Spectroscopic observations of the low-mass eclipsing binary NSVS 11868841 have been obtained and the radial velocities were derived for both components. The masses and radii determined for the components are $M_1$ =0.870$\pm$0.074\Msun, $M_2$=0.607$\pm$0.053\Msun and $R_1$ =0.983 $\pm$0.030 \Rsun, $R_2$ =0.901$\pm$0.026 \Rsun. Both the primary and secondary stars' radii are 10 \% and 57\% larger than those of zero-age-main-sequence stars with the same masses. This discrepancy may be arisen from the large spot coverage of both stars. We collected absolute parameters of 21 low mass double-lined eclipsing binaries and compared their positions in the mass-radius and mass-effective temperature panels. The large radii and lower effective temperatures are solved neither with difference in metallicity nor in mixing length parameters. These discrepancies in the low mass stars may be originated by magnetic fields causing inhibition convective energy transport which leads to large magnetic spot coverage on the surface of a low mass star.
We present our new photometric and spectroscopic observations of NSVS 02500276, NSVS 07453183, NSVS 11868841, NSVS 06550671 and NSVS 10653195. The first flare-like event was detected on NSVS07453183. Using the Wilson-Devinney program, the preliminary orbital solutions and starspot parameters are derived. The chromospheric activity indicators show NSVS10653195 and NSVS06550671 are active. Then, we discuss the starspot evolution on the short and long term scale. In the end, we give our future plan.
We present new photometric observations of the $β$ Lyrae-type eclipsing binary systems NSVS 7322420 and NSVS 5726288. These observations represent the first multi-band photometry performed on these systems. The light curves were analyzed with PHOEBE, a front-end GUI based on the Wilson-Devinney program, to produce models to describe our observations. Our preliminary solutions indicate that NSVS 7322420 is a primary filling semi-detached system with unusual features warranting further study. These features include a pronounced O'Connell effect, a temporal variance in the light curve, and an unu…
The paper presents observations and light curve solutions of the eclipsing stars CSS J075205.6+381909 and NSVS 691550. As a result their initial epochs were determined. The target periods turned out almost equal to the previous values. We found that NSVS 691550 is overcontact system whose components are close in temperature while CSS J075205.6+381909 has almost contact configuration and temperature difference of its components is around 2000 K. Both targets undergo partial eclipses. Their stellar components seem to obey the relations mass-temperature of MS stars.
We present the new results of our long-term observational project to detect the small variations in the orbital periods of low-mass and short-period eclipsing binaries. About 120 new precise mid-eclipse times were obtained for three relatively well-known dwarf eclipsing binaries: SDSS J143547.87+373338.5 (P = 0.126 d), NSVS 07826147 (0.162 d), and NSVS 14256825 (0.110 d). Observed-minus-calculated (O-C) diagrams of these systems were analyzed using all accurate timings, and, where possible, new parameters of the light-time effect were calculated. For the first time, we derive (or improve upon …
Photometric observations in V and I bands and low-dispersion spectra of ten ultrashort-period binaries (NSVS 2175434, NSVS 2607629, NSVS 5038135, NSVS 8040227, NSVS 9747584, NSVS 4876238, ASAS 071829-0336.7, SWASP 074658.62+224448.5, NSVS 2729229, NSVS 10632802) are presented. One of them, NSVS 2729229, is newly discovered target. The results from modeling and analysis of our observations revealed that: (i) Eight targets have overcontact configurations with considerable fillout factor (up to 0.5) while NSVS 4876238 and ASAS 0718-03 have almost contact configurations; (ii) NSVS 4876238 is rare …
