V453 Cyg is an eclipsing binary containing 14 Msun and 11 Msun stars in an eccentric short-period orbit. We have discovered $β$ Cep-type pulsations in this system using TESS data. We identify seven significant pulsation frequencies, between 2.37 and 10.51 d$^{-1}$, in the primary star. These include six frequencies which are separated by yet significantly offset from harmonics of the orbital frequency, indicating they are tidally-perturbed modes. We have determined the physical properties of the system to high precision: V453 Cyg A is the first $β$ Cep pulsator with a precise mass measurement. The system is a vital tracer of the physical processes that govern the evolution of massive single and binary stars.
V498 Cyg is an early-B-type binary known to show eclipses on a period of 3.48 d, and two sets of spectral lines. We present the discovery of a second set of eclipses, on a 1.44-d period, in the light curve of this object from the Transiting Exoplanet Survey Satellite (TESS). We develop a model of the light curve to simultaneously fit the properties of both eclipsing binaries and apply this to the TESS observations. We are able to fit the light curve of the fainter system well, but the light curve fit for the brighter system is unable to reproduce either its asymmetric primary eclipse or its ch…
We present a census of eclipsing binary systems with classical Cepheid as a component. All such systems known were found in the OGLE collection of classical Cepheids in the Magellanic System. We extend the list of potential candidates adding four new objects found in the OGLE-IV photometric data. One of the new Cepheids in the eclipsing system, OGLE-SMC-CEP-3235, revealed only one eclipse during 15 years of the OGLE photometric monitoring. However, it additionally shows very well pronounced light-time effect indicating that the binarity is real. We also search for the light-time effect in othe…
Results of the three-colour photoelectric observation of the close binary system XZ Cep, obtained at the Abastumani Astrophysical observatory, are presented.
We determine the age of the eclipsing binary V380 Cygni, whose components have a significant mass ratio, $M_B/M_A\approx$ 0.6. Because this binary exhibits spectral lines of both components, the values of masses and radii could be determined with a very high accuracy. Assuming that both components are on the main sequence, we derive the age of about 16 Myr. However, in this case the primary needs a large overshooting from the convective core ($f_{\rm{ov}} \approx 0.04$) and higher metallicity ($Z \approx 0.02$). It is difficult to tell whether such a high value of overshooting from the convect…
Combining with our newest CCD times of light minimum of EM Cygni, all 45 available times of light minimum including 7 data with large scatters are compiled and the updated O-C analysis is made. The bestfit for the O-C diagram of EM Cygni is a quadratic-plus-sinusoidal fit. The secular orbital period decrease rate -2.5(\pm 0.3)x10^{-11} s s^{-1} means that magnetic braking effect with a rate of mass loss via stellar wind, 2.3x10^{-10}Msunyr^{-1}, is needed for explaining the observed orbital period decrease. Moreover, for explaining the significant cyclical period change with a period of \sim 1…
We present the physical properties of the eclipsing binary V2281 Cyg, which shows a light-time effect due to a supposed tertiary component from its eclipse timing variation according to the $Kepler$ observations. The high-resolution spectra and $BVR$ photometric data of the system were obtained at Bohyunsan Optical Astronomy Observatory and Mount Lemmon Optical Astronomy Observatory, respectively. To determine the fundamental parameters of the eclipsing pair and its circumbinary object, we simultaneously analyzed the radial velocities, light curves, and eclipse times including the $Kepler$ dat…
CW Cep is an early B-type eclipsing binary with mass measurement precisions better than 1 \%. We report the discovery of pulsation signatures in the TESS time-series data of the system observed during Sectors 17 and 18. Our binary modeling indicates that the target star is a partially-eclipsing detached system with masses of 12.95 $M_\odot$ and 11.88 $M_\odot$ and radii of 5.52 $R_\odot$ and 5.09 $R_\odot$ in an eccentric orbit of $e$ = 0.0305. The distance to the eclipsing system, 928 $\pm$ 36 pc, is much more precise than the Gaia distance of 962 $\pm$ 453 pc. Applying multifrequency analyse…
New times of minima of the eclipsing binaries GK Cep and VY Cet, obtained at the Observatory of the University of Athens, have been used together with all reliable timings found in the literature in order to study the period variation and search for the presence of third body in the systems.
