arXiv subjects

Maja Vuckovic

Publications and source records attributed to Maja Vuckovic.

10 recordsLinked to original sources

arXiv2026

Extreme mass loss during common envelope evolution: the origin of the double low-mass white dwarf system J2102--4145

Eclipsing close double white dwarf (WD) systems provide a unique opportunity to directly constrain hydrogen-envelope retention and test common-envelope (CE) evolution in low-mass stars, since they allow precise determinations of stellar masses and radii. We analyze J2102-4145, an eclipsing binary composed of two low-mass helium-core white dwarfs in a 2.4-hour orbit. By comparing the observed radii and effective temperatures with updated evolutionary models for CE evolution and stable Roche-lobe overflow (SRLOF), we confirm that both stars are helium-core white dwarfs. The primary, with a mass of 0.375 solar masses, is consistent with SRLOF models that retain thick hydrogen envelopes and sustain residual nuclear burning, whereas the secondary, with a mass of 0.314 solar masses, can only be reproduced by CE models in which the hydrogen envelope is almost completely removed. The inferred cooling ages (approximately 220 Myr for the secondary and between about 260 and 510 Myr for the primary, depending on the contribution of residual nuclear burning) support a formation sequence in which the primary formed first through SRLOF, followed by a CE phase that produced the compact secondary. Reconstruction of the CE energy budget yields progenitor and orbital parameters consistent with this evolutionary picture. The unusually small radius of the secondary requires an extremely thin hydrogen envelope, with a mass below about 10e-7 solar masses, well below the values predicted by standard bifurcation criteria. J2102-4145 therefore provides one of the strongest observational constraints on the hydrogen-envelope mass of post-CE low-mass white dwarfs and represents a benchmark challenge for current prescriptions of envelope ejection.

astro-ph.SR↗

arXiv2023

Current status of the Extension of the FRIPON network in Chile

FRIPON is an efficient ground-based network for the detection and characterization of fireballs, which was initiated in France in 2016 with over one hundred cameras and which has been very successfully extended to Europe and Canada with one hundred more stations. After seven successful years of operation in the northern hemisphere, it seems necessary to extend this network towards the southern hemisphere - where the lack of detection is evident - to obtain an exhaustive view of fireball activity. The task of extending the network to any region outside the northern hemisphere presents the challenge of a new installation process, where the recommended and tested version of the several sub-systems that compose a station had to be replaced due to regional availability and compatibility considerations, as well as due to constant software and hardware obsolescence and updates. In Chile, we have a unique geography, with a vast extension in latitude, as well as desert regions, which have generated the need to evaluate the scientific and technical performance of the network under special conditions, prioritizing the optimization of a set of factors related to the deployment process, as well as the feasible and achievable versions of the required components, the geographical location of the stations, and their respective operational, maintenance, safety, and communication conditions. In this talk, we will present the current status of this effort, including a brief report on the obstacles and difficulties encountered and how we have solved them, the current operational status of the network in Northern Chile, as well as the challenges and prospects for the densification of the network over South America.

astro-ph.IM↗

arXiv2022

Asteroseismology of hot subdwarf B stars observed with TESS: discovery of two new gravity mode pulsating stars

TIC033834484 and TIC309658435 are long-period pulsating subdwarf B star, which were observed extensively (675 and 621 days, respectively) by the Transiting Exoplanet Survey Satellite (TESS). The high-precision photometric light curve reveals the presence of more than 40 pulsation modes including both stars. All the oscillation frequencies that we found are associated with gravity (g)-mode pulsations, with frequencies spanning from 80 $μ$Hz (2 500 s) to 400 $μ$Hz (12 000 s). We utilize the asteroseismic tools including asymptotic period spacings and rotational frequency multiplets in order to identify the pulsational modes. We found dipole (l = 1) mode sequences for both targets and calculate the mean period spacing of dipole modes ($ΔP_{l=1}$), which allows us to identify the modes. Frequency multiplets provide a rotation period of about 64 d for TIC033834484. From follow-up ground-based spectroscopy, we find that TIC\,033834484 has an effective temperature of 24 210 K (140), a surface gravity of logg = 5.28 (03) and TIC309658435 has an effective temperature of 25 910 K (150), a surface gravity of logg = 5.48 (03).