We carried out photometric and low-resolution spectral observations of six eclipsing ultrashort-period binaries with MS components. The light curve solutions of the Rozhen observations show that all targets are overcontact systems. We found well-defined empirical relation "period -- semi-major axis" for the short-period binaries and used it for estimation of the global parameters of the targets. Our results revealed that NSVS 925605 is quite interesting target: (a) it is one of a few contact binaries with M components; (b) it exhibits high activity (emission in H$α$ line, X-ray emission, large…
The multi-color photometric and spectroscopic (based on observations obtained with the T{Ü}B{İ}TAK National Observatory 1.5-meter telescope, which is owned and operated by the T{Ü}B{İ}TAK) observations of the newly discovered eclipsing binary NSVS 07394765 were obtained. The resultant light and radial velocities were analysed and the global parameters of the system: T$_{1}$=3 300 K; T$_{2}$=3 106 K; M$_1$=0.36 M$_{\odot}$; M$_2$=0.18 M$_{\odot}$; R$_1$=0.46 R$_{\odot}$; R$_2$=0.50 R$_{\odot}$; L$_{1}$=0.030 L$_{\odot}$; L$_2$=0.026 L$_{\odot}$; $i=89.2{^\circ}$; $a=5.97$ R$_{\odot}$; $d=28$ pc…
Low-mass stars in eclipsing binary systems show radii larger and effective temperatures lower than theoretical stellar models predict for isolated stars with the same masses. Eclipsing binaries with low-mass components are hard to find due to their low luminosity. As a consequence, the analysis of the known low-mass eclipsing systems is key to understand this behavior. We developed a physical model of the LMDEB system NSVS 10653195 to accurately measure the masses and radii of the components. We obtained several high-resolution spectra in order to fit a spectroscopic orbit. Standardized absolu…
We present optical spectroscopy and extensive $RI$ differential photometry of the double-lined eclipsing binary NSVS 02502726 (2MASS J08441103+5423473). Simultaneous solution of two-band light curves and radial velocities permits determination of precise emprical masses and radii for both components of the system. The analysis indicates that the primary and secondary components of NSVS 02502726 are in a circular orbit with 0.56-day orbital period and have stellar masses of M$_1$=0.714$\pm$0.019 \Msun, and M$_2$=0.347$\pm$0.012 \Msun. Both of the components have large radii, being R$_1$=0.67$\p…
We present an analysis of UBVR$_{\rm C}$I$_{\rm C}$JH photometry and phase-resolved optical spectroscopy of NSVS 14256825, an HW Vir type binary. The members of this class consist of a hot subdwarf and a main-sequence low-mass star in a close orbit ($P_{\rm orb} ~ 0.1$ d). Using the primary-eclipse timings, we refine the ephemeris for the system, which has an orbital period of 0.11037 d. From the spectroscopic data analysis, we derive the effective temperature, $T_1 = 40000 \pm 500$ K, the surface gravity, $\log g_1 = 5.50\pm0.05$, and the helium abundance, $n(\rm He)/n(\rm H)=0.003\pm0.001$, …
In this paper we present the results of a detailed spectroscopic and photometric analysis of the V=13$^m$.4 low-mass eclipsing binary NSVS 06507557 with an orbital period of 0.515 d. We obtained a series of mid-resolution spectra covering nearly entire orbit of the system. In addition we obtained simultaneous VRI broadband photometry using a small aperture telescope. From these spectroscopic and photometric data we have derived the system's orbital parameters and determined the fundamental stellar parameters of the two components. Our results indicate that NSVS 06507557 consists of a K9 and an…
NSVS 14256825 is the second sdOB + dM eclipsing binary systems with an orbital period of 2.65 hours. The special binary was reported to contain circumbinary planets or brown dwarfs by using the timing method. However, different results were derived by different authors because of the insufficient coverage of eclipse timings. Since 2008, we have monitored this binary for about 10 years by using several telescopes and 84 new times of light minimum in high precision were obtained. It is found that the O-C curve is increasing recently and it shows a cyclic variation with a period of 8.83 years and…
