The Pisa Stellar Evolution Data Base for low-mass stars

Dell’Omodarme, M.; Valle, G.; Degl’Innocenti, S.; Moroni, P. G. Prada

doi:10.1051/0004-6361/201118632

Cited by 98 publications

(81 citation statements)

References 140 publications

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“…Based on modelling only LL Aqr, we can conclude that a better treatment of convection than standard mixing-length theory, is necessary, which is also obvious in light of the hydrodynamical simulations. The treatment of diffusion is also still uncertain; see for example the discussions in Bressan et al (2012) and Dell'Omodarme et al (2012). When confronted with precise observables, stellar evolution theory is clearly deficient.…”

Section: Final Remarksmentioning

confidence: 99%

A solar twin in the eclipsing binary LL Aquarii

Graczyk

Smolec

Pavlovski

et al. 2016

A&A

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Aims. In the course of a project to study eclipsing binary stars in vinicity of the Sun, we found that the cooler component of LL Aqr is a solar twin candidate. This is the first known star with properties of a solar twin existing in a non-interacting eclipsing binary, offering an excellent opportunity to fully characterise its physical properties with very high precision. Methods. We used extensive multi-band, archival photometry and the Super-WASP project and high-resolution spectroscopy obtained from the HARPS and CORALIE spectrographs. The spectra of both components were decomposed and a detailed LTE abundance analysis was performed. The light and radial velocity curves were simultanously analysed with the Wilson-Devinney code. The resulting highly precise stellar parameters were used for a detailed comparison with PARSEC, MESA, and garstec stellar evolution models.Results. LL Aqr consists of two main-sequence stars (F9 V + G3 V) with masses of M 1 = 1.1949 ± 0.0007 and M 2 = 1.0337 ± 0.0007 M , radii R 1 = 1.321±0.006 and R 2 = 1.002±0.005 R , temperatures T 1 = 6080±45 and T 2 = 5703±50 K and solar chemical composition [M/H] = 0.02 ± 0.05. The absolute dimensions, radiative and photometric properties, and atmospheric abundances of the secondary are all fully consistent with being a solar twin. Both stars are cooler by about 3.5σ or less metal abundant by 5σ than predicted by standard sets of stellar evolution models. When advanced modelling was performed, we found that full agreement with observations can only be obtained for values of the mixing length and envelope overshooting parameters that are hard to accept. The most reasonable and physically justified model fits found with MESA and garstec codes still have discrepancies with observations but only at the level of 1σ. The system is significantly younger that the Sun, with an age between 2.3 Gyr and 2.7 Gyr, which agrees well with the relatively high lithium abundance of the secondary, A(Li) = 1.65 ± 0.10 dex.

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Section: Final Remarksmentioning

confidence: 99%

A solar twin in the eclipsing binary LL Aquarii

Graczyk

Smolec

Pavlovski

et al. 2016

A&A

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“…The standard estimation grid of stellar models is obtained using FRANEC stellar evolution code (Degl'Innocenti et al 2008;Tognelli et al 2011), in the same configuration as adopted to compute the Pisa Stellar Evolution Data Base 3 for low-mass stars (Dell'Omodarme et al 2012;Dell'Omodarme & Valle 2013). The grid consists of 141 680 points (110 points for 1288 evolutionary tracks), corresponding to evolutionary stages from the zero-age main sequence (ZAMS) to the central hydrogen de- (Cyburt et al 2004;Steigman 2006;Peimbert et al 2007a,b), and assuming ΔY/ΔZ = 2 (Pagel & Portinari 1998;Jimenez et al 2003;Gennaro et al 2010).…”

