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The post-common envelope binary V471 Tauri has been an object of interest for decades. V471 Tau shows various phenomena due to its evolutionary state and unique properties, e.g. its magnetic accretion and eclipse timing variation (ETV). Previous authors explained the ETVs by different, sometimes contradictory theories. In this paper, we present and analyse the variability of the eclipse timing of this star. We observed V471 Tauri over the last ten years and covered the second cycle of its period variation. Based on our analysis of the presented data, we assess the possible existence of a brown dwarf in this system and derive its orbital parameters. We compare the results of our dynamical modelling to the solution predicted by Applegate-mechanism theories, which have been developed in recent studies. We found that the observed ETV cannot be explained only by the presence of additional components to the binary., Comment: 10 pages, 4 figures, to be published in MNRAS

We present the discovery of a unique object, a chemically peculiar Ap-type star showing $\delta$ Scuti pulsations which is bound in an eclipsing binary system with an orbital period shorter than 3 days. HD 99458 is, therefore, a complex astrophysical laboratory opening doors for studying various, often contradictory, physical phenomena at the same time. It is the first Ap star ever discovered in an eclipsing binary. The orbital period of 2.722 days is the second shortest among all known chemically peculiar (CP2) binary stars. Pulsations of $\delta$ Scuti type are also extremely rare among CP2 stars and no unambiguously proven candidate has been reported. HD 99458 was formerly thought to be a star hosting an exoplanet, but we definitely reject this hypothesis by using photometric observations from the K2 mission and new radial velocity measurements. The companion is a low-mass red dwarf star ($M_{2}=0.45(2)$ M$_{\odot}$) on an inclined orbit ($i=73.2(6)$ degrees) that shows only grazing eclipses. The rotation and orbital periods are synchronized, while the rotation and orbital axes are misaligned. HD 99458 is an interesting system deserving of more intense investigations., Comment: 8 pages, 4 figures, 4 tables, accepted in MNRAS

We present and analyze 58 transit light curves of TrES-3b and 98 transit light curves of Qatar-1b observed by Transiting Exoplanet Survey Satellite (TESS), plus two transit light curves of Qatar-1b observed by us using a ground-based 1.23\,m telescope. These light curves are combined with the best-quality light curves taken from the Exoplanet Transit Database (ETD) and literature. The precisely determined mid-transit times from these light curves enable us to obtain the refined orbital ephemerides with improved precision for both hot Jupiters. From the timing analysis, we find an indication for the presence of transit timing variations (TTVs) in both systems. Since the observed TTVs are unlikely to be short-term and periodic, the possibility of additional planets in the orbits close to TrES-3b and Qatar-1b are ruled out. Possible causes of long-term TTVs such as orbital decay, apsidal precession, the Applegate mechanism and line-of-sight acceleration are also examined. However, none of these possibilities are found to explain the observed TTV of TrES-3b. In contrast to this, the line-of-sight acceleration appears to be a plausible explanation for the observed TTV of Qatar-1b. In order to confirm these findings, further high-precision transit and RV observations of both systems would be worthwhile., Comment: 38 pages, 16 figures, 8 tables, accepted for publication in AJ

There is a small group of peculiar early-type stars on the main sequence that show different rotation velocities from different spectral lines. This inconsistency might be due to the binary nature of these objects. We aim to verify this hypothesis by a more detailed spectroscopic and photometric investigation of one such object: HD 183986. We obtained 151 high and medium resolution spectra that covered an anticipated long orbital period. There is clear evidence of theorbital motion of the primary component. We uncovered a very faint and broad spectrum of the secondary component. The corresponding SB2 orbital parameters, and the component spectra, were obtained by Fourier disentangling using the KOREL code. The component spectra were further modeled by iSpec code to arrive at the atmospheric quantities and the projected rotational velocities. We have proven that this object is a binary star with the period $P$ = 1268.2(11) d, eccentricity $e$ = 0.5728(20), and mass ratio $q$ = 0.655. The primary component is a slowly rotating star ($v \sin i = 27$ km.s$^{-1}$) while the cooler and less massive secondary rotates much faster ($v \sin i \sim 120$ km.s$^{-1}$). Photometric observations obtained by the TESS satellite were also investigated to shed more light on this object. A multi-period photometric variability was detected in the TESS data ranging from hours (the $\delta$ Sct-type variability) to a few days (spots/rotational variability). The physical parameters of the components and the origin of the photometric variability are discussed in more detail., Comment: Accepted to AJ. arXiv admin note: text overlap with arXiv:1307.2553 by other authors. text overlap with arXiv:1307.2553 by other authors