NSVS 02502726 has been known as a double-lined, detached eclipsing binary that consists of two low-mass stars. We obtained $BVRI$ photometric follow-up observations in 2009 and 2011 to measure improved physical properties of the binary star. Each set of light curves, including the 2008 data given by \cCakirli et al., was simultaneously analyzed with the previously published radial-velocity curves using the Wilson-Devinney binary code. The conspicuous seasonal light variations of the system are satisfactorily modelled by a two-spot model with one starspot on each component and by changes of the…
The $VRC$ light curves were regularly measured for the eclipsing binary NSVS 7453183 as a part of our long-term observational project for studying of low-mass eclipsing binaries with a short orbital period and surface activity. The TESS light curve solution in Phoebe results to the detached configuration, where the temperature of primary component was adopted to $T_1$ = 4300 K according to the SED approximation. It gives us $T_2 =$ 4080 $\pm$ 100 K for the secondary component. The spectral type of the primary component was estimated to be K6 and the photometric mass ratio was derived $q = 0.86…
TESS light curves and surface activity in two low-mass eclipsing binaries: NSVS 01031772 and 2MASS J04100497+2931023
Astronomical Institute, Faculty of Mathematics and Physics, Charles University（查理大学数学物理学院天文研究所）；Valašské Meziříčí Observatory（瓦拉什梅济日奇天文台）；Czech Astronomical Society, Variable Star and Exoplanet Section（捷克天文学会变星与系外行星学部）；Research Centre for Theoretical Physics and Astrophysics, Institute of Physics, Silesian University（西里西亚大学物理学院理论物理与天体物理研究中心）；Astronomical Institute, Czech Academy of Sciences（捷克科学院天文研究所）；Private Observatory（私人天文台）；DARK SKY Beskydy（Beskydy暗夜天空保护区）；Institute of Theoretica（理论物理研究所）
We present an analysis of eclipse timings of the post-common envelope binary NSVS 14256825, which is composed of an sdOB star and a dM star in a close orbit (P_{orb} = 0.110374 days). High-speed photometry of this system was performed between July, 2010 and August, 2012. Ten new mid-eclipse times were analyzed together with all available eclipse times in the literature. We revisited the (O-C) diagram using a linear ephemeris and verified a clear orbital period variation. On the assumption that these orbital period variations are caused by light travel time effects, the (O-C) diagram can be exp…
New photometric observations of NSVS 01286630 were performed and two sets of four-color (B, V , Rc, Ic) light curves (LCs) were obtained. Using the 2013 version of the Wilson-Devinney (W-D) code, we analyzed these data. The photometric solutions reveal that NSVS 01286630 is an active detached eclipsing binary (EB) with a high orbit inclination. Remarkably, the temperature of the primary component (the hotter star) is higher than the secondary one, but, the value of mass ratio q(M2/M1) for NSVS 0128663 is more than 1, which can be explained that the surface of the secondary component of NSVS 01…
Period or amplitude variations in eclipsing binaries may reveal the presence of additional massive bodies in the system, such as circumbinary planets. Here, we have studied twelve previously-known eclipsing post-common-envelope binaries for evidence of such light curve variations, on the basis of multi-year observations in the SuperWASP archive. The results for HW Vir provided strong evidence for period changes consistent with those measured by previous studies, and help support a two-planet model for the system. ASAS J102322-3737.0 exhibited plausible evidence for a period increase not previo…
The variable star known as NSVS 5597754 was identified as a short period RRc field star from ground-based photometry. This star happens to fall in the Kepler field of view and has been observed for 3 years with the Kepler spacecraft. Renamed KIC 9832227, this star was reidentified as an eclipsing binary with a periodicity of 0.457970 days. The NSVS ground based photometry yielded a period solution of 0.229 days. The Kepler photometry, which sampled the light cycle every 30 minutes, shows a peculiar behavior that is not purely eclipsing superposed over the primary variation. Follow-up ground ba…
