arXiv subjects

Tamás Borkovits

Publications and source records attributed to Tamás Borkovits.

17 recordsLinked to original sources

arXiv2026

TIC 433545934: The first 2+2 type doubly eclipsing binary with extra, mutual eclipses

In this work we identify and photodynamically analyze TIC 433545934, the very first doubly eclipsing 2+2-type quadruple stellar system, which shows outer eclipses, too. One such outer eclipse was discovered with TESS, which triggered a special interest in this system. Most of the data for this study come from TESS observations, but we also obtained supplemental ground-based photometric measurements for this quadruple system. The eclipse timing variation curves extracted from the TESS and ground-based follow-up data, the photometric light curves, and the spectral energy distribution are combined in a complex photodynamical analysis to yield the stellar and orbital parameters of this dynamically interesting system. The periods of the two inner, eclipsing binaries were found to be $P_A=2.07$d and $P_B=1.41$d, while the outer period is $P_{AB}=224.5$d. The outer period alone makes this system the fifth most compact known 2+2-type quadruple. Moreover, what really makes TIC 433545934 unique is that TESS observed a triple-dipped extra eclipsing event when the stars of binary B eclipsed the two components of binary A. We identified similar extra eclipsing events in the archival, ground-based data of ASAS-SN and ATLAS, as well. We found, however, that these extra events occur only once during an outer revolution, that is, binary A does not eclipse the stars of binary B. This is in accord with our finding that the outer eccentricity is quite high, being $e_{AB}=0.62$. Our analysis reveals that binary A consists of two quite similar, but slightly evolved late A-type stars ($q_A=0.92$), while in the case of binary B, the primary star, whose mass is between the masses of the two stars of binary A, is quite dominant, with $q_B=0.60$. The system was found to be substantially flat, with mutual inclination angles below $\approx2\degr$.

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arXiv2026

TIC 295741342: A Triply-Eclipsing Triple Star System with a Giant Tertiary

We present the discovery and characterization of TIC 295741342, a triply-eclipsing triple star system with a giant tertiary. The eclipsing binary consists of two similar main-sequence stars in a 4.75-day orbit. The binary is in a 412.8-day orbit with the giant tertiary. We found two degenerate solutions for the system: one where the tertiary is ascending the Red Giant Branch (RGB), and the other where the tertiary is on the Horizontal Branch (HB) and will eventually ascend the Asymptotic Giant Branch (AGB). In both solutions, the system is near-perfectly coplanar. In TESS Sector 33, the binary passes behind the giant tertiary, producing a distinctive "head-and-shoulders" eclipse that directly constrains the relative flux contributions and radii of all three stars. We modeled the system using a comprehensive spectro-photodynamical model that simultaneously fits the TESS lightcurve, eclipse times, spectral energy distribution, and radial velocities from 48 TRES spectra obtained over four years of observation resolving all three components. Evolutionary analysis using MIST tracks indicates that, in both solutions, the tertiary will overflow its Roche lobe, one in the RGB and the other in the AGB. The Roche lobe overflow will initiate either a stable mass transfer to the binary or a common envelope evolution that will likely result in ejections and/or mergers. Our models predict the midpoint of the next outer eclipse will occur on September 1, 2026 and we encourage follow-up observations with a $\pm$3 day window to observe the full event and further constrain the system parameters.

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arXiv2025

The Discovery of Two Quadruple Star Systems with the Second and Third Shortest Outer Periods

We present the discovery of two quadruple star systems -- TIC 285853156 and TIC 392229331 -- each consisting of two bound eclipsing binary stars. Among the most compact quadruples known, TIC 392229331 and TIC 285853156 have the second and third shortest outer orbital periods (145 days and 152 days, respectively) after BU Canis Minoris (122 days, Pribulla et al. 2023). We demonstrate that both systems are long-term dynamically stable despite substantial outer orbital eccentricities (0.33 for TIC 285853156 and 0.56 for TIC 392229331). We previously reported these systems in Kostov et al. (2022) and Kostov et al. (2024) as 2+2 hierarchical quadruple candidates producing two sets of primary and secondary eclipses in TESS data, as well as prominent eclipse timing variations on both binary components. We combine all available TESS data and new spectroscopic observations into a comprehensive photodynamical model, proving that the component binary stars are gravitationally bound in both systems and finding accurate stellar and orbital parameters for both systems, including very precise determinations of the outer periods. TIC 285853156 and TIC 392229331 represent the latest addition to the small population of well-characterized proven quadruple systems dynamically interacting on detectable timescales.