BD And is a fairly bright (V = 10.8), active and close (P = 0.9258 days) eclipsing binary. The cyclic variability of the apparent orbital period as well as third light in the light curves indicate the presence of an additional late-type component. The principal aim is the spectroscopic testing of the third-body hypothesis and determination of absolute stellar parameters for both components of the eclipsing binary. First medium and high-resolution spectroscopy of the system was obtained. The broadening-function technique appropriate for heavily-broadened spectra of close binaries was used. The radial velocities were determined fitting the Gaussian functions and rotational profiles to the broadening functions. A limited amount of photometric data has also been obtained. Although the photometric observations were focused on the obtaining the timing information, a cursory light-curve analysis was also performed. Extracted broadening functions clearly show the presence of a third, slowly-rotating component. Its radial velocity is within error of the systemic velocity of the eclipsing pair, strongly supporting the physical bond. The observed systemic radial-velocity and third-component changes do not support the 9 year orbit found from the timing variability. Masses of the components of the eclipsing pair are determined with about 0.5% precision. Further characterization of the system would require long-term photometric and spectroscopic monitoring., 23 pages, 6 figures, online data table

We present a long-term spectroscopic monitoring of seven CP stars in which binarity has either been established or signs of possible companions have been indicated. The primary goal of the survey was to examine the radial velocities (RVs) variations of the stars published earlier and to study multiplicity of the objects.

Context. EE Cep is one of few eclipsing binary systems with a dark, dusty disk around an invisible object similar to {\epsilon} Aur. The system is characterized by grey and asymmetric eclipses every 5.6 yr, with a significant variation in their photometric depth, ranging from ~ 0 m .5 to ~ 2 m .0. Aims. The main aim of the observational campaign of the EE Cep eclipse in 2014 was to test the model of disk precession (Galan et al. 2012). We expected that this eclipse would be one of the deepest with a depth of ~ 2 m .0. Methods. We collected multicolor observations from almost 30 instruments located in Europe and North America. This photometric data covers 243 nights during and around the eclipse. We also analyse the low- and high-resolution spectra from several instruments. Results. The eclipse was shallow with a depth of 0 m .71 in V-band. The multicolor photometry illustrates small color changes during the eclipse with a total amplitude of order ~ +0 m . 15 in B-I color index. The linear ephemeris for this system is updated by including new times of minima, measured from the three most recent eclipses at epochs E = 9, 10 and 11. New spectroscopic observations were acquired, covering orbital phases around the eclipse, which were not observed in the past and increased the data sample, filling some gaps and giving a better insight into the evolution of the H {\alpha} and NaI spectral line profiles during the primary eclipse. Conclusions. The eclipse of EE Cep in 2014 was shallower than expected 0 m .71 instead of ~ 2 m . 0. This means that our model of disk precession needs revision., Comment: 10 pages, 13 figures, 29 tables in appendix, submited to Astronomy & Astrophysics

VW~LMi is the tightest known quadruple system with 2+2 hierarchy. It consists of a W UMa-type eclipsing binary (P12 = 0.47755 days) and another detached non-eclipsing binary (P34 = 7.93 days) orbiting around a common center of mass is about P1234 = 355 days. We present new observations of the system extending the time baseline to study long-term perturbations in the system and to improve orbital elements. The multi-dataset modeling of the system (4 radial-velocity curves for the components and the timing data) clearly showed an apsidal motion in the non-eclipsing binary at a rate of 4.6 degrees/yr, but no other perturbations. This is consistent with the nearly co-planarity of the outer, 355-day orbit, and the 7.93-day orbit of the non-eclipsing binary. Extensive N-body simulations enabled us to constrain the mutual inclination of the non-eclipsing binary and the outer orbits to j34-1234 < 10 degrees., 12 pages, 7 figures, MNRAS in press

