10,152 research outputs found
The Solar Twin Planet Search II. A Jupiter twin around a solar twin
Through our HARPS radial velocity survey for planets around solar twin stars,
we have identified a promising Jupiter twin candidate around the star HIP11915.
We characterize this Keplerian signal and investigate its potential origins in
stellar activity. Our analysis indicates that HIP11915 hosts a Jupiter-mass
planet with a 3800-day orbital period and low eccentricity. Although we cannot
definitively rule out an activity cycle interpretation, we find that a planet
interpretation is more likely based on a joint analysis of RV and activity
index data. The challenges of long-period radial velocity signals addressed in
this paper are critical for the ongoing discovery of Jupiter-like exoplanets.
If planetary in nature, the signal investigated here represents a very close
analog to the solar system in terms of both Sun-like host star and Jupiter-like
planet.Comment: 8 pages, 5 figures; A&A accepted; typos corrected in this versio
eleanor: An open-source tool for extracting light curves from the TESS Full-Frame Images
During its two year prime mission the Transiting Exoplanet Survey Satellite
(TESS) will perform a time-series photometric survey covering over 80% of the
sky. This survey comprises observations of 26 24 x 96 degree sectors that are
each monitored continuously for approximately 27 days. The main goal of TESS is
to find transiting planets around 200,000 pre-selected stars for which fixed
aperture photometry is recorded every two minutes. However, TESS is also
recording and delivering Full-Frame Images (FFIs) of each detector at a 30
minute cadence. We have created an open-source tool, eleanor, to produce light
curves for objects in the TESS FFIs. Here, we describe the methods used in
eleanor to produce light curves that are optimized for planet searches. The
tool performs background subtraction, aperture and PSF photometry,
decorrelation of instrument systematics, and cotrending using principal
component analysis. We recover known transiting exoplanets in the FFIs to
validate the pipeline and perform a limited search for new planet candidates in
Sector 1. Our tests indicate that eleanor produces light curves with
significantly less scatter than other tools that have been used in the
literature. Cadence-stacked images, and raw and detrended eleanor light curves
for each analyzed star will be hosted on MAST, with planet candidates on
ExoFOP-TESS as Community TESS Objects of Interest (CTOIs). This work confirms
the promise that the TESS FFIs will enable the detection of thousands of new
exoplanets and a broad range of time domain astrophysics.Comment: 21 pages, 13 figures, 2 tables, Accepted to PAS
Dynamics of Quintessence Models of Dark Energy with Exponential Coupling to the Dark Matter
We explore quintessence models of dark energy which exhibit non-minimal
coupling between the dark matter and the dark energy components of the cosmic
fluid. The kind of coupling chosen is inspired in scalar-tensor theories of
gravity. We impose a suitable dynamics of the expansion allowing to derive
exact Friedmann-Robertson-Walker solutions once the coupling function is given
as input. Self-interaction potentials of single and double exponential types
emerge as result of our choice of the coupling function. The stability and
existence of the solutions is discussed in some detail. Although, in general,
models with appropriated interaction between the components of the cosmic
mixture are useful to handle the coincidence problem, in the present study the
coincidence can not be evaded due to the choice of the solution generating
ansatz.Comment: 10 pages, 7 figure
Absence of Meissner State and Robust Ferromagnetism in the Superconducting State of UCoGe: Possible Evidence of Spontaneous Vortex State
We report ac magnetic susceptibility and dc magnetization measurements on the
superconducting ferromagnet UCoGe (with superconducting and Curie temperatures
of ~K and ~K, respectively).
In the normal, ferromagnetic state (), the
magnetization curve exhibits a hysteresis loop similar to that of a regular
itinerant ferromagnet. Upon lowering the temperature below , the
spontaneous magnetization is unchanged, but the hysteresis is markedly
enhanced. Even deeply inside the superconducting state, ferromagnetism is not
completely shielded, and there is no Meissner region, a magnetic field region
of (a lower critical field). From these results, we suggest
that UCoGe is the first material in which ferromagnetism robustly survives in
the superconducting state and a spontaneous vortex state without the Meissner
state is realized.Comment: 5 pages, 4 figures, to be published in J. Phys. Soc. Jp
Evolution of the fishtail-effect in pure and Ag-doped MG-YBCO
We report on magnetic measurements carried out in a textured
YBaCuO and YBa(CuAg)O (at
0.02) crystals. The so-called fishtail-effect (FE) or second
magnetization peak has been observed in a wide temperature range
0.4~~0.8 for . The origin of the FE arises for
the competition between surface barrier and bulk pinning. This is confirmed in
a non-monotonically behavior of the relaxation rate . The value
for Ag-doped crystals is larger than for the pure one due to the presence of
additional pinning centers, above all on silver atoms.Comment: 6 pages, 6 figure
Autonomous clustering using rough set theory
This paper proposes a clustering technique that minimises the need for subjective
human intervention and is based on elements of rough set theory. The proposed algorithm is
unified in its approach to clustering and makes use of both local and global data properties to
obtain clustering solutions. It handles single-type and mixed attribute data sets with ease and
results from three data sets of single and mixed attribute types are used to illustrate the
technique and establish its efficiency
Quintessence and variation of the fine structure constant in the CMBR
We study dependence of the CMB temperature anisotropy spectrum on the value
of the fine structure constant and the equation of state of the dark
energy component of the total density of the universe. We find that bounds
imposed on the variation of from the analysis of currently available
CMB data sets can be significantly relaxed if one also allows for a change in
the equation of state.Comment: 5 pages, 3 figures. Several references added and a few minor typos
corrected in the revised versio
Flux Creep and Flux Jumping
We consider the flux jump instability of the Bean's critical state arising in
the flux creep regime in type-II superconductors. We find the flux jump field,
, that determines the superconducting state stability criterion. We
calculate the dependence of on the external magnetic field ramp rate,
. We demonstrate that under the conditions typical for most of the
magnetization experiments the slope of the current-voltage curve in the flux
creep regime determines the stability of the Bean's critical state, {\it i.e.},
the value of . We show that a flux jump can be preceded by the
magneto-thermal oscillations and find the frequency of these oscillations as a
function of .Comment: 7 pages, ReVTeX, 2 figures attached as postscript file
Spherically symmetric solutions in f(R)-gravity via Noether Symmetry Approach
We search for spherically symmetric solutions of f(R) theories of gravity via
the Noether Symmetry Approach. A general formalism in the metric framework is
developed considering a point-like f(R)-Lagrangian where spherical symmetry is
required. Examples of exact solutions are given.Comment: 17 pages, to appear in Class. Quant. Gra
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