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arXiv2023

Observational Detection of Higher Order Secular Perturbations in Tight Hierarchical Triple Stars

In this work, we search for observational evidence of higher-order secular perturbations in three eclipsing binaries. These are slightly eccentric binaries, and they form the inner pairs of tight, compact, hierarchical triple star systems. We analyze simultaneously the high precision satellite ($Kepler$ and $TESS$) light curves, eclipse timing variations, combined spectral energy distributions (through catalog passband magnitudes) and, where available, radial velocities of KICs 9714358, 5771589 and TIC 219885468. Besides the determination of robust astrophysical and dynamical properties of the three systems, we find evidence that the observed unusual eclipse timing variations of KIC 9714358 are a direct consequence of the octupole-order secular eccentricity perturbations forced by an unusual, resonant behaviour between the lines of the apsides of the inner and outer orbital ellipses. We also show that, despite its evident cyclic eclipse depth variations, KIC~5771589 is an almost perfectly coplanar system (to within $0.3^\circ$), and we explain the rapid eclipse depth variations with the grazing nature of the eclipses. Finally, we find that the inner pair of TIC~219885468 consists of two twin stars and, hence, in this triple there are no octupole order three-body perturbations. Moreover, we show that this triple is also coplanar on the same level as the former one, but due to its deep eclipses, it does not exhibit eclipse depth variations. We intend to follow this work up with further analyses and a quantitative comparison of the theoretical and the observed perturbations.

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arXiv2023

Four New Compact Triply Eclipsing Triples found with Gaia and TESS

This paper presents a comprehensive analysis of four triply eclipsing triple star systems, namely TIC 88206187, TIC 14839347, TIC 298714297, and TIC 66893949. The four systems with third-body eclipses were found in the TESS lightcurves from among a sample of ~400 matches between known eclipsing binaries and the Gaia DR3 Non-Single Star (NSS; Gaia Collaboration 2022; Pourbaix et al. 2022) solution database. We combined photometric lightcurves, eclipse timing variations, archival spectral energy distributions, and theoretical evolution tracks in a robust photodynamical analysis to determine the orbital and system parameters. The triples have outer periods of 52.9, 85.5, 117, and 471 days, respectively. All dozen stars have masses $\lesssim$ 2.6 M$_\odot$. The systems are quite flat with mutual inclination angles between the inner and outer orbital planes that are all $\lesssim 4^\circ$. The outer mass ratios range from 0.39--0.76, consistent with our earlier collection of compact triply eclipsing triples. TIC 88206187 exhibits a fractional radius of the outer tertiary component $(r_B \equiv R_B/a_{\rm out})$ exceeding 0.1 (only the third such system known), and we consider its future evolution. Finally, we compare our photodynamical analysis results and the orbital parameters given in the Gaia DR3 NSS solutions, indicating decent agreement, but with the photodynamical results being more accurate.

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arXiv2023

BU Canis Minoris -- the Most Compact Known Flat Doubly Eclipsing Quadruple System

We have found that the 2+2 quadruple star system BU CMi is currently the most compact quadruple system known, with an extremely short outer period of only 121 days. The previous record holder was TIC 219006972 (Kostov et al. 2023), with a period of 168 days. The quadruple nature of BU CMi was established by Volkov et al. (2021), but they misidentified the outer period as 6.6 years. BU CMi contains two eclipsing binaries (EBs), each with a period near 3 days, and a substantial eccentricity of about 0.22. All four stars are within about 0.1 solar mass of 2.4 solar masses. Both binaries exhibit dynamically driven apsidal motion with fairly short apsidal periods of about 30 years, thanks to the short outer orbital period. The outer period of 121 days is found both from the dynamical perturbations, with this period imprinted on the eclipse timing variations (ETV) curve of each EB by the other binary, and by modeling the complex line profiles in a collection of spectra. We find that the three orbital planes are all mutually aligned to within 1 degree, but the overall system has an inclination angle near 83.5 degrees. We utilize a complex spectro-photodynamical analysis to compute and tabulate all the interesting stellar and orbital parameters of the system. Finally, we also find an unexpected dynamical perturbation on a timescale of several years whose origin we explore. This latter effect was misinterpreted by Volkov et al. (2021) and led them to conclude that the outer period was 6.6 years rather than the 121 days that we establish here.

