arXiv subjects

Jadwiga Daszynska-Daszkiewicz

Publications and source records attributed to Jadwiga Daszynska-Daszkiewicz.

10 recordsLinked to original sources

arXiv2024

Asteroseismology of the fast-rotating high-amplitude $δ$ Scuti star V2367 Cygni

We present the comprehensive analysis of the high-amplitude $δ$ Sct star V2367 Cygni. Firstly, we perform the frequency analysis for the whole available set of the {\it Kepler} and {\it TESS} photometry. Most of the frequency peaks are harmonics or combinations of the three known independent frequencies with the highest amplitudes, i.e., $ν_1=5.66106$\,d$^{-1}$, $ν_2=7.14898$\,d$^{-1}$ and $ν_3=7.77557$\,d$^{-1}$. The total number of independent frequencies is 26 and 25 from the {\it Kepler} and {\it TESS} light curve, respectively. Then, using the $UBVRI$ time-series photometry, we unambiguously identify the dominant frequency $ν_1$ as the radial mode, whereas in the case of frequencies $ν_2$ and $ν_3$ the most probable mode degrees are $\ell=0$ or $\ell=2$. However, only the frequency $ν_2$ can be associated with a radial mode, and only if higher order effects of rotation are taken into account. Including the rotational mode coupling, we constructed complex seismic models of V2367\,Cyg, which fit $ν_1$ and $ν_2$ as radial modes, and reproduce the amplitude of bolometric flux variations (the parameter $f$) for the dominant mode. The empirical values of $f$ are derived from the $UBVRI$ amplitudes and phases. We rely on the Bayesian analysis based on Monte Carlo simulations to derive constraints on evolutionary stage, mass, rotation, overshooting from the convective core and efficiency of convective transport in the envelope. Our seismic analysis clearly indicates that V2367\,Cyg is in a post-MS phase of evolution. This is the first extensive seismic modelling that takes into account the effect of rotational coupling between pulsation modes.

astro-ph.SR↗

arXiv2021

Mode identification and seismic study of $δ$ Scuti, the prototype of a class of pulsating stars

We present a seismic study of $δ$ Scuti based on a mode identification from multicoulor photometry. The dominant frequency can be associated only with a radial mode and the second frequency is, most probably, a dipole mode. The other six frequencies have more ambiguous identifications. The photometric mode identification provided also some constraints on the atmospheric metallicity [m/H]$\approx$+0.5 and microturbulent velocity $ξ_t\approx 4~\kms$.\\ For models reproducing the dominant frequency, we show that only the fundamental mode is possible and the first overtone is excluded. However, the location of $δ$ Scuti near the terminal age main sequence requires the consideration of three stages of stellar evolution. For the star to be on the main sequence, it is necessary to include overshooting from the convective core with a parameter of at least $α_{\rm ov}=0.25$ at the metallicity greater than $Z=0.019$. It turned out that the value of the relative amplitude of the bolometric flux variations (the nonadiabatic parameter $f$) is mainly determined by the position of the star in the HR diagram, i.e., by its effective temperature and luminosity, whereas the effect of the evolutionary stage is minor. On the other hand, the convective efficiency in the subphotospheric layers has a dominant effect on the value of the parameter $f$. %in the $δ$ Sct star models. Comparing the theoretical and empirical values of $f$ for the radial dominant mode, we obtain constraints on the mixing length parameter $α_{\rm MLT}$ which is less than about 1.0, independently of the adopted opacity data and chemical mixture. This value of $α_{\rm MLT}$ is substantially smaller than for a calibrated solar model indicating rather low to moderately efficient convection in the envelope of $δ$ Scuti.

astro-ph.SR↗

arXiv2019

Testing stellar opacities using asteroseismology

We present what constraints on opacities can be derived from the analysis of stellar pulsations of BA-type main-sequence stars. This analysis consists of the construction of complex seismic models which reproduce the observed frequencies as well as the bolometric flux amplitude extracted from the multi-colour photometric variations. Stellar seismology, i.e., {\it asteroseismology}, is a relatively young branch of astrophysics and, currently, provides the most accurate test of the theory of internal structure and evolution. We show that opacities under stellar conditions need to be modified at the depth of temperatures $T=110~000-290~000$\,K. The revision of opacity data is of great importance because they are crucial for all branches of astrophysics.

astro-ph.SR↗

arXiv2019

Diverse Variability of O and B Stars Revealed from 2-minute Cadence Light Curves in Sectors 1 and 2 of the TESS Mission: Selection of an Asteroseismic Sample

