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1

Empirical Scaling Relations for the Photospheric Magnetic Elements of the Flaring and Non-Flaring Active Regions

Moradhaseli M. A., Javaherian M., Fathalian N., Safari H.

Acta Astronomica

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2021

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Vol. 71, No. 2

163--188

EN

Here, we analyze magnetic elements of the solar active regions (ARs) observed in the line-of-sight magnetograms (the 6173 Å FeI line) recorded with the Solar Dynamics Observatory (SDO)/Hel\-ioseismic and Magnetic Imager (HMI). The Yet Another Feature Tracking Algorithm (YAFTA}) was employed to analyze the statistical properties of these features (e.g., filling factor, magnetic flux, and lifetime). Magnetic features were extracted from the areas of 180o×180o inside the flaring AR (NOAA 12443) for November 3-5, 2015 and non-flaring AR (NOAA 12446) for November 4-6, 2015. The mean filling factor of polarities was found to be about 0.49 for the flaring AR, while this value was 0.08 for the non-flaring AR. Time series of the filling factors of the negative and positive polarities for the flaring AR showed anti-correlated behavior (with the Pearson value of -0.80). However, there was a strong positive correlation (with the Pearson value of 0.95) for the non-flaring AR. A power-law function was fitted to the frequency distributions of flux (F), size (S), and lifetime ($T$). Power exponents of the distributions of flux, size, and lifetime for the flaring AR were found to be -2.36±0.27, -3.11±0.17, and -1.70±0.29, respectively, while for the non-flaring AR: -2.53±0.20, -3.42±0.21, and -1.61±0.19, respectively. The code detected a magnetic element with the maximum flux of 23.54×1020 Mx. The maximum size of detected patches was found to be about 300 Mm2. The most long-lived patch in the flaring AR belonged to an element with a lifetime of 2208 min. We showed that S, F, and T for patches in the flaring AR follow empirical scaling relations: S∼F0.66±0.01, F∼T0.48±0.04, and S∼T0.32±0.02, respectively. For patches in the non-flaring AR, we obtained S∼F0.64±0.02, F∼T0.37±0.06, and S∼T0.23±0.03, respectively. The comparisons indicated that correlations between parameters of F and T, and also, S and T for the flaring AR, are larger than those of the non-flaring AR. The scaling law relation between the flux growth rate of positive polarities and their size indicates a strong correlation of more than 0.7 in both ARs.

2

High-Velocity Moving Groups in the Solar Neighborhood in Gaia DR2

Baluev R. V., Shaidulin V. Sh., Veselova A. V.

Acta Astronomica

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2020

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Vol. 70, No. 2

141--168

EN

We use an improved wavelet analysis technique to reconstruct the (U,V,W) velocity distribution for ≈250 000 stars from Gaia DR2, located in the solar neighborhood of 200 pc. The 2D wavelet transforms for three bivariate distributions (U,V), (U,W), and (V,W) were investigated. Though most of currently known (low-velocity) stellar moving groups are densely overlapped in these diagrams, our analysis allowed us to detect and disentangle about twenty statistically significant 3D groups of stars with high velocities. Most of them appear to be new discoverirs. We also discuss the issue of correct noise thresholding in the wavelet transform and highlight the importance of using a global rather than local statistic for that. Using of a local significance measure may lead to an overstated statistical confidence for individual patterns due to the effect of multiple testing.

3

Cool Spot and Flare Activities of a RS CVn Binary KIC 7885570

Kunt M., Dal H. A.

Acta Astronomica

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2017

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Vol. 67, No. 4

345--362

EN

We present here the results of our studies on the physical nature and chromospheric activity of a RS CVn binary KIC 7885570 based on the Kepler Mission data. Assuming the primary component temperature, 6530 K, the temperature of the secondary component was found to be 5732±4 K. The mass ratio of the components (q) was found to be 0.43±0.01, while the inclination (i) of the system - 80.6°±0.1°. Additionally, the data were separated into 35 subsets to model the sinusoidal variation due to the rotational modulation, using the SpotModel program, as the light curve analysis indicated the chromospherically active secondary component. It was found that there are generally two spotted areas, whose radii, longitudes and latitudes are rapidly changing, located around the latitudes of +50° and +90° on the active component. Moreover, 113 flares were detected and their parameters were computed from the available data. The One Phase Exponential Association function model was derived from the parameters of these flares. Using the regression calculations, the Plateau value was found to be 1.9815±0.1177, while the half-life value was computed as 3977.2 s. In addition, the flare frequency (N1) - the flare number per hour, was estimated to be 0.00362 h-1, while flare frequency (N2 - the flare-equivalent duration emitted per hour, was computed as 0.00001. Finally, the times of eclipses were computed for 278 minima of the light curves, whose analysis indicated that the chromosphere activity nature of the system causes some effects on these minima times. Comparing the chromospheric activity patterns with the analogues of the secondary component, it is seen that the magnetic activity level is remarkably low. However, it is still at the expected level according to the B-V color index of 0.643 mag for the secondary component.