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arXiv2022

Newly identified compact hierarchical triple system candidates using Gaia DR3

Aims. We introduce a novel way to identify new compact hierarchical triple stars by exploiting the huge potential of Gaia DR3 and also its future data releases. We aim to increase the current number of compact hierarchical triples significantly. Methods. We utilize several eclipsing binary catalogs from different sky surveys totaling more than 1 million targets for which we search for Gaia DR3 Non-single Star orbital solutions with periods substantially longer than the eclipsing periods of the binaries. Those solutions in most cases should belong to outer orbits of tertiary stars in those systems. We also try to validate some of our best-suited candidates using TESS eclipse timing variations. Results. We find 403 objects with suitable Gaia orbital solutions of which 27 are already known triple systems. This makes 376 newly identified hierarchical triple system candidates in our sample. We analyze the cumulative probability distribution of the outer orbit eccentricities and find that it is very similar to the ones found by earlier studies based on the observations of the Kepler and OGLE missions. We found measurable non-linear eclipse timing variations or third-body eclipses in the TESS data for 192 objects which we also consider to be confirmed candidates. Out of these, we construct analytical light-travel time effect models for the eclipse timing variations of 22 objects with well-sampled TESS observations. We compare the outer orbital parameters from our solutions with the ones from the Gaia solutions and find that the most reliable orbital parameter is the orbital period, while the values of the other parameters should be used with caution.

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arXiv2022

Surface activity of the G dwarf primary in the quaternary star system V815 Her

We investigate the magnetic activity of the G dwarf primary star in the multiple system V815 Herculis. Recently, TESS Sector 26 data have revealed that V815 Her is in fact a four-star system consisting of two close binaries in a long-period orbit. We give preliminary orbital solution for the long-known but unseen "third body" V815 Her `B', which is itself a close eclipsing binary of two M dwarfs. Long-term spot activity of the G dwarf is presented along with the very first Doppler image reconstructions of its spotted surface.

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arXiv2022

TIC 114936199: A Quadruple Star System with a 12-day Outer Orbit Eclipse

We report the discovery with TESS of a remarkable quadruple star system with a 2+1+1 configuration. The two unique characteristics of this system are that (i) the inner eclipsing binary (stars Aa and Ab) eclipses the star in the outermost orbit (star C), and (ii) these outer 4th body eclipses last for $\sim$12 days, the longest of any such system known. The three orbital periods are $\sim$3.3 days, $\sim$51 days, and $\sim$2100 days. The extremely long duration of the outer eclipses is due to the fact that star B slows binary A down on the sky relative to star C. We combine TESS photometric data, ground-based photometric observations, eclipse timing points, radial velocity measurements, the composite spectral energy distribution, and stellar isochones in a spectro-photodynamical analysis to deduce all of the basic properties of the four stars (mass, radius, $T_{\rm eff}$, and age), as well as the orbital parameters for all three orbits. The four masses are $M_{\rm Aa} =0.382$M$_\odot$, $M_{\rm Ab} =0.300$M$_\odot$, $M_{\rm B} =0.540$M$_\odot$ and $M_{\rm C} =0.615$M$_\odot$, with a typical uncertainty of 0.015 M$_\odot$.

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arXiv2022

Eclipsing Binaries in Dynamically Interacting Close, Multiple Systems

Close, compact, hierarchical, multiple stellar systems, i.e., multiples having an outer orbital period from months to a few years, comprise a small, but continuously growing group of the triple and multiple star zoo. Many of them consist of at least one eclipsing pair of stars and, therefore, exhibit readily observable short-term dynamical interactions among the components. Thus, their dynamical and astrophysical properties can be explored with high precision. In this paper we present an overview of the history of the search for additional components around eclipsing binaries from the first serendipitous discoveries to more systematic recent studies. We describe the different observational detection methods and discuss their connections to the different kinds of astrophysical and dynamical information that can be mined from the different datasets. Moreover, the connection amongst the observable phenomena and the long-term dynamics of such systems is also discussed.

