Grids of stellar evolution are required in many fields of astronomy/astrophysics, such as planet hosting stars, binaries, clusters, chemically peculiar stars, etc. In this study, a grid of stellar ...evolution models with updated ingredients and {recently determined solar abundaces} is presented. The solar values for the initial abundances of hydrogen, heavy elements and mixing-length parameter are 0.0172, 0.7024 and 1.98, respectively. The mass step is small enough (0.01 M\(_\odot\)) that interpolation for a given star mass is not required. The range of stellar mass is 0.74 to 10.00 M\(_\odot\). We present results in different forms of tables for easy and general application. The second stellar harmonic, required for analysis of apsidal motion of eclipsing binaries, is also listed. We also construct rotating models to determine effect of rotation on stellar structure and derive fitting formula for luminosity, radius and the second stellar harmonic as a function of rotational parameter. We also compute and list colours and bolometric corrections of models required for transformation between theoretical and observational results. The results are tested for the Sun, the Hyades cluster, the slowly rotating chemically peculiar Am stars and the eclipsing binaries with apsidal motion. The theoretical and observational results along isochrones are in good agreement. The grids are also applicable to rotating stars provided that equatorial velocity is given.
Recently, our understanding of the origin of W UMa-type contact binaries has become clearer. Initial masses of their components were successfully estimated by Yıldız and Doğan using a new method ...mainly based on observational properties of overluminous secondary components. In this paper, we continue to discuss the results and make computations for age and orbital evolution of these binaries. It is shown that the secondary mass, according to its luminosity, also successfully predicts the observed radius. While the current mass of the primary component is determined by initial masses, the current secondary mass is also a function of initial angular momentum. We develop methods to compute the age of A- and W-subtype W UMa-type contact binaries {in terms of} initial masses and mass according to the luminosity of the secondaries. Comparisons of our results with the mean ages from kinematic properties of these binaries and data pertaining to contact binaries in open and globular clusters, have increased our confidence on this method. The mean ages of both A- and W-subtype contact binaries are found as 4.4 and 4.6 Gyr, respectively. From kinematic studies, these ages are given as 4.5 and 4.4 Gyr, respectively. We also compute orbital properties of A-subtype contact binaries at the time of the first overflow. Initial angular momentum of these binaries is computed by comparing them with the well-known detached binaries. The angular momentum loss rate derived in the present study for the detached phase is in very good agreement with the semi-empirical rates available in the literature. In addition to the limitations on the initial masses of W UMa-type contact binaries, it is shown that the initial period of these binaries is less than about 4.45 d.
Over the course of its history, the Milky Way has ingested multiple smaller
satellite galaxies. While these accreted stellar populations can be
forensically identified as kinematically distinct ...structures within the Galaxy,
it is difficult in general to precisely date the age at which any one merger
occurred. Recent results have revealed a population of stars that were accreted
via the collision of a dwarf galaxy, called \textit{Gaia}-Enceladus, leading to
a substantial pollution of the chemical and dynamical properties of the Milky
Way. Here, we identify the very bright, naked-eye star $\nu$\,Indi as a probe
of the age of the early in situ population of the Galaxy. We combine
asteroseismic, spectroscopic, astrometric, and kinematic observations to show
that this metal-poor, alpha-element-rich star was an indigenous member of the
halo, and we measure its age to be $11.0 \pm 0.7$ (stat) $\pm 0.8$ (sys)$\,\rm
Gyr$. The star bears hallmarks consistent with it having been kinematically
heated by the \textit{Gaia}-Enceladus collision. Its age implies that the
earliest the merger could have begun was 11.6 and 13.2 Gyr ago at 68 and 95%
confidence, respectively. Input from computations based on hierarchical
cosmological models tightens (i.e. reduces) slightly the above limits.
Binary stars in which oscillations can be studied in either or both components can provide powerful constraints on our understanding of stellar physics. The bright binary 12 Bo\"otis (12 Boo) is a ...particularly promising system because the primary is roughly 60 per cent brighter than the secondary despite being only a few per cent more massive. Both stars have substantial surface convection zones and are therefore, presumably, solar-like oscillators. We report here the first detection of solar-like oscillations and ellipsoidal variations in the TESS light curve of 12 Boo. Though the solar-like oscillations are not clear enough to unambiguously measure individual mode frequencies, we combine global asteroseismic parameters and a precise fit to the spectral energy distribution (SED) to provide new constraints on the properties of the system that are several times more precise than values in the literature. The SED fit alone provides new effective temperatures, luminosities and radii of \(6115\pm45\,\mathrm{K}\), \(7.531\pm0.110\,\mathrm{L}_\odot\) and \(2.450\pm0.045\,\mathrm{R}_\odot\) for 12 Boo A and \(6200\pm60\,\mathrm{K}\), \(4.692\pm0.095\,\mathrm{L}_\odot\) and \(1.901\pm0.045\,\mathrm{R}_\odot\) for 12 Boo B. When combined with our asteroseismic constraints on 12 Boo A, we obtain an age of \(2.67^{+0.12}_{-0.16}\,\mathrm{Gyr}\), which is consistent with that of 12 Boo B.
Binary systems, in particular eclipsing binaries, are essential sources of our knowledge of the fundamental properties of stars. The ages of binaries, members of open clusters, are constrained by ...their own fundamental properties and by those of the hosting cluster. The ages of eleven open clusters are here found by constructing models for the components of twelve eclipsing binaries. The difference between the ages we found and the ages of the clusters derived from isochrone fitting is up to 40%. For the binary system V497 Cep in NGC 7160, the difference is about 100%. Binary systems whose primary component is aboutto complete main-sequence life time, such as V453 Cyg and V906 Sco, are the most suitable systems for age determination. Using model results for these stars, we derive an expression for sensitive and uncomplicated relative age determination of binary systems (age divided by the main-sequence life time of the primary star). The expression is given as logarithm of radii ratio divided by a logarithm of mass ratio. Two advantages of this expression are that (i) it is nearly independent of assumed chemical composition of the models because of the appearance of the ratio of radii, and (ii) the ratios of radii and masses are observationally much more precise than their absolute values. We also derive another expression using luminosities rather than radii and compare results.
