Determining Ages of APOGEE Giants with Known Distances

Research output: Contribution to journalArticle

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.

Details

Authors
  • Diane Feuillet
  • Jo Bovy
  • Jon Holtzman
  • L. Girardi
  • Nick MacDonald
  • Steven R. Majewski
  • D. L. Nidever
External organisations
  • University of Washington
  • University of Toronto
  • New Mexico State University
  • INAF - Osservatorio Astronomico di Padova
  • University of Virginia
  • National Optical Astronomy Observatory
  • Montana State University
  • University of Michigan
  • Large Synoptic Survey Telescope
  • University of Arizona
Original languageEnglish
Number of pages14
JournalThe Astrophysical Journal
Volume817
Issue number1
Publication statusPublished - 2016 Jan
Publication categoryResearch
Peer-reviewedYes
Externally publishedYes