Isochrone ages for field dwarfs: method and application to the age–metallicity relation

By F. Pont, Laurent Eyer. 2004

159 citations recorded by the source corpus.

A new method is presented to compute age estimates from theoretical isochrones using temperature, luminosity and metallicity data for individual stars. Based on Bayesian probability theory, this method avoids the systematic biases affecting simpler strategies and provides reliable estimates of the age probability distribution function for late-type dwarfs. Basic assumptions concerning the a priori parameter distribution suitable for the solar neighbourhood are combined with the likelihood assigned to the observed data to yield the complete posterior age probability. This method is especially relevant for G dwarfs in the 3–15 Gyr range of ages, crucial to the study of the chemical and dynamical history of the Galaxy. In many cases, it yields markedly different results from the traditional approach of reading the derived age from the isochrone nearest to the data point. We show that the strongest process affecting the traditional approach is that of strongly favouring computed ages near the end-of-main-sequence lifetime. The Bayesian method compensates for this potential bias and generally assigns much higher probabilities to lower main-sequence ages, compared with short-lived evolved stages. This has a strong influence on any application to galactic studies, especially given the present uncertainties on the absolute temperature scale of the stellar evolution models. In particular, the known mismatch between the model predictions and the observations for moderately metal-poor dwarfs (−1 < [Fe/H] < −0.3) has a dramatic effect on the traditional age determination. We apply our method to the classic sample of Edvardsson et al., who derived the age–metallicity relation (AMR) of 189 field dwarfs with precisely determined abundances. We show how much of the observed scatter in the AMR is caused by the interplay between the systematic biases affecting the traditional age determination, the colour mismatch with the evolution models and the presence of undetected binaries. Using new parallax, temperature and metallicity data, our age determination for the same sample indicates that the intrinsic dispersion in the AMR is at most 0.15 dex and probably lower. In particular, we show that old, metal-rich objects ([Fe/H]∼ 0.0 dex, age > 5 Gyr) and young, metal-poor objects ([Fe/H] < −0.5 dex, age < 6 Gyr) in many observed AMR plots are artefacts caused by too simple a treatment of the age determination. The incompatibility of those AMR plots with a well-mixed interstellar medium may therefore only be apparent. Incidentally, our results tend to restore confidence in the method of age determination from the chromospheric activity for field dwarfs.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/bb6325e3c5adc47cdd9c96163f3c9513144f68ef

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In Astronomy and Astrophysics

1. D. Charbonneau
2. J. Johnson
3. G. Marcy
4. J. Southworth
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6. Timothy Morton
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In Instrumentation

