417 research outputs found
The massive star population of the Virgo Cluster galaxy NGC 4535
We analyzed the massive star population of the Virgo Cluster galaxy NGC 4535
using archival Hubble Space Telescope Wide Field Planetary Camera 2 images in
filters F555W and F814W, equivalent to Johnson V and Kron-Cousins I. We
performed high precision point spread function fitting photometry of 24353
sources including 3762 candidate blue supergiants, 841 candidate yellow
supergiants and 370 candidate red supergiants. We estimated the ratio of blue
to red supergiants as a decreasing function of galactocentric radius. Using
Modules for Experiments in Stellar Astrophysics isochrones at solar
metallicity, we defined the luminosity function and estimated the star
formation history of the galaxy over the last 60 Myrs. We conducted a
variability search in the V and I filters using three variability indexes: the
median absolute deviation, the interquartile range and the inverse von-Neumann
ratio. This analysis yielded 120 new variable candidates with absolute
magnitudes ranging from M = 4 to 11 mag. We used the MESA
evolutionary tracks at solar metallicity, to classify the variables based on
their absolute magnitude and their position on the color-magnitude diagram.
Among the new candidate variable sources are eight candidate variable red
supergiants, three candidate variable yellow supergiants and one candidate
luminous blue variable, which we suggest for follow-up observations.Comment: Accepted by A&A, 7 pages, 7 Tables, 53 figure
Comparative performance of selected variability detection techniques in photometric time series
Photometric measurements are prone to systematic errors presenting a
challenge to low-amplitude variability detection. In search for a
general-purpose variability detection technique able to recover a broad range
of variability types including currently unknown ones, we test 18 statistical
characteristics quantifying scatter and/or correlation between brightness
measurements. We compare their performance in identifying variable objects in
seven time series data sets obtained with telescopes ranging in size from a
telephoto lens to 1m-class and probing variability on time-scales from minutes
to decades. The test data sets together include lightcurves of 127539 objects,
among them 1251 variable stars of various types and represent a range of
observing conditions often found in ground-based variability surveys. The real
data are complemented by simulations. We propose a combination of two indices
that together recover a broad range of variability types from photometric data
characterized by a wide variety of sampling patterns, photometric accuracies,
and percentages of outlier measurements. The first index is the interquartile
range (IQR) of magnitude measurements, sensitive to variability irrespective of
a time-scale and resistant to outliers. It can be complemented by the ratio of
the lightcurve variance to the mean square successive difference, 1/h, which is
efficient in detecting variability on time-scales longer than the typical time
interval between observations. Variable objects have larger 1/h and/or IQR
values than non-variable objects of similar brightness. Another approach to
variability detection is to combine many variability indices using principal
component analysis. We present 124 previously unknown variable stars found in
the test data.Comment: 29 pages, 8 figures, 7 tables; accepted to MNRAS; for additional
plots, see http://scan.sai.msu.ru/~kirx/var_idx_paper
Ionization of hydrogen and hydrogenic ions by antiprotons
Presented here is a description of the ionization of hydrogen and hydrogenic
ions by antiproton-impact, based on very large scale numerical solutions of the
time-dependent Schr\"odinger equation in three spatial dimensions and on
analysis of the topology of the electronic eigenenergy surfaces in the plane of
complex internuclear distance. Comparison is made with other theories and very
recent measurements.Comment: RevTex document, 11 pages, 4 Postscript figures are available from
the authors, in press Phys. Rev. Let
Influence of physician empathy on the outcome of botulinum toxin treatment for upper limb spasticity in patients with chronic stroke: A cohort study.
