183 research outputs found
KIC 4150611: a rare multi-eclipsing quintuple with a hybrid pulsator
We present the results of our analysis of KIC 4150611 (HD 181469) - an
interesting, bright quintuple system that includes a hybrid
Sct/ Dor pulsator. Four periods of eclipses - 94.2, 8.65, 1.52 and 1.43
d - have been observed by the Kepler satellite, and three point sources (A, B,
and C) are seen in high angular resolution images.
From spectroscopic observations made with the HIDES spectrograph attached to
the 1.88-m telescope of the Okayama Astrophysical Observatory (OAO), for the
first time we calculated radial velocities (RVs) of the component B - a pair of
G-type stars - and combined them with Kepler photometry in order to obtain
absolute physical parameters of this pair. We also managed to directly measure
RVs of the pulsator, also for the first time. Additionally, we modelled the
light curves of the 1.52 and 1.43-day pairs, and measured their eclipse timing
variations (ETVs). We also performed relative astrometry and photometry of
three sources seen on the images taken with the NIRC2 camera of the Keck II
telescope. Finally, we compared our results with theoretical isochrones.
The brightest component Aa is the hybrid pulsator, transited every 94.2 days
by a pair of K/M-type stars (Ab1+Ab2), which themselves form a 1.52-day
eclipsing binary. The components Ba and Bb are late G-type stars, forming
another eclipsing pair with a 8.65 day period. Their masses and radii are
M, R for the
primary, and M, R
for the secondary. The remaining period of 1.43 days is possibly related to a
faint third star C, which itself is most likely a background object. The
system's properties are well-represented by a 35 Myr isochrone. There are also
hints of additional bodies in the system.Comment: 14 pages, 15 figures, 7 tables, to appear in A&A, abstract modified
in order to fit the arXiv limi
Exploring the phase structure of lattice QCD with twisted mass quarks
The phase structure of zero temperature twisted mass lattice QCD is
investigated. We find strong metastabilities in the plaquette observable when
the untwisted quark mass sweeps across zero.Comment: Talks presented at Lattice2004(spectrum), 6 pages, 6 figure
Twisted mass fermions: neutral pion masses from disconnected contributions
Twisted mass fermions allow light quarks to be explored but with the
consequence that there are mass splittings, such as between the neutral and
charged pion. Using a direct calculation of the connected neutral pion
correlator and stochastic methods to evaluate the disconnected correlations, we
determine the neutral pion mass. We explore the dependence on lattice spacing
and quark mass in quenched QCD. For dynamical QCD, we determine the sign of the
splitting which is linked, via chiral PT, to the nature of the phase transition
at small quark mass.Comment: 6 pages, poster (hadron spectrum and quark masses) at Lattice
2005,Dublin, July 25-3
A note on the determination of light quark masses
We provide a model-independent determination of the quantity B_0(m_d-m_u).
Our approach rests only on chiral symmetry and data from the decay of the eta
into three neutral pions. Since the low-energy prediction at next-to-leading
order fails to reproduce the experimental results, we keep the strong
interaction correction as an unknown parameter. As a first step, we relate this
parameter to the quark mass difference using data from the Dalitz plot. A
similar relation is obtained using data from the decay width. Combining both
relations we obtain B_0(m_d-m_u)=(4495+/-440) MeV^2. The preceding value,
combined with lattice determinations, leads to the values m_u(2
GeV)=(2.9+/-0.8) MeV and m_d(2 GeV)=(4.7+/-0.8) MeV.Comment: 8 pages, 1 figure, updated version with all detailed formulas, title
slighly change
Thin Sea-Ice Thickness as Inferred from Passive Microwave and In Situ Observations
Since microwave radiometric signals from sea-ice strongly reflect physical conditions of a layer near the ice surface, a relationship of brightness temperature with thickness is possible especially during the early stages of ice growth. Sea ice is most saline during formation stage and as the salinity decreases with time while at the same time the thickness of the sea ice increases, a corresponding change in the dielectric properties and hence the brightness temperature may occur. This study examines the extent to which the relationships of thickness with brightness temperature (and with emissivity) hold for thin sea-ice, approximately less than 0.2 -0.3 m, using near concurrent measurements of sea-ice thickness in the Sea of Okhotsk from a ship and passive microwave brightness temperature data from an over-flying aircraft. The results show that the brightness temperature and emissivity increase with ice thickness for the frequency range of 10-37 GHz. The relationship is more pronounced at lower frequencies and at the horizontal polarization. We also established an empirical relationship between ice thickness and salinity in the layer near the ice surface from a field experiment, which qualitatively support the idea that changes in the near-surface brine characteristics contribute to the observed thickness-brightness temperature/emissivity relationship. Our results suggest that for thin ice, passive microwave radiometric signals contain, ice thickness information which can be utilized in polar process studies
Equation of State and Heavy-Quark Free Energy at Finite Temperature and Density in Two Flavor Lattice QCD with Wilson Quark Action
We study the equation of state at finite temperature and density in
two-flavor QCD with the RG-improved gluon action and the clover-improved Wilson
quark action on a lattice. Along the lines of constant physics
at and 0.80, we compute the second and forth
derivatives of the grand canonical partition function with respect to the quark
