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Massive Search for Spot- and Facula-Crossing Events in 1598 Exoplanetary Transit Light Curves

Baluev R. V., Sokov E. N., Sokova I. A., Shaidulin V. Sh., Veselova A. V., Aitov V. N., Mitiani G. Sh., Valeev A. F., Gadelshin D. R., Gutaev A. G., Beskin G. M., Valyavin G. G., Antonyuk K., Barkaoui K., Gillon M., Jehin E., Delrez L., Guðmundsson S., Dale H. A., Fernández-Lajús E., Di Sisto R. P., Bretton M., Wunsche A., Hentunen V.-P., Shadick S., Jongen Y., Kang W., Kim T., Pakštienė E., Qvam J. K. T., Knight C. R., Guerra P., Marchini A., Salvaggio F., Papini R., Evans P., Salisbury M., Garlitz J., Esseiva N., Ogmen Y., Bosch-Cabot P., Selezneva A., Hinse T. C.

Acta Astronomica

2021

Vol. 71, No. 1

25--53

We developed a dedicated statistical test for a massive detection of spot- and facula-crossing anomalies in multiple exoplanetary transit light curves, based on the frequentist p-value thresholding. This test was used to augment our algorithmic pipeline for transit light curves analysis. It was applied to 1598 amateur and professional transit observations of 26 targets being monitored in the EXPANSION project. We detected 109 statistically significant candidate events revealing a roughly 2:1 asymmetry in favor of spots-crossings over faculae-crossings. Although some candidate anomalies likely appear non-physical and originate from systematic errors, such asymmetry between negative and positive events should indicate a physical difference between the frequency of star spots and faculae. Detected spot-crossing events also reveal positive correlation between their amplitude and width, possibly due to spot size correlation. However, the frequency of all detectable crossing events appears just about a few per cent, so they cannot explain excessive transit timing noise observed for several targets.

DV Psc: A Magnetically Active Hierarchical Triple System

Gazeas K., Palafouta S.

Acta Astronomica

2019

Vol. 69, No. 3

261--282

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.

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

2018

Vol. 68, No. 4

425--447

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.

Photometric Observations of LO Peg in 2014-2015

Savanov I. S., Puzin V. I., Dmitrienko E. S., Karpov S. V., Beskin G. M., Biryukov A. V., Bondar S. F., Ivanov E. A., Katkova E. V., Orekhova N., Perkov A. V., Sasyuk V. V., Romanyuk I. I., Semenko E. A., Kudryavtsev D., Karmakar S., Pandey J. C., Pandey S. B., Joshi S., Misra K.

Acta Astronomica

2016

Vol. 66, No. 3

381--390

We performed new observations of an ultra-fast rotator of the spectral class K - the LO Peg star - in SAO RAS in 2014 and in Zvenigorod Observatory of INASAN in 2015. The light curves were used to build the maps of temperature inhomogeneities on the LO Peg surface in order to determine the longitudes corresponding to the location of active regions. The obtained measurements suggest the ongoing evolution of movements of active regions and probably the cyclic character of such movements. According to our estimations, the area of the star surface covered with spots decreases and by now it reached 14% of the total visible area of its surface. New observations of the star in V filter allowed us to specify LO Peg long-term variability cycles. Based on spectropolarimetric observations of LO Peg the null result for measurements of mean longitudinal component of magnetic field is obtained.

CCD Photometry, Roche Modeling and Evolutionary History of the W UMa-type Eclipsing Binary TYC 01664-0110-1

Alton K. B., Stępień K.

Acta Astronomica

2016

Vol. 66, No. 3

357--379

TYC 01664-0110-1 (ASAS J212915+1604.9), a W UMa-type variable system (P=0.282962 d), was first detected over 17 years ago by the ROTSE-I telescope. Photometric data (B, V and Ic) collected at UnderOak Observatory (UO) resulted in five new times-of-minima for this variable star which were used to establish a revised linear ephemeris. No published radial velocity (RV) data are available for this system. However, since this W UMa binary undergoes a total eclipse, Roche modeling based on the Wilson-Devinney (W-D) code yielded a well-constrained photometric value for M2/M1 (q=0.356±0.001). There is a suggestion from ROTSE-I (1999) and ASAS survey data (2003, 2005, and 2008) that the secondary maximum is more variable than the primary one probably due to the so-called O'Connell effect. However, peak asymmetry in light curves (LC) from 2015 was barely evident during quadrature. Therefore, W-D model fits of these most recent data did not yield any substantive improvement with the addition of spot(s). Using the evolutionary model of cool close binaries we searched for a possible progenitor of TYC 01664-0110-1. The best fit is obtained if the initial binary has an orbital period between 3.3-3.8 d and component masses between 1.0-1.1 M⊙ and 0.30-0.35 M⊙. The model progenitor needs about 10 Gyr to attain the presently observed parameters of the variable. Its period slowly increases and the mass ratio decreases. According to the model predictions TYC 01664-0110-1 will go through the common envelope (CE) phase in the future, followed by merging of both components or formation of a double degenerate. Due to its apparent brightness (mV,max≈10.9 mag) and unique properties, the star is an excellent target for spectroscopic investigation of any possible deviations from a simple static model of a contact binary.

Eclipsing Binary Stars in the OGLE-III Galactic Disk Fields

Pietrukowicz P., Mróz P., Soszyński I., Udalski A., Poleski R., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K., Kozłowski S., Skowron J.

Acta Astronomica

2013

Vol. 63, No. 2

115--133

We present the analysis of 11589 eclipsing binary stars identified in twenty-one OGLE-III Galactic disk fields toward constellations of Carina, Centaurus, and Musca. All eclipsing binaries but 402 objects are new discoveries. The binaries have out-of-eclipse brightness between I=12.5 mag and I=21 mag. The completeness of the catalog is estimated at a level of about 75%. Comparison of the orbital period distribution for the OGLE-III disk binaries with systems detected in other recent large-scale Galactic surveys shows the maximum around 0.40 d and an almost flat distribution between 0.5 d and 2.5 d, independent of population. Ten doubly eclipsing systems and one eclipsing-ellipsoidal object were found among thousands of variables. Nine of them are candidates for quadruple systems. We also identify ten eclipsing subdwarf-B type binary stars and numerous eclipsing RS CVn type variables. All objects reported in this paper are part of the OGLE-III Catalog of Variable Stars.