arXiv subjects

D. Tarczay-Nehéz

Publications and source records attributed to D. Tarczay-Nehéz.

9 recordsLinked to original sources

arXiv2026

A blue-straggler merger scenario origin for the $γ$~Persei binary system

We used \texttt{MIST} isochrone fitting and a dedicated grid of stellar evolution models computed with MESA to constrain the ages of the components of the $γ$ Persei binary system. While individual stars can be matched to the models at specific metallicities, no joint isochrone solution reproduces both the observed masses and evolutionary states. The stellar evolutionary tracks calculated by MESA reveal a clear evolutionary mismatch. The primary component of the system is in a post-main-sequence phase consistent with the red giant branch or red clump. In contrast, the lighter secondary component lies near the turn-off point of the main sequence or is in the early phase of the subgiant branch. This discrepancy can be overcome by assuming that the $γ$ Persei system was born as a triple and the primary component is a rejuvenated star formed through a merger of a close-by pair of main-sequence stars. We show that the merger must have occurred no later than a few hundred megaryears after system formation, and the progenitor masses of the merging stars are restricted by a combination of stars that fall within a narrow band in the $(M_{1,a},M_{1,b})$ plane, corresponding to $M_{1,a}\simeq0.9$--$2.1\,M_\odot$ and $M_{1,b}\simeq2.3$--$2.5\,M_\odot$.

astro-ph.SR↗

arXiv2026

MESAlab: A Python pipeline for MESA grid processing with integrated GYRE/MESA-RSP execution

Modules for Experiments in Stellar Astrophysics (MESA) is a widely used open-source code for modeling stellar evolution. Many applications of the code rely on large computational grids containing thousands of models, which can be time-consuming to analyze. The mesalab package was developed to automate this post-processing. This Python-based, modular pipeline supports the analysis of large MESA grid outputs and can identify selected evolutionary features, such as the blue loop phase of the evolution of classical Cepheids. The pipeline can automatically prepare input files for and launch MESA-RSP and GYRE to investigate the pulsation properties associated with these evolutionary phases. The pipeline also includes tools for visualizing evolutionary tracks, including Hertzsprung-Russell diagrams and Gaia color-magnitude diagrams.

astro-ph.IM↗

arXiv2026

Trajectory-Based Dust Evolution in Disks: First Results from the RAPID Simulation Code

The rapid depletion of dust particles in protoplanetary disks limits the time available for planetesimal formation, as solids are typically accreted onto the central star before dust particles can undergo substantial growth. Dust traps formed at sharp viscosity transitions $-$ such as at the edges of the accretionally inactive dead zones $-$ can halt radial drift and enhance dust coagulation. In this study, dust dynamics is investigated using \texttt{RAPID}, a one-dimensional Lagrangian-Eulerian simulation code that tracks representative particle trajectories over time. In order to explore the effect of physical parameters on dust evolution, a grid of 243 models was run. The simulation grid covers a range of parameters such as viscosity, width of the transition region at the edges of the dead zone, disk surface density exponent, and the collisional fragmentation velocity of the dust particles. The computational domain extends from 1 to 50 AU and covers $5\times10^5$ years of disk evolution, assuming a disk mass of $\sim 0.005\,M_\odot$. The results show that pressure maxima can trap up to $3-10\,M_\oplus$ of dust, depending on the local disk conditions. However, increasing the fragmentation velocity, decreasing the viscosity, or widening the dead zone transition width tends to reduce the effectiveness of dust trapping. The simulation results with \texttt{RAPID} reveal that dust evolution is highly sensitive to the physical conditions of the disk, which governs the early stages of planetesimal growth.

astro-ph.EP↗

arXiv2025

Stranger Things: A Grid-based Survey of Strange Modes in Post-Main Sequence Models

