arXiv subjects

Pavol Gajdoš

Publications and source records attributed to Pavol Gajdoš.

12 recordsLinked to original sources

arXiv2026

Revision of the Detached Eclipsing System IR Cas from TESS Observations, Ground-Based Photometry and Spectroscopy

We present a new photometric and spectroscopic analysis of detached eclipsing binary IR Cas based on TESS observations, supplementary ground-based photometry in Sloan $g^\prime$, $r^\prime$, and $i^\prime$ filters, and newly obtained radial velocity measurements. The updated orbital and physical parameters of the system were derived using combined light-curve and radial-velocity modeling. The resulting solution indicates that both components are main-sequence stars with masses of approximately $1.32$ M$_{\odot}$ and $1.05$ M$_{\odot}$. We investigated in detail the fact, that the TESS light curves exhibit asymmetries near the maxima, which were reproduced by introducing a cool spot that moves on the surface of the secondary component. Long-term analysis of times of minima revealed quasi-periodic variations in the O$-$C diagram that can be interpreted as a light-time effect due to a possible third body with an orbital period of about 38 years. The positions of both components in the mass-radius diagram agree well with empirical relations for detached main-sequence binaries and do not indicate substantial deviations from standard stellar evolution. Overall, IR Cas appears to be an evolutionarily representative detached eclipsing system with moderate indications of stellar activity.

astro-ph.SR↗

arXiv2026

Rotational characteristics of five photometrically variable stars

This study explores photometric variability in a sample of hot stars in order to test whether variability arises from rotational modulation due to surface temperature spots. Frequencies determined from the projected rotational velocities were compared with frequencies estimated on the basis of TESS light curves. In all five cases, the spectroscopic frequency was lower than the photometric one preserving possibility that the observed brightness variations can be rotationally induced. In two of our targets, HT Cet and HD 219487, the photometric frequency spectra suggest more complex variability, likely pulsations. Our results suggest that spot activity inducing rotational modulation may exist in stars hotter than 6500 K, highlighting the value of combined spectroscopic and photometric analysis of variations.

astro-ph.SR↗

arXiv2026

PLATOSpec's first results: Three new transiting warm Jupiters from the WINE survey TIC 147027702, TIC 245076932 and TIC 87422071

We report the discovery and characterisation of three transiting warm Jupiters: TIC 147027702b, TIC 245076932b and TIC 87422071b. These systems were initially identified as transiting candidates using light curves generated from the full-frame images of the TESS mission. We confirmed the planetary nature of these objects with ground-based spectroscopic follow-up observations using FEROS and the new PLATOSpec spectrograph attached to the ESO 1.52 m telescope at the La Silla Observatory, and with ground-based photometric observations of the Observatoire Moana, Las Cumbres Observatory Global Telescope and ASTEP. From a global fit to the photometry and radial velocities, we determine that the planet TIC 147027702b has a low-eccentric orbit ($e = 0.13 \pm 0.05$) with a period of 44.4 days and has a mass of $1.09^{+0.07}_{-0.13}$ M$_J$ and a radius of $0.98 \pm 0.06$ R$_J$. TIC 245076932b has a moderately low mass of $0.51 \pm 0.05$ M$_J$, a radius of $0.97 \pm 0.05$ R$_J$, and an eccentric orbit ($e = 0.43 \pm 0.02$) with a period of 21.6 days. TIC 87422071b has a mass of $1.29 \pm 0.10$ M$_J$, a radius of $0.97 \pm 0.08$ R$_J$, and has a slightly eccentric orbit ($e = 0.12 \pm 0.07$) with a period of 11.3 days. These well-characterised warm Jupiters expand the currently limited sample of similar gas giants and provide valuable benchmarks for testing models of giant-planet formation, migration, and tidal evolution.

astro-ph.EP↗

arXiv2025

Morphological classification of eclipsing binary stars using computer vision methods

