scholarly journals Gaia Data Release 2

2018 ◽  
Vol 620 ◽  
pp. A127 ◽  
Author(s):  
László Molnár ◽  
Emese Plachy ◽  
Áron L. Juhász ◽  
Lorenzo Rimoldini
Keyword(s):  
Continuous Light ◽  
Variable Stars ◽  
Light Curves ◽  
Case Scenario ◽  
Worst Case ◽  
Rr Lyrae ◽  
Data Release ◽  
Cepheid Variables ◽  
Bulge Region ◽  
Targeted Observations

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%.

scholarly journals Theoretical Study of Cepheid Light Curves

1985 ◽  
Vol 82 ◽  
pp. 153-156
Author(s):  
C. G. Davis
Keyword(s):  
Theoretical Study ◽  
Heat Engine ◽  
Variable Stars ◽  
Light Curves ◽  
Diffusion Equations ◽  
Linear Features ◽  
Radiation Diffusion ◽  
Rr Lyrae ◽  
Non Linear ◽  
Linear Effects

Starting with the initial understanding that pulsation in variable stars is caused by the heat engine of Hydrogen and Helium ionization in their atmospheres (A.S. Eddington in Cox 1980) it was soon realized that non-linear effects were responsible for the detailed features on their light and velocity curves. With the advent of the computer we were able to solve the coupled set of hydrodynamics and radiation diffusion equations to model these non-linear features (Christy 1968, Cox et. al. 1966). Calculations including the effects of multi-frequency radiative transfer (Davis 1975) showed that grey diffusion was adequate for modeling Cepheids but not for the RR Lyrae or W Virginis type variables.

scholarly journals Cepheid Pulsation Theory and Multiperiodic Cepheid Variables

1976 ◽  
Vol 29 ◽  
pp. 115-131
Author(s):  
A. N. Cox ◽  
J. P. Cox
Keyword(s):  
Variable Stars ◽  
Radial Pulsation ◽  
Rr Lyrae Stars ◽  
The Third ◽  
The Past ◽  
Rr Lyrae ◽  
Cepheid Variables ◽  
Theory Calculation ◽  
Lyrae Stars ◽  
Radial Pulsations

In this review of the situation with regard to the multiperiodic Cepheid variables, our subject matter is divided into four parts. The first discusses general causes of pulsation of Cepheids and other variable stars, and their locations on the H-R diagram. For this section we draw upon the work during the past 10-15 years of J. P. Cox, Baker, Kippenhahn, A. N. Cox, King, Christy, Castor, Stobie, Stellingwerf, Davey, Iben, and Tuggle, mostly with the small amplitude linear nonadiabatic radial pulsation theory. In the second section we review the linear adiabatic and nonadiabatic theory calculation of radial pulsation periods and their application to the problem of masses of double-mode Cepheids. Contributions discussed are by Cogan, J. P. Cox, King, Stellingwerf, Petersen, Hansen, and Ross. Periodic solutions, and their stability, of the nonlinear radial pulsation equations for Cepheids and RR Lyrae stars are considered in the third section. This research has been done by Stellingwerf with previous development of methods by Baker and von Sengbusch and current work by A. N. Cox and Davey at Los Alamos. In the last section we give the latest results on nonlinear, nonperiodic, radial pulsations for Cepheids and RR Lyrae stars. This work has been done by Stellingwerf, King, A. N. Cox, J. P. Cox, and Davey.

scholarly journals DIRECT Distances to Local Group Galaxies

2000 ◽  
Vol 176 ◽  
pp. 182-186 ◽  
Author(s):  
Dimitar D. Sasselov
Keyword(s):  
Local Group ◽  
Variable Stars ◽  
Eclipsing Binaries ◽  
Light Curves ◽  
Stepping Stones ◽  
The Past ◽  
Cepheid Variables ◽  
Direct Distance ◽  
Nearby Galaxies

AbstractThe two nearby galaxies, M31 and M33, are stepping stones for most of our current efforts to understand the evolving universe at large scales. We are undertaking a long term project, called DIRECT, to improve the direct distance estimate to M31 and M33. The massive photometry we have obtained as part of our project over the past 3 years provides us with very good light curves for known and new Cepheid variables, a large number of eclipsing binaries and other variable stars.

scholarly journals LSST Observations of RR Lyrae Stars for Mapping the Galactic Halo

2010 ◽  
Vol 6 (S277) ◽  
pp. 300-304
Author(s):  
Hakeem M. Oluseyi ◽  
Andrew C. Becker ◽  
Christopher C. Culliton ◽  
Muhammad Furqan ◽  
Keri L. Hoadley ◽  
...  
Keyword(s):  
Light Curve ◽  
Local Group ◽  
Galactic Halo ◽  
Variable Stars ◽  
Light Curves ◽  
Chemical Compositions ◽  
Galactic Halos ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Lyrae Stars

