Determining Ages of APOGEE Giants with Known Distances
Abstract
We present a sample of 705 local giant stars observed using the New Mexico State University 1 m telescope with the Sloan Digital Sky Survey-III/Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectrograph, for which we estimate stellar ages and the local star formation history (SFH). The high-resolution (R ∼ 22,500), near infrared (1.51-1.7 μm) APOGEE spectra provide measurements of stellar atmospheric parameters (temperature, surface gravity, [M/H], and [α/M]). Due to the smaller uncertainties in surface gravity possible with high-resolution spectra and accurate Hipparcos distance measurements, we are able to calculate the stellar masses to within 30%. For giants, the relatively rapid evolution up the red giant branch allows the age to be constrained by the mass. We examine methods of estimating age using both the mass-age relation directly and a Bayesian isochrone matching of measured parameters, assuming a constant SFH. To improve the SFH prior, we use a hierarchical modeling approach to constrain the parameters of the model SFH using the age probability distribution functions of the data. The results of an α-dependent Gaussian SFH model show a clear age-[α/M] relation at all ages. Using this SFH model as the prior for an empirical Bayesian analysis, we determine ages for individual stars. The resulting age-metallicity relation is flat, with a slight decrease in [M/H] at the oldest ages and a ∼0.5 dex spread in metallicity across most ages. For stars with ages ≲1 Gyr we find a smaller spread, consistent with radial migration having a smaller effect on these young stars than on the older stars.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2016
- DOI:
- 10.3847/0004-637X/817/1/40
- arXiv:
- arXiv:1511.04088
- Bibcode:
- 2016ApJ...817...40F
- Keywords:
-
- Galaxy: disk;
- Galaxy: evolution;
- stars: abundances;
- stars: fundamental parameters;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 14 page, 18 figures, accepted to ApJ with minor revisions, full electronic table of data available upon publication
