192 research outputs found
Gaia Data Release 2: Validation of the classification of RR Lyrae and Cepheid variables with the Kepler and K2 missions
The second data release of the Gaia mission includes an advance catalog of
variable stars. The classification of these stars are based on sparse
photometry from the first 22 months of the mission. We set out to investigate
the purity and completeness of the all-sky Gaia classification results with the
help of the continuous light curves of the observed targets from the Kepler and
K2 missions, focusing specifically on RR Lyrae and Cepheid pulsators, outside
the Galactic Bulge region. We crossmatched the Gaia identifications with the
observations collected by the Kepler space telescope. We inspected the light
curves visually, then calculated the relative Fourier coefficients and period
ratios for the single- and double-mode K2 RR Lyrae stars to further classify
them. We identified 1443 and 41 stars classified as RR Lyrae or Cepheid
variables in Gaia DR2 in the targeted observations of the two missions and 263
more RR Lyre targets in the Full-Frame Images (FFI) of the original mission. We
provide the crossmatch of these sources. We conclude that the RR Lyrae catalog
has a completeness between 70-78%, and provide a purity estimate between 92-98%
(targeted observations) with lower limits of 75% (FFI stars) and 51% (K2
worst-case scenario). The low number of Cepheids prevents us from drawing
detailed conclusions but the purity of the DR2 sample is estimated to be around
66%.Comment: 15 pages, 12 figures, 10 tables, accepted into the Gaia DR2 Special
Issue in A&A. V1: submitted version, v2: accepted version. Lists available at
http://konkoly.hu/~lmolnar/gaiakepler_datafiles_R1.zi
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
Gaia Data Release 2. Validating the classification of RR Lyrae and Cepheid variables with the Kepler and K2 missions
Context. The second data release of the Gaia mission (DR2) includes an advance catalogue of variable stars. The classifications of these stars are based on sparse photometry from the first 22 months of the mission. Aims: We set out to investigate the purity and completeness of the all-sky Gaia classification results with the help of the continuous light curves of the observed targets from the Kepler and K2 missions, focusing specifically on RR Lyrae and Cepheid pulsators, outside the Galactic bulge region. Methods: We cross-matched the Gaia identifications with the observations collected by the Kepler space telescope. We inspected the light curves visually, then calculated the relative Fourier coefficients and period ratios for the single- and double-mode K2 RR Lyrae stars to further classify them. Results: We identified 1443 and 41 stars classified as RR Lyrae or Cepheid variables in Gaia DR2 in the targeted observations of the two missions and 263 more RR Lyre targets in the full-frame images (FFI) of the original mission. We provide the cross-match of these sources. We conclude that the RR Lyrae catalogue has a completeness between 70-78%, and provide a purity estimate of between 92 and 98% (targeted observations) with lower limits of 75% (FFI stars) and 51% (K2 worst- case scenario). The low number of Cepheids prevents us from drawing detailed conclusions, but the purity of the DR2 sample is estimated to be about 66%. Full Tables A1, A4, and A5 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/qcat?J/A+A/620/A12
Search for high-amplitude Delta Scuti and RR Lyrae stars in Sloan Digital Sky Survey Stripe 82 using principal component analysis
We propose a robust principal component analysis (PCA) framework for the
exploitation of multi-band photometric measurements in large surveys. Period
search results are improved using the time series of the first principal
component due to its optimized signal-to-noise ratio.The presence of correlated
excess variations in the multivariate time series enables the detection of
weaker variability. Furthermore, the direction of the largest variance differs
for certain types of variable stars. This can be used as an efficient attribute
for classification. The application of the method to a subsample of Sloan
Digital Sky Survey Stripe 82 data yielded 132 high-amplitude Delta Scuti
variables. We found also 129 new RR Lyrae variables, complementary to the
catalogue of Sesar et al., 2010, extending the halo area mapped by Stripe 82 RR
Lyrae stars towards the Galactic bulge. The sample comprises also 25
multiperiodic or Blazhko RR Lyrae stars.Comment: 23 pages, 17 figure
Gaia eclipsing binary and multiple systems. Two-Gaussian models applied to OGLE-III eclipsing binary light curves in the Large Magellanic Cloud
The advent of large scale multi-epoch surveys raises the need for automated
light curve (LC) processing. This is particularly true for eclipsing binaries
(EBs), which form one of the most populated types of variable objects. The Gaia
mission, launched at the end of 2013, is expected to detect of the order of few
million EBs over a 5-year mission.