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arXiv2021

Eclipse timing variation analysis of OGLE-IV eclipsing binaries toward the Galactic Bulge. II. Short periodic triple stellar systems

We report an eclipse timing variations (ETV) study to identify close, stellar mass companions to the eclipsing binaries monitored during the photometric survey OGLE-IV. We also present an alternative automatic way to determine the first and last contacts of an eclipse. Applying the phase dispersion minimization method to identify potential triples, we find close third components with outer periods less than 1500 days in 23 systems. We present outer orbit solution for 21 of 23 systems. For the ten, tightest triples we find that the ETV can only be modeled with the combination of the light-travel time effect (LTTE) and third-body perturbations, while in case of another 11 systems, pure LTTE solutions are found to be satisfactory. In the remaining two systems we identify extra eclipses connected to the outer component, but for the incomplete and noisy ETV curves, we are unable to find realistic three-body solutions. Therefore, in these cases we give only the outer period.

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arXiv2020

A low-luminosity core-collapse supernova very similar to SN 2005cs

We present observations and analysis of PSN J17292918+7542390, a low-luminosity Type II-P supernova (LL SN IIP). The observed sample of such events is still low, and their nature is still under debate. Such supernovae are similar to SN 2005cs, a well-observed low-luminosity Type II-P event, having low expansion velocities, and small ejected $^{56}$Ni mass. We have developed a robust and relatively fast Monte-Carlo code that fits semi-analytic models to light curves of core collapse supernovae. This allows the estimation of the most important physical parameters, like the radius of the progenitor star, the mass of the ejected envelope, the mass of the radioactive nickel synthesized during the explosion, among others. PSN J17292918+7542390 has $R_0 = 91_{-70}^{+119} \cdot 10^{11} \;\text{cm}$, $M_\text{ej} = 9.89_{-1.00}^{+2.10} \; M_{\odot}$, $E_{\mathrm{kin}} = 0.65_{-0.18}^{+0.19} \;\text{foe}$, $v_{\mathrm{exp}} = 3332_{-347}^{+216}$ km s$^{-1}$, for its progenitor radius, ejecta mass, kinetic energy and expansion velocity, respectively. The initial nickel mass of the PSN J17292918+7542390 turned out to be $1.55_{-0.70}^{+0.75} \cdot 10^{-3} M_{\odot}$. The measured photospheric velocity at the earliest observed phase is 7000 km s$^{-1}$. As far as we can tell based on the small population of observed low-luminosity Type II-P supernovae, the determined values are typical for these events.

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arXiv2020

TIC 278956474: Two close binaries in one young quadruple system, identified by \textit{TESS}

We have identified a quadruple system with two close eclipsing binaries in TESS data. The object is unresolved in Gaia and appears as a single source at parallax 1.08~$\pm$0.01 mas. Both binaries have observable primary and secondary eclipses and were monitored throughout TESS Cycle 1 (sectors 1-13), falling within the TESS Continuous Viewing Zone. In one eclipsing binary (P = 5.488 d), the smaller star is completely occluded by the larger star during the secondary eclipse; in the other (P = 5.674 d) both eclipses are grazing. Using these data, spectroscopy, speckle photometry, SED analysis and evolutionary stellar tracks, we have constrained the masses and radii of the four stars in the two eclipsing binaries. The Li I EW indicates an age of 10-50 Myr and, with an outer period of $858^{+7}_{-5}$ days, our analysis indicates this is one of the most compact young 2+2 quadruple systems known.

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arXiv2019

A 9-Hr CV With One Outburst in 4 Years of Kepler Data

During a visual search through the Kepler main-field lightcurves, we have discovered a cataclysmic variable (CV) that experienced only a single 4-day long outburst over four years, rising to three times the quiescent flux. During the four years of non-outburst data the Kepler photometry of KIC 5608384 exhibits ellipsoidal light variations (`ELV') with a $\sim$12% amplitude and period of 8.7 hours. Follow-up ground-based spectral observations have yielded a high-quality radial velocity curve and the associated mass function. Additionally, H$α$ emission lines were present in the spectra even though these were taken while the source was presumably in quiescence. These emission lines are at least partially eclipsed by the companion K star. We utilize the available constraints of the mass function, the ELV amplitude, Roche-lobe filling condition, and inferred radius of the K star to derive the system masses and orbital inclination angle: $M_{\rm wd} \simeq 0.46 \pm 0.02 \, M_\odot$, $M_{\rm K} \simeq 0.41 \pm 0.03 \, M_\odot$, and $i \gtrsim 70^\circ$. The value of $M_{\rm wd}$ is the lowest reported for any accreting WD in a cataclysmic variable. We have also run binary evolution models using MESA to infer the most likely parameters of the pre-cataclysmic binary. Using the mass-transfer rates from the model evolution tracks we conclude that although the rates are close to the critical value for accretion disk stability, we expect KIC 5608384 to exhibit dwarf nova outbursts. We also conclude that the accreting white dwarf most likely descended from a hot subdwarf and, most notably, that this binary is one of the first bona fide examples of a progenitor of AM CVn binaries to have evolved through the CV channel.

