Spectroscopic determination of masses (and implied ages) for red giants

TL;DR

This paper introduces a data-driven spectral model using The Cannon to accurately determine masses and ages of red giant stars from APOGEE spectra, enabling detailed Galactic archaeology.

Contribution

It presents the first method to infer stellar masses and ages directly from spectra with high precision, expanding the potential for Galactic studies.

Findings

Masses can be determined to ~0.07 dex accuracy.

Ages can be estimated with ~0.2 dex precision (40%).

Catalog of 80,000 giants with mass and age estimates across the Milky Way.

Abstract

The mass of a star is arguably its most fundamental parameter. For red giant stars, tracers luminous enough to be observed across the Galaxy, mass implies a stellar evolution age. It has proven to be extremely difficult to infer ages and masses directly from red giant spectra using existing methods. From the KEPLER and APOGEE surveys, samples of several thousand stars exist with high-quality spectra and asteroseismic masses. Here we show that from these data we can build a data-driven spectral model using The Cannon, which can determine stellar masses to $\sim$ 0.07 dex from APOGEE DR12 spectra of red giants; these imply age estimates accurate to $\sim$ 0.2 dex (40 percent). We show that The Cannon constrains these ages foremost from spectral regions with CN absorption lines, elements whose surface abundances reflect mass-dependent dredge-up. We deliver an unprecedented catalog of 80,000 giants (including 20,000 red-clump stars) with mass and age estimates, spanning the entire disk (from the Galactic center to R $\sim$ 20 kpc). We show that the age information in the spectra is not simply a corollary of the birth-material abundances [Fe/H] and [$\alpha$/Fe], and that even within a mono-abundance population of stars, there are age variations that vary sensibly with Galactic position. Such stellar age constraints across the Milky Way open up new avenues in Galactic archeology.