312 research outputs found
Searching for Radio Pulsars in 3EG Sources at Urumqi Observatory
Since mid-2005, a pulsar searching system has been operating at 18 cm on the
25-m radio telescope of Urumqi Observatory. Test observations on known pulsars
show that the system can perform the intended task. The prospect of using this
system to observe 3EG sources and other target searching tasks is discussed.Comment: a training project about MSc thesi
Efficient Seeds Computation Revisited
The notion of the cover is a generalization of a period of a string, and
there are linear time algorithms for finding the shortest cover. The seed is a
more complicated generalization of periodicity, it is a cover of a superstring
of a given string, and the shortest seed problem is of much higher algorithmic
difficulty. The problem is not well understood, no linear time algorithm is
known. In the paper we give linear time algorithms for some of its versions ---
computing shortest left-seed array, longest left-seed array and checking for
seeds of a given length. The algorithm for the last problem is used to compute
the seed array of a string (i.e., the shortest seeds for all the prefixes of
the string) in time. We describe also a simpler alternative algorithm
computing efficiently the shortest seeds. As a by-product we obtain an
time algorithm checking if the shortest seed has length at
least and finding the corresponding seed. We also correct some important
details missing in the previously known shortest-seed algorithm (Iliopoulos et
al., 1996).Comment: 14 pages, accepted to CPM 201
Cooler and bigger than thought? Planetary host stellar parameters from the InfraRed Flux Method
Effective temperatures and radii for 92 planet-hosting stars as determined
from the InfraRed Flux Method (IRFM) are presented and compared with those
given by other authors using different approaches. The IRFM temperatures we
have derived are systematically lower than those determined from the
spectroscopic condition of excitation equilibrium, the mean difference being as
large as 110 K. They are, however, consistent with previous IRFM studies and
with the colors derived from Kurucz and MARCS model atmospheres. Comparison
with direct measurements of stellar diameters for 7 dwarf stars, which
approximately cover the range of temperatures of the planet-hosting stars,
suggest that the IRFM radii and temperatures are reliable in an absolute scale.
A better understanding of the fundamental properties of the stars with planets
will be achieved once this discrepancy between the IRFM and the spectroscopic
temperature scales is resolved.Comment: 15 pages, 4 figures. Accepted for publication in Ap
Casorati Determinant Form of Dark Soliton Solutions of the Discrete Nonlinear Schr\"odinger Equation
It is shown that the -dark soliton solutions of the integrable discrete
nonlinear Schr\"odinger (IDNLS) equation are given in terms of the Casorati
determinant. The conditions for reduction, complex conjugacy and regularity for
the Casorati determinant solution are also given explicitly. The relationship
between the IDNLS and the relativistic Toda lattice is discussed.Comment: First version was uploaded in 23 Jun 2005. Published in Journal of
the Physical Society of Japan in May, 200
A Keck/HIRES Doppler Search for Planets Orbiting Metal-Poor Dwarfs. I. Testing Giant Planet Formation and Migration Scenarios
We describe a high-precision Doppler search for giant planets orbiting a
well-defined sample of metal-poor dwarfs in the field. This experiment
constitutes a fundamental test of theoretical predictions which will help
discriminate between proposed giant planet formation and migration models. We
present here details on the survey as well as an overall assessment of the
quality of our measurements, making use of the results for the stars that show
no significant velocity variation.Comment: 25 pages, 7 figures, accepted for publication in the Astrophysical
Journa
The puzzling abundance pattern of HD134439 and HD134440
Abundances of 18 elements are determined for the common proper-motion pair,
HD134439 and HD134440, which shows high [Mn/Fe] and low [\alpha/Fe] ratios as
compared to normal halo stars. Moreover, puzzling abundances are indicated from
elements whose origins are normally considered to be from the same
nucleosynthesis history. Particularly, we have found that [Mg/Fe] and [Si/Fe]
are lower than [Ca/Fe] and [Ti/Fe] by 0.1-0.3 dex. When elemental abundances
are interpreted in term of their condensation temperatures (Tc), obvious trends
of [X/Fe] vs. Tc for alpha elements and probably iron-peak elements as well are
shown. The hypothesis that these stars have formed from a dusty environment in
dSph galaxy provides a solution to the puzzling abundance pattern.Comment: 13 pages,5 figures, MN, in pres
Abundance Analysis of Planetary Host Stars I. Differential Iron Abundances
We present atmospheric parameters and iron abundances derived from
high-resolution spectra for three samples of dwarf stars: stars which are known
to host close-in giant planets (CGP), stars for which radial velocity data
exclude the presence of a close-in giant planetary companion (no-CGP), as well
as a random sample of dwarfs with a spectral type and magnitude distribution
similar to that of the planetary host stars (control). All stars have been
