The Y2 Isochrones for α-Element Enhanced Mixtures

By Yong-Cheol Kim, P. Demarque, S. Yi, D. Alexander. 2002

287 citations recorded by the source corpus.

We present a new set of isochrones in which the effect of the α-element enhancement is fully incorporated. These isochrones are an extension of the already published set of Y2 Isochrones (our Paper I), constructed for the scaled-solar mixture. As in Paper I, helium diffusion and convective core overshoot have been taken into account. The range of chemical compositions covered is 0.00001 ≤ Z ≤ 0.08. The models were evolved from the pre-main-sequence stellar birthline to the onset of helium burning in the core. The age range of the full isochrone set is 0.1-20 Gyr, while younger isochrones of age 1-80 Myr are also presented up to the main-sequence turn-off. Combining this set with that of Paper I for scaled-solar mixture isochrones, we provide a consistent set of isochrones that can be used to investigate populations of any value of α-enhancement. We confirm the earlier results of Paper I that inclusion of α-enhancement effects further reduces the age estimates of globular clusters by approximately 8% if [α/Fe]= +0.3. It is important to note the metallicity dependence of the change in age estimates (larger age reductions in lower metallicities). This reduces the age gap between the oldest metal-rich and metal-poor Galactic stellar populations and between the halo and the disk populations. We also investigate whether the effects of α-enhancement can be mimicked by increasing the total metal abundance in the manner proposed by Salaris and collaborators. We find such simple scaling formulae are valid at low metallicities but not at all at high metallicities near and above solar. Thus, it is essential to use the isochrones rigorously computed for α-enhancement when modeling metal-rich populations, such as bright galaxies. The isochrone tables, together with interpolation routines have been made available via internet.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/5d783db2cc34be909af5b11b95dc7f226d3c6401

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

Citations in the corpus

alpha-, r-, and s-process element trends in the Galactic thin and thick disks (2004, background): “The Yoshii-Yale (Y2) isochrones (Kim et al 2002; Yi et al. 2001) are distributed together with interpolation routines that makes it possible to construct a set of isochrones with any metallicity andα-enhancement.”
HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: URSA MAJOR II and COMA BERENICES (2009, methodology): “Figure 7 shows the adopted stellar parameters of our program stars in comparison with α-enhanced ([α/Fe] = 0.4) 12Gyr isochrones (Green et al. 1984; Kim et al. 2002) covering a range of metallicities.”
Astrophysical parameters of Galactic open clusters (2005, methodology): “There are three recently published data sets of Post-MS isochrones suitable for our purposes (Lejeune & Schaerer 2001, called the Geneva grid hereafter; Girardi et al. 2002 or the Padova grid; and Yi et al. 2001, Kim et al. 2002, and Yi et al.”
STELLAR DIAMETERS AND TEMPERATURES. I. MAIN-SEQUENCE A, F, AND G STARS (2011, methodology): “Isochrone Masses and Ages We determine an estimate of the stellar mass and age by fitting our temperatures and luminosities presented in section 4.2 to the Yonsei-Yale (Y 2) stellar isochrones (Yi et al. 2001; Kim et al. 2002; Yi et al. 2003; Demarque et al. 2004).”
Evolutionary population synthesis: models, analysis of the ingredients and application to high‐z galaxies (2004, background): “Element ratio effects are beingincorporated in stellar models (e.g. Bergbusch & Vandenberg 1992, 2001; Salasnich et al. 2000; Kim et al. 2002), but for the stellar trcks considered here, their[α/Fe]-enhanced version was either not yet available at the time these models were computed…”
The DART Imaging And CaT Survey of the Fornax Dwarf Spheroidal Galaxy (2006, methodology): “We chose to use the Yonsei-Yale isochrones (Yi et al. 2001; Kim et al. 2002) because they cover the range of ages and metallicities we require in a uniform way, and they allow for a variation in [α/Fe].”
MESA ISOCHRONES AND STELLAR TRACKS (MIST). I. SOLAR-SCALED MODELS (2016, unknown): “…Dotter et al. 2008), GARSTEC (Weiss & Schlattl 2008), Lyon (Baraffe et al. 1998, 2003, 2015), Padova/PARSEC (Girardi et al. 2002; Marigo et al. 2008; Bressan et al. 2012), Y2 (Yi et al. 2001; Kim et al. 2002; Yi et al. 2003; Demarque et al. 2004), Victoria-Regina (VandenBerg et al. 2006), and more.”
The s-Process in Low Metallicity Stars. II. Interpretation of High-Resolution Spectroscopic Observations with AGB models (2011, background): “By comparison, we overlap evolutionary tracks of models with initial mass 0.8 M⊙ at 11 Gyr and three metallicities ([Fe/H] = −1.5, −2.5 and −3.5) by Kim et al. (2002) and the Horizontal Branch (HB) track at [Fe/H] = −2.3 by Cassisi et al. (2004).”
Oxygen abundances in nearby stars - Clues to the formation and evolution of the Galactic disk (2007, methodology): “Given the impact of α-element enhancement on stellar evolution calculations (e.g., Kim et al. 2002), the use of models with solar-scaled chemical compositions (like those by Bertelli et al. 1994) introduces systematic errors in the age determination from isochrones.”
High-precision abundances of elements in solar twin stars - Trends with stellar age and elemental condensation temperature (2015, methodology): “5, where the stars are compared to a Yonsei-Yale set of isochrones (Yi et al. 2001; Kim et al. 2002).”
The Y2 Stellar Evolutionary Tracks (2002, background): “The Y 2 group has recently released their updated isochrones (Yi et al. 2001; Kim et al. 2002).”
Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs (2005, background): “Kim et al. (2002) tabulate the pattern of abundance changes in Y2 models with nonsolar values of [ /Fe].”
An Assessment of Dynamical Mass Constraints on Pre-Main-Sequence Evolutionary Tracks (2003, background): “The Y2 models cover 0.4–5.0M and have been published in a series of papers: Yi et al. (2001, 2003) and Kim et al. (2002).”
The Solar Twin Planet Search. I. Fundamental parameters of the stellar sample (2014, methodology): “Ramı́rez et al. (2013) implementation uses the Yonsei-Yale isochrone set (e.g., Yi et al. 2001; Kim et al. 2002).”