105,776 research outputs found
Probability of Detecting a Planetary Companion during a Microlensing Event
The probability of detecting a planetary companion of a lensing star during a
microlensing event toward the Galactic center, averaged over all relevant event
and galactic parameters, when the planet-star mass ratio has a
maximum exceeding 10% at an orbit semimajor axis near 1.5 AU for a uniform
distribution of impact parameters. The maximum probability is raised to more
than 20% for a distribution of source-lens impact parameters that is determined
by the efficiency of event detection. The averaging procedures are carefully
defined, and they determinine the dependence of the detection probabilities on
several properties of the Galaxy. The probabilities scale approximately as
. A planet is assumed detectable if the perturbation of the single
lens light curve exceeds for at least 20 consecutive photometric
points sometime during the event. Two meter telescopes with 60 second
integrations in I-band with high time resolution photometry throughout the
duration of an ongoing event are assumed. The probabilities are derived as a
function of , where they remain significant for AU. Dependence of
the detection probabilities on the lens mass function, luminosity function of
the source stars as modified by extinction, distribution of source-lens impact
parameters, and the line of sight to the source are also determined, and the
probabilities are averaged over the distribution of the projected planet
position, the lens mass function, the distribution of impact parameters, the
lens and source distances as weighted by their distributions along the line of
sight and over the -band apparent luminosity function of the sources. The
extraction of the probabilility as a function of for a particular from
empirical data is indicated.Comment: 32 pages, 20 figures, In Press, ApJ, Latex format with aas2pp4 forma
Fluorine Abundances of Galactic Low-Metallicity Giants
With abundances and 2{\sigma} upper limits of fluorine (F) in seven
metal-poor field giants, nucleosynthesis of stellar F at low metallicity is
discussed. The measurements are derived from the HF(1-0) R9 line at 23358{\AA}
using nearinfrared K-band high-resolution spectra obtained with CRIRES at the
Very Large Telescope. The sample reaches lower metallicities than previous
studies on F of field giants, ranging from [Fe/H] = -1.56 down to -2.13.
Effects of three-dimensional model atmospheres on the derived F and O
abundances are quantitatively estimated and shown to be insignificant for the
program stars. The observed F yield in the form of [F/O] is compared with two
sets of Galactic chemical evolution models, which quantitatively demonstrate
the contribution of Type II supernova (SN II) {\nu}-process and asymptotic
giant branch/Wolf-Rayet stars. It is found that at this low-metallicity region,
models cannot well predict the observed distribution of [F/O], while the
observations are better fit by models considering an SN II {\nu}-process with a
neutrino energy of E_{\nu} = 3 x 10^53 erg. Our sample contains HD 110281, a
retrograde orbiting low-{\alpha} halo star, showing a similar F evolution as
globular clusters. This supports the theory that such halo stars are possibly
accreted from dwarf galaxy progenitors of globular clusters in the halo.Comment: 8 pages, 8 figures, 2 tables, published in The Astrophysical Journa
NLTE study of scandium in the Sun
We investigate the formation of neutral and singly ionized scandium lines in
the solar photospheres. The research is aimed derive solar (Sc) values for scandium lines, which will later be used in
differential abundance analyses of metal-poor stars. Extensive statistical
equilibrium calculations were carried out for a model atom, which comprises 92
terms for \ion{Sc}{i} and 79 for \ion{Sc}{ii}. Photoionization cross-sections
are assumed to be hydrogenic. Synthetic line profiles calculated from the level
populations according to the NLTE departure coefficients were compared with the
observed solar spectral atlas. Hyperfine structure (HFS) broadening is taken
into account. The statistical equilibrium of scandium is dominated by a strong
underpopulation of \ion{Sc}{i} caused by missing strong lines. It is nearly
unaffected by the variation in interaction parameters and only marginally
sensitive to the choice of the solar atmospheric model. Abundance
determinations using the ODF model lead to a solar Sc abundance of between
and 3.13, depending on the choice of values.
The long known difference between photospheric and meteoritic scandium
abundances is confirmed for the experimental -values.Comment: 10 pages, 6 figures, A&A accepte
Intrinsic electron-doping in nominal "non-doped" superconducting (La,Y)CuO thin films grown by dc magnetron sputtering
The superconducting nominal "non-doped" (LYCO) thin
films are successfully prepared by dc magnetron-sputtering and in situ
post-annealing in vacuum. The best more than 13K is achieved in the
optimal LYCO films with highly pure c-axis oriented T'-type structure. In the
normal state, the quasi-quadratic temperature dependence of resistivity, the
negative Hall coefficient and effect of oxygen content in the films are quite
similar to the typical Ce-doped T'-214 cuprates, suggesting that T'-LYCO shows
the electron-doping nature like known n-type cuprates, and is not a band
superconductor as proposed previously. The charge carriers are considered to be
induced by oxygen deficiency.Comment: 5 pages, 7 figure
The wedding of modified dynamics and non-exotic dark matter in galaxy clusters
We summarize the status of Modified Newtonian Dynamics (MOND) in galaxy
clusters. The observed acceleration is typically larger than the acceleration
threshold of MOND in the central regions, implying that some dark matter is
necessary to explain the mass discrepancy there. A plausible resolution of this
issue is that the unseen mass in MOND is in the form of ordinary neutrinos with
masses just below the experimentally detectable limit. In particular, we show
that the lensing mass reconstructions of the clusters 1E0657-56 (the bullet
cluster) and Cl0024+17 (the ring) do not pose a new challenge to this scenario.
However, the mass discrepancy for cool X-ray emitting groups, in which
neutrinos cannot cluster, pose a more serious problem, meaning that dark
baryons could present a more satisfactory solution to the problem of unseen
mass in MOND clusters.Comment: to appear in World Scientific, proceedings of DARK 200
The non-linear evolution of bispectrum from the scale-free N-body simulation
We have accurately measured the bispectrum for four scale-free models of
structure formation with the spectral index , 0, -1, and -2. The
measurement is based on a new method that can effectively eliminate the alias
and numerical artifacts, and reliably extend the analysis into the strongly
non-linear regime. The work makes use of a set of state-of-the art N-body
simulations that have significantly increased the resolution range compared
with the previous studies on the subject. With these measured results, we
demonstrated that the measured bispectrum depends on the shape and size of
-triangle even in the strongly nonlinear regime. It increases with
wavenumber and decreases with the spectral index. These results are in contrast
with the hypothesis that the reduced bispectrum is a constant in the strongly
non-linear regime. We also show that the fitting formula of Scoccimarro &
Frieman (1999) does not describe our simulation results well (with a typical
error about 40 percent). In the end, we present a new fitting formula for the
reduced bispectrum that is valid for with a typical error of
10 percent only.Comment: 33 pages, including 1 table, 14 figures, accepted by Ap
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