Asteroseismic age determination for dwarfs and giants

Aguirre, V. Silva; Serenelli, Aldo

doi:10.1002/asna.201612379

Cited by 10 publications

(10 citation statements)

References 38 publications

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“…(vii) Further investigations are needed to confirm with different techniques and with higher precision the age distribution of the stars in Enceladus. Asteroseismology techniques currently provide the best way to probe stellar interiors, to determine with very high accuracy stellar ages (Casagrande et al 2016;Silva Aguirre & Serenelli 2016;Miglio et al 2017). In the future, asteroseismology combined with chemodynamical simulations will allow us to study the mass assembly history of our Galaxy with unprecedented temporal resolution, and this will be the subject of our future work.…”

Section: Discussionmentioning

confidence: 99%

The Fall of a Giant. Chemical evolution of Enceladus, alias the Gaia Sausage

Vincenzo

Spitoni

Calura

et al. 2019

Monthly Notices of the Royal Astronomical Society: Letters

139

108

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We present the first chemical evolution model for Enceladus, alias the Gaia Sausage, to investigate the star formation history of one of the most massive satellites accreted by the Milky Way during a major merger event. Our best chemical evolution model for Enceladus nicely fits the observed stellar [α/Fe]-[Fe/H] chemical abundance trends, and reproduces the observed stellar metallicity distribution function, by assuming low star formation efficiency, fast infall time scale, and mild outflow intensity. We predict a median age for Enceladus stars 12.33 +0.92 −1.36 Gyr, and -at the time of the merger with our Galaxy (≈ 10 Gyr ago from Helmi et al.) -we predict for Enceladus a total stellar mass M ≈ 5 × 10 9 M . By looking at the predictions of our best model, we discuss that merger events between the Galaxy and systems like Enceladus may have inhibited the gas accretion onto the Galaxy disc at high redshifts, heating up the gas in the halo. This scenario could explain the extended period of quenching in the star formation activity of our Galaxy about 10 Gyr ago, which is predicted by Milky Way chemical evolution models, in order to reproduce the observed bimodality in [α/Fe]-[Fe/H] between thick-and thin-disc stars.

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Section: Discussionmentioning

confidence: 99%

The Fall of a Giant. Chemical evolution of Enceladus, alias the Gaia Sausage

Vincenzo

Spitoni

Calura

et al. 2019

Monthly Notices of the Royal Astronomical Society: Letters

139

108

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“…The net result is that the properties of red giants that are determined All our evolutionary calculations and models are available at https://github.com/vsilvagui/aarhus_RG_challenge in this manner are largely dominated by statistical uncertainties (see e.g. Serenelli et al 2013;Silva Aguirre & Serenelli 2016).…”

Section: Introductionmentioning

confidence: 99%

The Aarhus red giants challenge

Aguirre

Christensen‐Dalsgaard

Cassisi

et al. 2020

A&A

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Context. With the advent of space-based asteroseismology, determining accurate properties of red-giant stars using their observed oscillations has become the focus of many investigations due to their implications in a variety of fields in astrophysics. Stellar models are fundamental in predicting quantities such as stellar age, and their reliability critically depends on the numerical implementation of the physics at play in this evolutionary phase. Aims. We introduce the Aarhus red giants challenge, a series of detailed comparisons between widely used stellar evolution and oscillation codes that aim to establish the minimum level of uncertainties in properties of red giants arising solely from numerical implementations. We present the first set of results focusing on stellar evolution tracks and structures in the red-giant-branch (RGB) phase. Methods. Using nine state-of-the-art stellar evolution codes, we defined a set of input physics and physical constants for our calculations and calibrated the convective efficiency to a specific point on the main sequence. We produced evolutionary tracks and stellar structure models at a fixed radius along the red-giant branch for masses of 1.0 M⊙, 1.5 M⊙, 2.0 M⊙, and 2.5 M⊙, and compared the predicted stellar properties. Results. Once models have been calibrated on the main sequence, we find a residual spread in the predicted effective temperatures across all codes of ∼20 K at solar radius and ∼30–40 K in the RGB regardless of the considered stellar mass. The predicted ages show variations of 2–5% (increasing with stellar mass), which we attribute to differences in the numerical implementation of energy generation. The luminosity of the RGB-bump shows a spread of about 10% for the considered codes, which translates into magnitude differences of ∼0.1 mag in the optical V-band. We also compare the predicted [C/N] abundance ratio and find a spread of 0.1 dex or more for all considered masses. Conclusions. Our comparisons show that differences at the level of a few percent still remain in evolutionary calculations of red giants branch stars despite the use of the same input physics. These are mostly due to differences in the energy generation routines and interpolation across opacities, and they call for further investigation on these matters in the context of using properties of red giants as benchmarks for astrophysical studies.

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“…A comprehensive list of age determination methods is given in Soderblom (2010). For a number of stars ages can be derived from asteroseismic observations (Silva Aguirre & Serenelli 2016) or from carbon and nitrogen abundances (Martig et al 2016). When these data are not available, a typical approach is to compare the parameters directly derived from spectroscopic measurements, which we designate as observed parameters, such as the effective temperature T eff , surface gravity log g, and metallicity [Fe/H], to a grid of stellar models.…”

Section: Introductionmentioning

confidence: 99%

A Unified tool to estimate Distances, Ages, and Masses (UniDAM) from spectrophotometric data

Mints

Hekker

2017

A&A

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Context. Galactic archaeology, the study of the formation and evolution of the Milky Way by reconstructing its past from its current constituents, requires precise and accurate knowledge of stellar parameters for as many stars as possible. To achieve this, a number of large spectroscopic surveys have been undertaken and are still ongoing. Aims. So far consortia carrying out the different spectroscopic surveys have used different tools to determine stellar parameters of stars from their derived effective temperatures (T eff ), surface gravities (log g), and metallicities ([Fe/H]); the parameters can be combined with photometric, astrometric, interferometric, or asteroseismic information. Here we aim to homogenise the stellar characterisation by applying a unified tool to a large set of publicly available spectrophotometric data. Methods. We used spectroscopic data from a variety of large surveys combined with infrared photometry from 2MASS and AllWISE and compared these in a Bayesian manner with PARSEC isochrones to derive probability density functions (PDFs) for stellar masses, ages, and distances. We treated PDFs of pre-helium-core burning, helium-core burning, and post helium-core burning solutions as well as different peaks in multimodal PDFs (i.e. each unimodal sub-PDF) of the different evolutionary phases separately. Results. For over 2.5 million stars we report mass, age, and distance estimates for each evolutionary phase and unimodal sub-PDF. We report Gaussian, skewed, Gaussian, truncated Gaussian, modified truncated exponential distribution or truncated Student's t-distribution functions to represent each sub-PDF, allowing us to reconstruct detailed PDFs. Comparisons with stellar parameter estimates from the literature show good agreement within uncertainties. Conclusions. We present UniDAM, the unified tool applicable to spectrophotometric data of different surveys, to obtain a homogenised set of stellar parameters.

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Asteroseismic age determination for dwarfs and giants

Cited by 10 publications

References 38 publications

The Fall of a Giant. Chemical evolution of Enceladus, alias the Gaia Sausage

The Fall of a Giant. Chemical evolution of Enceladus, alias the Gaia Sausage

The Aarhus red giants challenge

A Unified tool to estimate Distances, Ages, and Masses (UniDAM) from spectrophotometric data

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