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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.

2

Contemporaneous Broad-Band Photometry and Hα Observations of T Tau Stars

Frasca A., Montes D., Alcalá J. M., Klutsch A., Guillout P.

Acta Astronomica

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2018

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Vol. 68, No. 4

403--424

EN

In this paper we present the results of a simultaneous BVRI and Hα photometric monitoring, contemporaneous to medium-resolution spectroscopy of six T Tau stars in the Taurus-Auriga star forming region. We have characterized the Hα photometric system using synthetic templates and the contemporaneous spectra of the targets. We show that we can achieve a precision corresponding to 2–3 Å in the Hα equivalent width, in typical observing conditions. The spectral analysis has allowed us to determine the basic stellar parameters and the values of quantities related to the accretion. In particular, we have measured a significant veiling only for the three targets with the strongest Hα emission (T Tau, FM Tau, and DG Tau). The broad-band photometric variations are found to be in the range of 0.05–0.70 mag and are often paired to variations in the Hα intensity, which becomes stronger when the stellar continuum is weaker. In addition, we have mostly observed a redder V-I and a bluer B-V color as the stars become fainter. For most of the targets, the timescales of these variations seem to be longer than the rotation period. One exception is T Tau, for which the broad-band photometry varies with the rotation period. The most plausible interpretation of these photometric and Hα variations is that they are due to non-stationary mass accretion onto the stars, but rotational modulation can play a major role in some cases.

3

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

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2016

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Vol. 66, No. 3

381--390

EN

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.

4

Light Curves of Symbiotic Stars in Massive Photometric Surveys II. S and D'-Type Systems

Gromadzki M., Mikołajewska J., Soszyński I.

Acta Astronomica

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2013

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Vol. 63, No. 4

405--428

EN

We present results of period analysis of ASAS, MACHO and OGLE light curves of 79 symbiotic stars classified as S and D'-type. The light curves of 58 objects show variations with the orbital period. In case of 34 objects, orbital periods are estimated for the first time, which increases the number of symbiotic stars with known orbital periods by about 64%. The light curves of 46 objects show, in addition to the long-term or/and orbital variations, short-term variations with time scales of 50-200 days most likely due to stellar pulsations of the cool giant component. We also report eclipse-like minima and outbursts present in many of the light curves.

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Evolution of Cool Close Binaries - Rapid Mass Transfer and Near Contact Binaries

Stępień K., Kiraga M.

Acta Astronomica

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2013

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Vol. 63, No. 2

239--266

EN

We test the evolutionary model of cool close binaries developed by one of us (KS) on the observed properties of near contact binaries (NCBs). These are binaries with one component filling the inner critical Roche lobe and the other almost filling it. Those with a more massive component filling the Roche lobe are SD1 binaries whereas in SD2 binaries the Roche lobe filling component is less massive. Our evolutionary model assumes that, following the Roche lobe overflow by the more massive component (donor), mass transfer occurs until mass ratio reversal. A binary in an initial phase of mass transfer, before mass equalization, is identified with SD1 binary. We show that the transferred mass forms an equatorial bulge around the less massive component (accretor). Its presence slows down the mass transfer rate to the value determined by the thermal time scale of the accretor, once the bulge sticks out above the Roche lobe. It means, that in a binary with a (typical) mass ratio of 0.5 the SD1 phase lasts at least 10 times longer than resulting from the standard evolutionary computations neglecting this effect. This is why we observe so many SD1 binaries. Our explanation is in contradiction to predictions identifying the SD1 phase with a broken contact phase of the Thermal Relaxation Oscillations model. The continued mass transfer, past mass equalization, results in mass ratio reversed. SD2 binaries are identified with this phase. Our model predicts that the time scales of SD1 and SD2 phases are comparable to one another. Analysis of the observations of 22 SD1 binaries, 27 SD2 binaries and 110 contact binaries (CBs) shows that relative number of both types of NCBs favors similar time scales of both phases of mass transfer. Total masses, orbital angular momenta and orbital periods of SD1 and SD2 binaries are indistinguishable from each other whereas they differ substantially from the corresponding parameters of CBs. We conclude that the results of the analysis fully support the model presented in this paper.

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ASAS Photometry of ROSAT Sources. II. New Variables from the ASAS North Survey

Kiraga M., Stępień K.

Acta Astronomica

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2013

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Vol. 63, No. 1

53--66

EN

We present a catalog of 307 optical counterparts of the bright ROSAT X-ray sources, identified with the ASAS North survey data and showing periodic brightness variations. They all have declination north of -25°. Other data available from the literature for the listed stars are also included. All the tabulated stars are new variables, except for 13 previously known, for which the revised values of periods are given.

