FIRST RESULTS FROM TIEN-SHAN SURVEY TO SEARCH FOR VARIABLE STARS: LIGHTCURVE ANALYSIS AND VARIABLE STAR CLASSIFICATION

2020 ◽  
Vol 3 (331) ◽  
pp. 81-91
Author(s):  
Serebryanskiy A., ◽  
◽  
Aimanova G. K., ◽  
Kondratyeva L.N., ◽  
Omarov Ch., ◽  
...  
Keyword(s):  
Variable Star ◽  
Variable Stars ◽  
Tien Shan ◽  
First Results ◽  
Star Classification

scholarly journals Variable star monitoring in local group dwarf irregular galaxies

2004 ◽  
Vol 193 ◽  
pp. 70-74 ◽  
Author(s):  
Jan Snigula ◽  
Claus Gössl ◽  
Ulrich Hopp ◽  
Heinz Barwig
Keyword(s):  
Variable Star ◽  
Local Group ◽  
Dwarf Galaxy ◽  
Variable Stars ◽  
Star Formation History ◽  
Stellar Content ◽  
Irregular Galaxies ◽  
Formation History ◽  
First Results ◽  
Dwarf Irregular Galaxies

AbstractDwarf galaxies in the local group provide a unique astrophysical laboratory. Despite their proximity some of these systems still lack reliable distance determinations as well as studies of their stellar content and star formation history. We present first results of our survey of variable stars in a sample of six local group dwarf irregular galaxies. Taking the Leo A dwarf galaxy as an example we describe observational strategies and data reduction. We discuss the light curves of two newly found Cepheids and place them into the context of a previously derived P-L relation. Finally we discuss the LPV content of Leo A.

scholarly journals Imbalance learning for variable star classification

2020 ◽  
Vol 493 (4) ◽  
pp. 6050-6059
Author(s):  
Zafiirah Hosenie ◽  
Robert Lyon ◽  
Benjamin Stappers ◽  
Arrykrishna Mootoovaloo ◽  
Vanessa McBride
Keyword(s):  
Machine Learning ◽  
Data Augmentation ◽  
Variable Star ◽  
Variable Stars ◽  
Light Curves ◽  
Training Data ◽  
Classification Rate ◽  
Star Classification ◽  
Algorithm Level ◽  
Data Level

ABSTRACT The accurate automated classification of variable stars into their respective subtypes is difficult. Machine learning–based solutions often fall foul of the imbalanced learning problem, which causes poor generalization performance in practice, especially on rare variable star subtypes. In previous work, we attempted to overcome such deficiencies via the development of a hierarchical machine learning classifier. This ‘algorithm-level’ approach to tackling imbalance yielded promising results on Catalina Real-Time Survey (CRTS) data, outperforming the binary and multiclass classification schemes previously applied in this area. In this work, we attempt to further improve hierarchical classification performance by applying ‘data-level’ approaches to directly augment the training data so that they better describe underrepresented classes. We apply and report results for three data augmentation methods in particular: Randomly Augmented Sampled Light curves from magnitude Error (RASLE), augmenting light curves with Gaussian Process modelling (GpFit) and the Synthetic Minority Oversampling Technique (SMOTE). When combining the ‘algorithm-level’ (i.e. the hierarchical scheme) together with the ‘data-level’ approach, we further improve variable star classification accuracy by 1–4 per cent. We found that a higher classification rate is obtained when using GpFit in the hierarchical model. Further improvement of the metric scores requires a better standard set of correctly identified variable stars, and perhaps enhanced features are needed.

scholarly journals Variable Stars in the Fornax Dwarf Galaxy

2000 ◽  
Vol 176 ◽  
pp. 273-273
Author(s):  
D. Bersier ◽  
Peter R. Wood
Keyword(s):  
Dwarf Galaxy ◽  
Variable Stars ◽  
First Results

AbstractWe present the first results of a search for variable stars in the Fornax dwarf galaxy.

scholarly journals Analyzing Light Curves for Variable Star Classification

2020 ◽  
Author(s):  
Melinda Soares Furtado ◽  
Christopher Moore ◽  
Rachel McClure
Keyword(s):  
Variable Star ◽  
Light Curves ◽  
Star Classification

Times of maximum of KZ Hya from OACS -UNAH

2020 ◽  
Vol 8 (2) ◽  
pp. 90-93
Author(s):  
M. Meza ◽  
A. Pineda ◽  
C. Argueta ◽  
Y. Mendoza ◽  
M. C. Pereira ◽  
...  
Keyword(s):  
Variable Star ◽  
Variable Stars ◽  
Surface Layers ◽  
Maximum Light ◽  
Photometric Observations

