272 research outputs found
Measurements of Stellar Inclinations for Kepler Planet Candidates II: Candidate Spin-Orbit Misalignments in Single and Multiple-Transiting Systems
We present a test for spin-orbit alignment for the host stars of 25 candidate
planetary systems detected by the {\it Kepler} spacecraft. The inclination
angle of each star's rotation axis was estimated from its rotation period,
rotational line broadening, and radius. The rotation periods were determined
using the {\it Kepler} photometric time series. The rotational line broadening
was determined from high-resolution optical spectra with Subaru/HDS. Those same
spectra were used to determine the star's photospheric parameters (effective
temperature, surface gravity, metallicity) which were then interpreted with
stellar-evolutionary models to determine stellar radii. We combine the new
sample with the 7 stars from our previous work on this subject, finding that
the stars show a statistical tendency to have inclinations near 90, in
alignment with the planetary orbits. Possible spin-orbit misalignments are seen
in several systems, including three multiple-planet systems (KOI-304, 988,
2261). Ideally these systems should be scrutinized with complementary
techniques---such as the Rossiter-McLaughlin effect, starspot-crossing
anomalies or asteroseismology---but the measurements will be difficult owing to
the relatively faint apparent magnitudes and small transit signals in these
systems.Comment: 11 pages, 9 figures, accepted for publication in Ap
Delta-Function Bose Gas Picture of S=1 Antiferromagnetic Quantum Spin Chains Near Critical Fields
We study the zero-temperature magnetization curve (M-H curve) of the S=1
bilinear-biquadratic spin chain, whose Hamiltonian is given by 0 \leq \beta <1H_sH_cH_scH_c\beta\beta_c(\approx 0.41)0<\beta<\beta_cccM\sim \sqrt{H-H_c}\beta \to \beta_c-0M\sim (H-H_c)^{1/4}\beta_c<\beta <1c$ becomes negative.Comment: 6 pages, RevTeX, 8 ps figure
A Common Proper Motion Stellar Companion to HAT-P-7
We report that HAT-P-7 has a common proper motion stellar companion. The companion is located at approx. 3.9 arcsec to the east and estimated as an M5.5V dwarf based on its colors. We also confirm the presence of the third companion, which was first reported by Winn et al. (2009), based on long-term radial velocity measurements. We revisit the migration mechanism of HAT-P-7b given the presence of those companions, and propose sequential Kozai migration as a likely scenario in this system. This scenario may explain the reason for an outlier in the discussion of the spin-orbit alignment timescale for HAT-P-7b by Albrecht et al. (2012)
Middle-Field Cusp Singularities in the Magnetization Process of One-Dimensional Quantum Antiferromagnets
We study the zero-temperature magnetization process (M-H curve) of
one-dimensional quantum antiferromagnets using a variant of the density-matrix
renormalization group method. For both the S=1/2 zig-zag spin ladder and the
S=1 bilinear-biquadratic chain, we find clear cusp-type singularities in the
middle-field region of the M-H curve. These singularities are successfully
explained in terms of the double-minimum shape of the energy dispersion of the
low-lying excitations. For the S=1/2 zig-zag spin ladder, we find that the cusp
formation accompanies the Fermi-liquid to non-Fermi-liquid transition.Comment: 4 pages, RevTeX, 3 figures, some mistakes in references are correcte
Mutual Exclusion Statistics in Exactly Solvable Models in One and Higher Dimensions at Low Temperatures
We study statistical characterization of the many-body states in exactly
solvable models with internal degrees of freedom. The models under
consideration include the isotropic and anisotropic Heisenberg spin chain, the
Hubbard chain, and a model in higher dimensions which exhibits the Mott
metal-insulator transition. It is shown that the ground state of these systems
is all described by that of a generalized ideal gas of particles (called
exclusons) which have mutual exclusion statistics, either between different
rapidities or between different species. For the Bethe ansatz solvable models,
the low temperature properties are well described by the excluson description
if the degeneracies due to string solutions with complex rapidities are taken
into account correctly. {For} the Hubbard chain with strong but finite
coupling, charge-spin separation is shown for thermodynamics at low
temperatures. Moreover, we present an exactly solvable model in arbitrary
dimensions which, in addition to giving a perspective view of spin-charge
separation, constitutes an explicit example of mutual exclusion statistics in
more than two dimensions
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