The Sun and $\alpha$ Cen A and B are the nearest stars to us. Despite the
general agreement between their models and seismic and non-seismic constraints,
there are serious problems pertaining to ...their interior. The good agreement
between the sound speed and base radius of the convective zone of the Sun and
the solar models is broken apart by a recent revision in solar chemical
composition. For $\alpha$ Cen A and B, however, it is not possible to fit
models with the same age and chemical composition to all seismic and
non-seismic observational constraints. At the age deduced from seismic
constraints, the luminosity ratio ($L_{\rm A}/L_{\rm B}$) of the models is
significantly lower than the ratio taken from the observed luminosities.
Enhancement of opacity as a function of temperature is one way to restore the
agreement between solar models and the Sun, but such an enhancement does not
alter the situation for $\alpha$ Cen A and B. The reason is that models of both
components are influenced in a similar manner and consequently the luminosity
ratio doesn't change much. In the present study, problems pertaining to the
interior of these three stars with a single expression for opacity enhancement
are modelled. The opacity enhancement is expressed as a function of density,
ionization degree of heavy elements (oxygen), and temperature. According to
this expression, for improvement of the models the required opacity enhancement
for $\alpha$ Cen A and B at $\log(T)$= 6.5, for example, is about 7 and 22 per
cent, respectively. The enhancement tak es place in the region in which
pressure ionization is effective, and is higher for low-mass stars than for
high-mass stars. This result seems to be a possible explanation for the serious
differences between models and observational results of cool stars.
W UMa type binaries have two defining characteristics. These are (i) the effective temperatures of both components are very similar, and (ii) the secondary (currently less massive) component is ...overluminous for its current mass. We consider the latter to be an indication of its mass before the mass-transfer event. For these stars we define a mass difference (\(\delta M\)) between the mass determined from its luminosity and the present mass determined from fitting the binary orbit. We compare the observed values of the mass difference to stellar models with mass loss. The range of initial secondary masses that we find for observed W UMa type binaries is 1.3-2.6 M\(_{\odot}\). We discover that the A- and the W-subtype contact binaries have different ranges of initial secondary masses. Binary systems with an initial mass higher than \(1.8 \pm 0.1\) M\(_{\odot}\) become A-subtype while systems with initial masses lower than this become W-subtype. Only 6 per cent of systems violate this behavior. We also obtain the initial masses of the primaries using the following constraint for the reciprocal of initial mass ratio: \(0 < 1/q_i < 1\). The range of initial masses we find for the primaries is 0.2-1.5 M\(_{\odot}\), except for two systems. Finally in comparing our models to observed systems we find evidence that the mass transfer process is not conservative. We find that only 34 per cent of the mass from the secondary is transferred to the primary. The remainder is lost from the system.
Over the course of its history, the Milky Way has ingested multiple smaller satellite galaxies. While these accreted stellar populations can be forensically identified as kinematically distinct ...structures within the Galaxy, it is difficult in general to precisely date the age at which any one merger occurred. Recent results have revealed a population of stars that were accreted via the collision of a dwarf galaxy, called \textit{Gaia}-Enceladus, leading to a substantial pollution of the chemical and dynamical properties of the Milky Way. Here, we identify the very bright, naked-eye star \(\nu\)\,Indi as a probe of the age of the early in situ population of the Galaxy. We combine asteroseismic, spectroscopic, astrometric, and kinematic observations to show that this metal-poor, alpha-element-rich star was an indigenous member of the halo, and we measure its age to be \(11.0 \pm 0.7\) (stat) \(\pm 0.8\) (sys)\(\,\rm Gyr\). The star bears hallmarks consistent with it having been kinematically heated by the \textit{Gaia}-Enceladus collision. Its age implies that the earliest the merger could have begun was 11.6 and 13.2 Gyr ago at 68 and 95% confidence, respectively. Input from computations based on hierarchical cosmological models tightens (i.e. reduces) slightly the above limits.
The Transiting Exoplanet Survey Satellite (TESS) mission searches for new exoplanets. The observing strategy of TESS results in high-precision photometry of millions of stars across the sky, allowing ...for detailed asteroseismic studies of individual systems. In this work, we present a detailed asteroseismic analysis of the giant star HD 76920 hosting a highly eccentric giant planet (\(e = 0.878\)) with an orbital period of 415 days, using 5 sectors of TESS light curve that cover around 140 days of data. Solar-like oscillations in HD 76920 are detected around \(52 \, \mu\)Hz by TESS for the first time. By utilizing asteroseismic modeling that takes classical observational parameters and stellar oscillation frequencies as constraints, we determine improved measurements of the stellar mass (\(1.22 \pm 0.11\, M_\odot\)), radius (\(8.68 \pm 0.34\,R_\odot\)), and age (\(5.2 \pm 1.4\,\)Gyr). With the updated parameters of the host star, we update the semi-major axis and mass of the planet as \(a=1.165 \pm 0.035\) au and \(M_{\rm p}\sin{i} = 3.57 \pm 0.22\,M_{\rm Jup}\). With an orbital pericenter of \(0.142 \pm 0.005\) au, we confirm that the planet is currently far away enough from the star to experience negligible tidal decay until being engulfed in the stellar envelope. We also confirm that this event will occur within about 100\,Myr, depending on the stellar model used.
