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1

Blue Large-Amplitude Pulsators and Other Short-Period Variable Stars in the OGLE-IV Galactic Disk Fields

Borowicz J., Pietrukowicz P., Mróz P., Soszyński I., Udalski A., Szymański M. K., Ulaczyk K., Poleski R., Kozłowski S., Skowron J., Skowron D. M., Rybicki K., Iwanek P., Wrona M., Gromadzki M.

Acta Astronomica

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2023

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Vol. 73, No. 1

1--19

EN

Blue Large-Amplitude Pulsators (BLAPs) form a mysterious class of variable stars with typical periods of tens of minutes and amplitudes above 0.1 mag. In this work, we present results of a variability search focused on timescales shorter than 1 h, conducted in OGLE-IV Galactic disk fields containing about 1.1 billion stellar sources down to I≈20 mag. Twenty-five BLAPs have been detected, 20 of which are new discoveries. Their periods range from 8.4 min to 62.1 min. We have also found six new eclipsing binary systems with orbital periods from 38.3 min to 121.3 min and five short-period large-amplitude (> 0.17 mag in the I-band) variable stars of unknown type.

2

TIC 452991707 and TIC 452991693 as a Candidate Sextuple System with Three Eclipsing Binaries

Zasche P., Henzl Z.

Acta Astronomica

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2022

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Vol. 72, No. 2

103--111

EN

We present the discovery of a rare system detected in the TESS data showing three different eclipsing-like signals. TIC 452991707 and TIC 452991693 seem to be the second such system on the sky, whose two components separated about 16" are gravitationally bounded, or comprise a co-moving pair. The three periods detected from the TESS data are: PA=1.46155 d, PB= 1.77418 d, and PC=1.03989 d, respectively. The A and B periods belong to TIC 452991707, while the C comes from the component TIC 452991693. The pair A shows the deepest eclipses, and its orbit is very slightly eccentric. The third period C has lowest amplitude (eclipsing or ellipsoidal nature), but originates from TIC 452991693, which is connected to A+B because both visual components share similar proper motion and distance. Long-term collection of data from older photometry from various surveys also shows that the two inner pairs A and B orbit around their barycenter. Its period is probably of a few years, but for a final derivation of its orbital parameters one needs more up-to-date data. Hence, we call for new observations of this amazing system.

3

RR Draconis: An Algol-Type Eclipsing Binary with a Possible Massive Tertiary Companion

Şenavcı H. V., Čeki A., Esmer E. M., Yalçınkaya S., Latković O., Bahar E., Yılmaz M, Bastürk Ö., Özavcı İ., Yörükoğlu O., Selam S. O.

Acta Astronomica

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2022

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Vol. 72, No. 1

31--53

EN

In this study, we present spectoscopic observations of the eclipsing binary RR Dra carried out with our recently installed T80 telescope in Ankara University Kreiken Observatory and analyze the first radial velocity time series of this system. We simultaneously model TESS light curves along with our radial velocity data to derive absolute parameters of RR Dra system. Additionally, we investigate the period variation of the system using all the available eclipse timings in the literature. In this context, we discuss two possible explanations for the cyclic nature of the eclipse timings: i) light-time effect that corresponds to a high-mass but unseen additional component, ii) magnetic activity of the cooler component. The secular period increase in eclipse timings of RR Dra may be a combination of mass transfer and angular momentum loss, amplified by the presence of circumstellar material.

4

New Photometric and Spectroscopic Observations of the Eclipsing Binary V2080 Cygni

Dimitrov W., Kamiński K., Bąkowska K., Kamińska M. K., Tokarek J., Pawłowski M., Boneva D., Bartczak P., Kwiatkowski T., Schwarzenberg-Czerny A.

