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The rise of synoptic sky surveys has ushered in an era of big data in time-domain astronomy, making data science and machine learning essential tools for studying celestial objects. While tree-based models (e.g. Random Forests) and deep learning models dominate the field, we explore the use of different distance metrics to aid in the classification of astrophysical objects. We developed DistClassiPy, a new distance metric based classifier. The direct use of distance metrics is unexplored in time-domain astronomy, but distance-based methods can help make classification more interpretable and decrease computational costs. In particular, we applied DistClassiPy to classify light curves of variable stars, comparing the distances between objects of different classes. Using 18 distance metrics on a catalog of 6,000 variable stars across 10 classes, we demonstrate classification and dimensionality reduction. Our classifier meets state-of-the-art performance but has lower computational requirements and improved interpretability. Additionally, DistClassiPy can be tailored to specific objects by identifying the most effective distance metric for that classification. To facilitate broader applications within and beyond astronomy, we have made DistClassiPy open-source and available at https://pypi.org/project/distclassipy/. [ABSTRACT FROM AUTHOR]

Highlights • We analyzed the time series of R Sct light curve from 1970 to 2017. • Behavior of the light curve and period evolution were also reviewed and investigated. • We have shown the amplitude variation of two modes as time progresses. • An estimated value of seasonal variations is approximately 10 years, and hence, we suggested a magnetic field cycle for this system. Abstract The observation of R Scuti star has a long history. This unique characteristic of light curve allows us to search for evidence of period evolution. The behavior of R Sct is complex and has not been understood well. In the present work, we reviewed and analyzed the time series of light curve observations to search for period evolution. The irregular behavior of the light curve was investigated by power spectral density (PSD) and fast Fourier transform (FFT) techniques. A time-frequency technique was performed to show frequency evolution. Additionally, we studied the amplitude and frequency variations of the main and the second mode. The characteristics of the amplitude variation of two modes as time progresses are presented. An estimated value of the seasonal variations is approximately 10 years. The results suggest a magnetic field cycle for this system. [ABSTRACT FROM AUTHOR]

We present the results of our investigation of the geometrical parameters of the W UMa-type binary system VSX J045718.3+405643 (short name VSX J0457) based on new CCD B, V and I c light curves. Our observations were carried out during six nights in November and December 2016 using the 0.25 m telescope of the Stazione Astronomica Betelgeuse in Magnago, Northern Italy. Six new times of minima and light elements have been determined and the observed light curves were analysed using the Wilson–Devinney code. The output model reveals that the system is a contact binary of A-Subtype of the W Ursae Majoris systems with a mass ratio of q  ∼  0.26 and a degree of contact factor f  ∼  32%. The primary component is hotter than the secondary by 95 K, this suggests us that the system is under thermal contact. The high orbital inclination ( i = 82°.2) implies that VSX J0457 is a total eclipsing binary system and the photometric parameters here obtained are quite reliable. The absolute physical parameters of the two components in VSX J0457 are estimated. Based on these estimated parameters the evolutionary state of the system components is investigated and discussed. Combining our photometric solution with the 3-D correlation obtained for contact binaries by Gazeas (2009) we derive the masses and radii of the components of this eclipsing system as M 1 = 1.44M ⊙ , M 2 = 0.38M ⊙ , R 1 = 1.55R ⊙ and R 2 = 0.87R ⊙ . The distance to VSX J0457 was calculated as 147 pc from this analysis, taking into account interstellar extinction. [ABSTRACT FROM AUTHOR]

The LAMOST spectral survey provides a rich databases for studying stellar spectroscopic properties and chromospheric activity. We cross-matched a total of 105,287 periodic variable stars from several photometric surveys and databases (CSS, LINEAR, Kepler, a recently updated eclipsing star catalogue, ASAS, NSVS, some part of SuperWASP survey, variable stars from the Tsinghua University-NAOC Transient Survey, and other objects from some new references) with four million stellar spectra published in the LAMOST data release 2 (DR2). We found 15,955 spectra for 11,469 stars (including 5398 eclipsing binaries). We calculated their equivalent widths ( EWs ) of their H α , H β , H γ , H δ and Ca ii H lines. Using the H α line EW, we found 447 spectra with emission above continuum for a total of 316 stars (178 eclipsing binaries). We identified 86 active stars (including 44 eclipsing binaries) with repeated LAMOST spectra. A total of 68 stars (including 34 eclipsing binaries) show chromospheric activity variability. We also found LAMOST spectra of 12 cataclysmic variables, five of which show chromospheric activity variability. We also made photometric follow-up studies of three short period targets (DY CVn, HAT-192-0001481, and LAMOST J164933.24+141255.0) using the Xinglong 60-cm telescope and the SARA 90-cm and 1-m telescopes, and obtained new BVRI CCD light curves. We analyzed these light curves and obtained orbital and starspot parameters. We detected the first flare event with a huge brightness increase of more than about 1.5 magnitudes in R filter in LAMOST J164933.24+141255.0. [ABSTRACT FROM AUTHOR]