Uncertainties in stellar structure and evolution theory are largest for stars undergoing core convection on the main sequence. A powerful way to calibrate the free parameters used in the theory of stellar interiors is asteroseismology, which provides direct measurements of angular momentum and element transport. We report the detection and classification of new variable O and B stars using high-precision short-cadence (2-min) photometric observations assembled by the Transiting Exoplanet Survey Satellite (TESS). In our sample of 154 O and B stars, we detect a high percentage (90%) of variability. Among these we find 23 multiperiodic pulsators, 6 eclipsing binaries, 21 rotational variables, and 25 stars with stochastic low-frequency variability. Several additional variables overlap between these categories. Our study of O and B stars not only demonstrates the high data quality achieved by TESS for optimal studies of the variability of the most massive stars in the Universe, but also represents the first step towards the selection and composition of a large sample of O and B pulsators with high potential for joint asteroseismic and spectroscopic modeling of their interior structure with unprecedented precision.

astro-ph.SR↗

arXiv2018

What have we learnt from pulsations of B-type stars?

We review the main results obtained from our seismic studies of B-type main sequence pulsators, based on the ground-based, MOST, Kepler and BRITE observations. Important constraints on stellar opacities, convective overshooting and rotation are derived. In each studied case, a significant modification of the opacity profile at the depths corresponding to the temperature range $\log{T}\in (5.0-5.5)$ is indispensable to explain all pulsational properties. In particular, a huge amount of opacity (at least 200\%) at the depth of the temperature $\log T = 5.46$ (the "nickel" opacity) has to be added in early B-type stellar models to account for low frequencies which correspond to high-order g modes. The values of the overshooting parameter, $α_{\rm ov}$, from our seismic studies is below 0.3. In the case of a few stars, the deeper interiors have to rotate faster to get the g-mode instability in the whole observed range.

astro-ph.SR↗

arXiv2017

On possible explanations of pulsations in Maia stars

The long-time photometric surveys in a few young open clusters allowed to identify the light variability in stars located on the HR diagram between the well defined $δ$ Scuti variables and Slowly Pulsating B-type stars. Several objects of this type were suggested also from the analysis of the Kepler data. Assuming the pulsational origin of this variability, we try to explain the observed frequencies with pulsational models involving rotation and/or modification of the mean opacity profile.

astro-ph.SR↗

arXiv2009

Complex asteroseismology of the B-type main sequence pulsators

We present examples of an extended asteroseismic modelling in which we aim at fitting not only pulsational frequencies but also certain complex parameter related to each frequency. This kind of studies, called \textbf{complex asteroseismology}, has been successfully applied to a few main sequence B-type pulsators and provided, in particular, plausible constraints on \textbf{stellar opacities}. Here, we briefly describe our results for three early B-type stars.

astro-ph.SR↗

arXiv2009

Challenges for stellar pulsation and evolution theory

During the last few decades, great effort has been made towards understanding hydrodynamical processes which determine the structure and evolution of stars. Up to now, the most stringent constraints have been provided by helioseismology and stellar cluster studies. However, the contribution of asteroseismology becomes more and more important, giving us an opportunity to probe the interiors and atmospheres of very different stellar objects. A variety of pulsating variables allows us to test various parameters of micro- and macrophysics by means of oscillation data. I will review the most outstanding key problems, both observational and theoretical, of which our knowledge can be improved by means of asteroseismology.

astro-ph.SR↗

arXiv2007

Identifying pulsation modes from two-passband photometry

I discuss a prospect for mode identification from two-passband photometry of forthcoming BRITE space mission. Examples of photometric diagnostic diagrams are shown for three types of main sequence pulsating variables: $β$ Cephei, Slowly Pulsating B-type and $δ$ Scuti stars. I consider also taking into account the radial velocity data from simultaneous spectroscopy, which can be carried out from the ground. With such observations, much better discrimination of the spherical harmonic degree, $\ell$, can be accomplished and more constraints on stellar parameters and input physics can be derived.

astro-ph↗

arXiv2006

Pulsation properties of the $β$ Cephei star SY Equ from combined photometric and spectroscopic data

We present the analysis of simultaneous multicolour $uvyI_{\rm C}$ photometry and low-resolution spectroscopy for the rapidly rotating $β$ Cephei star SY Equ. From the photometric time series, we confirm the dominant pulsation frequency, $f_1$ = 6.029 d$^{-1}$, and we find an evidence for two additional modes. In spectroscopy, the highest peak occurs at $f_{\rm a}$ = 0.197 d$^{-1}$ or its alias 0.803 d$^{-1}$. It can be interpreted either in terms of a binary motion or as the $g$-mode pulsation. In addition, we reveal the pulsation mode with frequency of about 6.029 d$^{-1}$, i.e. the same which dominates photometric variations, and a few new candidates. For the dominant frequency we obtain mode identification from the combined photometric and spectroscopic observations. From non-adiabatic pulsation calculations, we show that the frequency of the dominant mode in SY Equ is consistent with the stellar models of much lower effective temperatures than used in many papers.

astro-ph↗