We present a systematic survey of strange mode pulsations in Cepheids using MESA and for the linear stability analysis, MESA RSP. Our model grid spans $2-15\,M_\odot$ in mass and [Fe/H] $= -0.95$-$0.17$ ($Z = 0.0015$-$0.0200$) in metallicity, with four convective overshoot prescriptions. Strange modes were identified in a relatively small fraction ($5-12.5$ %) of models, occurring at $n_\mathrm{pg} = 5-9$, with $n_\mathrm{pg} = 6$-$7$ as the most frequent radial modes. No unstable solutions were identified beyond $n_\mathrm{pg} = 9$, in contrast to earlier studies reporting strange modes at $n_\mathrm{pg} = 10-12$. We quantified the duration of the instability crossing phase ($τ_\mathrm{IS}$), the strange mode phase ($τ_\mathrm{s}$), and their ratio $\mathcal{P}_\mathrm{s} = τ_\mathrm{s} / τ_\mathrm{IS}$. Toward higher masses, both $τ_\mathrm{IS}$ and $τ_\mathrm{s}$ decrease, yet their ratio shows no systematic trend with mass in models that include convective core overshoot. The absolute timescales for strange modes remain short, typically $τ_\mathrm{s} \sim 10^{4.5}$-$10^{6}$ years, while $τ_\mathrm{IS}$ is often an order of magnitude shorter, implying that these stars may spend a larger fraction of their life in the strange mode phase than in the instability strip itself. The extended duration of the strange mode phase may enhance the detectability of strange mode pulsators, provided that observational precision is sufficient to capture their low-amplitude variability. The predicted periods ($0.6-6.3$ days) are well covered by a single $27-$day TESS sector, making strange mode pulsators potentially detectable with current space-based photometry, although blending with nearby sources may pose challenges.

astro-ph.SR↗

arXiv2022

Variable star classification with a Multiple-Input Neural Network

In this experiment, we created a Multiple-Input Neural Network, consisting of Convolutional and Multi-layer Neural Networks. With this setup the selected highest-performing neural network was able to distinguish variable stars based on the visual characteristics of their light curves, while taking also into account additional numerical information (e.g. period, reddening-free brightness) to differentiate visually similar light curves. The network was trained and tested on OGLE-III data using all OGLE-III observation fields, phase-folded light curves and period data. The neural network yielded accuracies of 89--99\% for most of the main classes (Cepheids, $δ$ Scutis, eclipsing binaries, RR Lyrae stars, Type-II Cepheids), only the first-overtone Anomalous Cepheids had an accuracy of 45\%. To counteract the large confusion between the first-overtone Anomalous Cepheids and the RRab stars we added the reddening-free brightness as a new input and only stars from the LMC field were retained to have a fixed distance. With this change we improved the neural network's result for the first-overtone Anomalous Cepheids to almost 80\%. Overall, the Multiple-input Neural Network method developed by our team is a promising alternative to existing classification methods.

astro-ph.SR↗

arXiv2021

On the evolution of vortex in locally isothermal self-gravitating discs: a parameter study

Gas rich dusty circumstellar discs observed around young stellar objects are believed to be the birthplace of planets and planetary systems. Recent observations revealed that large-scale horseshoe-like brightness asymmetries are present in dozens of transitional protoplanetary discs. Theoretical studies suggest that these brightness asymmetries bf could be caused by large-scale anticyclonic vortices triggered by the Rossby Wave Instability (RWI), which can be excited at the edges of the accretionally inactive region, the dead zone edge. Since vortices may play a key role in planet formation, investigating the conditions of the onset of RWI and the long-term evolution of vortices is inevitable. The aim of our work was to explore the effect of disc geometry (the vertical thickness of the disc), viscosity, the width of the transition region at the dead zone edge, and the disc mass on the onset, lifetime, strength and evolution of vortices formed in the disc. We performed a parametric study assuming different properties for the disc and the viscosity transition by running 1980 2D hydrodynamic simulations in the locally isothermal assumption with disc self-gravity included. Our results revealed that long-lived, large-scale vortex formation favours a shallow surface density slope and low- or moderate disc masses with Toomre $Q \lesssim 1/h$, where $h$ is the geometric aspect ratio of the disc. In general, in low viscosity models, stronger vortices form. However, rapid vortex decay and re-formation is more widespread in these discs.