A pulsating variable star is one whose brightness changes periodically due to the expansion and contraction of the surface layers of the star. Several times of maximum light can be obtained in brief observations of SX Phoenicis variable stars due to their short periods of pulsation (P ~ 1:0 - 1:75 h). We report three new times of maximum light of SX Phoenicis star KZ Hya obtained from photometric observations made on the night of April 5-6, 2019 from the Observatorio Astronómico Centroaméricano de Suyapa (OACS) of the Universidad Nacional Autónoma de Honduras

scholarly journals The AAVSO and its Variable Star Databank on Pulsating Stars

1995 ◽  
Vol 155 ◽  
pp. 421-422 ◽  
Author(s):  
Janet A. Mattei
Keyword(s):  
Variable Star ◽  
American Association ◽  
Variable Stars ◽  
Pulsating Stars

AbstractThe American Association of Variable Stars Observers is the world’s largest organization of variable star observers. Its services to the astronomical community and database on pulsating variables are described.

scholarly journals The Carina Dwarf Galaxy Variable Star Population

2002 ◽  
Vol 185 ◽  
pp. 134-135
Author(s):  
V. Ripepi ◽  
M. Dall’Ora ◽  
L. Pulone ◽  
M. Castellani ◽  
C. Corsi ◽  
...  
Keyword(s):  
Variable Star ◽  
Dwarf Galaxy ◽  
Variable Stars ◽  
Photometric Data ◽  
Wide Field ◽  
Preliminary Results

AbstractWe present some preliminary results based on new observations of the variable stars belonging to the Carina Dwarf Galaxy (DG). Photometric data were collected with the two wide field imagers available at ESO ([email protected].) and CTIO (4m prime focus).

scholarly journals AAVSO’s Astronomical Data Bank

1979 ◽  
Vol 53 ◽  
pp. 506-506
Author(s):  
Janet Akyüz Mattei
Keyword(s):  
Variable Star ◽  
Data Bank ◽  
Variable Stars ◽  
Astronomical Data ◽  
The World ◽  
Visual Magnitude ◽  
Recurrent Nova

The AAVSO founded in 1911 is the largest organization of variable star observers in the world, with 1100 members in 49 states and 38 countries. AAVSO Headquarters, in Cambridge, MA, receives about 150,000 observations a year from about 400 active observers. Since 1911, over 4 million observations have been compiled. The limiting visual magnitude of observations is about AAVSO’s observing program contains about 2000 variable stars of the following types: Mira (825); semiregular (350); cataclysmic-U Gem, Z Cam, nova, recurrent nova, novalike, symbiotic (200); cepheid (120); R Coronae Borealis (20); RV Tauri (30); nebular (100); flare (15); irregular (140); suspected variables (200). AAVSO has finder charts for most of the stars.

scholarly journals CCD VI time-series of the extremely metal-poor globular cluster M92: revisiting its variable star population

2020 ◽  
Vol 494 (3) ◽  
pp. 3212-3226 ◽  
Author(s):  
M A Yepez ◽  
A Arellano Ferro ◽  
D Deras
Keyword(s):  
Time Series ◽  
Globular Cluster ◽  
Variable Star ◽  
Variable Stars ◽  
Frequency Spectra ◽  
Fourier Decomposition ◽  
Rr Lyrae ◽  
Blazhko Effect ◽  
New Variables ◽  
Gaia Dr2

ABSTRACT We present an analysis of VI CCD time-series photometry of the Oo II type globular cluster M92. The variable star population of the cluster is studied with the aim of revising their classifications, identifications, frequency spectra, and to select indicators of the parental cluster metallicity and distance. The Fourier decomposition of RR Lyrae light curves lead to the estimation of mean [Fe/H]spec = −2.20 ± 0.18 and distance of 8.3 ± 0.2 kpc. Four new variables are reported: one RRd (V40), a multimode SX Phe (V41), an SR (V42), and one RRc (F1) that is most likely not a cluster member. The AC nature of V7 is confirmed. The double mode nature of the RRc star V11 is not confirmed and its amplitude modulations are most likely due to the Blazhko effect. Two modes are found in the known RRc variable V13. It is argued that the variable V30, previously classified as RRab is, in fact, a BL Her-type star not belonging to the cluster. Using the Gaia-DR2 proper motions, we identified 5012 stars in the field of the cluster, which are very likely cluster members, and for which we possess photometry, enabling the production of a refined colour–magnitude diagram. This also allowed us to identify a few variable stars that do not belong to the cluster. The RR Lyrae pulsation modes on the HB are cleanly separated by the first overtone red edge, a common feature in all Oo II-type clusters.

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