Only a few exoplanets are known to orbit around fast rotating stars. One of them is XO-6b, which orbits an F5V-type star. Shortly after the discovery, we started multicolor photometric and radial-velocity follow-up observations of XO-6b, using the telescopes of Astronomical Institute of the Slovak Academy of Sciences. Our main scientific goals were to better characterize the planetary system and to search for transit timing variations. We refined several planetary and orbital parameters. Based on our measurements, the planet XO-6b seems to be about 10% larger, which is, however, only about $2\sigma$ difference, but its orbit inclination angle, with respect to the plane of the sky, seems to be significantly smaller, than it was determined originally by the discoverers. In this case we found about $9.5\sigma$ difference. Moreover, we observed periodic transit timing variations of XO-6b with a semi-amplitude of about 14 min and with a period of about 450 days. There are two plausible explanations of such transit timing variations: (1) a third object in the system XO-6 causing light-time effect, or (2) resonant perturbations between the transiting planet XO-6b and another unknown low-mass planet in this system. From the O-C diagram we derived that the assumed third object in the system should have a stellar mass, therefore significant variations are expected in the radial-velocity measurements of XO-6. Since this is not the case, and since all attempts to fit radial velocities and O-C data simultaneously failed to provide a consistent solution, more realistic is the second explanation., Comment: Accepted for publication in MNRAS

Context. The structure of the wind from the cool giants in symbiotic binaries carries important information for understanding the wind mass transfer to their white dwarf companions and its fuelling. Aims. In this paper, we indicate a non-spherical distribution of the neutral wind zone around the red giant (RG) in the symbiotic binary star, EG And. Methods. We achieved this aim by analysing the periodic orbital variations of fluxes and radial velocities of individual components of the H$\alpha$ and [OIII]$\lambda$5007 lines observed on our high-cadence medium (R $\sim$ 11 000) and high-resolution (R $\sim$ 38 000) spectra. Results. The asymmetric shaping of the neutral wind zone at the near-orbital-plane region is indicated by: (i) the asymmetric course of the H$\alpha$ core emission fluxes along the orbit; (ii) the presence of their secondary maximum around the orbital phase $\varphi = 0.1$, which is possibly caused by the refraction effect; and (iii) the properties of the H$\alpha$ broad wing emission originating by Raman scattering on H$^0$ atoms. The wind is substantially compressed from polar directions to the orbital plane as constrained by the location of the [OIII]$\lambda$5007 line emission zones in the vicinity of the RG at/around its poles. The corresponding mass-loss rate from the polar regions of $\lesssim 10 ^{-8}$ Msun/yr is a factor of $\gtrsim 10$ lower than the average rate of $\approx 10^{-7}$Msun/yr derived from nebular emission of the ionised wind from the RG. Furthermore, it is two orders of magnitude lower than that measured in the near-orbital-plane region from Rayleigh scattering. Conclusions. The startling properties of the nebular [OIII]$\lambda$5007 line in EG And provides an independent indication of the wind focusing towards the orbital plane., Comment: 10 pages, 8 figures

We present long-term photometric observations of the young open cluster IC 348 with a baseline time-scale of 2.4 yr. Our study was conducted with several telescopes from the Young Exoplanet Transit Initiative (YETI) network in the Bessel R band to find periodic variability of young stars. We identified 87 stars in IC 348 to be periodically variable; 33 of them were unreported before. Additionally, we detected 61 periodic non-members of which 41 are new discoveries. Our wide field of view was the key to those numerous newly found variable stars. The distribution of rotation periods in IC 348 has always been of special interest. We investigate it further with our newly detected periods but we cannot find a statistically significant bimodality. We also report the detection of a close eclipsing binary in IC 348 composed of a low-mass stellar component (M ≳ 0.09 M⊙) and a K0 pre-main-sequence star (M ≈ 2.7 M⊙). Furthermore, we discovered three detached binaries among the background stars in our field of view and confirmed the period of a fourth one.

