure gradient. Our aim
is to determine the sun- / stellar-spots effect on the oscillation frequencies
and attempt to understand if this effect contributes strongly to the frequency
changes observed along the magnetic cycle. The total contribution of the spots
to the frequency shifts results from a combination of direct and indirect
effects of the magnetic field on the oscillations. In this first work we
considered only the indirect effect associated with changes in the
stratification within the starspot. Based on the solution of the wave equation
and the variational principle we estimated the impact of these stratification
changes on the oscillation frequencies of global modes in the sun and found
that the induced frequency shifts are about two orders of magnitude smaller
than the frequency shifts observed over the solar cycle.Comment: 4 pages, 6 figures, ESF Conference: The Modern Era of Helio- and
Asteroseismology, to be published on 3 December 2012 at Astronomische
Nachrichten 333, No. 10, 1032-103
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