Toward Better Age Estimates for Stellar Populations: The Y2 Isochrones for Solar Mixture

By S. Yi, P. Demarque, Yong-Cheol Kim, Young-Wook Lee, C. Ree, T. Lejeune, S. Barnes. 2001

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We have constructed a new set of isochrones, called the Y2 Isochrones, that represent an update of the Revised Yale Isochrones (RYI), using improved opacities and equations of state. Helium diffusion and convective core overshoot have also been taken into consideration. This first set of isochrones is for the scaled solar mixture. A subsequent paper will consider the effects of α-element enhancement, believed to be relevant in many stellar systems. Two additionally significant features of these isochrones are that (1) the stellar models start their evolution from the pre-main-sequence birthline instead of from the zero-age main sequence and (2) the color transformation has been performed using both the latest table of Lejeune et al., and the older, but now modified, Green et al. table. The isochrones have performed well under the tests conducted thus far. The reduction in the age of the Galactic globular clusters caused by this update in stellar models alone is approximately 15% relative to RYI-based studies. When the suggested modification for the α-element enhancement is made as well, the total age reduction becomes approximately 20%. When post-RGB evolutionary stages are included, we find that the ages of globular clusters derived from integrated colors are consistent with the isochrone fitting ages.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

TRANSIT TIMING OBSERVATIONS FROM KEPLER. IV. CONFIRMATION OF FOUR MULTIPLE-PLANET SYSTEMS BY SIMPLE PHYSICAL MODELS (2012, methodology): “From these values we performed a Bayesian analysis using Yonsei-Yale stellar isochrones (Yi et al. 2001) to extract best-fit and 68% confidence regions on M⋆ and R⋆ (e.g. Pont & Eyer 2004; Takeda et al. 2007).”
First stars V - Abundance patterns from C to Zn and supernova yields in the early Galaxy (2003, methodology): “Carretta et al. (2002) used another method: they deduced the gravity from isochrones (Yi et al. 2001), and found that the abundances of iron deduced from Fe I or Fe II lines show ionization equilibrium within 0.2 dex (cf. their Table 1).”
The Origin of T Tauri X-Ray Emission: New Insights from the Chandra Orion Ultradeep Project (2005, methodology): “A detailed discussion of the physics used in this study for the construction of stellar models can be found in Yi et al. (2001).”
The DART Imaging And CaT Survey of the Fornax Dwarf Spheroidal Galaxy (2006, methodology): “…stellar populations, whilst when comparing the distri- 1 Using different sets of isochrones, e.g. Geneva (Lejeune & Schaerer 2001) or Yonsei-Yale (Yi et al. 2001; Kimet al. 2002), would bring to slightly different results, however qualitatively in agreement. bution of an ancient population,…”
The Y2 Isochrones for α-Element Enhanced Mixtures (2002, background): “This paper presents an extension of the Y2 Isochrones: scaled-solar mixtures (Yi et al. 2001, hereafter Paper I).”
HE 0107–5240, a Chemically Ancient Star. I. A Detailed Abundance Analysis (2003, background): “Inspection of a 12 Gyr, Z ¼ 10 5 isochrone (Yi et al. 2001) suggests that a star of TeA ¼ 5100 K in a pre–helium core flash evolutionary state has either log g ¼ 2:2 (i.e., if it is on the red giant branch) or log g ¼ 4:8 (i.e., if it is on the main sequence).”
YREC: the Yale rotating stellar evolution code (2007, background): “Important research in stellar population studies and population synthesis continues to be carried out with the YonseiYale isochrones (YY isochrones) (Yi et al. 2001).”
Prevalence of Earth-size planets orbiting Sun-like stars (2013, background): “ But in this work, we extend our search in orbital period to P= 0.5–400 days. S5 Table S1. TERRA Grid Search Parameters P 1 P 2 Trial Transit Duration ( T) days days long cadence measurements 5.0 7.7 [3, 4, 5, 7, 9, 11] 7.7 12.0 [4, 5, 7, 9, 13] 12.0 18.6 [4, 5, 7, 9, 13, 15] 18.6 28.9 [5, 7, 9, 12,”