Section: Standard Stellar Model Gridmentioning

confidence: 99%

Grid-based estimates of stellar ages in binary systems

Valle

Dell’Omodarme

Moroni

et al. 2015

A&A

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Aims. We investigate the performance of grid-based techniques in estimating the age of stars in detached eclipsing binary systems. We evaluate the precision of the estimates due to the uncertainty in the observational constraints -masses, radii, effective temperatures, and [Fe/H] -and the systematic bias caused by the uncertainty in convective core overshooting, element diffusion, mixing-length value, and initial helium content. Methods. We adopted the SCEPtER grid, which includes stars with mass in the range [0.8; 1.6] M and evolutionary stages from the zero-age main sequence to the central hydrogen depletion. Age estimates have been obtained by a generalisation of the maximum likelihood technique described in our previous work. Results. We showed that the typical 1σ random error in age estimates -due only to the uncertainty affecting the observational constraints -is about ±7%, which is nearly independent of the masses of the two stars. However, such an error strongly depends on the evolutionary phase and becomes larger and asymmetric for stars near the zero-age main sequence where it ranges from about +90% to −25%. The systematic bias due to the including convective core overshooting -for mild and strong overshooting scenariosis about 50% and 120% of the error due to observational uncertainties. A variation of ±1 in the helium-to-metal enrichment ratio ΔY/ΔZ accounts for about ±150% of the random error. The neglect of microscopic diffusion accounts for a bias of about 60% of the error due to observational uncertainties. We also introduced a statistical test of the expected difference in the recovered age of two coeval stars in a binary system. We find that random fluctuations within the current observational uncertainties can lead genuine coeval binary components to appear to be non-coeval with a difference in age as high as 60%.

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“…Due to the fact that this paper is focused on He-enhanced theoretical models, in (see also Dotter et al 2008;Bertelli et al 2009;Di Criscienzo et al 2010;Dell'Omodarme et al 2012). In the left and middle panels, we show the comparison of evolutionary tracks with masses between 0.5 and 1.1 M in intervals of ΔM = 0.1 M .…”

Section: Comparison With Other Codesmentioning

confidence: 99%

Effects of helium enrichment in globular clusters

Valcarce

Catelan

Sweigart

2012

A&A

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Aims. Recently, the study of globular cluster (GC) color−magnitude diagrams (CMDs) has shown that some of them harbor multiple populations with different chemical compositions and/or ages. In the first case, the most common candidate is a spread in the initial helium abundance, but this quantity is difficult to determine spectroscopically due to the fact that helium absorption lines are not present in cooler stars, whereas for hotter GC stars gravitational settling of helium becomes important. As a consequence, indirect methods to determine the initial helium abundance among populations are necessary. For that reason, in this series of papers, we investigate the effects of a helium enrichment in populations covering the range of GC metallicities. Methods. In this first paper, we present the theoretical evolutionary tracks, isochrones, and zero-age horizontal branch (ZAHB) loci calculated with the Princeton-Goddard-PUC (PGPUC) stellar evolutionary code, which has been updated with the most recent input physics and compared with other theoretical databases. The chemical composition grid covers 9 metallicities ranging from Z = 1.60 × 10 −4 to 1.57 × 10 −2 (−2.25 < ∼ [Fe/H] < ∼ −0.25), 7 helium abundances from Y = 0.230 to 0.370, and an alpha-element enhancement of [α/Fe] = 0.3. Results. The effects of different helium abundances that can be observed in isochrones are: splits in the main sequence (MS), differences in the luminosity (L) and effective temperature (T eff ) of the turn off point, splits in the sub giant branch being more prominent for lower ages or higher metallicities, splits in the lower red giant branch (RGB) being more prominent for higher ages or higher metallicities, differences in L of the RGB bump (with small changes in T eff ), and differences in L at the RGB tip. At the ZAHB, when Y is increased there is an increase of L for low T eff , which is affected in different degrees depending on the age of the GC being studied. Finally, the ZAHB morphology distribution depending on the age explains how for higher GC metallicities a population with higher helium abundance could be hidden at the red ZAHB locus.

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The Pisa Stellar Evolution Data Base for low-mass stars

Cited by 98 publications

References 140 publications

A solar twin in the eclipsing binary LL Aquarii

A solar twin in the eclipsing binary LL Aquarii

Grid-based estimates of stellar ages in binary systems

Effects of helium enrichment in globular clusters

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