We present an application of computer vision methods to classify the light curves of eclipsing binaries (EB). We have used pre-trained models based on convolutional neural networks ($\textit{ResNet50}$) and vision transformers ($\textit{vit\_base\_patch16\_224}$), which were fine-tuned on images created from synthetic datasets. To improve model generalisation and reduce overfitting, we developed a novel image representation by transforming phase-folded light curves into polar coordinates combined with hexbin visualisation. Our hierarchical approach in the first stage classifies systems into detached and overcontact types, and in the second stage identifies the presence or absence of spots. The binary classification models achieved high accuracy ($>96\%$) on validation data across multiple passbands (Gaia~$G$, $I$, and $TESS$) and demonstrated strong performance ($>94\%$, up to $100\%$ for $TESS$) when tested on extensive observational data from the OGLE, DEBCat, and WUMaCat catalogues. While the primary binary classification was highly successful, the secondary task of automated spot detection performed poorly, revealing a significant limitation of our models for identifying subtle photometric features. This study highlights the potential of computer vision for EB morphological classification in large-scale surveys, but underscores the need for further research into robust, automated spot detection.

cs.CV↗

arXiv2024

Analysis of KIC 7023917 -- spotted low-mass ratio eclipsing binary with $δ$ Scuti pulsations

Times of minima of eclipsing binary KIC 7023917 show quasiperiodic anti-symmetric deviations from the calculated one with an amplitude of up to 10 minutes and a period of 200 - 300 days. These changes correlate with the observed variations of the light-curve maxima (amplitude and phase separation). We used photometric data obtained by Kepler and TESS missions to analyse the times of minima and determine system parameters. The phases and amplitudes of the maxima were measured to study the O'Connell effect. As an additional source of information, we performed ground-based multi-colour photometric observation and determined the radial velocities of the system from our spectroscopic measurements. We could explain long-term variations of the light-curve shape and times of the eclipses using the cold star spot located on the secondary component and the modification of its size. Based on our modelling, the system consists of a primary main-sequence star of spectral type A7 and an evolved, oversized secondary component with a mass ratio of only 0.1 due to past mass transfer. Calculation of absolute parameters gives us the mass of the primary component about 1.8 M$_\odot$ and 0.2 M$_\odot$ for the secondary one, and radii of 2.2 R$_\odot$ of the primary star and 0.9 R$_\odot$ of secondary one, respectively. The studied low-mass ratio eclipsing binary is probably a progenitor of the variable star of EL CVn type. A multiple-period photometric variability was disclosed in the TESS data ranging from half to two hours due to $δ$ Scuti-type pulsations of the primary component.

astro-ph.SR↗

arXiv2022

Chaos in multiplanetary extrasolar systems

Here we present an initial look at the dynamics and stability of 178 multiplanetary systems which are already confirmed and listed in the NASA Exoplanet Archive. To distinguish between the chaotic and regular nature of a system, the value of the MEGNO indicator for each system was determined. Almost three-quarters of them could be labelled as long-term stable. Only 45 studied systems show chaotic behaviour. We consequently investigated the effects of the number of planets and their parameters on the system stability. A comparison of results obtained using the MEGNO indicator and machine-learning algorithm SPOCK suggests that the SPOCK could be used as an effective tool for reviewing the stability of multiplanetary systems. A similar study was already published by Laskar and Petit in 2017. We compared their analysis based on the AMD criterion with our results. The possible discrepancies are discussed.

astro-ph.EP↗

arXiv2022

Revisiting the Transit Timing Variations in the TrES-3 and Qatar-1 systems with TESS data

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.

astro-ph.EP↗

arXiv2022

HD 183986: a high-contrast SB2 system with a pulsating component

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 $δ$ 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.

astro-ph.SR↗

arXiv2019

WASP-92, WASP-93 and WASP-118: Transit timing variations and long-term stability of the systems

