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1. The 16th Data Release of the Sloan Digital Sky Surveys: First Release from the APOGEE-2 Southern Survey and Full Release of eBOSS Spectra

   https://doi.org/10.3847/1538-4365/ab929e  

   Ahumada, Romina ; Prieto, Carlos Allende ; Almeida, Andrés ; Anders, Friedrich ; Anderson, Scott F. ; Andrews, Brett H. ; Anguiano, Borja ; Arcodia, Riccardo ; Armengaud, Eric ; Aubert, Marie ; et al ( July 2020 , The Astrophysical Journal Supplement Series)

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2. From dawn till disc: Milky Way’s turbulent youth revealed by the APOGEE+ Gaia data

   https://doi.org/10.1093/mnras/stac1267  

   Belokurov, Vasily ; Kravtsov, Andrey ( May 2022 , Monthly Notices of the Royal Astronomical Society)

   We use accurate estimates of aluminium abundance from the APOGEE Data Release 17 and Gaia Early Data Release 3 astrometry to select a highly pure sample of stars with metallicity −1.5 ≲ [Fe/H] ≲ 0.5 born in-situ in the Milky Way proper. The low-metallicity ([Fe/H]  ≲ −1.3) in-situ component we dub Aurora is kinematically hot with an approximately isotropic velocity ellipsoid and a modest net rotation. Aurora stars exhibit large scatter in metallicity and in many element abundance ratios. The median tangential velocity of the in-situ stars increases sharply with metallicity between [Fe/H] = −1.3 and −0.9, the transition that we call the spin-up. The observed and theoretically expected age–metallicity correlations imply that this increase reflects a rapid formation of the MW disc over ≈1–2 Gyr. The transformation of the stellar kinematics as a function of [Fe/H] is accompanied by a qualitative change in chemical abundances: the scatter drops sharply once the Galaxy builds up a disc during later epochs corresponding to [Fe/H] > −0.9. Results of galaxy formation models presented in this and other recent studies strongly indicate that the trends observed in the MW reflect generic processes during the early evolution of progenitors of MW-sized galaxies: a period of chaotic pre-disc evolution, when gas is accreted along cold narrow filaments and when stars are born in irregular configurations, and subsequent rapid disc formation. The latter signals formation of a stable hot gaseous halo around the MW progenitor, which changes the mode of gas accretion and allows development of coherently rotating disc.

    

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3. The Seventeenth Data Release of the Sloan Digital Sky Surveys: Complete Release of MaNGA, MaStar, and APOGEE-2 Data

   https://doi.org/10.3847/1538-4365/ac4414  

   Abdurro’uf ; Accetta, Katherine ; Aerts, Conny ; Silva Aguirre, Víctor ; Ahumada, Romina ; Ajgaonkar, Nikhil ; Filiz Ak, N. ; Alam, Shadab ; Allende Prieto, Carlos ; Almeida, Andrés ; et al ( March 2022 , The Astrophysical Journal Supplement Series)

   Abstract This paper documents the seventeenth data release (DR17) from the Sloan Digital Sky Surveys; the fifth and final release from the fourth phase (SDSS-IV). DR17 contains the complete release of the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which reached its goal of surveying over 10,000 nearby galaxies. The complete release of the MaNGA Stellar Library accompanies this data, providing observations of almost 30,000 stars through the MaNGA instrument during bright time. DR17 also contains the complete release of the Apache Point Observatory Galactic Evolution Experiment 2 survey that publicly releases infrared spectra of over 650,000 stars. The main sample from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), as well as the subsurvey Time Domain Spectroscopic Survey data were fully released in DR16. New single-fiber optical spectroscopy released in DR17 is from the SPectroscipic IDentification of ERosita Survey subsurvey and the eBOSS-RM program. Along with the primary data sets, DR17 includes 25 new or updated value-added catalogs. This paper concludes the release of SDSS-IV survey data. SDSS continues into its fifth phase with observations already underway for the Milky Way Mapper, Local Volume Mapper, and Black Hole Mapper surveys. 

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4. The APOGEE Data Release 16 Spectral Line List

   https://doi.org/10.3847/1538-3881/abefdc  

   Smith, Verne V. ; Bizyaev, Dmitry ; Cunha, Katia ; Shetrone, Matthew D. ; Souto, Diogo ; Allende Prieto, Carlos ; Masseron, Thomas ; Mészáros, Szabolcs ; Jönsson, Henrik ; Hasselquist, Sten ; et al ( May 2021 , The Astronomical Journal)

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5. Double-lined Spectroscopic Binaries in the APOGEE DR16 and DR17 Data

   https://doi.org/10.3847/1538-3881/ac1798  

   Kounkel, Marina ; Covey, Kevin R. ; Stassun, Keivan G. ; Price-Whelan, Adrian M. ; Holtzman, Jon ; Chojnowski, Drew ; Longa-Peña, Penélope ; Román-Zúñiga, Carlos G. ; Hernandez, Jesus ; Serna, Javier ; et al ( October 2021 , The Astronomical Journal)

   Abstract APOGEE spectra offer ≲1 km s −1 precision in the measurement of stellar radial velocities. This holds even when multiple stars are captured in the same spectrum, as happens most commonly with double-lined spectroscopic binaries (SB2s), although random line-of-sight alignments of unrelated stars can also occur. We develop a code that autonomously identifies SB2s and higher order multiples in the APOGEE spectra, resulting in 7273 candidate SB2s, 813 SB3s, and 19 SB4s. We estimate the mass ratios of binaries, and for a subset of these systems with a sufficient number of measurements we perform a complete orbital fit, confirming that most systems with periods of <10 days have circularized. Overall, we find an SB2 fraction ( F SB2 ) ∼ 3% among main-sequence dwarfs, and that there is not a significant trend in F SB2 with temperature of a star. We are also able to recover a higher F SB2 in sources with lower metallicity, however there are some observational biases. We also examine light curves from TESS to determine which of these spectroscopic binaries are also eclipsing. Such systems, particularly those that are also pre- and post-main sequence, are good candidates for a follow-up analysis to determine their masses and temperatures. 

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