arXiv subjects

Alžběta Oplištilová

Publications and source records attributed to Alžběta Oplištilová.

4 recordsLinked to original sources

arXiv2026

Refined reduction and standardisation of 53 years of UBV photometry at Hvar

Emission-line stars classified as Be exhibit light and colour variability on various timescales, ranging from days to decades. Their evolution must be constrained by long-term observations that are accurately calibrated and stable. Here, we provide a new reduction of photoelectric UBV observations obtained at the Hvar observatory, spanning more than 50 years. This unique dataset is highly complementary to TESS. We used new, non-linear reduction equations, with temporally variable extinction over the course of the night, which allowed us to achieve long-term accuracy of 0.008 to 0.016 mag (1-sig uncertainty), as verified by the Johnson standards. We then classified 59 Be stars into five classes, based on their variability patterns; namely, long-term envelope (LTE), long-term cyclic (LTC), binarity (BIN), rapid low-amplitude (RLA), and long-term quiescence (LTQ). According to our observations, the percentages of stars in the individual classes are 44%, 24%, 25%, 66%, and 19%, respectively. The stars in the sample often exhibited more than one pattern. We confirm that the LTE-positive variability is more common than the inverse (20 vs 6); in addition, two stars exhibited both types (zeta Tau and V1294 Aql). According to our observations, the LTC variability and the LTE-positive variability are almost mutually exclusive. Among 26 binary systems, circular orbits are more common than eccentric ones (18 vs 8). As for the brightness variations between different quiescent phases, an increasing trend is less common than a decreasing one (4 vs 7), spanning from -6.5 to +6.0 mmag/yr. Our observations provide well-calibrated UBV light curves spanning several decades, offering a valuable dataset for investigations of Be-star variability and tests of various models, including the viscous decretion disc model. Continuous monitoring is important for beta Lyr, EW Lac, delta Sco, gamma Cas, and V1294 Aql.

astro-ph.SR↗

arXiv2026

TESS light curves and surface activity in two low-mass eclipsing binaries: NSVS 01031772 and 2MASS J04100497+2931023

The VRIC light curves were regularly measured for two eclipsing binaries, NSVS 01031772 and 2MASS J04100497+2931023 as part of our long-term observational project to study low-mass eclipsing binaries with a short orbital period and surface activity. The solution of the TESS light curves in PHOEBE results in a detached configuration. Absolute parameters of all components were improved: for N103: M1 = 0.5475 +/- 0.0035 M\sun, R1 = 0.5297 +/- 0.0035 R\sun, M2 = 0.5038 +/- 0.0040 M\sun, R2 = 0.5217 +/- 0.0035 R\sun, for 2M0410: M1 = 0.639 +/- 0.045 M\sun, R1 = 0.655 +/- 0.035 R\sun, M2 = 0.609 +/- 0.045 M\sun, R2 = 0.631 +/- 0.035 R\sun, where the temperatures of the primary components were adopted according to previous studies. The spectral type of the primary components was confirmed to be M4 and K5, and the mass ratio was derived as q = 0.920 +/- 0.003 or 0.952 +/- 0.010, respectively. We propose the presence of a third body in these systems: in the case of N103, a companion with a minimal mass of 50 MJup, orbiting the eclipsing pair with a period of about 19 years, and in 2M0410 a third body with a minimal mass of about 0.1 M\sun and a short orbital period of about 2.1 years. For N103, the hierarchical structure (2+1)+1 of a possible quadruple system was tested, but its stability was not proven. The characteristics and statistics of the flare events and dark regions on the surface of the components were estimated on the basis of the TESS and our own data. For N103, a mean frequency of flares of one per 40 hours was determined. In the case of 2M0410, practically no flares were detected.

astro-ph.SR↗

arXiv2025

VLTI observations of the Orion Belt stars: I. eps Orionis

Massive stars play a decisive role in the evolution of the Universe. In order to constrain their current state and structure, we need sufficiently complex models, constrained by astrometric, interferometric, and spectroscopic observations. However, they are not available for distant stars. Instead, we focused on the nearest massive stars in the Orion Belt. We obtained VLTI interferometric observations of Orion Belt stars and calibrated visibility data from the GRAVITY and PIONIER instruments. Additionally, we obtained spectroscopic data from the CFHT and CTIO observatories. For modelling, we used a modified version of PHOEBE2, extended with new interferometric and spectroscopic modules. To describe non-spherical, rotating, or Roche-like stars, integrals over triangular meshes have to be computed, using extensive grids of synthetic spectra. For fitting, we used the simplex algorithm and chi2 mapping of the parameter space. In this paper, we present single-star models of the B0Ia supergiant eps Ori. Interferometric visibilities indicate that the star is not spherical but rotating close to its critical velocity. The preferred distance, d=(384+-8)pc, corresponds to the median of distances for the Orion OB1b association. We obtained the following parameters: m=(28.4+-2.0)Msol, R=(27.6+-1.5)Rsol, Teff=25000 K, i=45deg, longitude of the ascending node, Omega=300deg, and Prot=4.3+1.0d. This compromise model provides a reasonable fit to wind-free Balmer line profiles, but there is still some tension between interferometric and spectroscopic datasets, corresponding to a faster- vs. slower-rotating star. Our fast-rotating model implies that circumstellar matter should be naturally present, in the form of wind or disk, and contribute to continuum radiation. The fast rotation of eps Ori is compatible with a merger, formed from a multiple system of comparable mass, like del, zet or sig Ori.

astro-ph.SR↗

arXiv2025

Physics Of Eclipsing Binaries. VII. Interferometric module

Interferometric measurements are essential to constrain models of stellar systems, by spatially resolving angular distances and diameters well below the classical diffraction limit. In this work, we describe the interferometric module of Phoebe, which could be used just for this purpose. Since binaries in Phoebe are represented by a triangular mesh, our complex model is based on the integration over triangles. Consequently, Roche distortion, rotation, non-synchronicity, misalignment, eclipses of components, darkening, reflection, or irradiation are all accurately accounted for. For comparison purposes, we provide a simplified model, where components are represented by circular disks. The key point of our approach is a possibility of combination with other datasets (light curves, radial velocities), which allows to construct robust models of stellar systems. This draft refers to a development version of Phoebe, available at https://github.com/miroslavbroz/phoebe2/tree/interferometry . It is not yet included in the official Phoebe repository!

astro-ph.SR↗