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7. J. Winn
8. J. Johnson

Citations in the corpus

• Determination of stellar ages from isochrones: Bayesian estimation versus isochrone fitting (2005, background): “Aspects of the problem were recently discussed by Pont & Eyer (2004) from the viewpoint of Bayesian probability theory.”
• OXYGEN ABUNDANCES IN NEARBY FGK STARS AND THE GALACTIC CHEMICAL EVOLUTION OF THE LOCAL DISK AND HALO (2013, background): “A number of studies have shown that the probabilistic age determination approach that we have adopted is affected by biases that can often overestimate the stellar ages (e.g., Pont & Eyer 2004; Jørgensen & Lindegren 2005).”
• Vertical distribution of Galactic disk stars , IV. AMR and AVR from clump giants (2007, background): “Pont & Eyer (2004) have re-analysed Edvardsson et al.’s sample with a Bayesian approach and also find a significant trend with a dispersion σ[Fe/H] < 0.15 dex.”
• Origins of Eccentric Extrasolar Planets: Testing the Planet-Planet Scattering Model (2007, background): “However, like classical histograms, our summary distributions can be affected by biases (e.g., the terminal age bias for dating field stars with stellar models; Pont & Eyer 2004; Takeda et al. 2006).”
• The Gaia–Kepler Stellar Properties Catalog. II. Planet Radius Demographics as a Function of Stellar Mass and Age (2020, background): “For instance, isochrone ages are effective on the upper main sequence (Må1 M ) but uninformative on the lower main sequence, where stellar rotation, activity, and lithium abundances provide more discriminatory power (Pont & Eyer 2004; Epstein & Pinsonneault 2014).”
• Standing on the Shoulders of Dwarfs: the Kepler Asteroseismic LEGACY Sample. II. Radii, Masses, and Ages (2016, methodology): “The most widely used method to obtain ages of stars is to compare their observed atmospheric properties with those predicted by theoretical evolutionary sequences (e.g., Edvardsson et al. 1993; Ng & Bertelli 1998; Pont & Eyer 2004) or theoretical isochrones in the case of star clusters.”
• The Ages of Stars (2007, methodology): “Pont & Eyer (2004), for example, apply bayesian methods to the F and early-G dwarfs in the GenevaCopenhagen sample, in particular stars with τ ≈3-15 Gyr, which is to say stars that have evolved for at least ∼ 1/3 of their MS lifetime so that they have moved away from the ZAMS.”
• Misaligned spin-orbit in the XO-3 planetary system?† (2008, methodology): “For more detailed explanations of the method see Pont & Eyer (2004).”
• Basic physical parameters of a selected sample of evolved stars (2006, result): “As discussed by Nordström et al. (2004) and Pont & Eyer (2004), selection against old metal-rich dwarfs may have contributed to the steeper decline of [Fe/H] with age found in many of the previous stud- Fig.”
• GEODYNAMICS AND RATE OF VOLCANISM ON MASSIVE EARTH-LIKE PLANETS (2008, methodology): “We adopt a simple linear age-metallicity relationship with an increase of 1 dex (factor of 2.5) over the age of the Galaxy, with solar metallicity occuring 4.6 Gyr ago (e.g. Pont & Eyer (2004)).”
• Oxygen abundances in nearby stars - Clues to the formation and evolution of the Galactic disk (2007, methodology): “Even though this may be related to the “terminal age bias” discussed by Pont & Eyer (2004), it is more likely to be explained by systematic differences in the isochrones (note, again, that the input data used by the Pont & Eyer method includes isochrones computed with α-element enhancement).”
• Structure and Evolution of Nearby Stars with Planets. II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog (2006, methodology): “…position between the theoretically computed isochrones (Twarog 1980; Vandenberg 1985; Edvardsson et al. 1993a; Bertelli et al. 1994; Ng & Bertelli 1998; Lachaume et al. 1999; Ibukiyama & Arimoto 2002; Nordström et al. 2004; Pont & Eyer 2004; Jørgensen & Lindegren 2005; Karataş et al. 2005).”
• 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).”
• Evolution of interstellar dust and stardust in the solar neighbourhood (2007, background): “Pont & Eyer (2004) have shown, however, that the tremendous scattering most likely re-sults from the di ffi culty of obtaining reliable stellar ages from evolutionary isochrones and that any true internal scattering of metallicities at given age is probably less than 0.15 dex.”
• REVISED STELLAR PROPERTIES OF KEPLER TARGETS FOR THE QUARTER 1–16 TRANSIT DETECTION RUN (2013, unknown): “Matching observations to stellar isochrones is a non-trivial task, with important systematics such as the terminal age bias (Pont & Eyer 2004; Jørgensen & Lindegren 2005; Casagrande et al. 2011; Serenelli et al. 2013).”
• The Solar Twin Planet Search. I. Fundamental parameters of the stellar sample (2014, background): “Isochrone age determinations are subject to a number of sampling biases whose impact can be minimized using Bayesian statistics (e.g., Pont & Eyer 2004; Jørgensen & Lindegren 2005; da Silva et al. 2006; Casagrande et al. 2011).”
• The Gaia-ESO Survey : radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk (2014, methodology): “Also sophisticated methods based on Bayesian inferenc are now available that combine in a systematic way observational information and stellar evolution theory (Pont & Eyer 2004; Jørgensen & Lindegren 2005; Schoenrich & Bergemann 2013; Serenelli et al. 2013).”
• FUNDAMENTAL PARAMETERS AND CHEMICAL COMPOSITION OF ARCTURUS (2011, background): “…out that the determination of ages and other stellar parameters from isochrones can be severely affected by a number of statistical biases (Nordström et al. 2004; Pont & Eyer 2004; Jørgensen & Lindegren 2005; da Silva et al. 2006) which can be addressed, for example, using Bayesian methods.”
• Stellar ages and masses in the solar neighbourhood: Bayesian analysis using spectroscopy and Gaia DR1 parallaxes (2018, methodology): “…the use of priors and by employing the full set of observational constraints together with their uncertainties within a Bayesian framework (e.g., Pont & Eyer 2004; Jørgensen & Lindegren 2005; Serenelli et al. 2013; Maxted et al. 2015a; van Dyk et al. 2009; Schneider et al. 2016, 2014; Maxted et…”