Acta Astronomica

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2022

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Vol. 72, No. 1

55--67

EN

We present new spectroscopic and photometric measurements of the eclipsing binary V2080 Cyg. It is a detached system with similar components and an orbital period of 4.9 d. We collected spectroscopic data with two instruments, 1.88 m DDO telescope equipped with Cassegrain spectrograph and 0.5 m PST1 connected to a fiber-fed echell\'e spectrograph. We collected 127 measurements for each component, which significantly increase the number of available radial velocity measurements for the V2080 Cyg system. Obtained masses of the eclipsing components are M1=1.189± 0.007 and M2=1.138±0.007 M☉. We also collected a multicolor photometry. The three-band light curves obtained together with the radial velocity data enabled us to calculate the model of the system. New estimations of the orbital inclination and radii of the components were computed. We obtained as well new times of minima. The O-C diagrams indicate variation, which requires more recent data to be confirmed. The possible existence of a third body could cause a light-time effect in the system. In addition, we analyze the Gaia mission results. V2080 Cyg A has three visual companions. However, according to Gaia parallaxes and proper motions, they cannot be dynamically connected with the eclipsing binary and therefore are background stars.

5

Light Curve Modeling of Four Short-Period W UMa Binaries

Čeki A., Latković O.

Acta Astronomica

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2022

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Vol. 72, No. 3

183--194

EN

We use extensive model grids to estimate the global parameters of four partially-eclipsing W UMa contact binaries near the period cutoff. All four systems consist of K-type main sequence primaries and M-type secondaries that appear undersized and underluminous for their masses because of the energy transfer through the common envelope. Three of the four stars exhibit light curve asymmetry that is explained in terms of magnetic activity and modeled with dark spots. We discuss the reliability of the photometric mass ratios and derived absolute parameters in context of total or partial eclipses and compare them with a sample of totally-eclipsing short-period W UMa systems from the literature.

6

A Method of Improving Standard Stellar Luminosities with Multiband Standard Bolometric Corrections

Bakış V., Eker Z.

Acta Astronomica

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2022

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Vol. 72, No. 3

195--232

EN

Standard luminosity (L) of 406 main-sequence stars with the most accurate astrophysical parameters are calculated from their absolute magnitudes and bolometric corrections at Johnson BV, and Gaia EDR3 G, GBP, GRP filters. Required multiband BC and BC-Teff relations are obtained first from the parameters of 209 Double-lined Detached Eclipsing Binaries with main-sequence components and Gaia EDR3 parallaxes. A simplified SED is formulated to give filter dependent component light contributions and interstellar dimming, which are essential in computing BC of a component, virtually at any filter. The mean standard L of a star is calculated from the mean Mbolwhich is a mathematical average of independent Mboll values predicted at different filters, while the uncertainty of L is the uncertainty propagated from the uncertainty of the mean Mbol. The mean standard L of the sample stars are compared to the corresponding L values according to the Stefan-Boltzmann law. A very high correlation (R2>0.999) is found. Comparing histogram distributions of errors shows that uncertainties associated with the mean standard L (peak at ≈2.5 per cent) are much smaller than the uncertainties of L (peak at ≈8 per cent) by the Stefan-Boltzmann law. Increasing the number of filters used in predicting the mean Mbol increases the accuracy of the standard stellar luminosity. Extinction law, color-color relations and color excess vs. color excess relations for Gaia passbands are presented for the first time for main-sequence stars.

7

Roche Modeling and Evolutionary History of Six Low Mass Contact Binary Systems

Alton K. B., Stępień K.

Acta Astronomica

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2021

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Vol. 71, No. 2

123--161

EN

We describe six eclipsing binary systems that were first detected by the ROTSE-I telescope and ultimately shown to be low mass contact binaries (LMCB). New photometric data (B, V and Ic) acquired from V473 Cam, PV Com, EI CVn, V2790 Ori, V2802 Ori and PS Vir were used to calculate an orbital period for each system along with updated ephemerides. All systems were subject to secular changes in orbital period with evidence for a third gravitationally bound body in V473 Cam, EI CVn, V2790 Ori, and PS Vir. Since a total eclipse is observed in all six systems, Roche modeling based on the Wilson-Devinney (WD) code yielded in each case a well-constrained photometric value for the mass ratio. Potential progenitors of these LMCBs were evaluated using an evolutionary model of cool close binaries. The best fits were obtained when the initial detached binaries have orbital periods ranging from 2.70 d to 3.71 d, total masses between 1.36 M and 1.53 M with mass ratios ranging from 2.34 to 4.04. The model progenitors require between 7.75-10.9 Gyr to attain the presently observed orbital period and physical attributes. Collectively, the models show that about half of orbital periods will increase in the future leading to a common envelope resulting from the evolutionary expansion of the accretor whereas the other half will decrease resulting in the overflow of the outer critical Roche surface and an ultimate merger.