We perform a new analysis of the M dwarf-M dwarf eclipsing binary system NSVS 07394765 in order to investigate the reported hyper-inflated radius of one of the component stars. Our analysis is based on archival photometry from the Wide Angle Search for Planets (WASP), new photometry from the 32 cm {Command Module Observatory (CMO) telescope in Arizona and the 70 cm telescope at Thacher Observatory in California}, and new high-resolution infrared spectra obtained with the Immersion Grating Infrared Spectrograph (IGRINS) on the Discovery Channel Telescope. The masses and radii we measure for eac…
CCD photometric observations in VRI colors and spectroscopic observations of the newly discovered eclipsing binary GSC 2314-0530 (NSVS 6550671) with dMe components and very short period of P=0.192636 days are presented. The simultaneous light-curve solution and radial velocity solution allows to determine the global parameters of GSC 2314-0530: T_{1}=3735 K; T_{2}=3106 K; M_{1}=0.51 M_sun; M_{2}=0.26 M_sun; R_{1}=0.55 R_sun; R_{2}=0.29 R_sun; L_{1}=0.053 L_sun; L_{2}=0.007 L_sun; i=72.5 degr; a=1.28 R_sun; d=59 pc. The chromospheric activity of its components is revealed by strong emission in …
We present an analysis of NGC2204-S892 -- a new detached eclipsing binary composed of two late K dwarfs. Based on three photometric campaigns launched in 2008 we obtained 5 light curves (3 in V, 1 in B and 1 in I), and derived an orbital period of 0.451780+-0.000001 d. We also obtained 20 VLT/UVES spectra, enabling accurate radial velocity measurements. The derived masses and radii of the components (m1 = 0.733 +-0.005 Msun and R1 = 0.72 +-0.01 Rsun; m2 = 0.662 +-0.005 Msun and R2 = 0.68 \+-0.02 Rsun) are consistent with the empirical mass-radius relationship established recently for lower mai…
We report our spectroscopic monitoring of the detached, grazing, and slightly eccentric 12-day double-lined eclipsing binary EPIC 219568666 in the old nearby open cluster Ruprecht 147. This is the second eclipsing system to be analyzed in this cluster, following our earlier study of EPIC 219394517. Our analysis of the radial velocities combined with the light curve from the K2 mission yield absolute masses and radii for EPIC 219568666 of M1 = 1.121 +/- 0.013 M(Sun) and R1 = 1.1779 +/- 0.0070 R(Sun) for the F8 primary, and M2 = 0.7334 +/- 0.0050 M(Sun) and R2 = 0.640 +/- 0.017 R(Sun) for the fa…
We present the absolute properties of the eclipsing binary AO Ser with a pulsating component from our $BV$ photometric and high-resolution spectroscopic observations, which were performed between April and May 2017. The radial velocities (RVs) for both components were measured, and the effective temperature and projected rotational velocity of the primary star were determined to be $T_{\rm eff,1}$ = 8,820 $\pm$ 62 K and $v_1 \sin i_{1}$ = 90 $\pm$ 18 km s$^{-1}$, respectively, by comparing the observed spectrum with the Kurucz models. The accurate fundamental parameters of AO Ser were determin…
KIC~8262223 is an eclipsing binary with a short orbital period ($P=1.61$ d). The {\it Kepler} light curves are of Algol-type and display deep and partial eclipses, ellipsoidal variations, and pulsations of Delta Scuti type. We analyzed the {\it Kepler} photometric data, complemented by phase-resolved spectra from the R-C Spectrograph on the 4-meter Mayall telescope at Kitt Peak National Observatory and determined the fundamental parameters of this system. The low mass and oversized secondary ($M_2=0.20M_{\odot}$, $R_2=1.31R_{\odot}$) is the remnant of the donor star that transferred most of it…
