arXiv subjects

J. Daszyńska-Daszkiewicz

Publications and source records attributed to J. Daszyńska-Daszkiewicz.

At least 19 recordsLinked to original sources

arXiv2026

Asteroseismology of the multiperiodic field SX Phe pulsator BL Camelopardalis

BL Camelopardalis (BL Cam) is the most metal-poor SX Phoenicis star known in the Galactic field, making it an excellent test bed for studies of Population II stellar structure and evolution, as well as for investigating the formation channels of blue straggler stars. We aim to constrain fundamental stellar parameters and pulsational properties of BL Cam and identify the nature of its observed oscillation modes. We analysed high-precision space-based data from the TESS mission and long-term ground-based observations from the Zwicky Transient Facility (ZTF) survey. The ZTF data were primarily used to derive the orbital parameters of the system, while the TESS light curves enabled us to extract a rich oscillation spectrum. We identified multiple pulsation frequencies and performed seismic modelling using a Bayesian approach. We detected numerous pulsation frequencies, including a dominant radial mode and additional non-radial components. We predicted all fitted modes in our seismic models as excited. The models reproduced the two highest amplitude-independent frequencies (i.e. the radial fundamental mode and a dipole mode) and suggested the possible presence of additional radial overtones. The inferred stellar parameters confirm the extremely low metallicity of BL~Cam. We also confirm its binary nature, with an orbital period of 144 days. BL Cam provides a valuable benchmark for testing stellar models of metal-poor pulsators. The combination of space-based photometry and Bayesian seismic modelling enables robust constraints to be placed on its internal structure and pulsation properties.

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arXiv2026

Discovery of the First Octupole Pulsation Mode in a delta Scuti Star: A Stationary l = 3 Sectoral Mode

Aims. We are attempting to better understand how stellar pulsations in close binary systems are affected, and possibly induced, by tidal, Coriolis, and centrifugal forces. Methods. We analyzed TESS data for some 50,000 potential eclipsing binaries selected by machine learning algorithms in order to search for pulsation multiplets split by integer multiples of the orbital frequency. Results. We report on the discovery of an octupole pulsation mode in the binary star system TIC 287869463, which contains a delta Scuti star. This mode is actually a combination of Y3+3 and Y3-3 modes that are perturbed into a new eigenmode of the star via tidal, Coriolis, and centrifugal forces, which we call a Y33+ mode. The mode is stationary on the star. To our knowledge, this is the first time that such an l = 3 mode identification has been securely made in any delta Scuti star, and the first stationary l = 3 sectoral mode of this type seen in any star, including the Sun. The l = 3 pulsations appear as a combination of two components at 34.94617 per day and 39.31127 per day, split by exactly six times the frequency of the orbital motion to within better than 1 part in 100,000. We extract the pulsation frequencies from the TESS data spanning more than three years, and model the system to gain a better understanding of this novel asteroseismic discovery. The pulsation frequencies are found to be steadily increasing with time, but always maintaining a split equal to six times the orbital frequency. Conclusions. We discuss the implications for the broader class of "tidally tilted pulsators" and "tri-axial pulsators" that have been discovered to date. We conclude that these previous categories can all be interpreted as linear combinations of spherical harmonics whose axes coincide with the orbital axis and form new eigenmodes of the star via tidal, Coriolis, and centrifugal perturbations

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arXiv2025

Asteroseismology of blue stragglers in $ω$ Centauri: the case of five double-mode radial SX Phoenicis pulsators

We present the first extensive seismic modelling of SX Phe stars in the stellar system $ω$ Cen. First, using the new values of reddening $E(B-V)$ and distance modulus $(m-M)_V$, and bolometric corrections from Kurucz model atmospheres, we determine the effective temperatures and luminosities of all SX Phe variables in $ω$ Cen with available $(B-V)$ colours. Next, we carefully select SX Phe stars that have a frequency ratio strongly suggesting excitation of two radial modes, and, in addition, their preliminary pulsational models have the values of $(T_{\rm eff},~ L)$ consistent with observational determinations. For five double-mode radial pulsators, we perform an extensive seismic modeling using the Bayesian analysis based on Monte Carlo simulations. We study the effect of opacity tables and helium abundance. With the OPAL data and $Y=0.30$, we obtained masses in the range (1.0,~1.2) M$_{\odot}$, metallicity $Z\in(0.0007,~0.0029)$ and the age of about (1.9,~3.8) Gyr. The OP and OPLIB seismic models have always higher metallicites, sometimes outside the allowed range for $ω$ Cen. In the case of three stars, we find seismic models within the observed range of $(T_{\rm eff},~L)$ with all three opacity tables. In the case of two stars, with the highest metallicity, seismic models computed with the OP and OPLIB tables are located far outside the observed error box. The OPAL seismic models follow the age$-$metallicity relation known for $ω$ Cen from the literature.

