CAPELLA (<i>α</i>AURIGAE) REVISITED: NEW BINARY ORBIT, PHYSICAL PROPERTIES, AND EVOLUTIONARY STATE

Torres, Guillermo; Claret, A.; Pavlovski, K.; Dotter, Aaron

doi:10.1088/0004-637x/807/1/26

Cited by 231 publications

(69 citation statements)

References 60 publications

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“…Another case of a binary system with a strong difference in the Li abundance is Capella. Torres et al (2015) recently redetermined the lithium abundance for the primary and secondary to be A(Li) Prim = 1.08±0.11 and A(Li) Sec = 3.28±0.13 dex. This leads to a difference of 2.2 dex between both components, being found on the secondary clump and the main sequence, whereby the more massive component has already undergone Li depletion.…”

Section: Fundamental Parameters and Abundancesmentioning

confidence: 99%

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Beck

Kallinger

Pavlovski

et al. 2018

A&A

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Context. Binaries in double-lined spectroscopic systems (SB2) provide a homogeneous set of stars. Differences of parameters, such as age or initial conditions, which otherwise would have strong impact on the stellar evolution, can be neglected. The observed differences are determined by the difference in stellar mass between the two components. The mass ratio can be determined with much higher accuracy than the actual stellar mass. Aims. In this work, we aim to study the eccentric binary system KIC 9163796, whose two components are very close in mass and both are low-luminosity red-giant stars. Methods. We analyse four years of Kepler space photometry and we obtained high-resolution spectroscopy with the Hermes instrument. The orbital elements and the spectra of both components were determined using spectral disentangling methods. The effective temperatures, and metallicities were extracted from disentangled spectra of the two stars. Mass and radius of the primary were determined through asteroseismology. The surface rotation period of the primary is determined from the Kepler light curve. From representative theoretical models of the star, we derived the internal rotational gradient, while for a grid of models, the measured lithium abundance is compared with theoretical predictions. Results. From seismology the primary of KIC 9163796 is a star of 1.39±0.06 M ⊙ , while the spectroscopic mass ratio between both components can be determined with much higher precision by spectral disentangling to be 1.015±0.005. With such mass and a difference in effective temperature of 600 K from spectroscopy, the secondary and primary are, respectively, in the early and advanced stage of the first dredge-up event on the red-giant branch. The period of the primary's surface rotation resembles the orbital period within 10 days.The radial rotational gradient between the surface and core in KIC 9163796 is found to be 6.9 +2.0 −1.0 . This is a low value but not exceptional if compared to the sample of typical single field stars. The seismic average of the envelope's rotation agrees with the surface rotation rate. The lithium abundance is in agreement with quasi rigidly-rotating models. Conclusions. The agreement between the surface rotation with the seismic result indicates that the full convective envelope is rotating quasi-rigidly. The models of the lithium abundance are compatible with a rigid rotation in the radiative zone during the main sequence. Because of the many constraints offered by oscillating stars in binary systems, such objects are important test beds of stellar evolution.

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Section: Fundamental Parameters and Abundancesmentioning

confidence: 99%

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Beck

Kallinger

Pavlovski

et al. 2018

A&A

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“…5 The value of the mixing length parameter for the Sun in these models, with the same input physics as used here, is α MLT = 1.84 (see Torres et al 2015).…”

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confidence: 99%

“…For Paper I we had computed a grid of evolutionary tracks spanning a range of α ov values from 0.00 to 0.40 in steps of 0.05, and α MLT values between 1.0 and 2.0 (extended in some cases up to 2.7) with a step of 0.1. We have reused this grid here, not for actual fits but only in a differential sense, to gauge the direction in which predicted stellar parameters (temperature, radius, age) change as the overshooting or mix- Graczyk et al (2014); (2) Pilecki et al (2013); (3) Pietrzyński et al (2013); (4) Pilecki et al (2015); (5) Gieren et al (2015); (6) Graczyk et al (2012); (7) Torres et al (2010); (8) Torres et al (2015); (9) ing length are modified, and aid our manual search for better fits. As the relevant variable for this work is f ov rather than α ov , we assumed a rough scaling between the two (see also Section 5.1) such that α ov /f ov ≈ 10 (e.g., Herwig et al 1997;Noels et al 2010), and used it to relabel our coarse grid in terms of f ov , which we then used as indicated above to guide our solutions.…”