We present new photometric and spectroscopic observations for 2M 1533+3759 (= NSVS 07826147). It has an orbital period of 0.16177042 day, significantly longer than the 2.3--3.0 hour periods of the other known eclipsing sdB+dM systems. Spectroscopic analysis of the hot primary yields Teff = 29230 +/- 125 K, log g = 5.58 +/- 0.03 and log N(He)/N(H) = -2.37 +/- 0.05. The sdB velocity amplitude is K1 = 71.1 +/- 1.0 km/s. The only detectable light contribution from the secondary is due to the surprisingly strong reflection effect. Light curve modeling produced several solutions corresponding to dif…
We present high-speed, three-colour photometry of the eclipsing cataclysmic variables CTCV 1300, CTCV 2354 and SDSS 1152. All three systems are below the observed "period gap" for cataclysmic variables. For each system we determine the system parameters by fitting a parameterised model to the observed eclipse light curve by chi-squared minimisation. We also present an updated analysis of all other eclipsing systems previously analysed by our group. New donor masses are generally between 1 and 2 sigma of those originally published, with the exception of SDSS 1502 and DV UMa. We note that the do…
OO Dra is a short-period Algol system with a $δ$ Sct-like pulsator. We obtained time-series spectra between 2016 February and May to derive the fundamental parameters of the binary star and to study its evolutionary scenario. The radial velocity (RV) curves for both components were presented, and the effective temperature of the hotter and more massive primary was determined to be $T_{\rm eff,1}$ = 8260 $\pm$ 210 K by comparing the disentangling spectrum and the Kurucz models. Our RV measurements were solved with the $BV$ light curves of Zhang et al. (2014) using the Wilson-Devinney binary cod…
The observational mass-radius relation of main sequence stars with masses between ~0.3 and 1.0 Msun reveals deviations between the stellar radii predicted by models and the observed radii of stars in detached binaries. We generate an accurate physical model of the low-mass eclipsing binary T-Cyg1-12664 in the Kepler mission field to measure the physical parameters of its components and to compare them with the prediction of theoretical stellar evolution models. We analyze the Kepler mission light curve of T-Cyg1-12664 to accurately measure the times and phases of the primary and secondary ecli…
We present photometric and spectroscopic analysis of AE For -- a detached eclipsing binary composed of two late K dwarfs. The masses of the components are found to be 0.6314 +- 0.0035 and 0.6197 +- 0.0034 Msun and the radii to be 0.67 +- 0.03 and 0.63$ +- 0.03 Rsun for primary and secondary component, respectively. Both components are significantly oversized compared to theoretical models, which we attribute to their high activity. They show Halpha, Hbeta, Hgamma, Ca H and Ca K lines in emission, and are heavily spotted, causing large variations of the light curve.
We present analyses of improved photometric and spectroscopic observations for two detached eclipsing binaries at the turnoff of the open cluster NGC 752: the 1.01 day binary DS And and the 15.53 d BD $+$37 410. For DS And, we find $M_1 = 1.692\pm0.004\pm0.010 M_\odot$, $R_1 = 2.185\pm0.004\pm0.008 R_\odot$, $M_2 = 1.184\pm0.001\pm0.003 M_\odot$, and $R_2 = 1.200\pm0.003\pm0.005 R_\odot$. We either confirm or newly identify unusual characteristics of both stars in the binary: the primary star is found to be slightly hotter than the main sequence turn off and there is a more substantial discrep…
Astronomical data are typically irregular in time, e.g. the space (HIPPARCOS/TYCHO, KEPLER, GAIA, WISE etc.) and ground-based CCD (NSVS, ASAS, CRTS, SuperWASP etc.) and photographic (Harvard, Sonneberg, Odessa etc.) photometrical surveys. This leads to cancellation of the conditions, which lead to the orthogonality of the basic functions, and thus the simplified methods give biased parameters of the approximations. We have elaborated a series of algorithms and programs for statistically correct analysis, and have applied them to 2000+ variable stars of different types. The data were obtained f…