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arXiv2022

The eclipsing binary systems with $δ$ Scuti component -- II. AB Cas

We present a complex study of the eclipsing binary system, AB Cas. The analysis of the whole TESS light curve, corrected for the binary effects, reveals 112 significant frequency peaks with 17 independent signals. The dominant frequency $f_1 = $17.1564 d$^{-1}$ is a radial fundamental mode. The $O-C$ analysis of the times of light minima from over 92 years leads to a conclusion that due to the ongoing mass transfer the system exhibits a change of the orbital period at a rate of 0.03 s per year. In order to find evolutionary models describing the current stage of AB Cas, we perform binary evolution computations. Our results show the AB Cas system as a product of the rapid non-conservative mass transfer with about 5-26 % of transferred mass lost from the system. This process heavily affected the orbital characteristics of this binary and its components in the past. In fact, this system closely resembles the formation scenarios of EL CVn type binaries. For the first time, we demonstrate the effect of binary evolution on radial pulsations and determine the lines of constant frequency on the HR diagram. From the binary and seismic modelling, we obtain constraints on various parameters. In particular, we constrain the overshooting parameter, $f_{\rm ov}\in [0.010,~0.018]$, the mixing-length parameter, $α_{\rm MLT}\in[1.2,~1.5]$ and the age, $t \in [2.3,~3.4]$ Gyr.

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arXiv2021

The eclipsing binary systems with $δ$ Scuti component. I. KIC 10661783

We present a comprehensive study of the eclipsing binary system KIC 10661783. The analysis of the whole Kepler light curve, corrected for the binary effects, reveals a rich oscillation spectrum with 590 significant frequency peaks, 207 of which are independent. In addition to typical $δ$ Sct frequencies, we find small-amplitude signals in the low-frequency range that, most probably, are a manifestation of gravity-mode pulsations. We perform binary-evolution computations for this system in order to find an acceptable model describing its current stage. Our models show that the binary KIC 10661783 was formed by a rapid, almost conservative, mass transfer that heavily affected the evolution of both components in the past. One of the most important effects of binary evolution is the enormous enrichment of the outer layers of the main component with helium. This fact profoundly influences the pulsational properties of $δ$ Scuti star models. For the first time, we demonstrate the effect of binary evolution on pulsational instability. We construct pulsational models of the main component in order to account for the mode instability of the observed frequencies. Whereas the single-star evolution model is pulsational stable in the whole frequency range, its binary-evolution counterpart has unstable modes, both, in high and low-frequency range. However, to obtain instability in almost a whole range of the observed frequencies, the modification of the mean opacity at the depth corresponding to temperatures log T = 4.69 K and log T = 5.06 K was necessary.

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arXiv2021

KIC5950759: a high-amplitude $δ$ Sct star with amplitude and frequency modulation near the terminal age main sequence

Amongst the intermediate mass pulsating stars known as $δ$ Sct stars is a subset of high-amplitude and predominantly radial-mode pulsators known as high-amplitude $δ$ Sct (HADS) stars. From more than 2000 $δ$ Sct stars observed by the Kepler space mission, only two HADS stars were detected. We investigate the more perplexing of these two HADS stars, KIC5950759. We study its variability using ground- and space-based photometry, determine its atmospheric parameters from spectroscopy and perform asteroseismic modelling to constrain its mass and evolutionary stage. From spectroscopy, we find that KIC5950759 is a metal-poor star, which is in agreement with the inferred metallicity needed to reproduce its pulsation mode frequencies from non-adiabatic pulsation models. Furthermore, we combine ground-based WASP and Kepler space photometry, and measure a linear change in period of order $\dot{P}/P \simeq 10^{-6}$ yr$^{-1}$ for both the fundamental and first overtone radial modes across a time base of several years, which is at least two orders of magnitude larger than predicted by evolution models, and is the largest measured period change in a $δ$ Sct star to date. Our analysis indicates that KIC5950759 is a metal-poor HADS star near the short-lived contraction phase and the terminal-age main sequence, with its sub-solar metallicity making it a candidate SX Phe star. KIC5950759 is a unique object amongst the thousands of known $δ$ Sct stars and warrants further study to ascertain why its pulsation modes are evolving remarkably faster than predicted by stellar evolution.