Physical parameters were recently measured for several Cepheids in eclipsing binary systems in the LMC. It is a good opportunity to compare these results with models obtained from pulsation theory. Having well determined physical parameters of the stars, we can calculate the corresponding pulsation periods for a given mode and check for instability. For stars that lack data, unknown or poorly defined parameters can be further constrained. We present the comparison for six Cepheids, showing that, in general, the results are in very good agreement.
The recent discovery and analysis of a classical Cepheid in the well detached, double-lined, eclipsing binary OGLE-LMC-CEP0227, has provided the first determination of the dynamical mass of a classical Cepheid variable to an unprecedented 1% accuracy. We show here that modern stellar evolution models widely employed to study Galactic and extragalactic stellar systems, are able to match simultaneously mass and radius (and effective temperature) of the two components with a single value for the age of the system, without any specific fine-tuning. Our conclusion is that there is no discrepancy be…
We have analyzed the double-lined eclipsing binary system OGLE-LMC-CEP-1812 in the LMC and demonstrate that it contains a classical fundamental mode Cepheid pulsating with a period of 1.31 days. The secondary star is a stable giant. We derive the dynamical masses for both stars with an accuracy of 1.5%, making the Cepheid in this system the second classical Cepheid with a very accurate dynamical mass determination, following the OGLE-LMC-CEP-0227 system studied by Pietrzynski et al. (2010). The measured dynamical mass agrees very well with that predicted by pulsation models. We also derive the…
CCD multi-band light curves of the neglected eclipsing binaries V405 Cep, V948 Her, KR Mon and UZ Sge were obtained and analysed using the Wilson-Devinney code. New geometric and absolute parameters were derived and used to determine their current evolutionary state. V405 Cep, V948 Her and KR Mon are detached systems with their components in almost the same evolutionary stage. UZ Sge is a classical Algol system with a tertiary companion around it. Moreover, since the systems V405 Cep, V948 Her and UZ Sge contain an early type component, their light curves were examined for possible pulsation b…
New BVRI CCD observations of the semi-detached eclipsing binary EG Cep are presented. The observed light curves are analyzed with the Wilson-Devinney program and new geometrical and photometric elements are derived. These elements are used to compute the physical parameters of the system in order to study its evolutionary status.
We present new spectroscopic observations of the early type, double-lined eclipsing binary V446\,Cep. The radial velocities and the photometric data obtained by $Hipparcos$ were analysed for deriving the astrophysical parameters of the components. Masses and radii were determined as M$_p$=17.94$\pm$1.16 M$_{\odot}$ and R$_p$=8.33$\pm$0.29 R$_{\odot}$, M$_s$=2.64$\pm$0.30 M$_{\odot}$ and R$_s$=2.13$\pm$0.10 R$_{\odot}$ for the components of V446\,Cep. Our analyses show that V446\,Cep is a detached Algol-type system. Based on the position of the components plotted on the theoretical Hertzsprung-…
Cepheid stars play a considerable role as extragalactic distances indicators, thanks to the simple empirical relation between their pulsation period and their luminosity. They overlap with that of secondary distance indicators, such as Type Ia supernovae, whose distance scale is tied to Cepheid luminosities. However, the Period-Luminosity (P-L) relation still lacks a calibration to better than 5%. Using an original combination of interferometric astrometry with optical and ultraviolet spectroscopy, we measured the geometrical distance d = 720.35+/-7.84 pc of the 3.33 d period Cepheid V1334 Cyg…
The status of our work on binary classical cepheid systems in the Large Magellanic Cloud is presented. We report on results from our follow up of two eclipsing binary cepheids OGLE-LMC-CEP-0227 and OGLE-LMC-CEP-1812. Here we presented for the first time confirmation that a third cepheid OGLE-LMC-CEP-2532 is a true eclipsing binary cepheid with a period of 800 days. Two other very good candidates for eclipsing binaries detected during OGLE-IV survey are also discussed.