We studied three exoplanetary systems with transiting planets: WASP-92, WASP-93 and WASP-118. Using ground-based photometric observations of WASP-92 and WASP-93 and Kepler-K2 observations of WASP-118, we redetermined the orbital and physical parameters of these planets. The precise times of all transits were determined. We constructed O-C diagrams of transits and analysed possible transit timing variations. We did not observe any significant deviation from a linear ephemeris for any of the selected exoplanets. We put upper-mass limits for other hypothetical planets in these systems. Using long-term numerical simulation, we looked for stable regions where another planet could exist for a long time. We used the maximum eccentricity method for this purpose. We discuss the influence of values of initial inclination and eccentricity on the shape and size of regions of stability.

astro-ph.EP↗

arXiv2019

Transit Timing Variations and linear ephemerides of confirmed Kepler transiting exoplanets

We determined new linear ephemerides of transiting exoplanets using long-cadence de-trended data from quarters Q1 to Q17 of Kepler mission. We analysed TTV diagrams of 2098 extrasolar planets. The TTVs of 121 objects were excluded (because of insufficient data-points, the influence of stellar activity, etc). Finally, new linear ephemerides of 1977 exoplanets from the Kepler archive are presented. The significant linear trend was observed on TTV diagrams of approximately 35% of studied exoplanets. Knowing correct linear ephemeris is principal for successful follow-up observations of transits. Residual TTV diagrams of 64 analysed exoplanets show periodic variation, 43 of these TTV planets were not reported yet.

astro-ph.EP↗

arXiv2019

Transit timing variations, radial velocities and long-term dynamical stability of the system Kepler-410

Transit timing variations of Kepler-410Ab were already reported in a few papers. Their semi-amplitude is about 14.5 minutes. In our previous paper, we found that the transit timing variations could be caused by the presence of a stellar companion in this system. Our main motivation for this paper was to investigate variation in a radial-velocity curve generated by this additional star in the system. We performed spectroscopic observation of Kepler-410 using three telescopes in Slovakia and Czech Republic. Using the cross-correlation function, we measured the radial velocities of the star Kepler-410A. We did not observe any periodic variation in a radial-velocity curve. Therefore, we rejected our previous hypothesis about additional stellar companion in the Kepler-410 system. We ran different numerical simulations to study mean-motion resonances with Kepler-410Ab. Observed transit timing variations could be also explained by the presence of a small planet near to mean-motion resonance 2:3 with Kepler-410Ab. This resonance is stable on a long-time scale. We also looked for stable regions in the Kepler-410 system where another planet could exist for a long time.

astro-ph.EP↗

arXiv2017

Transit Timing Variations in the system Kepler-410Ab

We present a new analysis of the transit timing variations displayed by the extrasolar planet Kepler-410Ab. We obtained and improved orbital and physical parameters for the planet and analysed 70 transit times obtained by the Kepler satellite. In our analysis of the O-C diagram (Observed-Calculated), we assumed that the observed changes in the transit times are probably caused by the gravitational influence of another body in the system. To determine the mass of the perturbing body, we have considered the light-time effect and an analytical approximation of the perturbation model. The solutions resulting from both methods give comparable results, with an orbital period $P_3\sim$970 days and a slightly eccentric orbit of the third body. We also showed that this orbit is nearly coplanar with the orbit of the Neptune-like planet Kepler-410Ab (orbital period 17.8 days). We propose two possible models for the perturbing body orbiting a common barycentre with Kepler-410A: (i) a single star with mass at least 0.906 M$_{\odot}$, (ii) a binary star with the total mass of its components of at least 2.15 M$_{\odot}$. In both cases the star Kepler-410B is on a long orbit (period more than 2200 years). Small amplitude variations ($\sim$ 5-8 minutes) detected in O-C residuals can be explained by the stellar activity of the host star (spots and pulsations), which affects the shape of the light curve during the transit. The presence of single or binary companion of mentioned masses heavily affects the total observed flux from the system. After removing of the flux contamination from Kepler-410A light curve we found that radius of the transiting planet Kepler-410Ab should be in the range from about 3.7 to 4.2 R$_{\oplus}$.

astro-ph.SR↗