Toward Precise Stellar Ages: Combining Isochrone Fitting with Empirical Gyrochronology

Abstract

We present a new age-dating technique that combines gyrochronology with isochrone fitting to infer ages for FGKM main-sequence and subgiant field stars. Gyrochronology and isochrone fitting are each capable of providing relatively precise ages for field stars in certain areas of the Hertzsprung-Russell diagram: gyrochronology works optimally for cool main-sequence stars, and isochrone fitting can provide precise ages for stars near the main-sequence turnoff. Combined, these two age-dating techniques can provide precise and accurate ages for a broader range of stellar masses and evolutionary stages than either method used in isolation. We demonstrate that the position of a star on the Hertzsprung-Russell or color-magnitude diagram can be combined with its rotation period to infer a precise age via both isochrone fitting and gyrochronology simultaneously. We show that incorporating rotation periods with 5% uncertainties into stellar evolution models improves age precision for FGK stars on the main sequence, and can, on average, provide age estimates up to three times more precise than isochrone fitting alone. In addition, we provide a new gyrochronology -2relation, calibrated to the Praesepe cluster and the Sun, that includes a variance model to capture the rotational behavior of stars whose rotation periods do not lengthen with the square-root of time, and parts of the Hertzsprung-Russell diagram where gyrochronology has not been calibrated. This publication is accompanied by an open source Python package, stardate, for inferring the ages of main-sequence and subgiant FGKM stars from rotation periods, spectroscopic parameters and/or apparent magnitudes and parallaxes.

TOI-811b and TOI-852b: New Transiting Brown Dwarfs with Similar Masses and Very Different Radii and Ages from the TESS Mission

“…We note here that even though the Mamajek & Hillenbrand (2008) model for gyrochronology yields a relatively welldetermined estimate for the age of TOI-811, in general, there is a larger uncertainty in this age determination depending on the choice of coefficients in Equation (1). This idea can be demonstrated when choosing different coefficients (from Angus et al 2019), where the age of TOI-811 would be 230 ± 30 Myr instead of -+ 93 29 61 Myr. That said, our confirmation of the youth of the TOI-811 system remains unchanged.…”

TATOO: Tidal-chronology standalone tool to estimate the age of massive close-in planetary systems

“…While the most recent techniques only consider isolated stars (Angus et al 2019;Bellinger 2019), TATOO is currently the only tool that proposes to estimate the age of massive close-in planetary systems by taking into account the possible impact of the star-planet tidal interaction on the rotational evolution of the stellar surface. This tool can also be used even if no rotational departure is present.…”

“…nucleocosmochronology) or by using empirical laws. Gyrochronology (Barnes 2003(Barnes , 2007(Barnes , 2010Angus et al 2019) and magnetochronology (Vidotto et al 2014) are two examples of empirical methods that use surface rotation period measurements and magnetic field strength estimation (see Soderblom 2010, for a list of age estimation methods).…”

stardate: Combining dating methods for better stellar ages

“…stardate uses the emcee Python package (Foreman-Mackey, Hogg, Lang, & Goodman, 2013) to perform Markov Chain Monte Carlo sampling in order to estimate the posterior PDFs of the stellar parameters. The paper describing the method in more detail is (Angus et al, 2019).…”