We have obtained extensive high-quality spectroscopic observations of the OGLE-LMC-CEP-1718 eclipsing binary system in the Large Magellanic Cloud which Soszynski et al. (2008) had identified as a candidate system for containing two classical Cepheids in orbit. Our spectroscopic data clearly demonstrate binary motion of the Cepheids in a 413-day eccentric orbit, rendering this eclipsing binary system the first ever known to consist of two classical Cepheid variables. After disentangling the four different radial velocity variations in the system we present the orbital solution and the individua…
Eclipsing binary systems with pulsating components offer a unique possibility to accurately measure the most important parameters of pulsating stars, to study their evolution, and to test the pulsation theory. I will show what we can learn about the pulsating stars from the analysis of such systems and how we can do it. Special attention will be paid to the mass, radius, p-factor, and distance determination. Although the core of the method is based on the observations of double-lined eclipsing spectroscopic binaries, with the help of the pulsation theory, it is possible to measure absolute par…
Spectra that cover 0.63 - 0.69um with a spectral resolution ~ 17000 are presented of the W Serpentis system V367 Cygni. Absorption lines of FeII and SiII that form in a circumsystem shell are prominent features, and the depths of these are stable with time, suggesting that the shell is smoothly distributed and well-mixed. Further evidence of uniformity comes from modest radial velocity variations measured in the deepest parts of the shell lines. It is suggested that motions previously attributed to rotation of the shell are instead artifacts of contamination from the donor star spectrum. A don…
We aim at determining the masses of Cepheids in binary systems, as well as their geometric distances and the flux contribution of the companions. The combination of interferometry with spectroscopy will offer a unique and independent estimate of the Cepheid masses. Using long-baseline interferometry at visible and infrared wavelengths, it is possible to spatially resolve binary systems containing a Cepheid down to milliarcsecond separations. Based on the resulting visual orbit and radial velocities, we can then derive the fundamental parameters of these systems, particularly the masses of the …
We present an analysis of the high-mass eclipsing binary system VV Ori based on photometry from the TESS satellite. The primary star (B1V, 9.5 Msun) shows beta Cephei pulsations and the secondary (B7V, 3.8 Msun) is possibly a slowly-pulsating B star. We detect 51 significant oscillation frequencies, including two multiplets with separations equal to the orbital frequency, indicating that the pulsations are tidally perturbed. We analyse the TESS light curve and published radial velocities to determine the physical properties of the system. Both stars are only the second of their pulsation type …
We report new spectroscopic and photometric observations of the main-sequence, detached, eccentric, double-lined eclipsing binary V541 Cyg (P = 15.34 days, e = 0.468). Using these observations together with existing measurements we determine the component masses and radii to better than 1% precision: M1 = 2.335 +0.017/-0.013 MSun, M2 = 2.260 +0.016/-0.013 MSun, R1 = 1.859 +0.012/-0.009 RSun, and R2 = 1.808 +0.015/-0.013 RSun. The nearly identical B9.5 stars have estimated temperatures of 10650 +/- 200 K and 10350 +/- 200 K. A comparison of these properties with current stellar evolution models…
We present the first modern analysis of two young, eclipsing binaries, EK Cep and HS Her, based on new, ground-based, CCD multicolour light curves as well as the TESS observations, radial velocity curves, and eclipse timing measurements. The orbital and stellar parameters of the stars are determined by Roche modelling, and their evolutionary status is examined using a grid of isochrones and evolutionary tracks. We find that HS Her is 25-32 Myr old and its components are on the zero-age main sequence; at the age of 16-20 Myr, the primary of EK Cep is also on the ZAMS, but its secondary is a pre…