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The Optical Gravitational Lensing Experiment. Optical Counterparts to the X-ray Sources in the Galactic Bulge

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

Acta Astronomica

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2012

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Vol. 62, No. 2

133--151

EN

We present a sample of 209 variable objects - very likely optical counterparts to the X-ray sources detected in the direction of the Galactic center by the Galactic Bulge Survey (GBS) carried out with the Chandra satellite. The variable sources were found in the databases of the OGLE long term survey monitoring regularly the Galactic bulge since 1992. The counterpart candidates were searched based on the X-ray source position in the radius of 3.9 arcsec. Optical light curves of the candidates comprise a full variety of variability types: spotted stars, pulsating red giants (potentially secondary stars of symbiotic variables), cataclysmic variables, eclipsing binary systems, irregular non-periodic objects including an AGN (GRS 1734-292). Additionally, we find that positions of 19 non-variable stars brighter than 16.5 mag in the OGLE databases are so well aligned with the X-ray positions (<0.75 arcsec) that these objects are also likely optical counterparts to the GBS X-ray sources. We provide the OGLE astrometric and photometric information for all selected objects and their preliminary classifications. Photometry of the candidates is available from the OGLE Internet archive.

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ASAS Photometry of ROSAT Sources. I. Periodic Variable Stars Coincident with Bright Sources from the ROSAT All Sky Survey

Kiraga M.

Acta Astronomica

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2012

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Vol. 62, No. 1

67--95

EN

Photometric data from the ASAS - South (declination less than 29°) survey have been used for identification of bright stars located near the sources from the ROSAT All Sky Survey Bright Source Catalog (RBSC). In total 6028 stars brighter than 12.5 mag in I- or V-bands have been selected and analyzed for periodicity. Altogether 2302 variable stars have been found with periods ranging from 0.137 d to 193 d. Most of these stars have X-ray emission of coronal origin with a few cataclysmic binaries and early type stars with colliding winds. Whenever it was possible we collected data available in the literature to verify periods and to classify variable objects. The catalog includes 1936 stars (1233 new) considered to be variable due to presence of spots (rotationally variable), 127 detached eclipsing binary stars (33 new), 124 contact binaries (11 new), 96 eclipsing stars with deformed components (19 new), 13 ellipsoidal variables (4 new), 5 miscellaneous variables and one pulsating RR Lyr type star (blended with an eclipsing binary). More than 70% of new variable stars have amplitudes smaller than 0.1 mag, but for ASAS 063656-0521.0 we have found the largest known amplitude of brightness variations due to the presence of spots (up to ΔV=0.8 mag). The table with the compiled data and figures with light curves can be downloaded from Acta Astronomica Archive.

9

Evolution of Cool Close Binaries - Approach to Contact

Stępień K.

Acta Astronomica

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2011

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Vol. 61, No. 2

139--159

EN

As a part of a larger project, a set of 27 evolutionary models of cool close binaries was computed under the assumption that their evolution is influenced by the magnetized winds blowing from both components. Short period binaries with the initial periods of 1.5 d, 2.0 d and 2.5 d were considered. For each period three values of 1.3 Msun, 1.1 Msun and 0.9 Msun were taken as the initial masses of the more massive components. The initial masses of the less massive components were adjusted to avoid extreme mass ratios. Here the results of the computations of the first evolutionary phase are presented, which starts from the initial conditions and ends when the more massive component reaches its critical Roche lobe. In all considered cases this phase lasts for several Gyr. For binaries with the higher total mass and/or longer initial periods this time is equal to, or longer than the main sequence life time of the more massive component. For the remaining binaries it amounts to a substantial fraction of this life time. From the statistical analysis of models, the predicted period distribution of detached binaries with periods shorter than 2 d was obtained and compared to the observed distribution from the ASAS data. An excellent agreement was obtained under the assumption that the period distribution in this range is determined solely by magnetic braking (MB), i.e., the mass and angular momentum loss due to the magnetized winds, as considered in the present paper. This result indicates, in particular, that virtually all cool detached binaries with periods of a few tenths of a day, believed to be the immediate progenitors of W UMa-type stars, were formed from young detached systems with periods around 2-3 d. MB is the dominant formation mechanism of cool contact binaries. It operates on the time scale of several Gyr rendering them rather old, with age of 6-10 Gyr. The results of the present analysis will be used as input data to investigate the subsequent evolution of the binaries, through the mass exchange phase and contact or semi-detached configuration till the ultimate merging of the ultimate merging of the components.

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Multicolor Photometry of SV Cam in 1997

Kjurkchieva D., Marchev D., Ogłoza W.

Acta Astronomica

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2000

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Vol. 50, No. 4

517--528

EN

High speed BVR(I)C photometry of the short period RS CVn binary SV Cam is presented. Its light curve is asymmetric with a depression of brightness by 0.04-0.05 mag after the primary eclipse. Good fit of the synthetic light curve to the observational data in all colors can be obtained assuming presence of two cool spots with equal angular sizes of 20° and temperatures 4350 K located at middle latitude above and below the stellar equator on opposite hemispheres of the primary star.