ABSTRACT
V453 Cyg is an eclipsing binary containing 14 and 11 $\, {\rm M}_\odot$ stars in an eccentric short-period orbit. We have discovered β Cep-type pulsations in this system using Transiting ...Exoplanet Survey Satellite data. We identify seven significant pulsation frequencies, between 2.37 and 10.51 d−1, in the primary star. These include six frequencies that are separated by yet significantly offset from harmonics of the orbital frequency, indicating they are tidally perturbed modes. We have determined the physical properties of the system to high precision: V453 Cyg A is the first β Cep pulsator with a precise mass measurement. The system is a vital tracer of the physical processes that govern the evolution of massive single and binary stars.
ABSTRACT
We present an analysis of the high-mass eclipsing binary system VV Ori based on photometry from the TESS satellite. The primary star (B1 V, 9.5 $\, {\rm M}_\odot$) shows β Cephei pulsations ...and the secondary (B7 V, 3.8 $\, {\rm M}_\odot$) is possibly a slowly pulsating B star. We detect 51 significant oscillation frequencies, including two multiplets with separations equal to the orbital frequency, indicating that the pulsations are tidally perturbed. We analyse the TESS light curve and published radial velocities to determine the physical properties of the system. Both stars are only the second of their pulsation type with a precisely measured mass. The orbital inclination is also currently decreasing, likely due to gravitational interactions with a third body.
Context.
Eclipsing, spectroscopic double-lined binary star systems are excellent laboratories for calibrating theories of stellar interior structure and evolution. Their precise and accurate masses ...and radii measured from binary dynamics offer model-independent constraints and challenge current theories of stellar evolution.
Aims.
We aim to investigate the mass discrepancy in binary stars. This is the significant difference between stellar components’ masses measured from binary dynamics and those inferred from models of stellar evolution via positions of the components in the
T
eff
− log
g
Kiel diagram. We study the effect of near-core mixing on the mass of the convective core of the stars and interpret the results in the context of the mass discrepancy.
Methods.
We fitted stellar isochrones computed from a grid of
MESA
stellar evolution models to a homogeneous sample of eleven high-mass binary systems. Two scenarios are considered where individual stellar components of a binary system are treated independent of each other and where they are forced to have the same age and initial chemical composition. We also study the effect of the microturbulent velocity and turbulent pressure on the atmosphere model structure and stellar spectral lines, and its link with the mass discrepancy.
Results.
We find that the mass discrepancy is present in our sample and that it is anti-correlated with the surface gravity of the star. No correlations are found with other fundamental and atmospheric parameters, including the stellar mass. The mass discrepancy can be partially accounted for by increasing the amount of near-core mixing in stellar evolution models. We also find that ignoring the microturbulent velocity and turbulent pressure in stellar atmosphere models of hot evolved stars results in the overestimation of their effective temperature by up to 8%. Together with enhanced near-core mixing, this can almost entirely account for the ∼30% mass discrepancy found for the evolved primary component of V380 Cyg.
Conclusions.
We find a strong link between the mass discrepancy and the convective core mass. The mass discrepancy can be solved by considering the combined effect of extra near-core boundary mixing and the consistent treatment in the spectrum analysis of hot evolved stars. Our binary modelling results in convective core masses between 17 and 35% of the stellar mass, which is in excellent agreement with the results from gravity-mode asteroseismology of single stars. This implies larger helium core masses near the end of the main sequence than have been anticipated so far.
Context. KIC 10661783 is an eclipsing binary that shows δ Scuti-like oscillations. More than 60 pulsation frequencies have been detected in its light curve as observed by the Kepler satellite. Aims. ...We want to determine the fundamental stellar and system parameters of the eclipsing binary as a precondition for asteroseismic modelling of the pulsating component and to establish whether the star is a semi-detached Algol-type system. Methods. We measured the radial velocities of both components from new high-resolution spectra using TODCOR and compute the orbit using PHOEBE. We used the KOREL program to decompose the observed spectra into its components, and analysed the decomposed spectra to determine the atmospheric parameters. For this, we developed a new computer program for the normalisation of the KOREL output spectra. Fundamental stellar parameters are determined by combining the spectroscopic results with those from the analysis of the Kepler light curve. Results. We obtain Teff, log g, vsini, and the absolute masses and radii of the components, together with their flux ratio and separation. Whereas the secondary star rotates synchronously with the orbital motion, the primary star rotates subsynchronously by a factor of 0.75. The newly determined mass ratio of 0.0911 is higher than previously thought and means a detached configuration is required to fit the light curve. Conclusions. With its low orbital period and very low mass ratio, the system shows characteristics of the R CMa-type stars but differs from this group by being detached. Its current state is assumed to be that of a detached post-Algol binary system with a pulsating primary component.
ABSTRACT
Stars that are both pulsating and eclipsing offer an important opportunity to better understand many of the physical phenomena that occur in stars, because it is possible to measure the ...pulsation frequencies of stars for which the masses and radii are known precisely and accurately. KIC 9851944 is a double-lined detached eclipsing binary containing two F-stars which show both pressure and gravity mode pulsations. We present an analysis of new high-resolution spectroscopy of the system and high-quality light curves from the Kepler and TESS space missions. We determine the masses and effective temperatures of the stars to 0.6 per cent precision, and their radii to 1.0 and 1.5 per cent precision. The secondary component is cooler, but larger and more massive than the primary so is more evolved; both lie inside the δ Scuti and γ Doradus instability strips. We measure a total of 133 significant pulsation frequencies in the light curve, including 14 multiplets that each contain between 3 and 19 frequencies. We find evidence for tidal perturbations to some of the p and g modes, attribute a subset of the frequencies to either the primary or secondary star, and measure a buoyancy radius and near-core rotational frequency for the primary component. KIC 9851944 is mildly metal-rich and MIST isochrones from the MESA evolutionary code agree well with the observed properties of the system for an age of 1.25 Gyr.