The eclipsing and double-lined spectroscopic binary V380 Cyg is an extremely important probe of stellar evolution: its primary component is a high-mass star at the brink of leaving the main sequence whereas the secondary star is still in the early part of its main sequence lifetime. We present extensive high-resolution echelle and grating spectroscopy from Ondrejov, Calar Alto, Victoria and La Palma. We apply spectral disentangling to unveil the individual spectra of the two stars and obtain new spectroscopic elements. The secondary star contributes only about 6% of the total light, which rema…
We report spectroscopic observations of the 2.63 day, detached, F-type main-sequence eclipsing binary V2154 Cyg. We use our observations together with existing $uvby$ photometric measurements to derive accurate absolute masses and radii for the stars good to better than 1.5%. We obtain masses of M1 = 1.269 +/- 0.017 M(Sun) and M2 = 0.7542 +/- 0.0059 M(Sun), radii of R1 = 1.477 +/- 0.012 R(Sun) and R2 = 0.7232 +/- 0.0091 R(Sun), and effective temperatures of 6770 +/- 150 K and 5020 +/- 150 K for the primary and secondary stars, respectively. Both components appear to have their rotations synchr…
New CCD photometry is presented for the hot overcontact binary DK Cyg, together with reasonable explanations for the light and period variations. Historical light and velocity curves from 1962 to 2012 were simultaneously analyzed with the Wilson-Devinney (W-D) synthesis code. The brightness disturbances were satisfactorily modeled by applying a magnetic cool spot on the primary star. Based on 261 times of minimum light including 116 new timings and spanning more than 87 yrs, a period study reveals that the orbital period has varied due to a periodic oscillation superposed on an upward parabola…
We present here the first spectroscopic and photometric analysis of the double-lined eclipsing binary containing the classical, first-overtone Cepheid OGLE-LMC-CEP-2532 (MACHO 81.8997.87). The system has an orbital period of 800 days and the Cepheid is pulsating with a period of 2.035 days. Using spectroscopic data from three high-class telescopes and photometry from three surveys spanning 7500 days we are able to derive the dynamical masses for both stars with an accuracy better than 3%. This makes the Cepheid in this system one of a few classical Cepheids with an accurate dynamical mass dete…
We performed a new and accurate fit of light and radial velocity curves of the Large Magellanic Cloud (LMC) Cepheid --OGLE-LMC-CEP-0227-- belonging to a detached double-lined eclipsing binary system. We computed several sets of nonlinear, convective models covering a broad range in stellar mass, effective temperature and in chemical composition. The comparison between theory and observations indicates that current theoretical framework accounts for luminosity --V and I band-- and radial velocity variations over the entire pulsation cycle. Predicted pulsation mass --M=4.14+-0.06 Mo-- and mean e…
The first photometric analysis of V811 Cep was carried out. The first complete light curves of V, R and I bands are given. The analysis was carried out by Wilson-Devinney (W-D) program, and the results show that V811 Cep is a median-contact binary ($f=33.9(\pm4.9)\%$) with a mass ratio of 0.285. It is a W-subtype contact binary, that is, the component with less mass is hotter than the component with more mass, and the light curves are asymmetric (O'Connell effect), which can be explained by the existence of a hot spot on the component with less mass. The orbital inclination is $i=88.3^{\circ}$…
The photometric and spectroscopic observational campaign organized for the 2008/9 eclipse of EE Cep revealed features, which indicate that the eclipsing disk in the EE Cep system has a multi-ring structure. We suggest that the gaps in the disk can be related to the possible planet formation.
