27,702 research outputs found
Chemical signatures of planets: beyond solar-twins
Elemental abundance studies of solar twin stars suggest that the solar
chemical composition contains signatures of the formation of terrestrial
planets in the solar system, namely small but significant depletions of the
refractory elements. To test this hypothesis, we study stars which, compared to
solar twins, have less massive convective envelopes (therefore increasing the
amplitude of the predicted effect) or are, arguably, more likely to host
planets (thus increasing the frequency of signature detections). We measure
relative atmospheric parameters and elemental abundances of a late-F type dwarf
sample (52 stars) and a sample of metal-rich solar analogs (59 stars). We
detect refractory-element depletions with amplitudes up to about 0.15 dex. The
distribution of depletion amplitudes for stars known to host gas giant planets
is not different from that of the rest of stars. The maximum amplitude of
depletion increases with effective temperature from 5650 K to 5950 K, while it
appears to be constant for warmer stars (up to 6300 K). The depletions observed
in solar twin stars have a maximum amplitude that is very similar to that seen
here for both of our samples. Gas giant planet formation alone cannot explain
the observed distributions of refractory-element depletions, leaving the
formation of rocky material as a more likely explanation of our observations.
More rocky material is necessary to explain the data of solar twins than
metal-rich stars, and less for warm stars. However, the sizes of the stars'
convective envelopes at the time of planet formation could be regulating these
amplitudes. Our results could be explained if disk lifetimes were shorter in
more massive stars, as independent observations indeed seem to suggest.Comment: Astronomy and Astrophysics, in press. Full tables available in the
source downloa
Stellar Chemical Abundances: In Pursuit of the Highest Achievable Precision
The achievable level of precision on photospheric abundances of stars is a
major limiting factor on investigations of exoplanet host star characteristics,
the chemical histories of star clusters, and the evolution of the Milky Way and
other galaxies. While model-induced errors can be minimized through the
differential analysis of spectrally similar stars, the maximum achievable
precision of this technique has been debated. As a test, we derive differential
abundances of 19 elements from high-quality asteroid-reflected solar spectra
taken using a variety of instruments and conditions. We treat the solar spectra
as being from unknown stars and use the resulting differential abundances,
which are expected to be zero, as a diagnostic of the error in our
measurements. Our results indicate that the relative resolution of the target
and reference spectra is a major consideration, with use of different
instruments to obtain the two spectra leading to errors up to 0.04 dex. Use of
the same instrument at different epochs for the two spectra has a much smaller
effect (~0.007 dex). The asteroid used to obtain the solar standard also has a
negligible effect (~0.006 dex). Assuming that systematic errors from the
stellar model atmospheres have been minimized, as in the case of solar twins,
we confirm that differential chemical abundances can be obtained at sub-0.01
dex precision with due care in the observations, data reduction and abundance
analysis.Comment: Accepted for publication in ApJ; 13 pages, 6 figures, 7 table
Quantum Backflow States from Eigenstates of the Regularized Current Operator
We present an exhaustive class of states with quantum backflow -- the
phenomenon in which a state consisting entirely of positive momenta may have
negative current and the probability flows in the opposite direction to the
momentum. They are characterized by a general function of momenta subject to
very weak conditions. Such a family of states is of interest in the light of a
recent experimental proposal to measure backflow. We find one particularly
simple state which has surprisingly large backflow -- about 41 percent of the
lower bound on flux derived by Bracken and Melloy. We study the eigenstates of
a regularized current operator and we show how some of these states, in a
certain limit, lead to our class of backflow states. This limit also clarifies
the correspondence between the spectrum of the regularized current operator,
which has just two non-zero eigenvalues in our chosen regularization, and the
usual current operator.Comment: 16 pages, 2 figure
Search for the Higgs Boson at LHC in 3-3-1 Model
We present an analysis of production and signature of neutral Higgs boson
() on the version of the 3-3-1 model containing heavy leptons at the
Large Hadron Collider. We studied the possibility to identify it using the
respective branching ratios. Cross section are given for the collider energy,
14 TeV. Event rates and significances are discussed for two
possible values of integrated luminosity, 300 fb and 3000 fb.Comment: 17 pages 7 figures. arXiv admin note: substantial text overlap with
arXiv:1205.404
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