Theodor Pribulla

Aims. We are striving to better understand the stellar and orbital properties of compact and tight triple star systems with large dynamical interactions. Methods. We analyze TESS photometric data, radial velocity measurements, and eclipse timing variation curves for the triple star system, TIC 366240660, with a photodynamical code to infer the properties of all three stars and orbital motions. Results. With an outer orbital period of only 30.5 d, this is the second most compact triple reported in the literature. We have determined the masses and T _eff values of the three stars with an accuracy of about 1% and the radii to about 2%. The inclination angles of the two planes, and the mutual inclination angle are found with an accuracy of better than 1/3°. The system is determined to be quite flat (to within 1/2°), but with an outer eccentricity of e _out ≃ 0.33. We find that the properties of the secondary star of the inner binary are completely inconsistent with the evolution of a single star in isolation, and it must have transferred most of its envelope to the current primary star in the inner binary during a prior episode of mass transfer. The eclipse timing variation (ETV) curve derived from the TESS photometric data shows that, in addition to a typical dynamical delay curve at the period of the outer orbit, there is also a much larger amplitude anomalous sinusoidal-like delay with a period of 840 d. This latter feature in the ETV curve is not yet describable in simple analytic terms, but it appears certain that it can be explained by the near integer (≃13:1) ratio of the outer to the inner orbital periods. Conclusions. We have extensively explored the exotic and anomalous ETVs of this highly compact triple system and found that they can exceed hours for the inner binary eclipses, and several days for the outer orbital eclipses. We provide a preliminary explanation for how these are related to the 13:1 mean motion resonance of the outer to inner orbits.

Context. The Pennsylvania-Toruń Planet Search, which operates on a sample of ∼1000 northern-hemisphere stars, has been underway since 2004. Stars with radial velocity (RV) amplitudes exceeding 2 km s ⁻¹ represent a backup subprogram sample dedicated to monitoring binary stars with multiple instruments. Aims. We used almost 21 years of combined RV measurements to search for Doppler signals consistent with stellar or brown dwarf companions and to produce a catalog of both known and previously unpublished binary stars in our planet-search sample. Methods. We analyzed the combined RV measurements, searching for stellar companions and obtaining orbital solutions for both known and new binary systems. We also searched for periods in available long-term photometric monitoring data from All Sky Automated Survey (ASAS), and applied Gaia astrometric data whenever available. Results. We report the results of long-term RV monitoring of 16 systems: new detections of low-mass companions to 11 stars and updated orbital elements based on combined sets of our new and literature data for five systems. For two objects (TYC 3318-00789-1 and TYC 3318-01538-1), we find evidence of activity or the influence of another unseen companion, possibly due to line-profile variations or unresolved spectral contamination. We present true masses for three systems in our sample: TYC 1931-1040-1, TYC 3451-1449-1, and TYC 3667-1636-1. We obtained these masses using Gaia DR3 non-single star data.

We present new CHEOPS transit observations of AU Mic b and AU Mic c obtained between June and September 2024, extending the baseline of transit-timing measurements of this young planetary system. For AU Mic b, the timing signal is well established, with a semi-amplitude (10 ± 3 min) and a characteristic modulation timescale (1168 ± 20 d) consistent with previous determinations. By contrast, the new CHEOPS data show that the large transit-timing deviation of AU Mic c reported previously was not sustained. After the steadily increasing timing trend observed in 2022 and 2023, the 2024 timings returned closer to the zero point of the observed-minus-calculated diagram, indicating a reversal of the previously reported behavior. For AU Mic c, both the transit-timing semi-amplitude (46 ± 26 min) and the characteristic modulation timescale (2150 ± 110 d) remain tentative. These results highlight the importance of continued long-term monitoring of the AU Mic system.

We present a comprehensive photometric analysis of 83 eclipsing binary systems using high-precision space photometry from the Transiting Exoplanet Survey Satellite (TESS). The targets were selected from the catalog of Avvakumova et al. to resolve historical classification uncertainties and characterize systems lacking modern data. Using the ELISa modeling code and a Markov Chain Monte Carlo approach, we derived fundamental photometric parameters as: q —photometric mass ratio, i —inclination, T ₂ / T ₁ —temperature ratio, Ω ₁ , Ω ₂ —surface potentials, R 1 e q , R 2 e q —equivalent radii in units of semimajor axis. The eight systems exhibit continuous period changes, three show potential light-time effects, and eleven require a third-light contribution. We modeled 26 active systems by incorporating a stellar spot. Using period–color and temperature–color diagrams, we identified several highly anomalous systems that challenge traditional classification schemes. The long-period contact candidate IT Nor ( P ≈ 1.75 days) is reinterpreted as a semidetached Algol-type system. Conversely, GX Nor ( P ≈ 0.27 days) is identified as a rare, short-period detached binary near the contact boundary. The hot, early-type systems V884 Mon and V395 And also occupy atypical parameter space for their short orbital periods, likely representing key transitional evolutionary phases.