astro-ph.SR↗

arXiv2022

RR Lyrae From Binary Evolution: Abundant, Young and Metal-Rich

RR Lyrae are a well-known class of pulsating horizontal branch stars widely used as tracers of old, metal-poor stellar populations. However, mounting observational evidence shows that a significant fraction of these stars may be young and metal-rich. Here, through detailed binary stellar evolution modelling, we show that all such metal-rich RR Lyrae can be naturally produced through binary interactions. Binary companions of these RR Lyrae stars formed through binary interactions partly strip their progenitor's envelopes during a preceding red giant phase. As a result, stripped horizontal branch stars become bluer than their isolated stellar evolution counterparts and thus end up in the instability strip. In contrast, in the single evolution scenario, the stars can attain such colours only at large age and low metallicity. While binary-made RR Lyrae can possess any ages and metallicities, their Galactic population is relatively young (1 to 9 Gyr) and dominated by the Thin Disc and the Bulge. We show that Galactic RR Lyrae from binary evolution are produced at rates compatible with the observed metal-rich population and have consistent G-band magnitudes, Galactic kinematics and pulsation properties. Furthermore, these systems dominate the RR Lyrae population in the Solar Neighbourhood. We predict that all metal-rich RR Lyrae have an A, F, G or K-type companion with a long orbital period (P > 1000 d). Observationally characterising the orbital periods and masses of such stellar companions will provide valuable new constraints on mass and angular momentum-loss efficiency for Sun-like accretors and the nature of RR Lyrae populations.

astro-ph.SR↗

arXiv2022

Pulsating hydrogen-deficient white dwarfs and pre-white dwarfs observed with TESS -- IV. Discovery of two new GW Vir stars: TIC0403800675 and TIC1989122424

We present two new GW Vir-type pulsating white dwarf stars, TIC\,0403800675 (WD\,J115727.68-280349.64) and TIC\,1989122424 (WD J211738.38-552801.18) discovered in the Transiting Exoplanet Survey Satellite (TESS) photometric data. For both stars, the TESS light curves reveal the presence of oscillations with periods in a narrow range between 400 and 410\,s, which are associated with typical gravity ($g$)-modes. Follow-up ground-based spectroscopy shows that both stars have similar effective temperature ($T_\mathrm{eff} = 110,000 \pm 10,000$\,K) and surface gravity ($\log g = 7.5 \pm 0.5$), but different He/C composition (mass fractions): He\,=\,0.75 and C\,=\,0.25 for TIC\,0403800675, and He\,=\,0.50 and C\,=\,0.50 for TIC\,1989122424. By performing a fit to their spectral energy distributions, we found for both stars radii and luminosities of $R=0.019\pm0.002\,R_\odot$ and $\log(L/L_\odot)=1.68^{+0.15}_{-0.24}$, respectively. By employing evolutionary tracks of PG~1159 stars, we find the masses of both stars to be $0.56\pm0.18 M_{\odot}$ from the $\log g$-$T_\mathrm{eff}$ diagram and $0.60^{+0.11}_{-0.09} M_{\odot}$ from the Hertzsprung Russell diagram.

astro-ph.SR↗

arXiv2021

Looking into the cradle of the grave: J22564-5910, a young post-merger hot subdwarf?