To examine the relationship between patient-rated physician empathy and outcome of botulinum toxin treatment for post-stroke upper limb spasticity.Cohort study.Twenty chronic stroke patients with upper limb spasticity.All patients received incobotulinumtoxinA injection in at least one muscle for each of the following patterns: flexed elbow, flexed wrist and clenched fist. Each treatment was performed by 1 of 5 physiatrists with equivalent clinical experience. Patient-rated physician empathy was quantified with the Consultation and Relational Empathy Measure immediately after botulinum toxin treatment. Patients were evaluated before and at 4 weeks after botulinum toxin treatment by means of the following outcome measures: Modified Ashworth Scale; Wolf Motor Function Test; Disability Assessment Scale; Goal Attainment Scaling.Ordinal regression analysis showed a significant influence of patient-rated physician empathy (independent variable) on the outcome (dependent variables) of botulinum toxin treatment at 4 weeks after injection, as measured by Goal Attainment Scaling (p<0.001).These findings support the hypothesis that patient-rated physician empathy may influence the outcome of botulinum toxin treatment in chronic stroke patients with upper limb spasticity as measured by Goal Attainment Scaling
Gaia Data Release 3. The first Gaia catalogue of eclipsing binary candidates
We present the first Gaia catalogue of eclipsing binary candidates released
in Gaia DR3, describe its content, provide tips for its usage, estimate its
quality, and show illustrative samples. The catalogue contains 2,184,477
sources with G magnitudes up to 20 mag. Candidate selection is based on the
results of variable object classification performed within the Gaia Data
Processing and Analysis Consortium, further filtered using eclipsing
binary-tailored criteria based on the G light curves. To find the orbital
period, a large ensemble of trial periods is first acquired using three
distinct period search methods applied to the cleaned G light curve. The G
light curve is then modelled with up-to two Gaussians and a cosine for each
trial period. The best combination of orbital period and geometric model is
finally selected using Bayesian model comparison based on the BIC. A global
ranking metric is provided to rank the quality of the chosen model between
sources. The catalogue is restricted to orbital periods larger than 0.2 days.
About 530,000 of the candidates are classified as eclipsing binaries in the
literature as well, out of ~600,000 available crossmatches, and 93% of them
have published periods compatible with the Gaia periods. Catalogue completeness
is estimated to be between 25% and 50%, depending on the sky region, relative
to the OGLE4 catalogues of eclipsing binaries towards the Galactic Bulge and
the Magellanic Clouds. The analysis of an illustrative sample of ~400,000
candidates with significant parallaxes shows properties in the observational HR
diagram as expected for eclipsing binaries. The subsequent analysis of a
sub-sample of detached bright candidates provides further hints for the
exploitation of the catalogue. The orbital periods, light curve model
parameters, and global rankings are all published in the catalogue with their
related uncertainties where applicable.Comment: Submitted to A&A. Main text: 23 pages, 35 figures. Four appendices
(17 pages) with 38 figure
Large-amplitude variables in Gaia Data Release 2. Multi-band variability characterization
The second data release (DR2) of Gaia provides mean photometry in three bands
for 1.4 billion sources, but light curves and variability properties are
available for only 0.5 million of them. Here, we provide a census of
large-amplitude variables with amplitudes larger than 0.2 mag in the
band for objects with mean brightnesses between 5.5 and 19 mag. To achieve
this, we rely on variability amplitude proxies in , and
computed from the uncertainties on the magnitudes published in DR2. We then
apply successive filters to identify two subsets containing respectively
sources with reliable mean and (for studies using colours)
and sources having compatible amplitude proxies in , and
(for multi-band variability studies). The full catalogue gathers
large-amplitude variable candidates, and the two subsets with increased levels
of purity contain respectively and sources. A
multi-band variability analysis of the catalogue shows that different types of
variable stars can be globally categorized in four groups according to their
colour and blue-to-red amplitude ratios as determined from the ,
and amplitude proxies. The catalogue constitutes the first census of
Gaia large-amplitude variable candidates, extracted from the public DR2
archive. The overview presented here illustrates the added-value of the mission
for multi-band variability studies even at this stage when epoch photometry is
not yet available for all sources. (Abridged abstract)Comment: Final version, A&A, in press. Main text: 20 pages, 26 figures. Four
appendixe
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