8

The Clusters AgeS Experiment (CASE). Variable Stars in the Field of the Globular Cluster NGC 3201

Rozyczka M., Pych W., Thompson I. B., Mazur B.

Acta Astronomica

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2020

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Vol. 70, No. 4

291--299

EN

We report the detection of 20 new variables in the field of NGC 3201. Among them there are 15 confirmed cluster members. Follow-up observations are desirable for two blue stragglers with variable light curves (probably resulting from magnetic activity), and for a yellow straggler coinciding with a Chandra X-ray source. Two of the eclipsing binaries, newly detected at the turnoff in cluster's CMD, and an eclipsing binary on the red giant branch, are potentially suitable for the determination of age and distance of NGC 3201.

9

Orbital Period Analysis of Four Eclipsing Binaries XY Boo, RW Com, MR Del and AK Her

Özavcı İ., Özuyar D., Şenavcı H. V., Yılmaz M, Bahar E., Baştürk Ö., Kılıçoğlu T., Elmaslı A., Çalışkan Ş., İzci D. D., Yörükoğlu O., Selam S. O.

Acta Astronomica

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2020

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Vol. 70, No. 1

33--52

EN

The orbital period variations of the eclipsing binaries XY Boo, RW Com, MR Del, and AK Her are investigated. This study includes the first orbital period analysis of the detached eclipsing binary MR Del and necessary updates for the remaining stars with addition of new mid-eclipse times calculated from our recent observations carried out at Ankara University Kreiken Observatory. The analysis shows that the period variations may result from mass exchange/loss and a third body for XY Boo, two additional bodies for RW Com, a substellar third component for MR Del, and mass exchange/loss, additional bodies and/or magnetic activity for AK Her. The hypothetical third component of MR Del with an estimated mass of 0.069 M⊙, appears to be very close to the borderline between stars and brown dwarfs.

10

On the Pulsations of the δ Scuti Star of the Binary System KIC 6629588

Liakos A.

Acta Astronomica

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2020

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Vol. 70, No. 4

265--289

EN

his work includes a comprehensive analysis of the Kepler detached eclipsing binary system KIC 6629588 that aims at the detailed study of the oscillation properties of its pulsating component. Ground-based spectroscopic observations were obtained and used to classify the components of the system. The spectroscopic results were used as constraints for the modeling of the short-cadence Kepler light curves and for the estimation of the absolute parameters of the components. Furthermore, the light curve residuals are analyzed using Fourier transformation techniques in order to search for pulsation frequencies. The primary component of the system is identified as a δ Sct star that pulsates in seven eigenfrequencies in the range of 13-22 d-1, while more than 270 combination frequencies were also detected. The absolute and the oscillation parameters of this pulsating star are compared with those of other δ Sct stars members of detached binary systems using evolutionary and correlation diagrams. Finally, the distance to the system is also estimated.

11

A Comprehensive Study of the Eclipsing Binaries V1241 Tau and GQ Dra

Ulaş B., Gazeas K., Liakos A., Ulusoy C., Stateva I., Erkan N., Napetova M., Iliev I. K.

Acta Astronomica

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2020

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Vol. 70, No. 3

219--240

EN

We present new photometric and spectroscopic observations and analyses for the eclipsing binary systems V1241 Tau and GQ Dra. Our photometric light and radial velocity curve analyses combined with the TESS light curves show that both are conventional semi-detached binary systems. Their absolute parameters are also derived. We present the O-C analyses of the systems and we propose the most likely orbital period modulating mechanisms. Furthermore, Fourier analyses are applied to the photometric residual data of the systems to check for the pulsational behavior of the components. We conclude that the primary component of the system GQ Dra is a δ Sct type pulsator with a dominant pulsation frequency of 18.58 d-1 based on our B filter residual light curve although it can not be verified by 30-minute cadence TESS data. No satisfactory evidence of pulsational behavior for V1241 Tau was verified. Finally, the evolutionary tracks of the components of both systems are calculated. Their locations within evolutionary diagrams are compared with other Algol-type systems.

12

Triple Eccentric Systems V0345 Lac, YY Sgr, and DR Vul

Wolf M., Zasche P., Kučáková H., Mašek M., Hoňková K., Juryšek J., Paschke A., Šmelcer L., Zejda M.

