369 research outputs found
Linearized stability of charged thin-shell wormholes
The linearized stability of charged thin shell wormholes under spherically
symmetric perturbations is analized. It is shown that the presence of a large
value of charge provides stabilization to the system, in the sense that the
constrains onto the equation of state are less severe than for non-charged
wormholes.Comment: 8 pages, 2 figures; v2: minor changes. Accepted for publication in
General Relativity and Gravitatio
Chemical fingerprints of hot Jupiter planet formation
The current paradigm to explain the presence of Jupiters with small orbital
periods (P 10 days; hot Jupiters) that involves their formation beyond the
snow line following inward migration, has been challenged by recent works that
explored the possibility of in situ formation. We aim to test whether stars
harbouring hot Jupiters and stars with more distant gas-giant planets show any
chemical peculiarity that could be related to different formation processes.
Our results show that stars with hot Jupiters have higher metallicities than
stars with cool distant gas-giant planets in the metallicity range +0.00/+0.20
dex. The data also shows a tendency of stars with cool Jupiters to show larger
abundances of elements. No abundance differences between stars with
cool and hot Jupiters are found when considering iron peak, volatile elements
or the C/O, and Mg/Si ratios. The corresponding -values from the statistical
tests comparing the cumulative distributions of cool and hot planet hosts are
0.20, 0.01, 0.81, and 0.16 for metallicity, , iron-peak, and
volatile elements, respectively. We confirm previous works suggesting that more
distant planets show higher planetary masses as well as larger eccentricities.
We note differences in age and spectral type between the hot and cool planet
hosts samples that might affect the abundance comparison. The differences in
the distribution of planetary mass, period, eccentricity, and stellar host
metallicity suggest a different formation mechanism for hot and cool Jupiters.
The slightly larger abundances found in stars harbouring cool Jupiters
might compensate their lower metallicities allowing the formation of gas-giant
planets.Comment: Accepted by Astronomy & Astrophysic
Connecting substellar and stellar formation. The role of the host star's metallicity
Most of our current understanding of the planet formation mechanism is based
on the planet metallicity correlation derived mostly from solar-type stars
harbouring gas-giant planets. To achieve a far more reaching grasp on the
substellar formation process we aim to analyse in terms of their metallicity a
diverse sample of stars (in terms of mass and spectral type) covering the whole
range of possible outcomes of the planet formation process (from planetesimals
to brown dwarfs and low-mass binaries). Our methodology is based on the use of
high-precision stellar parameters derived by our own group in previous works
from high-resolution spectra by using the iron ionisation and equilibrium
conditions. All values are derived in an homogeneous way, except for the M
dwarfs where a methodology based on the use of pseudo equivalent widths of
spectral features was used. Our results show that as the mass of the substellar
companion increases the metallicity of the host star tendency is to lower
values. The same trend is maintained when analysing stars with low-mass stellar
companions and a tendency towards a wide range of host star's metallicity is
found for systems with low mass planets. We also confirm that more massive
planets tend to orbit around more massive stars. The core-accretion formation
mechanism for planet formation achieves its maximum efficiency for planets with
masses in the range 0.2 and 2 M. Substellar objects with higher
masses have higher probabilities of being formed as stars. Low-mass planets and
planetesimals might be formed by core-accretion even around low-metallicity
stars.Comment: Accepted by A&
A Theoretical Construction of Thin Shell Wormhole from Tidal Charged Black hole
Recently, Dadhich et al [ Phys.Lett.B 487, 1 (2000)] have discovered a black
hole solution localized on a three brane in five dimensional gravity in the
Randall-Sundrum scenario. In this article, we develop a new class of thin shell
wormhole by surgically grafting above two black hole spacetimes. Various
aspects of this thin wormhole are also analyzed.Comment: 14 pages, 6 figures, Accepted in Gen.Rel.Gra
DescripciĂłn de Tipula (Yamatotipula) lateralis intermedia ssp. n. de la PenĂnsula IbĂ©rica (Diptera, Tipulidae)
Thin-shell wormholes from charged black holes in generalized dilaton-axion gravity
This paper discusses a new type of thin-shell wormhole constructed by
applying the cut-and-paste technique to two copies of a charged black hole in
generalized dilaton-axion gravity, which was inspired by low-energy string
theory. After analyzing various aspects of this thin-shell wormhole, we discuss
its stability to linearized spherically symmetric perturbations.Comment: Minor changes, 6 pages, 4 figures. Accepted for publication in Gen.
Rel. Gra
Searching for signatures of planet formation in stars with circumstellar debris discs
(Abridged) Tentative correlations between the presence of dusty debris discs
and low-mass planets have been presented. In parallel, detailed chemical
abundance studies have reported different trends between samples of planet and
non-planet hosts. We determine in a homogeneous way the metallicity, and
abundances of a sample of 251 stars including stars with known debris discs,
with debris discs and planets, and only with planets. Stars with debris discs
and planets have the same [Fe/H] behaviour as stars hosting planets, and they
also show a similar -Tc trend. Different behaviour in the -Tc
trend is found between the samples of stars without planets and the samples of
planet hosts. In particular, when considering only refractory elements,
negative slopes are shown in cool giant planet hosts, whilst positive ones are
shown in stars hosting low-mass planets. Stars hosting exclusively close-in
giant planets show higher metallicities and positive -Tc slope. A
search for correlations between the -Tc slopes and the stellar
properties reveals a moderate but significant correlation with the stellar
radius and as well as a weak correlation with the stellar age. The fact that
stars with debris discs and stars with low-mass planets do not show neither
metal enhancement nor a different -Tc trend might indicate a
correlation between the presence of debris discs and the presence of low-mass
planets. We extend results from previous works which reported differences in
the -Tc trends between planet hosts and non hosts. However, these
differences tend to be present only when the star hosts a cool distant planet
and not in stars hosting exclusively low-mass planets.Comment: Accepted for publication in Astronomy and Astrophysic
Gravitational microlensing of gamma-ray blazars
We present a detailed study of the effects of gravitational microlensing on
compact and distant -ray blazars. These objects have -ray
emitting regions which are small enough as to be affected by microlensing
effects produced by stars lying in intermediate galaxies. We analyze the
temporal evolution of the gamma-ray magnification for sources moving in a
caustic pattern field, where the combined effects of thousands of stars are
taken into account using a numerical technique. We propose that some of the
unidentified -ray sources (particularly some of those lying at high
galactic latitude whose gamma-ray statistical properties are very similar to
detected -ray blazars) are indeed the result of gravitational lensing
magnification of background undetected Active Galactic Nuclei (AGNs).Comment: 30 pages, 27 figures. Four figures are being submitted only as .gif
files, and should be printed separately. The abstract below has been
shortened from the actual version appearing in the pape
Chromaticity effects in microlensing by wormholes
Chromaticity effects introduced by the finite source size in microlensing
events by presumed natural wormholes are studied. It is shown that these
effects provide a specific signature that allow to discriminate between
ordinary and negative mass lenses through the spectral analysis of the
microlensing events. Both galactic and extragalactic situations are discussed.Comment: To appear in Modern Physics Letters A, 200
On the possibility of an astronomical detection of chromaticity effects in microlensing by wormhole-like objects
We study the colour changes induced by blending in a wormhole-like
microlensing scenario with extended sources. The results are compared with
those obtained for limb darkening. We assess the possibility of an actual
detection of the colour curve using the difference image analysis method.Comment: Accepted for publication in Modern Physics Letters A. 13 report
pages, 7 figure
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