9,516 research outputs found
Gaia Eclipsing Binary and Multiple Systems. A study of detectability and classification of eclipsing binaries with Gaia
In the new era of large-scale astronomical surveys, automated methods of
analysis and classification of bulk data are a fundamental tool for fast and
efficient production of deliverables. This becomes ever more imminent as we
enter the Gaia era. We investigate the potential detectability of eclipsing
binaries with Gaia using a data set of all Kepler eclipsing binaries sampled
with Gaia cadence and folded with the Kepler period. The performance of fitting
methods is evaluated with comparison to real Kepler data parameters and a
classification scheme is proposed for the potentially detectable sources based
on the geometry of the light curve fits. The polynomial chain (polyfit) and
two-Gaussian models are used for light curve fitting of the data set.
Classification is performed with a combination of the t-SNE (t-distrubuted
Stochastic Neighbor Embedding) and DBSCAN (Density-Based Spatial Clustering of
Applications with Noise) algorithms. We find that approximately 68% of Kepler
Eclipsing Binary sources are potentially detectable by Gaia when folded with
the Kepler period and propose a classification scheme of the detectable sources
based on the morphological type indicative of the light curve, with subclasses
that reflect the properties of the fitted model (presence and visibility of
eclipses, their width, depth, etc.).Comment: 9 pages, 18 figures, accepted for publication in Astronomy &
Astrophysic
Methods for Analysing Endothelial Cell Shape and Behaviour in Relation to the Focal Nature of Atherosclerosis
The aim of this thesis is to develop automated methods for the analysis of the
spatial patterns, and the functional behaviour of endothelial cells, viewed under
microscopy, with applications to the understanding of atherosclerosis.
Initially, a radial search approach to segmentation was attempted in order to
trace the cell and nuclei boundaries using a maximum likelihood algorithm; it
was found inadequate to detect the weak cell boundaries present in the available
data. A parametric cell shape model was then introduced to fit an equivalent
ellipse to the cell boundary by matching phase-invariant orientation fields of the
image and a candidate cell shape. This approach succeeded on good quality
images, but failed on images with weak cell boundaries. Finally, a support
vector machines based method, relying on a rich set of visual features, and a
small but high quality training dataset, was found to work well on large numbers
of cells even in the presence of strong intensity variations and imaging noise.
Using the segmentation results, several standard shear-stress dependent parameters
of cell morphology were studied, and evidence for similar behaviour
in some cell shape parameters was obtained in in-vivo cells and their nuclei.
Nuclear and cell orientations around immature and mature aortas were broadly
similar, suggesting that the pattern of flow direction near the wall stayed approximately
constant with age. The relation was less strong for the cell and
nuclear length-to-width ratios.
Two novel shape analysis approaches were attempted to find other properties
of cell shape which could be used to annotate or characterise patterns, since a
wide variability in cell and nuclear shapes was observed which did not appear
to fit the standard parameterisations. Although no firm conclusions can yet be
drawn, the work lays the foundation for future studies of cell morphology.
To draw inferences about patterns in the functional response of cells to flow,
which may play a role in the progression of disease, single-cell analysis was performed
using calcium sensitive florescence probes. Calcium transient rates were
found to change with flow, but more importantly, local patterns of synchronisation
in multi-cellular groups were discernable and appear to change with flow.
The patterns suggest a new functional mechanism in flow-mediation of cell-cell
calcium signalling
Extragalactic Science, Cosmology and Galactic Archaeology with the Subaru Prime Focus Spectrograph (PFS)
The Subaru Prime Focus Spectrograph (PFS) is a massively-multiplexed
fiber-fed optical and near-infrared 3-arm spectrograph (N_fiber=2400,
380<lambda<1260nm, 1.3 degree diameter FoV), offering unique opportunities in
survey astronomy. Here we summarize the science case feasible for a survey of
Subaru 300 nights. We describe plans to constrain the nature of dark energy via
a survey of emission line galaxies spanning a comoving volume of 9.3 (Gpc/h)^3
in the redshift range 0.8<z<2.4. In each of 6 redshift bins, the cosmological
distances will be measured to 3% precision via BAO, and redshift-space
distortions will be used to constrain structure growth to 6% precision. In the
GA program, radial velocities and chemical abundances of stars in the Milky Way
and M31 will be used to infer the past assembly histories of spiral galaxies
and the structure of their dark matter halos. Data will be secured for 10^6
stars in the Galactic thick-disk, halo and tidal streams as faint as V~22,
including stars with V < 20 to complement the goals of the Gaia mission. A
medium-resolution mode with R = 5000 to be implemented in the red arm will
allow the measurement of multiple alpha-element abundances and more precise
velocities for Galactic stars, elucidating the detailed chemo-dynamical
structure and evolution of each of the main stellar components of the Milky Way
Galaxy and of its dwarf spheroidal galaxies. For the extragalactic program, our
simulations suggest the wide avelength range will be powerful in probing the
galaxy population and its clustering over a wide redshift range. We propose to
conduct a color-selected survey of 1<z<2 galaxies and AGN over 16 deg^2 to
J~23.4, yielding a fair sample of galaxies with stellar masses above ~10^{10}Ms
at z~2. A two-tiered survey of higher redshift LBGs and LAEs will quantify the
properties of early systems close to the reionization epoch.Comment: This document describes the scientific program and requirements for
the Subaru Prime Focus Spectrograph (PFS) project. Made significant revision
based on studies for the Preliminary Design Review (PRD) held in Feb 2013.