We report results of the first five observing campaigns for the open stellar cluster NGC 7243 in the frame of project Young Exoplanet Transit Initiative (YETI). The project focuses on the monitoring of young and nearby stellar clusters, with the aim to detect young transiting exoplanets and to study other variability phenomena on time-scales from minutes to years. After five observing campaigns and additional observations during 2013 and 2014, a clear and repeating transit-like signal was detected in the light curve of J221550.6+495611. Furthermore, we detected and analysed 37 new eclipsing binary stars in the studied region. The best fit parameters and light curves of all systems are given. Finally, we detected and analysed 26 new, presumably pulsating variable stars in the studied region. The follow-up investigation of these objects, including spectroscopic measurements of the exoplanet candidate, is currently planned. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The star V426 Sge (HBHA~1704-05), originally classified as an emission-line object and a semi-regular variable, brightened at the beginning of August 2018, showing signatures of a symbiotic star outburst. We aim to confirm the nature of V426 Sge as a classical symbiotic star, determine the photometric ephemeris of the light minima, and suggest the path from its 1968 symbiotic nova outburst to the following 2018 Z And-type outburst. We re-constructed an historical light curve (LC) of V426 Sge from approximately the year 1900, and used original low- and high-resolution spectroscopy complemented with Swift-XRT and UVOT, optical UBVRcIc and near-infrared JHKL photometry obtained during the 2018 outburst and the following quiescence. The historical LC reveals no symbiotic-like activity from 1900 to 1967. In 1968, V426 Sge experienced a symbiotic nova outburst that ceased around 1990. From approximately 1972, a wave-like orbitally related variation with a period of $493.4\pm 0.7$ days developed in the LC. This was interrupted by a Z And-type outburst from the beginning of August 2018 to the middle of February 2019. At the maximum of the 2018 outburst, the burning white dwarf (WD) increased its temperature to $>2\times 10^5$ K, generated a luminosity of $\sim 7\times 10^{37}(d/3.3kpc)^2$ erg/s, and blew a wind at the rate of $\sim 3\times 10^{-6}$ M$_{\odot}$/yr. The donor is a normal M4-5 III giant and the accretor is a low-mass $\sim$0.5 M$_{\odot}$ WD. During the transition from the symbiotic nova outburst to the quiescent phase, a pronounced sinusoidal variation along the orbit develops in the LC of most symbiotic novae. The following eventual outburst is of Z And-type, when the accretion by the WD temporarily exceeds the upper limit of the stable burning. At this point the system becomes a classical symbiotic star., 19 pages, 12 figures, 9 tables, 2 appendices, accepted for A&A, Tables A.1, A.2 and A.3 are only available at the CDS, added references for section 1

A new fiber-fed spectrograph was installed at the 60 cm telescope of the Stara Lesna Observatory. The article presents tests of its performance (spectral resolution, signal-to-noise ratio, radial-velocity stability) and reports observations of selected variable stars and exoplanet host stars. First test observations show that the spectrograph is an ideal tool to observe bright eclipsing and spectroscopic binaries but also symbiotic and nova-like stars. The radial-velocity stability (60–80 m s–1) is sufficient to study spectroscopic binaries and to detect easily the orbital motion of hot-Jupiter extrasolar planets around bright stars. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

AG Dra is a well known bright symbiotic binary with a white dwarf and a pulsating red giant. The long-term photometry monitoring and a new behaviour of the system are presented. The detailed period analysis of photometry as well as spectroscopy was carried out. In the system of AG Dra, two periods of variability are detected. The longer one around 550 days is related to the orbital motion, and the shorter one around 355 days is interpreted as pulsations of the red giant in our older paper. In addition the active stages change distinctively, but the outbursts are repeated with the periods from 359 to 375 days.

We report our investigation of the first transiting planet candidate from the YETI project in the young (~4 Myr old) open cluster Trumpler 37. The transit-like signal detected in the lightcurve of the F8V star 2M21385603+5711345 repeats every 1.364894+/-0.000015 days, and has a depth of 54.5+/-0.8 mmag in R. Membership to the cluster is supported by its mean radial velocity and location in the color-magnitude diagram, while the Li diagnostic and proper motion are inconclusive in this regard. Follow-up photometric monitoring and adaptive optics imaging allow us to rule out many possible blend scenarios, but our radial-velocity measurements show it to be an eclipsing single-lined spectroscopic binary with a late-type (mid-M) stellar companion, rather than one of planetary nature. The estimated mass of the companion is 0.15-0.44 solar masses. The search for planets around very young stars such as those targeted by the YETI survey remains of critical importance to understand the early stages of planet formation and evolution.

We report new multi-colour photometry and high-resolution spectroscopic observations of the long-period variable V501 Aur, previously considered to be a weak-lined T-Tauri star belonging to the Taurus-Auriga star-forming region. The spectroscopic observations reveal that V501 Aur is a single-lined spectroscopic binary system with a 68.8-day orbital period, a slightly eccentric orbit (e ~ 0.03), and a systemic velocity discrepant from the mean of Taurus-Auriga. The photometry shows quasi-periodic variations on a different, ~55-day timescale that we attribute to rotational modulation by spots. No eclipses are seen. The visible object is a rapidly rotating (vsini ~ 25 km/s) early K star, which along with the rotation period implies it must be large (R > 26.3 Rsun), as suggested also by spectroscopic estimates indicating a low surface gravity. The parallax from the Gaia mission and other independent estimates imply a distance much greater than the Taurus-Auriga region, consistent with the giant interpretation. Taken together, this evidence together with a re-evaluation of the LiI~$\lambda$6707 and H$\alpha$ lines shows that V501 Aur is not a T-Tauri star, but is instead a field binary with a giant primary far behind the Taurus-Auriga star-forming region. The large mass function from the spectroscopic orbit and a comparison with stellar evolution models suggest the secondary may be an early-type main-sequence star., Comment: 13 pages, 7 figures. Accepted to MNRAS