Our main aim is the first detailed analysis of the two eclipsing binaries V456 Oph and V490 Cyg. The system V456 Oph has been studied both photometrically via an analysis of its light curve observed by the INTEGRAL/OMC and by the period analysis of all available times of minima. V490 Cyg has been studied by means of a period analysis only. Many new times of minima for both systems have recently been observed and derived. This allows us for the first time to study in detail the processes that affect both binaries. The main result is the discovery that both systems have eccentric orbits. For V45…
Binaries are not always neatly aligned. Previous observations of the DI Her system showed that the spin axes of both stars are highly inclined with respect to one another and the orbital axis. Here we report on a measurement of the spin-axis orientation of the primary star of the NY Cep system, which is similar to DI Her in many respects: it features two young early-type stars (~6 Myr, B0.5V+B2V), in an eccentric and relatively long-period orbit (e=0.48, P=15.d3). The sky projections of the rotation vector and the spin vector are well-aligned (beta_p = 2 +- 4 degrees), in strong contrast to DI…
We present spectroscopic observations of the double-lined early type eclipsing binary V1898\,Cyg. The radial velocities were obtained by means of the cross-correlation technique. Analyses of the BV light curves and RVs led to determination of the fundamental stellar parameters of the V1898\,Cyg's components. We derived new ephemerides for the eclipsing pair using the observed times of mid-eclipses. The residuals between the observed and computed times of mid-eclipses were analysed and a rate of the period change $\dot{P}/P= 6.68 \times 10^{-7}\,yr^{-1}$ was obtained. The orbital period is incr…
We present a detailed study of the classical Cepheid in the double-lined, highly eccentric eclipsing binary system OGLE-LMC562.05.9009. The Cepheid is a fundamental mode pulsator with a period of 2.988 days. The orbital period of the system is 1550 days. Using spectroscopic data from three 4-8-m telescopes and photometry spanning 22 years, we were able to derive the dynamical masses and radii of both stars with exquisite accuracy. Both stars in the system are very similar in mass, radius and color, but the companion is a stable, non-pulsating star. The Cepheid is slightly more massive and bigg…
We present a new Bayesian approach to constrain the intrinsic parameters (stellar mass, age) of the eclipsing binary system CEP0227 in the LMC. We computed evolutionary models covering a broad range in chemical compositions and in stellar mass. Independent sets of models were constructed either by neglecting or by including a moderate convective core overshooting (beta=0.2) during central H-burning phases. Models were also constructed either by neglecting or by assuming a canonical (eta=0.4,0.8) or an enhanced (eta=4) mass loss rate. The solutions were computed in three different planes: lumin…
Based on new observations and improved modeling techniques, we have reanalyzed seven Cepheids in the Large Magellanic Cloud. Improved physical parameters have been determined for the exotic system OGLE LMC-CEP-1718 composed of two first-overtone Cepheids and a completely new model was obtained for the OGLE LMC-CEP-1812 classical Cepheid. This is now the shortest period Cepheid for which the projection factor is measured. The typical accuracy of our dynamical masses and radii determinations is 1%. The radii of the six classical Cepheids follow period--radius relations in the literature. Our ver…
New CCD photometry during 4 successive years from 2005 is presented for the eclipsing binary GW Cep, together with reasonable explanations for the light and period variations. All historical light curves, obtained over a 30-year interval, display striking light changes, and are best modeled by the simultaneous existence of a cool spot and a hot spot on the more massive cool component star. The facts that the system is magnetically active and that the hot spot has consistently existed on the inner hemisphere of the star indicate that the two spots are formed by (1) magnetic dynamo-related activ…
GT\,Cep is a semi-detached close binary system with an orbital period of 4.91 days, containing a massive star. I have obtained spectroscopic observations and derived radial velocities of both components. Combining the analyses of radial velocities and available photometric observations we have measured the absolute parameters of both components of GT\,Cep. The components are shown to be a B2\,V primary with a mass M$_p$=10.70$\pm$0.50 M$_{\odot}$ and radius R$_p$=6.83$\pm$0.19 R$_{\odot}$ and a A0\,IV secondary with a mass M$_s$=2.58$\pm$0.14 M$_{\odot}$ and radius R$_s$=7.56$\pm$0.21 R$_{\odo…
