arXiv subjects

Dóra Tarczay-Nehéz

Publications and source records attributed to Dóra Tarczay-Nehéz.

4 recordsLinked to original sources

arXiv2026

Asteroseismic Analysis of the Merger Product Red Giant in the $γ$ Persei System

Context. $γ$ Persei is a long-period eclipsing binary system ($P\approx 14.6$ years) containing a red giant primary, and it is well known for its multi-faceted classification as a visual and spectroscopic binary. Its brightness and binary nature together make it a valuable target for both photometric and spectroscopic studies, particularly in the context of asteroseismology and stellar evolution, as the primary star likely formed through a stellar merger. Aims. We aim to determine the seismic parameters $ν_{\rm max}$, $Δν$, and the oscillation amplitudes of the primary component, an evolved giant, to estimate its seismic mass $-$ which we can compare to its estimated dynamic mass. Methods. We use Transiting Exoplanet Survey Satellite (TESS) data obtained during Sectors 58, 85, and 86 and to complement the space-based observations, we incorporate high-resolution RV measurements acquired by the Stellar Observations Network Group (SONG) during two distinct epochs; 2017 and 2024. Results. We successfully detect solar-like oscillations in $γ$ Per and infer a seismic mass of $3.25\pm0.13$ M$_\odot$, which is slightly below the dynamical mass. We find the photometric oscillation amplitudes to be significantly lower than predicted from scaling relations, but in line with other high-mass red giants. We also find that radial velocity amplitudes along the Hertzsprung-Russell diagram cannot be fitted uniformly with current scaling relations.

astro-ph.SR↗

arXiv2024

Stellar Evolution in Real Time II: R Hydrae and an Open-Source Grid of >3000 Seismic TP-AGB Models Computed with MESA

We present a comprehensive characterization of the evolved thermally pulsing asymptotic giant branch (TP-AGB) star R Hydrae, building on the techniques applied in Stellar Evolution in Real Time I (Molnár et al. 2019) to T Ursae Minoris. We compute over 3000 theoretical TP-AGB pulse spectra using MESA and GYRE and combine these with classical observational constraints and nearly 400 years of measurements of R Hya's period evolution to fit R Hya's evolutionary and asteroseismic features. Two hypotheses for the mode driving R Hya's period are considered. Solutions that identify this as the fundamental mode (FM) as well as the first overtone (O1) are consistent with observations. Using a variety of statistical tests, we find that R Hya is most likely driven by the FM and currently occupies the ``power down'' phase of an intermediate pulse (TP ~ 9-16). We predict that its pulsation period will continue to shorten for millennia. Using supplementary calculations from the Monash stellar evolution code, we also find that R Hya is likely to have undergone third dredge-up in its most recent pulse. The MESA+GYRE model grid used in this analysis includes exact solutions to the adiabatic equations of stellar oscillation for the first 10 radial-order pressure modes for every time step in every evolutionary track. The grid is fully open-source and packaged with a data visualization application. This is the first publicly available grid of TP-AGB models with seismology produced with MESA.

astro-ph.SR↗

arXiv2023

Testing ultralow amplitude Cepheid candidates in the Galactic disk by TESS and Gaia

Ultralow amplitude (ULA) and strange mode Cepheids are thought to be pulsating variable stars that are near to or are at the edges of the classical instability strip. Until now, a few dozen such variable star candidates have been found both in the Large Magellanic Cloud and the Milky Way. For the present work, we studied six ULA Cepheid candidates in the Milky Way, identified by using CoRoT and 2MASS data. In order to identify their positions in the period--luminosity and color--magnitude diagrams, we used the Gaia DR3 parallax and brightness data of each star to calculate their reddening-free absolute magnitudes and distances. Furthermore, we calculated the Fourier parameters (e.g., period and amplitude) of the light variations based on CoRoT and TESS measurements, and established the long-term phase shifts for four out of six stars. Based on the results, we conclude that none of the six ULA Cepheid candidates are pulsating variable stars, but rather rotation-induced variable stars (rotational spotted and $α^2$~Canum Venaticorum variables) that are either bluer or fainter than Cepheids would be.

astro-ph.SR↗

arXiv2021

Dipper-like variability of the Gaia alerted young star V555 Ori

V555 Ori is a T Tauri star, whose 1.5 mag brightening was published as a Gaia science alert in 2017. We carried out optical and near-infrared photometric, and optical spectroscopic observations to understand the light variations. The light curves show that V555 Ori was faint before 2017, entered a high state for about a year, and returned to the faint state by mid-2018. In addition to the long-term flux evolution, quasi-periodic brightness oscillations were also evident, with a period of about 5 days. At optical wavelengths both the long-term and short-term variations exhibited colourless changes, while in the near-infrared they were consistent with changing extinction. We explain the brightness variations as the consequence of changing extinction. The object has a low accretion rate whose variation in itself would not be enough to reproduce the optical flux changes. This behaviour makes V555 Ori similar to the pre-main sequence star AA Tau, where the light changes are interpreted as periodic eclipses of the star by a rotating inner disc warp. The brightness maximum of V555 Ori was a moderately obscured ($A_V$=2.3 mag) state, while the extinction in the low state was $A_V$=6.4 mag. We found that while the Gaia alert hinted at an accretion burst, V555 Ori is a standard dipper, similar to the prototype AA Tau. However, unlike in AA Tau, the periodic behaviour was also detectable in the faint phase, implying that the inner disc warp remained stable in both the high and low states of the system.

astro-ph.SR↗