We present the discovery of J22564-5910, a new type of hot subdwarf (sdB) which shows evidence of gas present in the system and has shallow, multi-peaked hydrogen and helium lines which vary in shape over time. All observational evidence points towards J22564-5910 being observed very shortly after the merger phase that formed it. Using high-resolution, high signal-to-noise spectroscopy, combined with multi-band photometry, Gaia astrometry, and TESS light curves, we aim to interpret these unusual spectral features. The photometry, spectra and light curves are all analyzed, and their results are combined in order to support our interpretation of the observations: the likely presence of a magnetic field combined with gas features around the sdB. Based on the triple-peaked H lines, the magnetic field strength is estimated and, by using the shellspec code, qualitative models of gas configurations are fitted to the observations. All observations can either be explained by a magnetic field of ~650 kG which enables the formation of a centrifugal magnetosphere, or a non-magnetic hot subdwarf surrounded by a circumstellar gas disk/torus. Both scenarios are not mutually exclusive and both can be explained by a recent merger. J22564-5910 is the first object of its kind. It is a rapidly spinning sdB with gas still present in the system. It is the first post-merger star observed this early after the merger event, and as such is very valuable system to test merger theories. If the magnetic field can be confirmed, it is not only the first magnetic sdB, but it hosts the strongest magnetic field ever found in a pre-white dwarf object. Thus, it could represent the long-sought for immediate ancestor of strongly magnetic WDs.

astro-ph.SR↗

arXiv2021

Asteroseismic analysis of variable hot subdwarf stars observed with TESS I. The mean g-mode period spacings in hot subdwarf B stars

We present photometric and spectroscopic analyses of gravity (g-mode) long-period pulsating hot subdwarf B (sdB) stars. We perform a detailed asteroseismic and spectroscopic analysis of five pulsating sdB stars observed with {\it TESS} aiming at the global comparison of the observations with the model predictions based on our stellar evolution computations coupled with the adiabatic pulsation computations. We apply standard seismic tools for mode identification, including asymptotic period spacings and rotational frequency multiplets. We calculate the mean period spacing for $l = 1$ and $l = 2$ modes and estimate the errors by means of a statistical resampling analysis. For all stars, atmospheric parameters were derived by fitting synthetic spectra to the newly obtained low-resolution spectra. We have computed stellar evolution models using {\tt LPCODE} stellar evolution code, and computed $l = 1$ g-mode frequencies with the adiabatic non-radial pulsation code {\tt LP-PUL}. Derived observational mean period spacings are then compared to the mean period spacings from detailed stellar evolution computations coupled with the adiabatic pulsation computations of g-modes. The atmospheric parameters derived from spectroscopic data are typical of long-period pulsating sdB stars with the effective temperature ranging from 23\,700\,K to 27\,600\,K and surface gravity spanning from 5.3\,dex to 5.5\,dex. In agreement with the expectations from theoretical arguments and previous asteroseismological works, we find that the mean period spacings obtained for models with small convective cores, as predicted by a pure Schwarzschild criterion, are incompatible with the observations. We find that models with a standard/modest convective boundary mixing at the boundary of the convective core are in better agreement with the observed mean period spacings and are therefore more realistic.

astro-ph.SR↗

arXiv2020

TOI-481 b & TOI-892 b: Two long period hot Jupiters from the Transiting Exoplanet Survey Satellite

We present the discovery of two new 10-day period giant planets from the Transiting Exoplanet Survey Satellite ($TESS$) mission, whose masses were precisely determined using a wide diversity of ground-based facilities. TOI-481 b and TOI-892 b have similar radii ($0.99\pm0.01$ $\rm R_{J}$ and $1.07\pm0.02$ $\rm R_{J}$, respectively), and orbital periods (10.3311 days and 10.6266 days, respectively), but significantly different masses ($1.53\pm0.03$ $\rm M_{J}$ versus $0.95\pm0.07$ $\rm M_{J}$, respectively). Both planets orbit metal-rich stars ([Fe/H]= $+0.26\pm 0.05$ dex and [Fe/H] = $+0.24 \pm 0.05$ dex, for TOI-481 and TOI-892, respectively) but at different evolutionary stages. TOI-481 is a $\rm M_{\star}$ = $1.14\pm0.02$ $\rm M_{\odot}$, $\rm R_{\star}$ = $1.66\pm0.02$ $\rm R_{\odot}$ G-type star ($T_{\rm eff}$ = $5735 \pm 72$ K), that with an age of 6.7 Gyr, is in the turn-off point of the main sequence. TOI-892, on the other hand, is a F-type dwarf star ($T_{\rm eff}$ = $6261 \pm 80$ K), which has a mass of $\rm M_{\star}$ = $1.28\pm0.03$ $\rm M_{\odot}$, and a radius of $\rm R_{\star}$ = $1.39\pm0.02$ $\rm R_{\odot}$. TOI-481 b and TOI-892 b join the scarcely populated region of transiting gas giants with orbital periods longer than 10 days, which is important to constrain theories of the formation and structure of hot Jupiters.

