Measuring the vertical age structure of the Galactic disc using asteroseismology and SAGA

By L. Casagrande, V. S. Aguirre, K. Schlesinger, D. Stello, Daniel Huber, A. Serenelli, R. Schönrich, Santi Cassisi, Adriano Pietrinferni, S. Hodgkin and 3 more. 2015

111 citations recorded by the source corpus.

The existence of a vertical age gradient in the Milky Way disc has been indirectly known for long. Here, we measure it directly for the first time with seismic ages, using red giants observed by Kepler. We use Stromgren photometry to gauge the selection function of asteroseismic targets, and derive colour and magnitude limits where giants with measured oscillations are representative of the underlying population in the field. Limits in the 2MASS system are also derived. We lay out a method to assess and correct for target selection effects independent of Galaxy models. We find that low-mass, i. e. old red giants dominate at increasing Galactic heights, whereas closer to the Galactic plane they exhibit a wide range of ages and metallicities. Parametrizing this as a vertical gradient returns approximately 4 Gyr kpc(-1) for the disc we probe, although with a large dispersion of ages at all heights. The ages of stars show a smooth distribution over the last similar or equal to 10 Gyr, consistent with a mostly quiescent evolution for the Milky Way disc since a redshift of about 2. We also find a flat age-metallicity relation for disc stars. Finally, we show how to use secondary clump stars to estimate the present-day intrinsic metallicity spread, and suggest using their number count as a new proxy for tracing the ageing of the disc. This work highlights the power of asteroseismology for Galactic studies; however, we also emphasize the need for better constraints on stellar mass-loss, which is a major source of systematic age uncertainties in red giant stars. (Less)

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

Yule-Simpson’s paradox in Galactic Archaeology (2019, background): “While the shape indeed depends on the particular target selection when the total sample is considered Casagrande et al. (2016), such effects will be significantly reduced if we split in mono-rbirth populations, relying on the assumption that stars with a particular value of [Fe/H] and age were born…”
Asteroseismology of 16,000 Kepler Red Giants: Global Oscillation Parameters, Masses, and Radii (2018, background): “It has also provided an excellent opportunity to implement Galactic archaeology (Miglio et al. 2013; Stello et al. 2015; Casagrande et al. 2016; Sharma et al. 2016) and to characterize exoplanet properties (Huber et al. 2013a; Quinn et al. 2015).”
The Updated BaSTI Stellar Evolution Models and Isochrones. I. Solar-scaled Calculations (2018, background): “…greatly and thus further extend the impact of asteroseismology in the fields of stellar physics (e.g., Beck et al. 2011; Verma et al. 2014), exoplanet studies (Huber et al. 2013; Silva Aguirre et al. 2015, e.g.,), and Galactic archaeology (e.g., Casagrande et al. 2016; Silva Aguirre et al. 2017).”
The GALAH survey: observational overview and Gaia DR1 companion (2016, unknown): “…in combining asteroseismic information with stellar surface temperature and composition data from photometry and spectroscopy (e.g., Miglio et al. 2013; Casagrande et al. 2016), bringing a new level of precision to determinations of stellar age, mass, radius and surface gravity for red giant stars.”
Standing on the Shoulders of Dwarfs: the Kepler Asteroseismic LEGACY Sample. II. Radii, Masses, and Ages (2016, background): “These properties, ages in particular, are crucial to our understanding of different fields of astrophysics (such as Galactic Archaeology, see e.g., Miglio et al. 2013; Casagrande et al. 2016).”
PLATO as it is: a legacy mission for Galactic archaeology (2017, unknown): “…uncertainties on stellar radius, mass, and age for red giant stars depend on the assumed constraints and on (some of) the uncertainties in the models, we refer to for example Noels & Bragaglia (2015), Noels et al. (2016), Casagrande et al. (2016), Rodrigues et al. (2017), and Rendle et al. (2017).”
The vertical metallicity gradients of mono-age stellar populations in the Milky Way with the RAVE and Gaia data (2017, methodology): “In the probabilistic model, we also consider the effect of the stellar population bias as suggested in Casagrande et al. (2016).”
Confirming chemical clocks: asteroseismic age dissection of the Milky Way disc(s) (2017, methodology): “…stellar properties have median uncertainties of the order of 2.7 per cent (radius), 3.3 per cent (distance), 7.0 per cent (mass), and 28.5 per cent (age), in line with those obtained by e.g. Casagrande et al. (2014, 2016), Anders et al. (2017), and Rodrigues et al. (2017) using similar approaches.”
The Lives of Stars: Insights from the TGAS–RAVE–LAMOST Data Set (2018, methodology): “Feuillet et al. (2016) found an age distribution peaked at around 3-4 Gyr using giants in APOGEE and Hipparcos; Casagrande et al. (2016) found astroseismic ages for giants observed by Kepler (Borucki et al. 2010) to have a double peak at around 2 Gyr and 4 Gyr; Nordström et al. (2004) find ages pea”
A RADIAL AGE GRADIENT IN THE GEOMETRICALLY THICK DISK OF THE MILKY WAY (2016, background): “This is roughly consistent with a vertical age gradient of 4±2 Gyr kpc−1 measured for giant stars at the solar radius by Casagrande et al. (2016).”
Impacts of a flaring star-forming disc and stellar radial mixing on the vertical metallicity gradient (2016, methodology): “The positive vertical metallicity gradient is inconsistent with the current observational evidence in the thin disc of the Milky Way, including the negative vertical metallicity gradients that we obtained for different age ranges of the young stars in Casagrande et al. (2016) (Sec.”