AbstractThe Large Synoptic Survey Telescope (LSST) is an anticipated to undertake a 10–year, 3π steradian survey that promises to observe millions of new periodic variable stars. We report on a study to determine the efficiency of the LSST to recover the light curve properties of RR Lyrae stars. An LSST light curve simulation tool was used to sample input idealized light curves or RR Lyrae stars observed in SDSS Stripe 82 data, returning each as it would have been observed by LSST, including realistic photometric scatter, limiting magnitudes, and telescope downtime. Our results show that the LSST will be capable of mapping the spatial distributions and chemical compositions of halo stellar overdensities using RR Lyrae discovered across 3π steradians and out to nearly 1.5 Mpc. LSST will thus enable the mapping of halo merger streams, the discovery of new dwarf galaxies, and the mapping galactic halos throughout the Local Group galaxies.

scholarly journals Cepheid Variables in Ecliping Binary Systems

2005 ◽  
Vol 13 ◽  
pp. 460-460
Author(s):  
Douglas Welch
Keyword(s):  
Binary Systems ◽  
Variable Stars ◽  
Eclipsing Binaries ◽  
Type I ◽  
Rr Lyrae Stars ◽  
Additional Information ◽  
Rr Lyrae ◽  
Future Success ◽  
Cepheid Variables ◽  
Lyrae Stars

Microlensing surveys of the Large and Small Magellanic Clouds have revealed the existence of Type I and II Cepheid variable stars in eclipsing binary systems. In this review I will summarize the state of the known published and unpublished observations of these systems describe what has been learned to date and discuss what the prospects are for extracting additional information from the known systems using future observations. This review will also discuss the known state of searches for RR Lyrae stars in both spectroscopic and eclipsing binaries and suggest strategies for future success in detecting such systems.

scholarly journals A theoretical scenario for Galactic RR Lyrae in the Gaia data base: constraints on the parallax offset

2020 ◽  
Vol 500 (4) ◽  
pp. 5009-5023
Author(s):  
M Marconi ◽  
R Molinaro ◽  
V Ripepi ◽  
S Leccia ◽  
I Musella ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Data Base ◽  
Light Curves ◽  
Weighted Mean ◽  
Complementary Information ◽  
Rr Lyrae ◽  
Individual Metal ◽  
Data Release ◽  
Non Linear ◽  
Metal Abundances

ABSTRACT On the basis of an extended set of non-linear convective RR Lyrae pulsation models we derive the first theoretical light curves in the Gaia bands G, GBP, and GRP and the corresponding intensity-weighted mean magnitudes and pulsation amplitudes. The effects of chemical composition on the derived Bailey diagrams in the Gaia filters are discussed for both Fundamental and first overtone mode pulsators. The inferred mean magnitudes and colours are used to derive the first theoretical Period–Wesenheit relations for RR Lyrae in the Gaia filters. The application of the theoretical Period–Wesenheit relations for both the Fundamental and first overtone mode to Galactic RR Lyrae in the Gaia Data Release 2 data base and complementary information on individual metal abundances allows us to derive theoretical estimates of their individual parallaxes. These results are compared with the astrometric solutions to conclude that a very small offset, consistent with zero, is required in order to reconcile the predicted distances with Gaia results.

scholarly journals Optical and Near-infrared Pulsation Properties of RR Lyrae and Population II Cepheid Variables in the Messier 15 Globular Cluster

2021 ◽  
Vol 922 (1) ◽  
pp. 20
Author(s):  
Anupam Bhardwaj ◽  
Marina Rejkuba ◽  
G. C. Sloan ◽  
Marcella Marconi ◽  
Soung-Chul Yang
Keyword(s):  
Globular Cluster ◽  
Near Infrared ◽  
Variable Stars ◽  
Log P ◽  
Distance Modulus ◽  
Distance Measurements ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Cepheid Variables ◽  
Lyrae Stars

Abstract Messier 15 (NGC 7078) is an old and metal-poor post core-collapse globular cluster that hosts a rich population of variable stars. We report new optical (gi) and near-infrared (NIR, JK s ) multi-epoch observations for 129 RR Lyrae, 4 Population II Cepheids (3 BL Herculis, 1 W Virginis), and 1 anomalous Cepheid variable candidate in M15 obtained using the MegaCam and the WIRCam instruments on the 3.6 m Canada–France–Hawaii Telescope. Multi-band data are used to improve the periods and classification of variable stars, and determine accurate mean magnitudes and pulsational amplitudes from the light curves fitted with optical and NIR templates. We derive optical and NIR period–luminosity relations for RR Lyrae stars which are best constrained in the K s band, m K s = − 2.333 ( 0.054 ) log P + 13.948 ( 0.015 ) with a scatter of only 0.037 mag. Theoretical and empirical calibrations of RR Lyrae period–luminosity–metallicity relations are used to derive a true distance modulus to M15: 15.196 ± 0.026 (statistical) ± 0.039 (systematic) mag. Our precise distance moduli based on RR Lyrae stars and Population II Cepheid variables are mutually consistent and agree with recent distance measurements in the literature based on Gaia parallaxes and other independent methods.