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arXiv2016

The Continuing Story of SN IIb 2013df: New Optical and IR Observations and Analysis

SN 2013df is a nearby Type IIb supernova that seems to be the spectroscopic twin of the well-known SN 1993J. Previous studies revealed many, but not all interesting properties of this event. Our goal was to add new understanding of both the early and late-time phases of SN 2013df. Our spectral analysis is based on 6 optical spectra obtained with the 9.2m Hobby-Eberly Telescope during the first month after explosion, complemented by a near-infrared spectrum. We applied the SYNAPPS spectral synthesis code to constrain the chemical composition and physical properties of the ejecta. A principal result is the identification of "high-velocity" He I lines in the early spectra of SN 2013df, manifest as the blue component of the double-troughed profile at ~5650 A. This finding, together with the lack of clear separation of H and He lines in velocity space, indicates that both H and He features form at the outer envelope during the early phases. We also obtained ground-based BVRI and g'r'i'z' photometric data up to +45 days and unfiltered measurements with the ROTSE-IIIb telescope up to +168 days. From the modelling of the early-time quasi-bolometric light curve, we find $M_{ej} \sim 3.2-4.6 M_{\odot}$ and $E_{kin} \sim 2.6-2.8 \times 10^{51}$ erg for the initial ejecta mass and the initial kinetic energy, respectively, which agree well with the values derived from the separate modelling of the light-curve tail. Late-time mid-infrared excess indicates circumstellar interaction starting ~1 year after explosion, in accordance with previously published optical, X-ray, and radio data.

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arXiv2012

Dynamical masses, absolute radii and 3D orbits of the triply eclipsing star HD 181068 from Kepler photometry

HD 181068 is the brighter of the two known triply eclipsing hierarchical triple stars in the Kepler field. It has been continuously observed for more than 2 years with the Kepler space telescope. Of the nine quarters of the data, three have been obtained in short-cadence mode, that is one point per 58.9 s. Here we analyse this unique dataset to determine absolute physical parameters (most importantly the masses and radii) and full orbital configuration using a sophisticated novel approach. We measure eclipse timing variations (ETVs), which are then combined with the single-lined radial velocity measurements to yield masses in a manner equivalent to double-lined spectroscopic binaries. We have also developed a new light curve synthesis code that is used to model the triple, mutual eclipses and the effects of the changing tidal field on the stellar surface and the relativistic Doppler-beaming. By combining the stellar masses from the ETV study with the simultaneous light curve analysis we determine the absolute radii of the three stars. Our results indicate that the close and the wide subsystems revolve in almost exactly coplanar and prograde orbits. The newly determined parameters draw a consistent picture of the system with such details that have been beyond reach before.

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arXiv2010

Transit timing variations in eccentric hierarchical triple exoplanetary systems. I. Perturbations on the time-scale of the orbital period of the perturber

We study the long-term time-scale (i.e. period comaprable to the orbital period of the outer perturber object) transit timing variations in transiting exoplanetary systems which contain a further, more distant (a_2>>a_1) either planetary, or stellar companion. We give an analytical form of the O-C diagram (which describes such TTV-s) in trigonometric series, valid for arbitrary mutual inclinations, up to the sixth order in the inner eccentricity. We show that the dependence of the O-C on the orbital and physical parameters can be separated into three parts. Two of these are independent of the real physical parameters (i.e. masses, separations, periods) of a concrete system, and depend only on dimensionless orbital elements, and so, can be analyzed in general. We analyze these dimensionless amplitudes for different arbitrary initial parameters, as well as for two particular systems CoRoT-9b and HD 80606b. We find in general, that while the shape of the O-C strongly varies with the angular orbital elements, the net amplitude (departing from some specific configurations) depends only weakly on these elements, but strongly on the eccentricities. As an application, we illustrate how the formulae work for the weakly eccentric CoRoT-9b, and the highly eccentric HD 80606b. We consider also the question of detection, as well as the correct identification of such perturbations. Finally, we illustrate the operation and effectiveness of Kozai cycles with tidal friction (KCTF) in the case of HD 80606b.

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