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arXiv2019

Complex asteroseismology of SX Phoenicis

We present seismic analysis of the prototype SX Phoenicis that aims at fitting the two radial-mode frequencies and the corresponding values of the bolometric flux amplitude (the parameter $f$), whose empirical values are derived from multi-coulor photometric observations. Seismic model that meets these conditions is of low mass, $M=1.05 M_\odot$, has moderately effective convection in the outer layers, described by the mixing length parameter $α_{\rm MLT} \approx 0.7$, and the microturbulent velocity in the atmospheres of about $ξ_{\rm t}\approx 8$km/s. Such seismic studies of stars like SX Phe are very important for deriving constraints on outer-layer convection, because the object is on the border between very effective and ineffective convection.

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arXiv2019

The first view of $δ$ Scuti and $γ$ Doradus stars with the TESS mission

We present the first asteroseismic results for $δ$ Scuti and $γ$ Doradus stars observed in Sectors 1 and 2 of the TESS mission. We utilise the 2-min cadence TESS data for a sample of 117 stars to classify their behaviour regarding variability and place them in the Hertzsprung-Russell diagram using Gaia DR2 data. Included within our sample are the eponymous members of two pulsator classes, $γ$ Doradus and SX Phoenicis. Our sample of pulsating intermediate-mass stars observed by TESS also allows us to confront theoretical models of pulsation driving in the classical instability strip for the first time and show that mixing processes in the outer envelope play an important role. We derive an empirical estimate of 74% for the relative amplitude suppression factor as a result of the redder TESS passband compared to the Kepler mission using a pulsating eclipsing binary system. Furthermore, our sample contains many high-frequency pulsators, allowing us to probe the frequency variability of hot young $δ$ Scuti stars, which were lacking in the Kepler mission data set, and identify promising targets for future asteroseismic modelling. The TESS data also allow us to refine the stellar parameters of SX Phoenicis, which is believed to be a blue straggler.

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arXiv2019

Age determination of galactic B-type stars in double-lined eclipsing binaries

We present the results of age determination for galactic B-type main sequence stars which are components of double-lined eclipsing binaries. Only detached systems are considered. We analyze 38 binary systems that meet such criteria. The analysis is based on evolutionary computations and we consider that the age is determined if there is a common value from the radius-age diagrams and the agreement in the position of both components in the Hertzsprung-Russel diagram. In some cases, to meet these two conditions, it was necessary to adjust the value of the metallicity, Z or/and the parameter of overshooting from the convective core, $α_{ov}$. We determine the consistent age for 33 binaries out of 38. Besides, we made an extensive computations and for each system we give the range of $α_{ov}$ and Z, for which the consistent solutions exist. The age of the studied B-type main sequence stars ranges, as counted from the Zero Age Main Sequence, from about 2.5 Myr to about 200 Myr.

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arXiv2018

Evolutionary stage of the massive component of the double-lined eclipsing binary V380 Cygni

We determine the age of the eclipsing binary V380 Cygni, whose components have a significant mass ratio, $M_B/M_A\approx$ 0.6. Because this binary exhibits spectral lines of both components, the values of masses and radii could be determined with a very high accuracy. Assuming that both components are on the main sequence, we derive the age of about 16 Myr. However, in this case the primary needs a large overshooting from the convective core ($f_{\rm{ov}} \approx 0.04$) and higher metallicity ($Z \approx 0.02$). It is difficult to tell whether such a high value of overshooting from the convective core is reliable or rather mimics other mixing processes, which took place on the whole main sequence evolution, e.g., resulting from diffusion, rotation etc. If the primary is already in the overall contraction phase or just after, then the age of the system is about 13 Myr. Based on the available observations, we cannot resolve what is the evolutionary stage of the V380 Cyg system. The analysis of the Kepler light curve does not show any significant periodicity besides the orbital frequency and, most probably, the rotational frequency and their multiplets.