observed with the same instrument and have been analyzed using the same model
atmospheres, atomic data and equivalent width modeling program. Abundances have
been derived differentially to the Sun, using a solar spectrum obtained with
Callisto as the reflector with the same instrumentation. We find that the iron
abundances of CGP dwarfs are on average by 0.22 dex greater than that of no-CGP
dwarfs. The iron abundance distributions of both the CGP and no-CGP dwarfs are
different than that of the control dwarfs, while the combined iron abundances
have a distribution which is very similar to that of the control dwarfs. All
four samples (CGP, no-CGP, combined, control) have different effective
temperature distributions. We show that metal enrichment occurs only for CGP
dwarfs with temperatures just below solar and approximately 300 K higher than
solar, whereas the abundance difference is insignificant at Teff around 6000 K.Comment: 52 pages (aastex 11pt, preprint style), including 17 figures and 13
tables; accepted for publication in AJ (scheduled for the October 2003 issue
A systematic method for constructing time discretizations of integrable lattice systems: local equations of motion
We propose a new method for discretizing the time variable in integrable
lattice systems while maintaining the locality of the equations of motion. The
method is based on the zero-curvature (Lax pair) representation and the
lowest-order "conservation laws". In contrast to the pioneering work of
Ablowitz and Ladik, our method allows the auxiliary dependent variables
appearing in the stage of time discretization to be expressed locally in terms
of the original dependent variables. The time-discretized lattice systems have
the same set of conserved quantities and the same structures of the solutions
as the continuous-time lattice systems; only the time evolution of the
parameters in the solutions that correspond to the angle variables is
discretized. The effectiveness of our method is illustrated using examples such
as the Toda lattice, the Volterra lattice, the modified Volterra lattice, the
Ablowitz-Ladik lattice (an integrable semi-discrete nonlinear Schroedinger
system), and the lattice Heisenberg ferromagnet model. For the Volterra lattice
and modified Volterra lattice, we also present their ultradiscrete analogues.Comment: 61 pages; (v2)(v3) many minor correction
Supernova type Ia luminosities, their dependence on second parameters, and the value of H_0
A sample of 35 SNe Ia with good to excellent photometry in B and V, minimum
internal absorption, and 1200 < v < \approx 30000 km/s is compiled from the
literature. As far as their spectra are known they are all Branch-normal. For
29 of the SNe Ia also peak magnitudes in I are known. The SNe Ia have uniform
colors at maximum, i.e. =-0.012 mag (sigma=0.051) and =-0.276 mag
(sigma=0.078). In the Hubble diagram they define a Hubble line with a scatter
of =0.21-0.16 mag, decreasing with wavelength. The scatter is further
reduced if the SNe Ia are corrected for differences in decline rate Delta_m_15
or color (B-V). A combined correction reduces the scatter to sigma<=0.13 mag.
After the correction no significant dependence remains on Hubble type or
galactocentric distance. The Hubble line suggests some curvature which can be
differently interpreted. A consistent solution is obtained for a cosmological
model with Omega_M=0.3, Omega_Lambda=0.7, which is indicated also by much more
distant SNe Ia. Absolute magnitudes are available for eight equally blue
(Branch-normal) SNe Ia in spirals, whose Cepheid distances are known. If their
well defined mean values of M_B, M_V, and M_I are used to fit the Hubble line
to the above sample of SNe Ia one obtains H_0=58.3 km/s/Mpc, or, after
adjusting all SNe Ia to the average values of Delta_m_15 and (B-V), H_0=60.9
km/s/Mpc. Various systematic errors are discussed whose elimination tends to
decrease H_0. The finally adopted value at the 90-percent level, including
random and systematic errors, is H_0=58.5 +/- 6.3 km/s/Mpc. Several higher
values of H_0 from SNe Ia, as suggested in the literature, are found to depend
on large corrections for variations of the light curve parameter and/or on an
unwarranted reduction of the Cepheid distances of the calibrating SNe Ia.Comment: 42 pages, including 9 figures; submitted to Ap
Dynamics of Binary Mixtures with Ions: Dynamic Structure Factor and Mesophase Formation
Dynamic equations are presented for polar binary mixtures containing ions in
the presence of the preferential solvation. In one-phase states, we calculate
the dynamic structure factor of the composition accounting for the ion motions.
Microphase separation can take place for sufficiently large solvation asymmetry
of the cations and the anions. We show two-dimensional simulation results of
the mesophase formation with an antagonistic salt, where the cations are
hydrophilic and the anions are hydrophobic. The structure factor S(q) in the
resultant mesophase has a sharp peak at an intermediate wave number on the
order of the Debye-Huckel wave number. As the quench depth is increased, the
surface tension nearly vanishes in mesophases due to an electric double layer.Comment: 24 pages, 10 figures, to appear in Journal of Physics: Condensed
Matte
- âŠ