# APOGEE Data and Spectral Analysis from SDSS Data Release 16: Seven Years of Observations Including First Results from APOGEE-South

**Authors:** Henrik Jönsson, Jon A. Holtzman, Carlos Allende Prieto, Katia Cunha, D. A. García-Hernández, Sten Hasselquist, Thomas Masseron, Yeisson Osorio, Matthew Shetrone, Verne Smith, Guy S. Stringfellow, Dmitry Bizyaev, Bengt Edvardsson, Steven R. Majewski, Szabolcs Mészáros, Diogo Souto, Olga Zamora, Rachael L. Beaton, Jo Bovy, John Donor  
**arXiv:** [2007.05537](https://arxiv.org/abs/2007.05537)  
**Date:** 2020-07-10  
**Summary page:** https://www.summarizepaper.com/en/paper/2007.05537v1/

## Key points

- The latest data release (DR16; December 2019) from the APOGEE-2/SDSS-IV survey includes about 200,000 new stellar spectra, of which 100,000 are from a new southern APOGEE instrument.
- All of the data have been re-reduced and re-analyzed using the latest pipelines, resulting in a total of 473,307 spectra of 437,445 stars.
- Changes to the analysis methods for this release include using MARCS model atmospheres for calculation of synthetic spectra and a new method for filling "holes" in the grids due to unconverged model atmospheres.
- A new scheme for continuum normalization is also included as well as abundances of neutron capture element Ce for the first time.
- Compared to DR14, radial velocities derived for this release more closely match those in the Gaia DR2 database and there is an improvement in spectral analysis of coolest giants.
- The reduced spectra as well as results from analysis can be downloaded through links provided on SDSS DR16 web page.
- These findings provide valuable insights into our understanding of stellar evolution and will be useful for future studies exploring various aspects related to star formation and galactic dynamics.

## Summary

The latest data release (DR16; December 2019) from the high-resolution near-infrared APOGEE-2/SDSS-IV survey has been described in a recent study. This release includes about 200,000 new stellar spectra, of which 100,000 are from a new southern APOGEE instrument mounted on the 2.5 m du Pont telescope at Las Campanas Observatory in Chile. All of the data have been re-reduced and re-analyzed using the latest pipelines, resulting in a total of 473,307 spectra of 437,445 stars. Compared to the previous APOGEE data release (DR14; July 2017), DR16 includes all data taken up to August 2018. Changes to the analysis methods for this release include using MARCS model atmospheres for calculation of the entire main grid of synthetic spectra used in the analysis and a new method for filling "holes" in the grids due to unconverged model atmospheres. A new scheme for continuum normalization is also included as well as abundances of neutron capture element Ce for the first time. Additionally, there is a new scheme for estimating uncertainties of derived quantities using stars with multiple observations and calibrated values of surface gravities for dwarf stars are now supplied. Compared to DR14, radial velocities derived for this release more closely match those in the Gaia DR2 database and there is an improvement in spectral analysis of coolest giants. The reduced spectra as well as results from analysis can be downloaded through links provided on SDSS DR16 web page. These findings provide valuable insights into our understanding of stellar evolution and will be useful for future studies exploring various aspects related to star formation and galactic dynamics.