We present Kepler photometry and ground-based spectroscopy of KIC 4544587, a short-period eccentric eclipsing binary system with self-excited pressure and gravity modes, tidally excited modes, ...tidally influenced p modes and rapid apsidal motion of 182 yr per cycle. The primary and secondary components of KIC 4544587 reside within the δ Scuti and γ Dor instability region of the Hertzsprung-Russell diagram, respectively. By applying the binary modelling software phoebe to prewhitened Kepler photometric data and radial velocity data obtained using the William Herschel Telescope and 4-m Mayall telescope at Kitt Peak Northern Observatory (KPNO), the fundamental parameters of this important system have been determined, including the stellar masses, 1.98 ±0.07 and 1.60 ± 0.06 M, and radii, 1.76 ± 0.03 and 1.42 ± 0.02 R⊙, for the primary and secondary components, respectively. Frequency analysis of the residual data revealed 31 modes, 14 in the gravity mode region and 17 in the pressure mode region. Of the 14 gravity modes, 8 are orbital harmonics: a signature of tidal resonance. While the measured amplitude of these modes may be partially attributed to residual signal from binary model subtraction, we demonstrate through consideration of the folded light curve that these frequencies do in fact correspond to tidally excited pulsations. Furthermore, we present an echelle diagram of the pressure mode frequency region (modulo the orbital frequency) and demonstrate that the tides are also influencing the p modes. A first look at asteroseismology hints that the secondary component is responsible for the p modes, which is contrary to our expectation that the hotter star should pulsate in higher radial overtone, higher frequency p modes.
ABSTRACT
The internal structures and properties of oscillating red-giant stars can be accurately inferred through their global oscillation modes (asteroseismology). Based on 1460 d of Kepler ...observations we perform a thorough asteroseismic study to probe the stellar parameters and evolutionary stages of three red giants in eclipsing binary systems. We present the first detailed analysis of individual oscillation modes of the red-giant components of KIC 8410637, KIC 5640750, and KIC 9540226. We obtain estimates of their asteroseismic masses, radii, mean densities, and logarithmic surface gravities by using the asteroseismic scaling relations as well as grid-based modelling. As these red giants are in double-lined eclipsing binaries, it is possible to derive their independent dynamical masses and radii from the orbital solution and compare it with the seismically inferred values. For KIC 5640750 we compute the first spectroscopic orbit based on both components of this system. We use high-resolution spectroscopic data and light curves of the three systems to determine up-to-date values of the dynamical stellar parameters. With our comprehensive set of stellar parameters we explore consistencies between binary analysis and asteroseismic methods, and test the reliability of the well-known scaling relations. For the three red giants under study, we find agreement between dynamical and asteroseismic stellar parameters in cases where the asteroseismic methods account for metallicity, temperature, and mass dependence as well as surface effects. We are able to attain agreement from the scaling laws in all three systems if we use $\Delta \nu _{\rm ref,emp} = 130.8 \pm 0.9 \,\mu$Hz instead of the usual solar reference value.
Context. Intermediate-mass stars are often overlooked. They are not supernova progenitors, but still host convective cores and complex atmospheres that require computationally expensive treatment. ...This means that there is a general lack of this class of stars modelled by state-of-the-art stellar structure and evolution codes. Aims. We used high-quality spectroscopy to update the dynamically obtained stellar parameters and to produce a new evolutionary assessment of the bright B0.5+B0.5 and B5V+B5V binary systems CW Cep and U Oph. Methods. We used new spectroscopy obtained with the Hermes spectrograph to revisit the photometric binary solution of the two systems. The updated mass ratio and effective temperatures are incorporated to obtain new dynamical masses for the primary and secondary. With these data we performed evolutionary modelling using isochrone-clouds to investigate the core properties of these stars. Results. We report the first abundances for CW Cep and U Oph, and we report an updated dynamical solution for the two systems. We find that we cannot uniquely constrain the amount of core boundary mixing in any of the stars we consider. Instead, we report their core masses and compare our results to previous studies. Conclusions. We find that the per-cent level precision on fundamental stellar quantities are accompanied with core mass estimates to a precision between ∼5% and 15%. We find that differences in analysis techniques can lead to substantially different evolutionary modelling results, which calls for the compilation of a homogeneously analysed sample to draw inferences on internal physical processes.
We present a detailed analysis and interpretation of the high-mass binary V380 Cyg, based on high-precision space photometry gathered with the Kepler space mission as well as high-resolution ...ground-based spectroscopy obtained with the HERMES spectrograph attached to the 1.2 m Mercator telescope. We derive a precise orbital solution and the full physical properties of the system, including dynamical component mass estimates of 11.43 ± 0.19 and 7.00 ± 0.14 M for the primary and secondary, respectively. Our frequency analysis reveals the rotation frequency of the primary in both the photometric and spectroscopic data and additional low-amplitude stochastic variability at low frequency in the space photometry with characteristics that are compatible with recent theoretical predictions for gravity-mode oscillations excited either by the convective core or by sub-surface convective layers. Doppler imaging analysis of the silicon lines of the primary suggests the presence of two high-contrast stellar surface abundance spots which are located either at the same latitude or longitude. Comparison of the observed properties of the binary with present-day single-star evolutionary models shows that the latter are inadequate and lack a serious amount of near-core mixing.
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