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confidence: 99%

The Dependence of Convective Core Overshooting on Stellar Mass: A Semi-empirical Determination Using the Diffusive Approach with Two Different Element Mixtures

Claret

Torres

2017

ApJ

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Convective core overshooting has a strong influence on the evolution of stars of moderate and high mass. Studies of double-lined eclipsing binaries and stellar oscillations have renewed interest in the possible dependence of overshooting on stellar mass, which has been poorly constrained by observations so far. Here we have used a sample of 29 well-studied double-lined eclipsing binaries in key locations of the H-R diagram to establish the explicit dependence of f ov on mass, where f ov is the free parameter in the diffusive approximation to overshooting. Measurements of the masses, radii, and temperatures of the binary components were compared against stellar evolution calculations based on the MESA code to infer semi-empirical values of f ov for each component. We find a clear mass dependence such that f ov rises sharply from zero in the range 1.2-2.0 M ⊙ , and levels off thereafter up to the 4.4 M ⊙ limit of our sample. Tests with two different element mixtures indicate the trend is the same, and we find it is also qualitatively similar to the one established in our previous study with the classical step-function implementation of overshooting characterized by the free parameter α ov . Based on these measurements we infer an approximate relationship between the two overshooting parameters of α ov /f ov = 11.36 ± 0.22, with a possible dependence on stellar properties.

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“…The 'non-spotted' sample contains 14 LMC and SMC systems (Graczyk et al 2012;Pietrzyński et al 2013;Pilecki et al 2013;Graczyk et al 2014), KIC 8410673 (Frandsen et al 2013), AI Phe (Andersen et al 1988;He lminiak et al 2009), TZ For (Andersen et al 1991), OW Gem (Ga lan et al 2008), α Aur (Torres et al 2009(Torres et al , 2015, CF Tau (Lacy et al 2012), V432 Aur (Siviero et al 2004), HD187669 (He lminiak et al 2015), ASAS J180057-2333.8, (Suchomska et al 2015), ASAS J182510-2435.5 (Ratajczak et al 2013), and two more systems we have analysed but not published yet (ASAS-061, V64). We want to note, that the 'non-spotted' systems may also be active, but the activity level must be lower than for the 'spotted' ones, as there is no clear sign of variability in the published photometry, usually more precise than the ASAS data.…”

Section: Giants With and Without Spots In Eclipsing Binariesmentioning

confidence: 99%

Orbital and physical parameters of eclipsing binaries from the ASAS catalogue – IX. Spotted pairs with red giants

Ratajczak

Hełminiak

Konacki

et al. 2016

Mon. Not. R. Astron. Soc.

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We present spectroscopic and photometric solutions for three spotted systems with red giant components. Absolute physical and orbital parameters for these double-lined detached eclipsing binary stars are presented for the first time. These were derived from the V -, and I -band ASAS and WASP photometry, and new radial velocities calculated from high quality optical spectra we obtained with a wide range of spectrographs and using the two-dimensional cross-correlation technique (TODCOR). All of the investigated systems (ASAS J184949-1518.7, BQ Aqr, and V1207 Cen) show the differential evolutionary phase of their components consisting of a main sequence star or a subgiant and a red giant, and thus constitute very informative objects in terms of testing stellar evolution models. Additionally, the systems show significant chromospheric activity of both components. They can be also classified as classical RS CVn-type stars. Besides the standard analysis of radial velocities and photometry, we applied spectral disentangling to obtain separate spectra for both components of each analysed system which allowed for a more detailed spectroscopic study. We also compared the properties of red giant stars in binaries that show spots, with those that do not, and found that the activity phenomenon is substantially suppressed for stars with Rossby number higher than ∼1 and radii larger than ∼20 R ⊙ .

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CAPELLA (αAURIGAE) REVISITED: NEW BINARY ORBIT, PHYSICAL PROPERTIES, AND EVOLUTIONARY STATE

Cited by 231 publications

References 60 publications

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

Seismic probing of the first dredge-up event through the eccentric red-giant and red-giant spectroscopic binary KIC 9163796

The Dependence of Convective Core Overshooting on Stellar Mass: A Semi-empirical Determination Using the Diffusive Approach with Two Different Element Mixtures

Orbital and physical parameters of eclipsing binaries from the ASAS catalogue – IX. Spotted pairs with red giants

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