16,719 research outputs found
Double-lined M dwarf eclipsing binaries from Catalina Sky Survey and LAMOST
Eclipsing binaries provide a unique opportunity to determine fundamental
stellar properties. In the era of wide-field cameras and all-sky imaging
surveys, thousands of eclipsing binaries have been reported through light curve
classification, yet their basic properties remain unexplored due to the
extensive efforts needed to follow them up spectroscopically. In this paper we
investigate three M2-M3 type double-lined eclipsing binaries discovered by
cross-matching eclipsing binaries from the Catalina Sky Survey wtih
spectroscopically classified M dwarfs from the Large Sky Area Multi-Object
Fiber Spectroscopic Telescope survey data release one and two. Because these
three M dwarf binaries are faint, we further acquire radial velocity
measurements using GMOS on the Gemini North telescope with R~40000, enabling us
to determine the mass and radius of individual stellar components. By jointly
fitting the light and radial velocity curves of these systems, we derive the
mass and radius of the primary and secondary components of these three systems,
in the range between 0.28-0.42 M_sun and 0.29-0.67 R_sun, respectively. Future
observations with a high resolution spectrograph will help us pin down the
uncertainties in their stellar parameters, and render these systems benchmarks
to study m dwarfs, providing inputs to improving stellar models in the low mass
regime, or establishing an empirical mass-radius relation for M dwarf stars.Comment: RAA accepted. arXiv admin note: text overlap with arXiv:1701.0529
Flexible parametric bootstrap for testing homogeneity against clustering and assessing the number of clusters
There are two notoriously hard problems in cluster analysis, estimating the
number of clusters, and checking whether the population to be clustered is not
actually homogeneous. Given a dataset, a clustering method and a cluster
validation index, this paper proposes to set up null models that capture
structural features of the data that cannot be interpreted as indicating
clustering. Artificial datasets are sampled from the null model with parameters
estimated from the original dataset. This can be used for testing the null
hypothesis of a homogeneous population against a clustering alternative. It can
also be used to calibrate the validation index for estimating the number of
clusters, by taking into account the expected distribution of the index under
the null model for any given number of clusters. The approach is illustrated by
three examples, involving various different clustering techniques (partitioning
around medoids, hierarchical methods, a Gaussian mixture model), validation
indexes (average silhouette width, prediction strength and BIC), and issues
such as mixed type data, temporal and spatial autocorrelation
Bulk-boundary correspondence for three-dimensional symmetry-protected topological phases
We derive a bulk-boundary correspondence for three-dimensional (3D)
symmetry-protected topological (SPT) phases with unitary symmetries. The
correspondence consists of three equations that relate bulk properties of these
phases to properties of their gapped, symmetry-preserving surfaces. Both the
bulk and surface data appearing in our correspondence are defined via a
procedure in which we gauge the symmetries of the system of interest and then
study the braiding statistics of excitations of the resulting gauge theory. The
bulk data is defined in terms of the statistics of bulk excitations, while the
surface data is defined in terms of the statistics of surface excitations. An
appealing property of this data is that it is plausibly complete in the sense
that the bulk data uniquely distinguishes each 3D SPT phase, while the surface
data uniquely distinguishes each gapped, symmetric surface. Our correspondence
applies to any 3D bosonic SPT phase with finite Abelian unitary symmetry group.
It applies to any surface that (1) supports only Abelian anyons and (2) has the
property that the anyons are not permuted by the symmetries.Comment: 31 pages, 14 figures, 1 tabl
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