Acta Astronomica

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2019

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Vol. 69, No. 1

63--78

EN

We present more results of our long-term observational project to analyze the variations of the orbital period for early-type eccentric eclipsing binaries. About sixty new precise mid-eclipse times were measured or derived for three eclipsing binaries, namely V0345 Lac, YY Sgr, and DR Vul. Based on current O-C diagrams, we found in all cases that beside the typical apsidal motion the times of minima show additional cyclical changes likely caused by a third body orbiting the eclipsing pair. The new light curve solution of V0345 Lac results in a moderate orbital eccentricity (e=0.26) of this binary. The periods of apsidal motion are 1580 yr, 295 yr, and 36 yr, respectively. The relativistic contributions to the total apsidal-motion rate are small for all three eccentric binaries - about 5-14%. The third-body orbital periods are relatively short: 24 yr, 19 yr and 66 yr, and the minimal masses of third bodies are: 2.0 M☉, 0.8 M☉, and 7.2 M☉, respectively.

13

DV Psc: A Magnetically Active Hierarchical Triple System

Gazeas K., Palafouta S.

Acta Astronomica

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2019

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Vol. 69, No. 3

261--282

EN

The eclipsing binary system DV Psc has been known to be magnetically active for almost two decades. However, there has been no evidence of a magnetic cycle on this system until recently. This study focuses on the long-term photometric monitoring of DV Psc between 2005-2017. A total of 50 individual light curves in BVRI optical bands were collected, in order to investigate its magnetic activity and cycle, as well as determine its orbital and physical properties. The combined photometric and spectroscopic observations of this study resulted in a unified model for the system, which describes accurately the light curves throughout the years, as a result of the variable spot activity. A total of 105 new times of minimum light are calculated through the entire time span of observations and they are combined with the 203 bibliographic ones since 1997, increasing significantly the existing sample. This resulted in an accurate ephemeris and an updated O-C diagram for a total span of 20 yr (1997-2017). It is found that the system exhibits intense magnetic activity, which is shown through the strong asymmetries on the light curves (O'Connell effect) and the periodic variation of the O-C diagram. The existence of a third body, orbiting the eclipsing binary with a period of Porb=9.79±0.60 yr in an eccentric orbit with eccentricity e=0.83±0.24, as well as a magnetic cycle of 14.74±0.84 yr are most likely connected with this variability. The absolute physical parameters of the system are calculated for a new and unified model, which explains the light curves through the entire observing season. The evolution state of DV Psc is studied through the mass-radius and temperature-luminosity (HR) diagrams, as well as the location of the two components with respect to the ZAMS and TAMS region.

14

Spectroscopy of the Eclipsing Binary BD-00°2862. Possible Multiplicity

Dimitrov W., Żywucka N, Polińska M., Kamiński K., Kamińska M. K.

Acta Astronomica

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2018

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Vol. 68, No. 3

269--284

EN

We present the first spectroscopic analysis of the eclipsing binary BD-00°2862. The All Sky Automated Survey light curves yield orbital period of the system of 2.15 d. The shape of the light curve reveals that the components are almost spherical and the binary is detached. The eclipses depths show significant difference of the components' temperature. We acquired spectra with 0.5-m telescope equipped with an echellé spectrograph. The spectra are dominated by the lines of the more luminous component, which is about five times more luminous than its close companion. Obtained radial velocities together with the light curves enabled us to obtain a model of the system using the Wilson-Devinney method. The mass ratio of the stars is 0.67 and the size of the semi-major axis is 8.6 R⊙. The masses of the eclipsing components are M1=1.08±0.03 M⊙ and M2=0.72±0.02 M⊙. The stars are not evolved and the radii are close to the main sequence values: R1=1.21±0.01 R⊙ and R2=0.71±0.01 R⊙. The evolutionary tracks show that the system is probably on the pre main sequence stage. The photometric parallax yields distance of 131 pc, which is comparable with the one obtained by Gaia mission - 130 pc. We carried out a spectrum analysis for the main component obtaining its temperature of 5600±400 K and the metallicity - [M/H]=-0.30±0.20. The star has a visual companion separated by about 12". The companion has proper motion comparable to the one of the main star. Additionally, its distance based on the trigonometric parallax is equal within errors with the distance of component A. Therefore, the companion is probably a part of the system. Its spectral type is M3 and the estimated mass - about 0.3M⊙.