The star formation and chemical evolution history of the Fornax dwarf spheroidal galaxy (2012, methodology): “Figure 15 shows the SFH solution of the central region of Fornax (rell ≤ 0.194 degrees) obtained using three different isochrone sets (Dotter et al. 2008; Pietrinferni et al. 2004; Yi et al. 2001).”
PLANET HUNTERS: A TRANSITING CIRCUMBINARY PLANET IN A QUADRUPLE STAR SYSTEM (2012, methodology): “…they tend to be larger and cooler than predicted (Ribas 2003; Torres & Ribas 2002; López-Morales – 21 – & Ribas 2005; Morales et al. 2009; Torres 2012) Figure 13 compares the measured properties of the Aa star in the Teff–log g plane with models from the Y2 (Yonsei-Yale) series (Yi et al. 2001).”
The Sirius System and Its Astrophysical Puzzles: Hubble Space Telescope and Ground-based Astrometry (2017, methodology): “In the left panel of C16’s Figure 8, they show an IFMR based on cluster ages calibrated using the Yonsei-Yale (Y2) isochrones database (Yi et al. 2001; Demarque et al. 2004), which only contains tracks up to 5.0M⊙.”
KEPLER-18b, c, AND d: A SYSTEM OF THREE PLANETS CONFIRMED BY TRANSIT TIMING VARIATIONS, LIGHT CURVE VALIDATION, WARM-SPITZER PHOTOMETRY, AND RADIAL VELOCITY MEASUREMENTS (2011, methodology): “Stellar parameters were determined in a separate MCMC analysis using the Yonsei-Yale isochrones (Yi et al. 2001, et seq.) with Teff , [Fe/H] and fitted value of the meanstellar density as constraints.”
New constraints on the chemical evolution of the solar neighbourhood and galactic disc(s) - improved astrophysical parameters for the Geneva-Copenhagen Survey (2011, background): “From this the overall metal–to–hydrogen ratio [M/H] can be computed (e.g., Yi et al. 2001).”
Accurate fundamental parameters for lower main‐sequence stars (2006, methodology): “For stars with α-element estimates, we compute [M/H] (Yi et al. 2001): [M/H] = [Fe/H] + log(0.694 fα + 0.306), (1) where fα = 10[α/Fe] (2) is the enhancement factor and [α/Fe] has been computed by averaging the α-elements.”
VALIDATION OF KEPLER'S MULTIPLE PLANET CANDIDATES. II. REFINED STATISTICAL FRAMEWORK AND DESCRIPTIONS OF SYSTEMS OF SPECIAL INTEREST (2014, methodology): “The stellar parameters were derived following the procedures of Torres et al. (2008) from a fit of Yonsei-Yale isochrones (Yi et al. 2001) to the spectroscopically measured temperature (5994 ± 77 K) and metallicity ([Fe/H] = +0.04 ± 0.10) of the star and using the stellar density from the light…”
THE MASS OF KOI-94d AND A RELATION FOR PLANET RADIUS, MASS, AND INCIDENT FLUX (2013, methodology): “Applying the evolutionary constraints of the Yi et al. (2001) model isochrones and the simultaneous solution of the lightcurve and RVs, we determine the mass (M?”
HAT-P-16b: A 4 MJ PLANET TRANSITING A BRIGHT STAR ON AN ECCENTRIC ORBIT, (2010, methodology): “We then used the a/R⋆ distribution together with Gaussian distributions for Teff⋆ and [Fe/H], with 1σ uncertainties as reported previously, to estimate M⋆ and R⋆ by comparison with the stellar evolution models of Yi et al. (2001).”
MESA ISOCHRONES AND STELLAR TRACKS (MIST) 0: METHODS FOR THE CONSTRUCTION OF STELLAR ISOCHRONES (2016, background): “…et al. 2004), Dartmouth (Dotter et al. 2008), PARSEC (Bressan et al. 2012), Pisa (Tognelli et al. 2011), Victoria-Regina (VandenBerg et al. 2006), and YaleYonsei (Yi et al. 2001), are based on the more-sophisticated approach, one implementation of which is described in the following sections.”
FUNDAMENTAL PARAMETERS AND CHEMICAL COMPOSITION OF ARCTURUS (2011, methodology): “Briefly, we use a fine grid of YonseiYale isochrones (Yi et al. 2001; Kim et al. 2002), which consider α-element enhancement at sub-solar metallicities, increasing linearly from [α/Fe] = 0.0 at [Fe/H] = 0.0 to [α/Fe] = +0.3 at [Fe/H] = −1.0.”