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arXiv2015

Identification of pulsational modes in rotating slowly pulsating B-type stars

Knowledge of the geometry of pulsational modes is a prerequisite for seismic modelling of stars. In the case of slowly pulsating B-type (SPB) pulsators, the simple zero-rotation approach so far used for mode identification is usually not valid because pulsational frequencies are often of the order of the rotational frequency. Moreover, this approach allows us to determine only the spherical harmonic degree, $\ell$, while the azimuthal order, $m$, is beyond its reach. On the other hand, because of the density of oscillation spectra of SPB stars, knowledge of $m$ is indispensable if one wants to assign the radial order, $n$, to the observed frequency peaks. Including the effects of rotation via the traditional approximation, we perform identification of the mode angular numbers ($\ell,~m$) for 31 SPB stars with available multicolour time series photometry. Simultaneously, constraints on the rotational velocity, $V_{\rm rot}$, and the inclination angle, $i$, are determined assuming uniform rotation and a constant value of $V_{\rm rot}\sin i$. Dependence of the results on the adopted model is tested using HD\,21071 as an example. Despite some model uncertainties and limitations of the method, our studies show the correct approach to identifying the low-frequency oscillation modes.

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arXiv2014

Pulsations in B-type supergiants with masses $M<20M_\odot$ before and after core helium ignition

Evolutionary tracks and pulsational analysis of models with masses of 13-18 $M_\odot$ are presented. We address two important questions. The first one deals with one of the most unresolved problems in astrophysics, i.e., the existence of a blue loop after core helium ignition; the so called "to loop or not to loop" problem. We show that inward overshooting from the outer convective zone in the red giant phase is prerequisite for the development of the blue loop. Our second question concerns pulsational instability of models in the core helium burning phase. We present for the first time that models on the blue loop can have unstable modes driven by the $κ$ mechanism operating in the $Z-$bump. Contrary to post-main sequence models in the shell hydrogen burning phases, pulsational instability of the blue loop models depends mainly on effective temperature and metallicity is of secondary importance. Finally, we try to interpret the oscillation spectrum of the blue supergiant HD 163899, the only member of the SPBsg class, and to get some clue on the evolutionary status of the star.

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arXiv2014

Oscillation modes in the rapidly rotating Slowly Pulsating B-type star $\bmu$ Eridani

We present results of a search for identification of modes responsible for the six most significant frequency peaks detected in the rapidly rotating SPB star $μ$ Eridani. All published and some unpublished photometric data are used in our new analysis. The mode identification is carried out with the method developed by Daszyńska-Daszkiewicz et al. employing the phases and amplitudes from multi-band photometric data and relying on the traditional approximation for the treatment of oscillations in rotating stars. Models consistent with the observed mean parameters are considered. For the five frequency peaks, the candidates for the identifications are searched amongst unstable modes. In the case of the third frequency, which is an exact multiple of the orbital frequency, this condition is relaxed. The systematic search is continued up to a harmonic degree $\ell =6$. Determination of the angular numbers, $(\ell,m)$, is done simultaneously with the rotation rate, $V_{\rm rot}$, and the inclination angle, $i$, constrained by the spectroscopic data on the projected rotational velocity, $V_{\rm rot}\sin i$, which is assumed constant. All the peaks may be accounted for with g-modes of high radial orders and the degrees $\ell\le 6$. There are differences in some identifications between the models. For the two lowest--amplitude peaks the identifications are not unique. Nonetheless, the equatorial velocity is constrained to a narrow range of (135, 140) km/s. Our work presents the first application of the photometric method of mode identification in the framework of the traditional approximation and we believe that it opens a new promising direction in studies of SPB stars.

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arXiv2013

Application of the Baade-Wesselink method to a pulsating cluster Herbig Ae star: H254 in IC348

In this paper we present new photometric and radial velocity data for the PMS $δ$ Sct star H254, member of the young cluster IC 348. Photometric V,R$_C$,I$_C$ light curves were obtained at the Loiano and Asiago telescopes. The radial velocity data was acquired by means of the SARG@TNG spectrograph. High-resolution spectroscopy allowed us to derive precise stellar parameters and the chemical composition of the star, obtaining: T$_{\rm eff}$\,=\,6750\,$\pm$\,150 K; $\log g$\,=\,4.1\,$\pm$\,0.4 dex; [Fe/H]=-0.07$\pm$0.12 dex. Photometric and spectroscopic data were used to estimate the total absorption in the $V$ band A$_{\rm V}$=2.06$\pm$0.05 mag, in agreement with previous estimates. We adopted the technique of the difference in phase and amplitude between different photometric bands and radial velocities to verify that H254 is (definitely) pulsating in a radial mode. This occurrence allowed us to apply the CORS realization of the Baade--Wesselink method to obtain a value for the linear radius of H254 equal to 3.3$\pm$0.7 $R_\odot$. This result was used in conjunction with photometry and effective temperature to derive a distance estimate of 273$\pm$23 pc for H254, and, in turn for IC 348, the host cluster. This value is in agreement within the errors with the results derived from several past determinations and the evaluation obtained through the Hipparcos parallaxes. Finally, we derived the luminosity of H254 and studied its position in the Hertzsprung--Russell diagram. From this analysis it results that this $δ$--Scuti occupies a position close to the red edge of the instability strip, pulsates in the fundamental mode, has a mass of about 2.2 $M_\odot$ and an age of 5$\pm$1 Myr, older than previous estimates.