We present results from 28 stellar occultations by the large trans-Neptunian object (50000) Quaoar registered between 2018 and 2025. By performing a joint analysis of this occultation dataset, along with nine other published events, we were able to fit an oblate ellipsoid shape, with equatorial semiaxes a and b of 566 . 1 − 2.2 + 2.5 km, and a polar semiaxis, c , of 511 . 2 − 3.7 + 3.6 km. It provides an equivalent volumetric diameter of 1094.4 ± 4.6 km and polar oblateness of 0.097 ± 0.011. Considering an absolute magnitude of H = 2.79 ± 0.35, we derive a geometric albedo of p _V = 0.125 ± 0.038. We have derived new upper limits to the surface pressure of a CH ₄ atmosphere of 0.15 nbar (1 σ ) and 0.65 nbar (3 σ ). We also provide a table with the 36 new astrometric positions for Quaoar. Using the new system mass derived from Weywot’s orbit around Quaoar, we calculated a density of 1.760 ± 0.109 g cm ⁻³ . Moreover, from the derived size and rotation period (8.8394 ± 0.0002 hr, we calculated that, if Quaoar is in Maclaurin hydrostatic equilibrium state, it would have a density of 1.859 ± 0.200 g cm ⁻³ . This result, within the error bars, is compatible with the value we found. Therefore, this work shows that Quaoar can be a Maclaurin object, being eligible as a dwarf planet.

Context . Stellar variability may originate from various phenomena such as binarity, pulsations, or rotation. These mechanisms can induce flux variations of similar magnitudes, shapes, and periods. Aims . We aim to determine mechanisms responsible for the sinusoidal variations in main-sequence stars hotter than 6500 K. Methods . We conducted our analysis using TESS long-cadence data complemented with high-resolution spectra from three spectrographs. From the initial sample of almost 46 000 objects, we selected 35 targets for spectroscopic follow-up. The comparison of light curves and radial-velocity curves allowed for the robust classification of these targets. Results . Among the 35 selected objects, 18 displayed variability, suggesting the presence of a companion (including the discovery of seven new binary systems and one candidate for a triple-star system), one was identified as a new pulsator, nine as new candidates for spotted stars, and seven objects had uncertain classification. Our analysis shows that at least half of randomly selected stars with sinusoidal brightness variations are binaries. Conclusions . The presented results illustrate the need for an individual approach to stellar classification, especially in cases where the photometric data alone is insufficient for determining the underlying phenomena behind the observed variations.

Aims. We have identified more than a hundred close triply eclipsing hierarchical triple star systems from data taken with the space telescope TESS. Many of them have outer periods less than, or close to, 100 days, and hence we call them ‘ultracompact hierarchical triples’. These systems are noteworthy in that we can potentially determine their dynamical and astrophysical parameters with a high precision, in many cases even without radial velocity data. In the present paper, we report the comprehensive study of ten new ultracompact triply eclipsing triple star systems, located in the northern ecliptic hemisphere, taken from this larger sample: TICs 198581208, 265274458, 283846096, 337993842, 351404069, 378270875, 403792414, 403916758, 405789362, and 461500036. Methods. Most of the data for this study come from TESS observations, but we obtained supplemental ground-based photometric measurements for two of the systems. The eclipse timing variation curves extracted from the TESS and the ground-based follow-up data, the photometric light curves, and the spectral energy distribution were combined in a complex photodynamical analysis to yield the stellar and orbital parameters of all ten systems. Results. The outer periods are in the range of 46.8–101.4 days. We found third-body-forced, rapid apsidal motion in four systems. Moreover, TIC 403916758 was found to be a double twin triple (i.e. both the inner and the outer mass ratios are close to unity). All of the systems are substantially flat, with mutual inclination angles of ≲5°. Finally, we have taken the results for the ten systems in the present paper and combined them with the system parameters for more than 30 other compact triples that we have reported on in previous work, in order to examine some of the global properties of these systems on a statistical basis.

We present an investigation of the classical nova V615 Vul that erupted on July 29, 2024. The results obtained are based on our multicolor observations at AI SAS, the M. R. Stefánik Observatory in Hlohovec and MAO NASU, as well as photometry from the AAVSO and ASAS-SN database. We also present spectral observations obtained with the 1.3-meter telescope at Skalnaté Pleso Observatory , when the very broad asymmetric H α emission line dominated during the nova’s decline. From the constructed light curves, we determined the brightness decay rates at 2 and 3 magnitudes, obtaining t 2,V = 5 d.2, t 3,V = 8 d.9 and t 3,B = 11 d.6, which corresponds to fast novae. We analyzed short-term brightness variations detected in the light curve around day 35 from the onset of the outburst. Using our V RcIc data, we found a period of 0 d .2238 ± 0.005, which we interpret as the orbital period of V615 Vul. We calculated color indices and estimated the color temperature of the system. The tracks in the the V −Rc and Rc −Ic diagrams exhibit loop-like variations caused by changes in the intensity and profile of the broad H α emission line, while the tracks in U − B/B − V diagram reflect changes in color temperature during the outburst-behavior typical of many cataclysmic variables and novae. We also estimated the main parameters of the system, such as the absolute magnitude, its distance, and the mass of the white dwarf.