astro-ph.EP↗

arXiv2020

The Exotic Type Ic Broad-Lined Supernova SN 2018gep: Blurring the Line Between Supernovae and Fast Optical Transients

In the last decade a number of rapidly evolving transients have been discovered that are not easily explained by traditional supernovae models. We present optical and UV data on onee such object, SN 2018gep, that displayed a fast rise with a mostly featureless blue continuum around maximum light, and evolved to develop broad features more typical of a SN Ic-bl while retaining significant amounts of blue flux throughout its observations. The blue excess is most evident in its near-UV flux that is over 4 magnitudes brighter than other stripped envelope supernovae, but also visible in optical g$-$r colors at early times. Its fast rise time of $t_{\rm rise,V} \lesssim 6.2 \pm 0.8$ days puts it squarely in the emerging class of Fast Evolving Luminous Transients, or Fast Blue Optical Transients. With a peak absolute magnitude of M$_r=-19.49 \pm 0.23 $ mag it is on the extreme end of both the rise time and peak magnitude distribution for SNe Ic-bl. Only one other SN Ic-bl has similar properties, iPTF16asu, for which less of the important early time and UV data have been obtained. We show that the objects SNe 2018gep and iPTF16asu have similar photometric and spectroscopic properties and that they overall share many similarities with both SNe Ic-bl and Fast Evolving Transients. We obtain IFU observations of the SN 2018gep host galaxy and derive a number of properties for it. We show that the derived host galaxy properties for both SN 2018gep and iPTF16asu are overall consistent with the SNe Ic-bl and GRB/SNe sample while being on the extreme edge of the observed Fast Evolving Transient sample. These photometric observations are consistent with a simple SN Ic-bl model that has an additional form of energy injection at early times that drives the observed rapid, blue rise, and we speculate that this additional power source may extrapolate to the broader Fast Evolving Transient sample.

astro-ph.HE↗

arXiv2020

Image-based Classification of Variable Stars: First Results from Optical Gravitational Lensing Experiment Data

Recently, machine learning methods presented a viable solution for automated classification of image-based data in various research fields and business applications. Scientists require a fast and reliable solution to be able to handle the always growing enormous amount of data in astronomy. However, so far astronomers have been mainly classifying variable star light curves based on various pre-computed statistics and light curve parameters. In this work we use an image-based Convolutional Neural Network to classify the different types of variable stars. We used images of phase-folded light curves from the OGLE-III survey for training, validating and testing and used OGLE-IV survey as an independent data set for testing. After the training phase, our neural network was able to classify the different types between 80 and 99%, and 77-98% accuracy for OGLE-III and OGLE-IV, respectively.

astro-ph.SR↗

arXiv2020

On the vortex evolution in non-isothermal protoplanetary discs

It is believed that large-scale horseshoe-like brightness asymmetries found in dozens of transitional protoplanetary discs are caused by anticyclonic vortices. These vortices can play a key role in planet formation, as mm-sized dust -- the building blocks of planets -- can be accumulated inside them. Anticyclonic vortices are formed by the Rossby wave instability, which can be excited at the gap edges opened by a giant planet or at sharp viscosity transitions of accretionally inactive regions. It is known that vortices are prone to stretching and subsequent dissolution due to disc self-gravity for canonical disc masses in the isothermal approximation. To improve the hydrodynamic model of protoplanetary discs, we include the disc thermodynamics in our model. In this paper, we present our results on the evolution of the vortices formed at the outer edge of an accretionally inactive region (dead zone) assuming an ideal equation of state and taking $PdV$ work, disc cooling in the $β$-approximation, and disc self-gravity into account. Thermodynamics affects the offset and the mode number (referring to the number of small vortices at the early phase) of the RWI excitation, as well as the strength, shape, and lifetime of the large-scale vortex formed through merging of the initial small vortices. We found that the inclusion of gas thermodynamics results in stronger, however decreased lifetime vortices. Our results suggest that a hypothetical vortex-aided planet formation scenario favours effectively cooling discs.

astro-ph.EP↗