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arXiv2013

Pulsational instability in B-type supergiant stars

We present results of the instability analysis of the post-main sequence massive star models against radial and nonradial pulsations. We confirm that both p- and g-modes can be excited by the $κ$-mechanism acting in the metal opacity bump. However, as opposed to the previous claims, we find that an intermediate convective zone (ICZ) related to the hydrogen burning shell is not necessary for excitation of g-modes. These modes can be reflected at a minimum of the Brunt-Väisälä frequency, located at the top of the chemical composition gradient region surrounding the radiative helium core. This minimum is associated with the change of actual temperature gradient from the adiabatic value in the semiconvective zone to the radiative value above it. Thus, the existence of pulsations at this evolutionary stage does not prove the existence of the convective zone but only some reflective layer. Finally, we show that no regular patterns can be expected in oscillation spectra of blue supergiant pulsators but there is a prospect for identification of the mode degree, $\ell$, from multicolour photometry.

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arXiv2013

The $β$ Cep/SPB star 12 Lacertae: extended mode identification and complex seismic modelling

Results of mode identification and seismic modelling of the $β$ Cep/SBP star 12 Lacertae are presented. Using data on the multi-colour photometry and radial velocity variations, we determine or constrain the mode degree, $\ell$, for all pulsational frequencies. Including the effects of rotation, we show that the dominant frequency, $ν_1$, is most likely a pure $\ell=1$ mode and the low frequency, $ν_A$, is a dipole retrograde mode. We construct a set of seismic models which fit two pulsational frequencies corresponding to the modes $\ell= 0,$ p$_1$ and $\ell= 1,$ g$_1$ and reproduce also the complex amplitude of the bolometric flux variations, $f$, for both frequencies simultaneously. Some of these seismic models reproduce also the frequency $ν_A$, as a mode $\ell= 1,$ g$_{13}$ or g$_{14}$, and its empirical values of $f$. Moreover, it was possible to find a model fitting the six 12 Lac frequencies (the first five and $ν_A$), only if the rotational splitting was calculated for a velocity of $V_{\rm rot}\approx 75$ km/s. In the next step, we check the effects of model atmospheres, opacity data, chemical mixture and opacity enhancement. Our results show that the OP tables are preferred and an increase of opacities in the $Z-$bump spoils the concordance of the empirical and theoretical values of $f$.

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arXiv2011

Identification of Pulsation Modes in Main Sequence Stars: Potentials and Limits

We review the present-day methods of mode identification applied to main sequence pulsators focusing on those that make use of multicolour photometry and radial velocity data. The effects which may affect diagnostic properties of these observables are discussed. We also raise the problem of identification of high degree modes which can dominate oscillation spectra obtained from space-based projects.

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arXiv2010

Effect of NLTE model atmospheres on photometric amplitudes and phases of early B-type pulsating stars

We study all possible sources of inaccuracy in theoretical values of the photometric observables, i.e. amplitude ratios and phase differences, of early B-type main sequence pulsators. Here, we discuss effects of parameters coming from both models of stellar atmospheres and linear nonadiabatic theory of stellar pulsation. In particular, we evaluate for the first time the effect of the departure from the LTE approximation. The atmospheric input comes from line-blanketed, LTE and NLTE plane-parallel, hydrostatic models. To compute the limb-darkening coefficients for NLTE models, we use the Least-Square Method taking into account the accuracy of the flux conservation. We present effects of NLTE atmospheres, chemical composition and opacities on theoretical values of the photometric observables of early B-type pulsators. To this end, we compute tables with the passband fluxes, flux derivatives over effective temperature and gravity as well as the non-linear limb-darkening coefficients in 12 most often used passbands, i.e. in the Strömgern system, $uvby$, and in the Johnson-Cousins-Glass system, $UBVRIJHK$. We make these tables public available at the Wrocław HELAS Web page, http://helas.astro.uni.wroc.pl.

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