chemical potential and the isospin chemical potential
at vanishing chemical potentials, and study the
behaviors of thermodynamic quantities at finite using these derivatives
for the case . In particular, we study density fluctuations at
none-zero temperature and density by calculating the quark number and isospin
susceptibilities and their derivatives with respect to . To suppress
statistical fluctuations, we also examine new techniques applicable at low
densities. We find a large enhancement in the fluctuation of quark number when
the density increased near the pseudo-critical temperature, suggesting a
critical point at finite terminating the first order transition line
between hadronic and quark gluon plasma phases. This result agrees with the
previous results using staggered-type quark actions qualitatively. Furthermore,
we study heavy-quark free energies and Debye screening masses at finite density
by measuring the first and second derivatives of these quantities for various
color channels of heavy quark-quark and quark-anti-quark pairs. The results
suggest that, to the leading order of , the interaction between two
quarks becomes stronger at finite densities, while that between quark and
anti-quark becomes weaker.Comment: 38 pages, 63 figure
Charm quark system at the physical point of 2+1 flavor lattice QCD
We investigate the charm quark system using the relativistic heavy quark
action on 2+1 flavor PACS-CS configurations previously generated on lattice. The dynamical up-down and strange quark masses are set to
the physical values by using the technique of reweighting to shift the quark
hopping parameters from the values employed in the configuration generation. At
the physical point, the lattice spacing equals GeV and the
spatial extent fm. The charm quark mass is determined by the
spin-averaged mass of the 1S charmonium state, from which we obtain m_{\rm
charm}^{\msbar}(\mu = m_{\rm charm}^{\msbar}) = 1.260(1)(6)(35) GeV, where the
errors are due to our statistics, scale determination and renormalization
factor. An additional systematic error from the heavy quark is of order
, which is estimated to be a percent
level if the factor analytic in is of order unity. Our
results for the charmed and charmed-strange meson decay constants are
MeV, MeV, again up to the heavy quark
errors of order . Combined with the CLEO
values for the leptonic decay widths, these values yield , , where the last error is on
account of the experimental uncertainty of the decay widths.Comment: 16 pages, 12 figure
Physical and Radiative Characteristic and Long-term Variability of the Okhotsk Sea Ice Cover
Much of what we know about the large scale characteristics of the Okhotsk Sea ice cover has been provided by ice concentration maps derived from passive microwave data. To understand what satellite data represent in a highly divergent and rapidly changing environment like the Okhotsk Sea, we take advantage of concurrent satellite, aircraft, and ship data acquired on 7 February and characterized the sea ice cover at different scales from meters to hundreds of kilometers. Through comparative analysis of surface features using co-registered data from visible, infrared and microwave channels we evaluated the general radiative and physical characteristics of the ice cover as well as quantify the distribution of different ice types in the region. Ice concentration maps from AMSR-E using the standard sets of channels, and also only the 89 GHz channel for optimal resolution, are compared with aircraft and high resolution visible data and while the standard set provides consistent results, the 89 GHz provides the means to observe mesoscale patterns and some unique features of the ice cover. Analysis of MODIS data reveals that thick ice types represents about 37% of the ice cover indicating that young and new ice types represent a large fraction of the ice cover that averages about 90% ice concentration according to passive microwave data. These results are used to interpret historical data that indicate that the Okhotsk Sea ice extent and area are declining at a rapid rate of about -9% and -12 % per decade, respectively
Physical and Radiative Characteristics and Long Term Variability of the Okhotsk Sea Ice Cover
Much of what we know about the large scale characteristics of the Okhotsk Sea ice cover comes from ice concentration maps derived from passive microwave data. To understand what these satellite data represents in a highly divergent and rapidly changing environment like the Okhotsk Sea, we analyzed concurrent satellite, aircraft, and ship data and characterized the sea ice cover at different scales from meters to tens of kilometers. Through comparative analysis of surface features using co-registered data from visible, infrared and microwave channels we evaluated how the general radiative and physical characteristics of the ice cover changes as well as quantify the distribution of different ice types in the region. Ice concentration maps from AMSR-E using the standard sets of channels, and also only the 89 GHz channel for optimal resolution, are compared with aircraft and high resolution visible data and while the standard set provides consistent results, the 89 GHz provides the means to observe mesoscale patterns and some unique features of the ice cover. Analysis of MODIS data reveals that thick ice types represents about 37% of the ice cover indicating that young and new ice represent a large fraction of the lice cover that averages about 90% ice concentration, according to passive microwave data. A rapid decline of -9% and -12 % per decade is observed suggesting warming signals but further studies are required because of aforementioned characteristics and because the length of the ice season is decreasing by only 2 to 4 days per decade
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