A new off-shelf low-cost echelle spectrograph was installed recently on the 0.6m telescope at the Star\'a Lesn\'a Observatory (Slovakia). In this paper we describe in details the radial velocity (RV) analysis of the first three transiting planetary systems, HAT-P-2, WASP-14 and XO-3, observed with this instrument. Furthermore, we compare our data with the RV data achieved with echelle spectrographs of other sub-meter-, meter- and two-meter-class telescopes in terms of their precision. Finally, we investigate the applicability of our RV data for modeling orbital parameters., Comment: AN accepted

Project Dwarf is a new observing campaign focused on the detection of substellar companions to low-mass (composed of late-type, subdwarf (sd) or/and white dwarf (WD) components) detached eclipsing binaries using minima timing. The crucial condition for the object selection for this campaign is possibility to determine times of the minima with high precision. This is naturally fullfilled for eclipsing binaries with deep and narrow minima or systems hosting a WD component showing fast ingress or egress.The observing project includes three groups of close eclipsing binaries indicating presence of substellar circum-binary components: (i)systems with K or/and M dwarf components(ii)systems with hot subdwarf (sd) and M dwarf components(iii)systems with white dwarf (WD) component(s). The sample of the eclipsing systems have orbital periods in range of 0.1 to almost 3 days and their brightness fits possibilities of small telescopes equipped with a low-end CCD camera and at least VRI filter set. Such kind of telescopes allow us to develop observing network including also amateur astronomers.

As part of our ongoing effort to investigate transit timing variations (TTVs) of known exoplanets, we monitored transits of the four exoplanets HAT-P-18b, HAT-P-19b, HAT-P-27b/WASP-40b and WASP-21b. All of them are suspected to show TTVs due to the known properties of their host systems based on the respective discovery papers. During the past three years 46 transit observations were carried out, mostly using telescopes of the Young Exoplanet Transit Initiative. The analyses are used to refine the systems' orbital parameters. In all cases we found no hints for significant TTVs, or changes in the system parameters inclination, fractional stellar radius and planet-to-star radius ratio. However, comparing our results with those available in the literature shows that we can confirm the already published values. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

IU Persei (IU Per) is an eclipsing semi detached (SD) binary with pulsating component (oscillating eclipsing Algol - oEA). Using our ground base photometry in Johnson's B and V filters and INTEGRAL/OMC (Optical Monitoring Camera) data in V filter we introduce the model of this system. We determined the (O - C) diagram behavior. Moreover, the short term variations of the light curve were detected. Whats more, we obtained residua, by comparison of observational and synthetic light curves (LC), of which the detailed period analysis enabled to characterize and localize their source, that can be explained as the pulsation activity of the primary component. The secondary, less massive component, is beyond the instability belt on H-R diagram and fulfills its Roche lobe. The accreting primary component pulsates in modes typical for the δ Scuti stars.

Intermediate polars (IPs) represent more than 70% of all cataclysmic variables (CVs) detected by INTEGRAL in hard X-ray. Nevertheless, only a quarter of all known IPs have been detected in this spectral band. This fact can be related to the activity state of these object ruled by changes in the mass accretion rate.

Intermediate polars represent a major fraction of all cataclysmic variables detected by INTEGRAL in hard X-rays. Nevertheless, only 25% of all known intermediate polars have been was detected in hard X-rays. This fact can be related to the activity state of these close interacting binaries. Multi-frequency (optical to X-ray) investigation of intermediate polars is essential to understand the physical mechanisms responsible for the observed activity of these objects.

We can show that analysis of the (O-C) diagram is a powerful method of detecting new bodies in binary systems. For this purpose we need very symmetric minima with precisely determined shapes. In the case of good covering by observations with high time resolution, it is possible to determine the times of such minima with sufficient accuracy. In the case of V471 Tau, the (O-C) diagram gave us residua which can be explained by the presence of a fourth body with substellar mass in the system.

IU Per is an eclipsing semi-detached binary with a pulsating component. Using our own ground-based, as well as INTEGRAL satellite photometric observations in the B and V passbands, we derived geometrical and physical parameters of this system. We detected the short-term variations of IU Per in the residuals of brightness after the subtraction of synthetic light curves. Analysis of these residuals enabled us to characterize and localize the source of short-term variations as the pulsations of the primary component typical to δ Scuti-type stars.