The higher-resolution paper file is available from
http://member.ipmu.jp/masahiro.takada/pfs_astroph_rv.pd
IPHAS and the symbiotic stars. I. Selection method and first discoveries
The study of symbiotic stars is essential to understand important aspects of
stellar evolution in interacting binaries. Their observed population in the
Galaxy is however poorly known, and is one to three orders of magnitudes
smaller than the predicted population size. IPHAS, the INT Photometric Halpha
survey of the Northern Galactic plane, gives us the opportunity to make a
systematic, complete search for symbiotic stars in a magnitude-limited volume,
and discover a significant number of new systems.
A method of selecting candidate symbiotic stars by combining IPHAS and
near-IR (2MASS) colours is presented. It allows us to distinguish symbiotic
binaries from normal stars and most of the other types of Halpha emission line
stars in the Galaxy. The only exception are T Tauri stars, which can however be
recognized because of their concentration in star forming regions. Using these
selection criteria, we discuss the classification of a list of 4338 IPHAS stars
with Halpha in emission. 1500 to 2000 of them are likely to be Be stars. Among
the remaining objects, 1183 fulfill our photometric constraints to be
considered candidate symbiotic stars. The spectroscopic confirmation of three
of these objects, which are the first new symbiotic stars discovered by IPHAS,
proves the potential of the survey and selection method.Comment: Accepted for publication on Astronomy and Astrophysics. 12 pages, 8
figure
The Open Cluster NGC 2437 (Messier 46)
The stellar content of the open cluster NGC 2437 (Messier 46) is investigated
using moderately deep u*,g', and r' MegaCam images. When compared with solar
metallicity isochrones, the (g', u'-g') and (r', g'-r') CMDs are consistent
with an age log(t_yr) = 8.35 +/- 0.15, a distance modulus 11.05 +/- 0.05, and a
color excess E(B-V) = 0.115 +/- 0.035. The r' luminosity function (LF) of main
sequence stars in the magnitude range r' 0.8 solar) has a
shape that follows solar neighborhood star counts. However, at fainter
magnitudes the cluster LF is flat, in contrast with what would be expected from
solar neighborhood counts. The clustering properties of stars in NGC 2437 are
investigated by examining the two-point angular correlation functions of main
sequence stars in different brightness ranges. Main sequence stars fainter than
r' = 17 are less centrally concentrated than brighter stars and are found over
a larger area of the sky, suggesting that there is a corona of faint main
sequence stars around NGC 2437. Based on the flat LF and extended spatial
distribution of faint stars, it is concluded that NGC 2437 is actively shedding
stars with masses < 0.8 solar.Comment: To appear in the PAS
Ly-alpha emitting galaxies at redshift z~4.5 in the LALA Cetus field
We present a large sample of Ly-alpha emitting galaxies spectroscopically
confirmed at z~4.5, based on IMACS spectroscopic observations of candidate LAEs
in the LALA Cetus field. We identify 110 z~4.5 LAEs based on single line
detections with no continuum emission blueward of the line. The Ly-alpha
confirmation rate varies from <50% to 76% for candidates selected in different
narrowband filters at slightly different redshifts. We find a drop in the LAE
density at redshift 4.50+-0.03 from redshift 4.39-4.47 by a factor of 66%,
which could be a large scale void in the distribution of star-forming galaxies
(~18Mpc along the line of sight and ~80Mpc across). The sample includes many
objects with equivalent widths >200A. These large EW candidates are
spectroscopically confirmed at the same rate as candidates with more modest
EWs. A composite spectrum of all 110 confirmed LAEs shows the characteristic
asymmetry of the Ly-alpha line. It also places new and stringent upper limits
on the CIV 1549/Ly-alpha and HeII 1640/Ly-alpha line ratios, providing a new
upper limit on the fraction of active galactic nuclei in Ly-alpha selected
galaxy samples, and on the contribution of Pop III populations. Finally, we
calculate the Ly-alpha luminosity function for our z~4.5 sample, which is
consistent with those at other redshifts, showing that there is no evolution in
Ly-alpha luminosity function from z~3.1-6.6.Comment: 30 pages, 10 figures, ApJ submitte
The Multiscale Morphology Filter: Identifying and Extracting Spatial Patterns in the Galaxy Distribution
We present here a new method, MMF, for automatically segmenting cosmic
structure into its basic components: clusters, filaments, and walls.
Importantly, the segmentation is scale independent, so all structures are
identified without prejudice as to their size or shape. The method is ideally
suited for extracting catalogues of clusters, walls, and filaments from samples
of galaxies in redshift surveys or from particles in cosmological N-body
simulations: it makes no prior assumptions about the scale or shape of the
structures.}Comment: Replacement with higher resolution figures. 28 pages, 17 figures. For
Full Resolution Version see:
http://www.astro.rug.nl/~weygaert/tim1publication/miguelmmf.pd
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