We determined the orbits and stellar parameters of three eccentric eclipsing binaries by light curve solutions of their Kepler data. KIC 10992733 and KIC 5632781 undergo total eclipses while KIC 10026136 reveals partial eclipses. The components of the targets are G and K stars. KIC 10992733 exhibited variations which were attributed to variable visibility of spot(s) on asynchronously rotating component. KIC 5632781 and KIC 1002613 reveal tidally-induced features at periastron, i.e. they might be considered as eclipsing heartbeat stars. The characteristics of the periastron features (shape, width and amplitude) confirm the theoretical predictions. [ABSTRACT FROM AUTHOR]

New BVRI photometric observations covering seven minima times for the eclipsing binary GSC 3581-1856 were presented. The light curves in BVRI colours were analysed by using PHOEBE code for the system parameters. New minima times were used in revising the light elements. The system is found a W-type contact binary with mass ratio of q = 1.3362 ± 0.0042 and a fill out parameter of f = 16.89 ± 3.17% . The smaller and less massive component was found hotter component ( T 1  ≃  5590 K ). Lower temperature ( T 2 = 5295 K) of the mass accreting more massive component is probably due to a disk or envelope around this star. The original temperature of the more massive secondary component would be at least T 2  ≃  5590 K. The preliminary absolute dimensions ( M 1 = 0.78 ± 0.01 M ⊙ , M 2 = 1.05 ± 0.01 M ⊙ , R 1 = 0.92 ± 0.10 R ⊙ , R 2 = 1.05 ± 0.20 R ⊙ , L 1 =0.86 ± 0.20 L ⊙ and L 2 = 1.00 ± 0.20 L ⊙ ) indicate a relatively young marginal contact binary for GSC 3581-1856 system. The present luminosity of the less massive but hotter component would be not much different from its main sequence luminosity, and thus its original mass was estimated to be slightly more than one solar mass. This means it could be transferred and/or lost about 30% of its original mass which place the system in relatively young system in contact phase. [ABSTRACT FROM AUTHOR]

As part of an effort to better characterize bright cataclysmic variables (CVs) and related systems which have received little attention in the past light curves of four systems (V504 Cen, KT Eri, Ret 1 and CTCV 2056-3014) are analyzed. For some of these stars no time resolved photometry has been published previously. While flickering is observed in all systems except Ret 1, it is particularly strong in V504 Cen and CTCV 2056-3014. In the latter star, a previously observed 15.4 m period, leading to its tentative classification as an intermediate polar, is probably spurious. Variations on time scales of hundredths of days observed in the pre-outburst light curve of the classical nova KT Eri continue after the outburst but appear not to be strictly periodic. Furthermore, the long term post-outburst light curve exhibits modulations with quasi-periods of quite different length. Thus, these variations cannot be due to aspect related variations in a system with a giant component similar to some recurrent novae. Instead, the system possibly exhibits variations with a period of 0.1952 d which may be orbital. However, any such conclusion still requires confirmation. The absence of flickering in Ret 1 indicates that the system probably does not contain an accretion disk. Instead, the observation of slow variations supports a previous suspicion of low amplitude variability with a period  >12 h. [ABSTRACT FROM AUTHOR]

Variability Search Toolkit (VaST) is a software package designed to find variable objects in a series of sky images. It can be run from a script or interactively using its graphical interface. VaST relies on source list matching as opposed to image subtraction. SExtractor is used to generate source lists and perform aperture or PSF-fitting photometry (with PSFEx). Variability indices that characterize scatter and smoothness of a lightcurve are computed for all objects. Candidate variables are identified as objects having high variability index values compared to other objects of similar brightness. The two distinguishing features of VaST are its ability to perform accurate aperture photometry of images obtained with non-linear detectors and handle complex image distortions. The software has been successfully applied to images obtained with telescopes ranging from 0.08 to 2.5 m in diameter equipped with a variety of detectors including CCD, CMOS, MIC and photographic plates. About 1800 variable stars have been discovered with VaST. It is used as a transient detection engine in the New Milky Way (NMW) nova patrol. The code is written in C and can be easily compiled on the majority of UNIX-like systems. VaST is free software available at http://scan.sai.msu.ru/vast/ . [ABSTRACT FROM AUTHOR]

