65,343 research outputs found
Regular black holes in gravity
In this work, we study the possibility of generalizing solutions of regular
black holes with an electric charge, constructed in general relativity, for the
theory, where is the Gauss-Bonnet invariant. This type of solution
arises due to the coupling between gravitational theory and nonlinear
electrodynamics. We construct the formalism in terms of a mass function and it
results in different gravitational and electromagnetic theories for which mass
function. The electric field of these solutions are always regular and the
strong energy condition is violated in some region inside the event horizon.
For some solutions, we get an analytical form for the function. Imposing
the limit of some constant going to zero in the function we recovered
the linear case, making the general relativity a particular case.Comment: 22 pages, 25 figures.Version published in EPJ
On the asymptotic acoustic-mode phase in red-giant stars and its dependence on evolutionary state
Asteroseismic investigations based on the wealth of data now available,in
particular from the CoRoT and Kepler missions, require a good understanding of
the relation between the observed quantities and the properties of the
underlying stellar structure. Kallinger et al. 2012 found a relation between
their determination of the asymptotic phase of radial oscillations in evolved
stars and the evolutionary state, separating ascending-branch red giants from
helium-burning stars in the `red clump'. Here we provide a detailed analysis of
this relation, which is found to derive from differences between these two
classes of stars in the thermodynamic state of the convective envelope. There
is potential for distinguishing red giants and clump stars based on the phase
determined from observations that are too short to allow distinction based on
determination of the period spacing for mixed modes. The analysis of the phase
may also point to a better understanding of the potential for using the
helium-ionization-induced acoustic glitch to determine the helium abundance in
the envelopes of these stars.Comment: MNRAS, in the pres
Tests of the asymptotic large frequency separation of acoustic oscillations in solar-type and red giant stars
Asteroseismology, i.e. the study of the internal structures of stars via
their global oscillations, is a valuable tool to obtain stellar parameters such
as mass, radius, surface gravity and mean density. These parameters can be
obtained using certain scaling relations which are based on an asymptotic
approximation. Usually the observed oscillation parameters are assumed to
follow these scaling relations. Recently, it has been questioned whether this
is a valid approach, i.e., whether the order of the observed oscillation modes
are high enough to be approximated with an asymptotic theory. In this work we
use stellar models to investigate whether the differences between observable
oscillation parameters and their asymptotic estimates are indeed significant.
We compute the asymptotic values directly from the stellar models and derive
the observable values from adiabatic pulsation calculations of the same models.
We find that the extent to which the atmosphere is included in the models is a
key parameter. Considering a larger extension of the atmosphere beyond the
photosphere reduces the difference between the asymptotic and observable values
of the large frequency separation. Therefore, we conclude that the currently
suggested discrepancies in the scaling relations might have been overestimated.
Hence, based on the results presented here we believe that the suggestions of
Mosser et al. (2013) should not be followed without careful consideration.Comment: 6 pages, 4 figures, 1 table, accepted for publication by MNRAS as a
Letter to the Edito
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