15

Roche Modeling and Evolutionary History of Multiple Low Mass Contact Binary Systems

Alton K. B., Stępień K.

Acta Astronomica

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2018

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Vol. 68, No. 4

449--482

EN

The Northern Sky Variable Survey (NSVS) has been a rich source of variable stars many of which have only been studied to a limited extent. Herein we describe five eclipsing binary systems that were first detected by the ROTSE-I telescope and ultimately shown to be low mass contact binaries. Photometric data (B, V and Ic) acquired from MU Cnc (NSVS 10133793, TYC 1397-1030-1), V596 Peg (NSVS 6225359, GSC 2765-0348), TYC 1597-2327-1 (NSVS 11082150), GSC 2723-2376 (NSVS 8849526) and GSC 4946-0765 (NSVS 13176410) were used to calculate an orbital period for each system along with new linear ephemerides. Except for MU Cnc, the limited number of time-of-minimum values precluded the characterization of any long-term period change. Since a total eclipse is observed with all five systems, Roche modeling based on the Wilson-Devinney W-D code yielded in each instance a well-constrained photometric value for the mass ratio. Using the evolutionary model of cool close binaries we searched for possible progenitors of the investigated binaries. The best fit is obtained if the initial binaries have orbital periods from the interval between 2.4–3.4 d, total masses between 6% and 9% higher than presently observed and mass ratios between 2.2 and 3.3. The model progenitors need between 7.5–10 Gyr to attain the presently observed parameters of the variables. The present periods of three models slowly increase with simultaneous mass ratio decrease, which suggests the formation of the common envelope in the future. However, in four other models the period decreases and the model computations predict the ultimate overflow of the outer Roche lobe.

16

Hybrid Pulsations and Tidal Splitting detected in the Kepler Eclipsing and Spotted Binary System KIC 6048106

Samadi Ghadim A., Lampens P., Jassur D. M.

Acta Astronomica

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2018

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Vol. 68, No. 4

425--447

EN

We present a new asteroseismic analysis of KIC 6048106, a Kepler Algol-type eclipsing binary star in a circularized orbit with Porb=1.559361±0.000036 d. Based on a physical model for the binary and its corresponding set of fundamental parameters (Teff=7033±187 K, M1=1.55±0.11 M☉, R1=1.58±0.12 R☉ and Teff=4522±103 K, M2=0.33±0.07 M☉, R2=1.78±0.16 R☉, respectively for the primary and the secondary component), we obtained the residual light curve after removal of the full binary model, including a 290-d activity cycle for the secondary component. In this work, we used the method of Fourier analysis of the residual light curve in combination with least squares optimization for the frequency analysis. We detected seven dominant, independent gravity (g) modes as well as 34 low-amplitude acoustic (p) modes. The g modes in the range of 1.96–2.85 d-1 have a mean spacing of ΔΠmean=1517.92±131.54 s. Though of much lower amplitude, additional significant frequencies were detected in the intervals 7.49–15.2 d-1 and 19–22.5 d-1 (i.e., in the p mode region), with corresponding dominant modes νmax1=11.745±0.001 d-1 and νmax2=20.960±0.002 d-1 From its position in the HR diagram, we conclude that the primary component is the source of the detected hybrid pulsations. Consequently, the pulsation constants, Q, of the high frequencies cover the range of 0.028–0.064 d. Furthermore, ν43 (19.037±0.002 d-1) might correspond to the fundamental radial mode (Q=0.033±0.007 d). The other frequencies in the range of 19–22.5 d-1 could be radial or non-radial overtone modes. Moreover, the low-amplitude p modes show an equidistant splitting by forb, which we interpret as tidal splitting following theoretical predictions.

17

GT Ursae Majoris AB - a Possible Quadruple System

Dimitrov W., Tomov T., Kamiński K., Polińska M., Iliev I., Kamińska M. K.