astro-ph.EP↗

arXiv2020

Observed binary populations reflect the Galactic history. Explaining the orbital period-mass ratio relation in wide hot subdwarf binaries

Wide hot subdwarf B (sdB) binaries with main-sequence companions are outcomes of stable mass transfer from evolved red giants. The orbits of these binaries show a strong correlation between their orbital periods and mass ratios. The origins of this correlation have, so far, been lacking a conclusive explanation. We aim to find a binary evolution model which can explain the observed correlation. Radii of evolved red giants, and hence the resulting orbital periods, strongly depend on their metallicity. We have performed a small but statistically significant binary population synthesis study with the binary stellar evolution code MESA. We have used a standard model for binary mass loss and a standard Galactic metallicity history. The resulting sdBs were selected based on the same criteria as used in observations and then compared with the observed population. We have achieved an excellent match to the observed period - mass ratio correlation without explicitly fine-tuning any parameters. Furthermore, our models produce a good match to the observed period - metallicity correlation. We predict several new correlations which link the observed sdB binaries to their progenitors, and a correlation between the period, metallicity and core mass for subdwarfs and young low-mass He white dwarfs. We also predict that sdB binaries have distinct orbital properties depending on whether they formed in the bulge, thin or thick disc, or the halo. We demonstrate, for the first time, how the metallicity history of the Milky Way is imprinted in the properties of the observed post-mass transfer binaries. We show that Galactic chemical evolution is an important factor in binary population studies of interacting systems containing at least one evolved low-mass (Mi < 1.6 Msol) component. Finally, we provide an observationally supported model of mass transfer from low-mass red giants onto main-sequence stars.

astro-ph.SR↗

arXiv2017

The orbits of subdwarf-B + main-sequence binaries: III. The period - eccentricity distribution

The predicted orbital-period distribution of the subdwarf-B (sdB) population is bi-modal with a peak at short (< 10 days) and long (> 500 days) periods. Observationally, many short-period sdB systems are known, but only few wide sdB binaries have been studied in detail. Based on a long-term monitoring program the wide sdB sample has been increased, finding an unexpected correlation between the eccentricity and period. In this article we present the orbital solution and spectral analysis of four new systems, BD-7.5977, EC11031-1348, TYC2084-448-1 and TYC3871-835-1, and update the orbital solution of PG1104+243. Using the whole sample of wide sdBs, we aim at finding possible correlations between orbital and spectral properties, with as goal improving theoretical models of Roche-lobe overflow. High-resolution spectra were obtained to determine the radial velocities of both the sdB and MS components. Surface gravities and temperatures of both component were derived from photometric spectral-energy distributions. Spectral parameters of the cool companion were verified using the GSSP code. Furthermore the amount of accreted mass was estimated. Orbital parameters matching the earlier observed period-eccentricity relation were found for three systems, while TYC 2084-448-1 is found to have a lower eccentricity than expected from the period-eccentricity trend indicated by the other systems. Based on new observations, the orbit of PG 1104+243 has a small but significant eccentricity of 0.04 $\pm$ 0.02, matching other systems with similar periods. Furthermore, a correlation between accreted mass and orbital period was found, as well as a possible relation between the initial mass-ratio and the final period-eccentricity. The wide sdB-binary sample shows interesting possible correlations between orbital and spectral properties. However, a larger sample is necessary to statistically validate them.

astro-ph.SR↗