A novel method of analysis of double-lined eclipsing binaries containing a radially pulsating star is presented. The combined pulsating-eclipsing light curve is built up from a purely eclipsing light curve grid created using an existing modeling tool. For every pulsation phase the instantaneous radius and surface brightness are taken into account, being calculated from the disentangled radial velocity curve of the pulsating star and from its out-of-eclipse pulsational light curve and the light ratio of the components, respectively. The best model is found using the Markov Chain Monte Carlo met…
The short-period (1.64 d) near-contact eclipsing WN6+O9 binary system CQ Cep provides an ideal laboratory for testing the predictions of X-ray colliding wind shock theory at close separation where the winds may not have reached terminal speeds before colliding. We present results of a Chandra X-ray observation of CQ Cep spanning ~1 day during which a simultaneous Chandra optical light curve was acquired. Our primary objective was to compare the observed X-ray properties with colliding wind shock theory, which predicts that the hottest shock plasma (T > 20 MK) will form on or near the line-of-c…
Eclipsing systems are essential objects for understanding the properties of stars and stellar systems. Eclipsing systems with pulsating components are furthermore advantageous because they provide accurate constraints on the component properties, as well as a complementary method for pulsation mode determination, crucial for precise asteroseismology. The outcome of space missions aiming at delivering high-accuracy light curves for many thousands of stars in search of planetary systems has also generated new insights in the field of variable stars and revived the interest of binary systems in g…
Pulsation periods reveal tension between theoretical and empirical radii for classical Cepheids in eclipsing binary systems
Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（尼古拉·哥白尼天文中心，波兰科学院）；Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学，蔚蓝海岸天文台，法国国家科学研究中心，拉格朗日实验室）
Oscillating Algol-type eclipsing binaries (oEA) are very interesting objects that have three observational features of eclipse, pulsation, and mass transfer. Direct measurement of their masses and radii from the double-lined radial velocity data and photometric light curves would be the most essential for understanding their evolutionary process and for performing the asteroseismological study. We present the physical properties of the oEA star XX Cep from high-resolution time-series spectroscopic data. The effective temperature of the primary star was determined to be 7,946 $\pm$ 240 K by com…
As many as 10\% of OB-type stars have global magnetic fields, which is surprising given their internal structure is radiative near the surface. A direct probe of internal structure is pulsations, and some OB-type stars exhibit pressure modes ($β$ Cep pulsators) or gravity modes (slowly pulsating B-type stars; SPBs); a few rare cases of hybrid $β$ Cep/SPBs occupy a narrow instability strip in the H-R diagram. The most precise fundamental properties of stars are obtained from eclipsing binaries (EBs), and those in clusters with known ages and metallicities provide the most stringent constraints …
BVR light curves and radial velocities for the double-lined eclipsing binary V1135\,Her were obtained. The brighter component of V1135\,Her is a Cepheid variable with a pulsation period of 4.22433$\pm$0.00026 days. The orbital period of the system is about 39.99782$\pm$0.00233 days, which is the shortest value among the known Type\,II Cepheid binaries. The observed B, V, and R magnitudes were cleaned for the intrinsic variations of the primary star. The remaining light curves, consisting of eclipses and proximity effects, are obtained. Our analyses of the multi-colour light curves and radial v…
We present a detailed analysis of the bright Cepheid-type variable star V1154 Cygni using 4 years of continuous observations by the Kepler space telescope. We detected 28 frequencies using standard Fourier transform method.We identified modulation of the main pulsation frequency and its harmonics with a period of ~159 d. This modulation is also present in the Fourier parameters of the light curve and the O-C diagram. We detected another modulation with a period of about 1160 d. The star also shows significant power in the low-frequency region that we identified as granulation noise. The effect…