Acta Astronomica

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2018

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Vol. 68, No. 2

141--158

EN

We present the first spectroscopic study of an eclipsing system GT UMa. Our spectra show that the main visual component A is a triple-lined star, which consists of a close eclipsing pair and a farther third component. Radial velocity measurements show evidence of reflex motion. We used Hipparcos and our own R-band light curves for the analysis. These results enabled us to calculate absolute parameters of the eclipsing binary system: 1.37 M⊙ and 1.31 M⊙ and corresponding radii 2.11 R⊙ and 1.63 R⊙. Both eclipsing components are evolved. The orbital period of the eclipsing subsystem is 1.2 d and the semi-major axis - 6.5 R⊙. The wide orbit has low radial velocity amplitude and its parameters are difficult to determine. We obtained a preliminary solution which must be confirmed with future observations. The preliminary period of the wide orbit is 394 d and the lower limit for the semi-major axis - 174 R⊙ (0.81 a.u.). We estimated the mass of the third body to about 1.1 M⊙. Additionally, we investigated the visual companion B. We obtained spectra of this star and measured the radial velocity which is very close to the one of the component A. The proper motions and the parallax are also similar. These are strong arguments that component B is gravitationally bound with the main triple system A.

18

CCD Photometry, Light Curve Modeling and Period Analysis of the Overcontact Eclipsing Binary BN Ari

Alton K. B., Nelson R. H., Boyd D. R. S.

Acta Astronomica

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2018

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Vol. 68, No. 2

159--181

EN

We present photometric and spectroscopic data of BN Ari, a totally eclipsing variable star. 15 new times-of-minimum have been determined. These along with other published eclipse timings were used to update the linear ephemeris and evaluate changes in orbital periodicity. Radial velocity data along with a definitive classification spectrum are reported for the first time. Simultaneous modeling of multicolor light curves and radial velocity data was accomplished using the Wilson-Devinney code with optimization by differential corrections. The weight of evidence from evaluating both the eclipse timing differences and light curve modeling indicates that BN Ari is most likely a triple system.

19

The Triple Eccentric Systems V974 Cyg, RU Mon, and V456 Oph

Wolf M., Zasche P., Kučáková H., Hoňková K., Juryšek J., Mašek M., Uhlař R., Urbaník M.

Acta Astronomica

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2017

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Vol. 67, No. 3

257--271

EN

We present results of a long-term program for timing the eclipses of eccentric eclipsing binaries. About 40 new precise mid-eclipse times were measured for the eclipsing binary V974 Cyg, RU Mon and V456 Oph. Based on current O-C diagrams, we found in all cases that times of minima besides the typical apsidal motion show additional cyclical changes caused very probably by the third bodies orbiting the eclipsing pair. The periods of apsidal motion are 1470 yr, 361 yr and 22.6 yr, respectively. The period of V456 Oph this is one of the shortest known apsidal-motion periods. The relativistic contributions to the total apsidal-motion rate are significant for V974 Cyg (about 30%) and negligible for RU Mon and V456 Oph (1-2.5%). The third-body orbital periods are relatively short: 30.6 yr, 59.8 yr and 7.4 yr, and their minimal masses are 0.40 M☉, 1.6 M☉, and 0.27 M☉, respectively.

20

The Strange Case of OGLE-SMC-ECL-0277

Zasche P., Wolf M., Vraštil J., Fatka P., Galád A., Hornoch K., Janák Z., Janík J., Kortusová E., Kurfürst P., Kušnirák P., Paunzen E., Řezba L., Votruba V., Zejda M., Zieliński P.

Acta Astronomica

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2017

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Vol. 67, No. 3

243--255

EN

The eclipsing system OGLE-SMC-ECL-0277 was found to exhibit unusual photometric variability. Beside its eclipsing nature additional variations with the periodicity of about 1500~d are also seen. Variations of the eclipse depth during the time span of the observational data (mainly taken from the OGLE survey, partly our new ones) are the most pronounced. The complex behavior of all these changes makes this system absolutely unique, no such variability was ever detected and studied in other systems before. Hence, are there some new phenomena, new physics or an unknown effects playing a role? We tried to understand these variations using four different hypotheses (\ie inclination change, spot evolution, and/or pulsation of one or both components) and comparing their results we discussed which of them is the most likely. Neither of the presented hypotheses is able to describe in detail the behavior of OGLE-SMC-ECL-0277. We also discuss a possibility that the variable can be a member of the so-called double periodic variables group.