The vast majority of Milky Way stellar halo stars were likely accreted from a small number (<~3) of relatively large
dwarf galaxy accretion events. However, the timing of these events is poorly constrained and predominantly relies
on indirect dynamical mixing arguments or imprecise age measurements of stars associated with debris structures.
Here, we aim to infer robust stellar ages for stars associated with galactic substructures to more directly constrain
the merger history of the Galaxy. By combining kinematic, asteroseismic, and spectroscopic data where available,
we infer stellar ages for a sample of 10 red giant stars that were kinematically selected to be within the stellar halo,
a subset of which are associated with the Gaia–Enceladus–Sausage halo substructure, and compare their ages to 3
red giant stars in the Galactic disk. Despite systematic differences in both absolute and relative ages determined
here, age rankings of stars in this sample are robust. Passing the same observable inputs to multiple stellar age
determination packages, we measure a weighted average age for the Gaia–Enceladus–Sausage stars in our sample
of 8+/-3 (stat.)+/-1 (sys.) Gyr. We also determine hierarchical ages using isochrones for the populations of
Gaia–Enceladus–Sausage, in situ halo and disk stars, finding a Gaia–Enceladus–Sausage population age of
8.0+2.3-3.2 Gyr. Although we cannot distinguish hierarchical population ages of halo or disk structures with our limited
data and sample of stars, this framework should allow a distinct characterization of Galactic substructures using
larger stellar samples and additional data available in the near future
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Chemo-dynamics and asteroseismic ages of seven metal-poor red giants from the Kepler field
In this work, we combine information from solar-like oscillations, high-resolution spectroscopy, and Gaia astrometry to derive stellar ages, chemical abundances, and kinematics for a group of seven metal-poor red giants and characterize them in a multidimensional chrono-chemo-dynamical space. Chemical abundance ratios were derived through classical spectroscopic analysis employing 1D LTE atmospheres on Keck/HIRES spectra. Stellar ages, masses, and radii were calculated with grid-based modelling, taking advantage of availability of asteroseismic information from Kepler. The dynamical properties were determined with galpy using Gaia EDR3 astrometric solutions. Our results suggest that underestimated parallax errors make the effect of Gaia parallaxes more important than different choices of model grid or – in the case of stars ascending the red giant branch – mass-loss prescription. Two of the stars in this study are identified as potentially evolved halo blue stragglers. Four objects are likely members of the accreted Milky Way halo, and their possible relationship with known accretion events is discussed.
more » « less- NSF-PAR ID:
- 10361155
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 510
- Issue:
- 2
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 1733-1747
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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