This paper documents the 16th data release (DR16) from the Sloan Digital Sky Surveys (SDSS), the fourth and penultimate from the fourth phase (SDSS-IV). This is the first release of data from the Southern Hemisphere survey of the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2); new data from APOGEE-2 North are also included. DR16 is also notable as the final data release for the main cosmological program of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and all raw and reduced spectra from that project are released here. DR16 also includes all the data from the Time Domain Spectroscopic Survey and new data from the SPectroscopic IDentification of ERosita Survey programs, both of which were co-observed on eBOSS plates. DR16 has no new data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey (or the MaNGA Stellar Library “MaStar”). We also preview future SDSS-V operations (due to start in 2020), and summarize plans for the final SDSS-IV data release (DR17).

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.

The Open Cluster Chemical Abundances and Mapping (OCCAM) survey aims to constrain key Galactic dynamical and chemical evolution parameters by the construction of a large, comprehensive, uniform, infrared-based spectroscopic data set of hundreds of open clusters. This fourth contribution

Context. VISTA Variables in the Vía Láctea (VVV) is one of the six ESO Public Surveys operating on the new 4-m Visible and Infrared Survey Telescope for Astronomy (VISTA). VVV is scanning the Milky Way bulge and an adjacent section of the disk, where star formation activity is high. One of the principal goals of the VVV Survey is to find new star clusters of different ages. Aims. In order to trace the early epochs of star cluster formation we concentrated our search in the directions to those of known star formation regions, masers, radio, and infrared sources. Methods. The disk area covered by VVV was visually inspected using the pipeline processed and calibrated K S -band tile images for stellar overdensities. Subsequently, we examined the composite JHK S and Z JK S color images of each candidate. PSF photometry of 15 × 15 arcmin fields centered on the candidates was then performed on the Cambridge Astronomy Survey Unit reduced images. After statistical field-star decontamination, color-magnitude and color-color diagrams were constructed and analyzed. Results. We report the discovery of 96 new infrared open clusters and stellar groups. Most of the new cluster candidates are faint and compact (with small angular sizes), highly reddened, and younger than 5 Myr. For relatively well populated cluster candidates we derived their fundamental parameters such as reddening, distance, and age by fitting the solar-metallicity Padova isochrones to the color-magnitude diagrams.

Context. Recently, Carraro (2005) drew attention to the remarkable star cluster Whiting 1 by showing that it lies about 40 kpc from the Sun and is therefore unquestionably a member of the Galactic halo (b = −60.6 deg). Its Color Magnitude Diagram (CMD) indicated that Whiting 1 is very young (∼5 Gyr) for a globular cluster. It is very likely that Whiting 1 originated in a dwarf galaxy that has since been disrupted by the Milky Way. Aims. The main goals of this investigation were to constrain better the age, metallicity, and distance of Whiting 1 and to assess whether it belongs to a stellar stream from the Sagittarius dwarf spheroidal galaxy (Sgr dSph). Methods. Deep CCD photometry in the BVI pass-bands obtained with the VLT is used to improve the quality of the CMD and to determine the cluster's luminosity function and surface density profile. High-resolution spectrograms obtained with Magellan are used to measure the cluster's radial velocity and to place limits on its possible metallicity. The measurements of distance and radial velocity are used to test the cluster's membership in the stellar streams from the Sgr dSph. Results. From our CMD of Whiting 1, we derive new estimates for the cluster's age (6.5 +1.0 −0.5 Gyr), metallicity (Z = 0.004 ± 0.001, [Fe/H] = -0.65), and distance (29.4 +1.8 −2.0 kpc). From echelle spectrograms of three stars, we obtain -130.6 ± 1.8 km s −1 for the cluster's radial velocity and show from measurements of two infra-red CaII lines that the [Fe/H] of the cluster probably lies in the range -1.1 to -0.4. Both the luminosity function and the surface density profile suggest that the cluster has undergone tidal stripping by the Milky Way. We demonstrate that the position of Whiting 1 on the sky, its distance from the Sun, and its radial velocity are identical to within the errors of both the theoretical predictions of the trailing stream of stars from the Sgr dSph galaxy and the previous observations of the M giant stars that delineate the streams. Conclusions. With the addition of Whiting 1, there is now strong evidence that 6 globular clusters formed within the Sgr dSph. Whiting 1 is particularly interesting because it is the youngest and among the most metal rich. The relatively young age of Whiting 1 demonstrates that this dwarf galaxy was able to form star clusters for a period of at least 6 Gyr, and the age and metallicity of Whiting 1 are consistent with the age-metallicity relationship in the main body of the Sgr dSph. The presence now of Whiting 1 in the Galactic halo provides additional support for the view that the young halo clusters originated in dwarf galaxies that have been accreted by the Milky Way.