4

Robust Filtering of Artifacts in Difference Imaging for Rapid Transients Detection

Klencki J., Wyrzykowski Ł., Kostrzewa-Rutkowska Z., Udalski A.

Acta Astronomica

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2016

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Vol. 66, No. 1

15--29

EN

Real-time analysis and classification of observational data collected within synoptic sky surveys is a huge challenge due to constant growth of data volumes. Machine learning techniques are often applied in order to perform this task automatically. The current bottleneck of transients detection in most surveys is the process of filtering numerous artifacts from candidate detection. We present a new method for automated artifact filtering based on hierarchical unsupervised classifier employing Self-Organizing Maps (SOMs). The system accepts 97% of real transients and removes 97.5% of artifacts when tested on the OGLE-IV Transient Detection System. The improvement of the artifacts filtering allows for single-frame-based detection of transients within OGLE-IV, which now alerts on transient discoveries in less than 15 minutes from the image acquisition.

5

On Estimating Non-Uniform Density Distributions Using N Nearest Neighbors

Woźniak P. R., Kruszewski A.

Acta Astronomica

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2012

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Vol. 62, No. 4

409--417

EN

We consider density estimators based on the nearest neighbors method applied to discrete point distributions in spaces of arbitrary dimensionality. If the density is constant, the volume of a hypersphere centered at a random location is proportional to the expected number of points falling within the hypersphere radius. The distance to the N-th nearest neighbor alone is then a sufficient statistic for the density. In the non-uniform case the proportionality is distorted. We model this distortion by normalizing hypersphere volumes to the largest one and expressing the resulting distribution in terms of the Legendre polynomials. Using Monte Carlo simulations we show that this approach can be used to effectively address the trade-off between smoothing bias and estimator variance for sparsely sampled distributions.

6

The Light Curve Statistical Moments Analysis: The Identification of Eclipsing Binaries

Graczyk D., Eyer L.

Acta Astronomica

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2010

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Vol. 60, No. 2

109--119

EN

A semi-automatic method of identifying eclipsing binaries in large photometric surveys, based on the analysis of the light curve statistical moments, is presented. This method was tested on the OGLE-II database of variable stars in the Large Magellanic Cloud. As a result 99.0% of eclipsing binaries in Wyrzykowski et al. (2003) catalog and 100% of eclipsing binaries in Groenewegen (2005) catalog were recovered. Additionally we identified 752 new eclipsing binaries in the LMC that were not presented in earlier catalogs thereby increasing detection rates by about 25%. The method is more focusing on detached and semi-detached eclipsing binaries. We conclude that this method is well suited for use in eclipsing binary searches of large surveys such as OGLE-III.

7

Extinction in the Galaxy from Surface Brightnesses of ESO-LV Galaxies: Testing ''Standard'' Extinction Maps

Chołoniewski J., Valentijn E. A.

Acta Astronomica

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2003

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Vol. 56, No. 3

265--280

EN

The relative extinction in the Galaxy computed with new method by Chołoniewski and Valentijn is compared with three patterns: Schlegel, Finkbeiner and Davis, Burstein and Heiles and the cosecans law. It is shown that extinction of SFD is more reliable than that of BH since it stronger correlates with our new extinction. The smallest correlation coefficient was obtained for the cosecans law. Linear regression analysis show that SFD overestimate the extinction by a factor of 1.4. Our results clearly indicate that there is non-zero extinction at the Galactic South pole and that the extinction near the Galactic equator (|b|<40°) is significantly larger in the Southern than in the Northern hemisphere.

8

Extinction in the Galaxy from Surface Brightnesses of ESO-LV Galaxies: Determination of AR/AB ratio

Chołoniewski J., Valentijn E. A.

Acta Astronomica

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2003

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Vol. 56, No. 3

249--264

EN

A new method for the determination of the extinction in the Galaxy is proposed. The method uses surface brightnesses of external galaxies in the B and R-bands. The observational data have been taken from the ESO-LV galaxy catalog. As a first application of our model we derive the ratio of R-band to B-band extinction. We introduce two methods for computing the ratio which give: 0.62±0.05 (the first method) and 0.64±0.06 (the second method) which is in agreement with the recent literature value of 0.61. This agreement confirms the validity and efficiency of our model and is an independent verification for the standard value of the "total to selective extinction". The method of extinction determination introduced in this paper will be explored in subsequent publication.