The variable star V1129 Cen is classified in the GCVS as being of β Lyr type. Unusual for such stars, it exhibits outbursts roughly once a year, lasting for ∼ 40 days. For this reason, a relationship to the dwarf novae has been suspected. Here, for the first time a detailed analysis of the light curve of the system is presented. Based on observations with high time resolution obtained at the Observatório do Pico dos Dias and on the long term ASAS light curve the orbital variations of the system are studied. They are dominated by ellipsoidal variations and partial eclipses of a probably slightly evolved F2 star in a binary with an orbital period of 21 h 26 m . Comparison with the characteristics of dwarf novae show that the observational properties of V1129 Cen can be explained if it is just another dwarf novae, albeit with an unusually bright and early type mass donor which outshines the accretion disk and the mass gainer to a degree that many normal photometric and spectroscopic hallmarks of cataclysmic variables remain undetected. [ABSTRACT FROM AUTHOR]

In this article, we present the new product and its description developed by the CoLiTec (Collection Light Technology) project (Khlamov & Savanevych 2020), called CoLiTecVS (CoLiTec Variable Stars) software as a set of tools for the automated light curve creation of variable stars using the sensor data received from the different sensors. CoLiTecVS allows performing the photometry and light curve creation with minimal user interaction in two different modes. The first one is an observation mode when the data are received online from the sensors directly and immediately processed by the OnLine Data Analysis System (OLDAS). This mode is called "OLDAS-Night" mode. The second one is processing the existing observations when sensor data are already received and saved. This mode is called "CoLiTec-Day" mode. Nowadays, the modern sensors (robotic ground-based telescopes equipped with different cameras with charge-coupled device (CCD)) still have a lack of capabilities, like non-uniform sensitivity of the matrix pixels, non-linearity of the pixel response to the number of photons that have fallen, oversaturation of bright objects leads to charge transfer to neighboring pixels and the presence of cold or hot pixels. All these shortcomings of modern sensors complicate the process of obtaining the accurate photometric measurements. Such lack of capabilities of modern sensors also makes the plotting of light curves a difficult and routine task. The latter shifts astronomer's main attention from research to the very time-consuming tasks of processing sensor data and light curve creation. To solve this problem, we developed a new tool for the automated reduction of photometric observations, which includes the computational method for the brightness assessment of the investigated and comparison stars; brightness equalization of astronomical images using an inverse median filter; and light curve plotting and its processing using different tools. This new CoLiTecVS software provides a tool for high accurate stellar brightness measuring and automated light curve creation with aperture photometry uncertainties less than 0.04 magnitude, the value of which generally depends on various imaging characteristics of telescopes, detectors, and sensors. CoLiTecVS has been tested on many different time series of 20-600 CCD-frames with variable stars and has produced high-quality photometric light curves in a fraction of the usual processing time. [ABSTRACT FROM AUTHOR]

Abstract: Achromatic breaks in afterglow light curves of gamma-ray bursts (GRBs) arise naturally if the product of the jet’s Lorentz factor and opening angle satisfies at the onset of the afterglow phase, i.e., soon after the conclusion of the prompt emission. Magnetohydrodynamic (MHD) simulations of collimated GRB jets generally give , suggesting that MHD models may be inconsistent with jet breaks. We work within the collapsar paradigm and use axisymmetric relativistic MHD simulations to explore the effect of a finite stellar envelope on the structure of the jet. Our idealized models treat the jet–envelope interface as a collimating rigid wall, which opens up outside the star to mimic loss of collimation. We find that the onset of deconfinement causes a burst of acceleration accompanied by a slight increase in the opening angle. In our fiducial model with a stellar radius equal to times that of the central compact object, the jet achieves an asymptotic Lorentz factor far outside the star and an asymptotic opening angle , giving . These values are consistent with observations of typical long-duration GRBs, and explain the occurrence of jet breaks. We provide approximate analytic solutions that describe the numerical results well. [Copyright &y& Elsevier]