scholarly journals Analysis of pulsating variable stars using the visibility graph algorithm

PLoS ONE ◽  
2021 ◽  
Vol 16 (11) ◽  
pp. e0259735
Author(s):  
Víctor Muñoz ◽  
N. Elizabeth Garcés
Keyword(s):  
Graph Algorithm ◽  
Variable Stars ◽  
Visibility Graph ◽  
Clustering Coefficient ◽  
Light Curves ◽  
Rr Lyrae ◽  
Visibility Graphs ◽  
Pulsating Variable Stars ◽  
Law Degree ◽  
Horizontal Visibility Graph

We study the light curves of pulsating variable stars using a complex network approach to build visibility graphs. We consider various types of variables stars (e.g., Cepheids, δ Scuti, RR Lyrae), build two types of graphs (the normal visibility graph (VG) and the horizontal visibility graph (HVG)), and calculate various metrics for the resulting networks. We find that all networks have a power-law degree distribution for the VG and an exponential distribution for the HVG, suggesting that it is a universal feature, regardless of the pulsation features. Metrics such as the average degree, the clustering coefficient and the transitivity coefficient, can distinguish between some star types. We also observe that the results are not strongly affected by the presence of observation gaps in the light curves. These findings suggest that the visibility graph algorithm may be a useful technique to study variability in stars.

scholarly journals The Characteristics of the Field RR Lyrae Stars in the Magellanic Clouds

1974 ◽  
Vol 59 ◽  
pp. 107-108
Author(s):  
J. A. Graham
Keyword(s):  
Stellar Evolution ◽  
Large Magellanic Cloud ◽  
Variable Stars ◽  
Magellanic Cloud ◽  
Magellanic Clouds ◽  
Light Curves ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
First Results ◽  
Lyrae Stars

The Magellanic Clouds are well known as being very suitable for observing the various stages of stellar evolution. During the last few years, I have been studying the RR Lyrae variable stars in each of the two Clouds. Some first results were reported at IAU Colloquium No. 21 in 1972 (Graham, 1973). Here, I would like to update these results on the basis of more recent data and to comment on some of the characteristics of the field RR Lyrae stars in each system. Periods and light curves are now available for 63 RR Lyrae stars in a 1° x 1.3° field centered on the cluster NGC 1783 in the Large Magellanic Cloud (LMC) and for 62 stars in a 1° x 1.3° field centered on the cluster NGC 121 in the Small Magellanic Cloud (SMC). Both ab and c type variables are represented and, viewed individually, the Cloud RR Lyraes are identical in characteristics to those known in our Galaxy. Studied as groups, however, there are small but significant differences between the RR Lyrae stars in each system. The following four specific features seem to be emerging from the study.

scholarly journals Gaia Data Release 2

2018 ◽  
Vol 618 ◽  
pp. A30 ◽  
Author(s):  
B. Holl ◽  
M. Audard ◽  
K. Nienartowicz ◽  
G. Jevardat de Fombelle ◽  
O. Marchal ◽  
...  
Keyword(s):  
Time Series ◽  
Variable Stars ◽  
Great Promise ◽  
Published Data ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Short Timescale ◽  
Classical Statistics ◽  
Data Release ◽  
Lyrae Stars

Context. The Gaia Data Release 2 (DR2) contains more than half a million sources that are identified as variable stars. Aims. We summarise the processing and results of the identification of variable source candidates of RR Lyrae stars, Cepheids, long-period variables (LPVs), rotation modulation (BY Dra-type) stars, δ Scuti and SX Phoenicis stars, and short-timescale variables. In this release we aim to provide useful but not necessarily complete samples of candidates. Methods. The processed Gaia data consist of the G, GBP, and GRP photometry during the first 22 months of operations as well as positions and parallaxes. Various methods from classical statistics, data mining, and time-series analysis were applied and tailored to the specific properties of Gaia data, as were various visualisation tools to interpret the data. Results. The DR2 variability release contains 228 904 RR Lyrae stars, 11 438 Cepheids, 151 761 LPVs, 147 535 stars with rotation modulation, 8882 δ Scuti and SX Phoenicis stars, and 3018 short-timescale variables. These results are distributed over a classification and various Specific Object Studies tables in the Gaia archive, along with the three-band time series and associated statistics for the underlying 550 737 unique sources. We estimate that about half of them are newly identified variables. The variability type completeness varies strongly as a function of sky position as a result of the non-uniform sky coverage and intermediate calibration level of these data. The probabilistic and automated nature of this work implies certain completeness and contamination rates that are quantified so that users can anticipate their effects. Thismeans that even well-known variable sources can be missed or misidentified in the published data. Conclusions. The DR2 variability release only represents a small subset of the processed data. Future releases will include more variable sources and data products; however, DR2 shows the (already) very high quality of the data and great promise for variability studies.

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