We present an automated procedure to characterize EBs based on the geometric
morphology of their LCs with two aims: first to study an ensemble of EBs on a
statistical ground without the need to model the binary system, and second to
enable the automated identification of EBs that display atypical LCs. We model
the folded LC geometry of EBs using up to two Gaussian functions for the
eclipses and a cosine function for any ellipsoidal-like variability that may be
present between the eclipses. The procedure is applied to the OGLE-III data set
of EBs in the Large Magellanic Cloud (LMC) as a proof of concept. The bayesian
information criterion is used to select the best model among models containing
various combinations of those components, as well as to estimate the
significance of the components.
Based on the two-Gaussian models, EBs with atypical LC geometries are
successfully identified in two diagrams, using the Abbe values of the original
and residual folded LCs, and the reduced . Cleaning the data set from
the atypical cases and further filtering out LCs that contain non-significant
eclipse candidates, the ensemble of EBs can be studied on a statistical ground
using the two-Gaussian model parameters. For illustration purposes, we present
the distribution of projected eccentricities as a function of orbital period
for the OGLE-III set of EBs in the LMC, as well as the distribution of their
primary versus secondary eclipse widths.Comment: 20 pages, 29 figures. Submitted to A&
Student understanding of rotational and rolling motion concepts
We investigated the common difficulties that students have with concepts
related to rotational and rolling motion covered in the introductory physics
courses. We compared the performance of calculus- and algebra-based
introductory physics students with physics juniors who had learned rotational
and rolling motion concepts in an intermediate level mechanics course.
Interviews were conducted with six physics juniors and ten introductory
students using demonstration-based tasks. We also administered free-response
and multiple-choice questions to a large number of students enrolled in
introductory physics courses, and interviewed six additional introductory
students on the test questions (during the test design phase). All students
showed similar difficulties regardless of their background, and higher
mathematical sophistication did not seem to help acquire a deeper
understanding. We found that some difficulties were due to related difficulties
with linear motion, while others were tied specifically to the more intricate
nature of rotational and rolling motion.Comment: 23 pages, 3 figures, 2 tables; it includes a multiple-choice test (in
Appendix B
Search for high-amplitude δ Scuti and RR Lyrae stars in Sloan Digital Sky Survey Stripe 82 using principal component analysis
We propose a robust principal component analysis framework for the exploitation of multiband photometric measurements in large surveys. Period search results are improved using the time-series of the first principal component due to its optimized signal-to-noise ratio. The presence of correlated excess variations in the multivariate time-series enables the detection of weaker variability. Furthermore, the direction of the largest variance differs for certain types of variable stars. This can be used as an efficient attribute for classification. The application of the method to a subsample of Sloan Digital Sky Survey Stripe 82 data yielded 132 high-amplitude δ Scuti variables. We also found 129 new RR Lyrae variables, complementary to the catalogue of Sesar et al., extending the halo area mapped by Stripe 82 RR Lyrae stars towards the Galactic bulge. The sample also comprises 25 multiperiodic or Blazhko RR Lyrae star
Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automated classification of the Hipparcos periodic variable stars into 26 types. The sub-sample with the most reliable variability types available in the literature is used to train supervised algorithms to characterize the type dependencies on a number of attributes. The most useful attributes evaluated with the random forest methodology include, in decreasing order of importance, the period, the amplitude, the V−I colour index, the absolute magnitude, the residual around the folded light-curve model, the magnitude distribution skewness and the amplitude of the second harmonic of the Fourier series model relative to that of the fundamental frequency. Random forests and a multi-stage scheme involving Bayesian network and Gaussian mixture methods lead to statistically equivalent results. In standard 10-fold cross-validation (CV) experiments, the rate of correct classification is between 90 and 100 per cent, depending on the variability type. The main mis-classification cases, up to a rate of about 10 per cent, arise due to confusion between SPB and ACV blue variables and between eclipsing binaries, ellipsoidal variables and other variability types. Our training set and the predicted types for the other Hipparcos periodic stars are available onlin
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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