New multi-color UBVR light curves of the eclipsing binary KR Cyg were obtained in 2005. Photometric solutions were derived using the Wilson- Devinney method. The result shows that KR Cyg is a near-contact binary system with a large effective temperature difference between the components, approximately 5230 K. All the times of minimum light were collected and combined with our observations obtained in 2010 and 2011. Analysing all the times of mid-eclipse, we found for the first time a possible periodic oscillation with an amplitude of 0.001 days and a period of ~76 years. The periodic oscillati…
Classical Cepheids, like binary stars, are laboratories for stellar evolution and Cepheids in binary systems are especially powerful ones. About one-third of Galactic Cepheids are known to have companions and Cepheids in eclipsing binary systems have recently been discovered in the Large Magellanic Cloud. However, there are no known Galactic binary Cepheids with orbital periods less than one year. We compute population synthesis models of binary Cepheids to compare to the observed period and eccentricity distributions of Galactic Cepheids as well as to the number of observed eclipsing binary C…
Ensemble pulsational characteristics of eclipsing binaries containing $β$ Cep stars observed by the TESS mission
University of Nigeria, Nsukka（尼日利亚恩苏卡大学）；KU Leuven（荷语鲁汶大学）；Newcastle University（纽卡斯尔大学）；Radboud University Nijmegen（奈梅亨拉德堡德大学）；Max Planck Institut für Astronomie（马克斯·普朗克天文学研究所）；Nicolaus Copernicus Astronomical Centre, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文中心）
Determining the expansion of the universe, i.e. the Hubble constant (H0) to better than 2% is required in order to understand the nature of dark energy. However, the two most accurate methods to do it, the cosmic microwave background and the distance scale ladder are inconsistent today, which is refereed as the "tension". One of the key to resolve this tension is related to the calibration of the period-luminosity (PL) of Cepheids : what is its zero-point ? Is it metallicity dependent ? Can we reduce the dispersion of the PL relation ? The eclipsing binaries method was recently used to determi…
Multi-color light curves and radial velocities for TYC\,1031\,1262\,1 have been obtained and analyzed. TYC\,1031\,1262\,1 includes a Cepheid with a period of 4.15270$\pm$0.00061 days. The orbital period of the system is about 51.2857$\pm$0.0174 days. The pulsation period indicates a secular period increase with an amount of 2.46$\pm$0.54 min/yr. The observed B, V, and R magnitudes were cleaned for the intrinsic variations of the primary star. The remaining light curves, consisting of eclipses and proximity effects, are obtained and analyzed for orbital parameters. The system consists of two ev…
We present the analysis of a peculiar W~Virginis (pWVir) type-II Cepheid, OGLE-LMC-T2CEP-211 ($P_{puls}=9.393\,d$), in a double-lined binary system ($P_{orb}=242\,d$), which shed light on virtually unknown evolutionary status and structure of pWVir stars. The dynamical mass of the Cepheid (first ever for a type-II Cepheid) is $0.64\pm{}0.02\,M_\odot$ and the radius $R=25.1\pm{}0.3\,R_\odot$. The companion is a massive ($5.67\,M_\odot$) main-sequence star obscured by a disk. Such configuration suggests a mass transfer in the system history. We found that originally the system ($P_{orb}^{init}=1…
This paper presents CCD observations of the Algol-type eclipsing binaries RZ Dra and EG Cep. The light curves have been analyzed with the PHOEBE software and Wilson-Devinney code (2003 version). A detailed photometric analysis, based on these observations, is presented for both binarity and pulsation. The results indicate semidetached systems where the secondary component fills its Roche lobe. After the subtraction of the theoretical light curve, a frequency analysis was performed in order to check for pulsations of the primary component of each system. Moreover, a period analysis was performe…
Orbital and stellar parameter determination of eclipsing $β$ Cep pulsators
University of Nigeria, Nsukka（尼日利亚恩苏卡大学）；Çanakkale Onsekiz Mart University（恰纳卡莱十月马特大学）；Villanova University（维拉诺瓦大学）；Royal Observatory of Belgium（比利时皇家天文台）；Nicolaus Copernicus Astronomical Centre, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）
A prerequisite for probing theortical evolutionary models for high-mass stars is the determination of stellar physical properties with a high accuracy. We do this for three binary systems containing components with masses above 10 Msun: V478 Cyg, AH Cep and V453 Cyg. New high-resolution and high-S/N echelle spectra were secured and analysed using spectral disentangling, yielding improved orbital elements and the individual spectra for the component stars. In conjuction with a re-analysis of archival light curves, the stellar masses and radii were measured to accuracies of 1.5-2.5% and 1.0-1.9%…
