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Wide-field and deep DECam multi-band photometry, combined with HST data for the core of the Galactic globular cluster NGC 2808, allowed us to study the distribution of various stellar sub-populations and stars in different evolutionary phases out to the cluster tidal radius. We used the C_ugi = (u-g)-(g-i) index to identify three chemically distinct sub-populations along the red giant branch and compared their spatial distributions. The most light-element enriched sub-population (P3) is more centrally concentrated; however, it shows a more extended distribution in the external regions of the cluster compared to the primordial (P1) and intermediate (P2) composition populations. Furthermore, the P3 sub-population centroid is off-center relative to those of the P1 and P2 groups. We also analyzed the spatial distribution of horizontal branch stars and found that the relative fraction of red horizontal branch stars increases for radial distances larger than ~ 1.5' while that of the blue and hotter stars decreases. These new observations, combined with literature spectroscopic measurements, suggest that the red horizontal branch stars are the progeny of all the stellar sub-populations in NGC 2808, i.e. primordial and light-element enhanced, while the blue stars are possibly the result of a combination of the "hot-flasher" and the "helium-enhanced" scenarios. A similar distribution of different red giant branch sub-populations and horizontal branch stars was also found for the most massive Galactic globular cluster, omega Cen, based on combined DECam and HST data, which suggests the two may share a similar origin., Comment: Accepted for publication in AJ; 22 pages; 16 figures; the full version of table 2 will be available in electronic form with the published version

The Blanco DECam Bulge Survey (BDBS) has imaged more than 200 square degrees of the Southern Galactic bulge, providing photometry in the ugrizY filters for ~250 million unique stars. An accurate cross-match of BDBS with the latest data release (EDR3) of Gaia results in more than 140 million sources with BDBS photometry and Gaia EDR3 photometry and astrometry. In this talk, I will show how Gaia EDR3 parallaxes and proper motions can be used to statistically remove foreground sources, allowing us to produce clean color-magnitude diagrams (CMDs) and transverse kinematic maps for stars in the bulge. We observe kinematic patterns consistent with the X-shaped nature of the bulge, and rotation signatures due to the presence of the bar. I will present cleaned CMDs for over a hundred individual Southern Galactic bulge fields, showing no evidence for a conspicuous young population of stars in the bulge, but confirming previous studies identifying a mean age for the bulge stars of ~10 Gyr.Finally, I will conclude by discussing the implications of our findings in the context of possible formation scenarios for the Milky Way bulge, and the improvements from future Gaia data releases that will allow more precise identification of bulge members.

The ultra-faint dwarf galaxy Reticulum~II was enriched by a single rare and prolific r-process event. The r-process content of Reticulum~II thus provides a unique opportunity to study metal mixing in a relic first galaxy. Using multi-object high-resolution spectroscopy with VLT/GIRAFFE and Magellan/M2FS, we identify 32 clear spectroscopic member stars and measure abundances of Mg, Ca, Fe, and Ba where possible. We find $72^{+10}_{-12}$% of the stars are r-process-enhanced, with a mean $\left\langle\mbox{[Ba/H]}\right\rangle=-1.68~\pm~0.07$ and unresolved intrinsic dispersion $\sigma_{\rm [Ba/H]} < 0.20$. The homogeneous r-process abundances imply that Ret~II's metals are well-mixed by the time the r-enhanced stars form, which simulations have shown requires at least 100 Myr of metal mixing in between bursts of star formation to homogenize. This is the first direct evidence of bursty star formation in an ultra-faint dwarf galaxy. The homogeneous dilution prefers a prompt and high-yield r-process site, such as collapsar disk winds or prompt neutron star mergers. We also find evidence from [Ba/H] and [Mg/Ca] that the r-enhanced stars in Ret~II formed in the absence of substantial pristine gas accretion, perhaps indicating that ${\approx}70$% of Ret~II stars formed after reionization., Comment: 37 pages, 12 figures, 10 tables, accepted to AJ

The last decade has seen an era of intensive research on the Galactic bulge spearheaded by large spectroscopic surveys, such as the Bulge Radial Velocity Assay (BRAVA; [1], [2], [3]) and ARGOS [4], along with deep near-IR imaging campaigns such as VVV [5]. However, optical imaging remains an important tool for examining the formation history of the bulge since optical colors are more sensitive to stellar metallicity than the near-IR, and such observations are not as expensive as high-resolution spectroscopy. The modern era has lacked a uniform, deep, multi-band optical survey of the bulge, but the potential scientific return on such an analysis is too great to ignore. Motivated by these considerations, we undertook the Blanco DECam Bulge Survey (BDBS; [6], [7]), named in honor of the scientific contributions of Víctor and Betty Blanco, which is a survey of ~200 square degrees of the Southern bulge (Figure 1) using the mainly US Department of Energy (DOE)-funded Dark Energy Camera (DECam) on the Víctor M. Blanco 4m telescope and imaging in its ugrizY passbands.

We recommend configuring the LSST coverage of the inner Galactic plane to allow the production of the definitive age/metallicity map of the Galactic bulge from LSST data, matched to external surveys where appropriate. This will allow the formation history of the Galactic bulge to be reconstructed, as well as furnishing a huge legacy dataset to support one of the key LSST science goals (Mapping the Milky Way). We recommend precise multi-color $grizy$~photometry as deeply as spatial crowding will allow (ideally completing early in the project), complemented by a single-filter survey spread over the entire 10-year time baseline. Both strands should cover as broad an area within the Bulge as possible, with image quality sufficient to reach at least the bulge main sequence turn-off in seeing-limited observations. We specify metrics and a figure of merit by which candidate observing strategies could be evaluated with respect to `static' bulge science (proper motions and photometry), Comment: White Paper submitted to the 2018 call for LSST cadence proposals

Dust production is explored around 14 metal-poor ([Fe/H] = -1.91 to -0.98) giant stars in the Galactic globular cluster omega Centauri using new Spitzer IRS spectra. This sample includes the cluster's post-AGB and carbon stars and is thus the first representative spectral study of dust production in a metal-poor ([Fe/H] < -1) population. Only the more metal rich stars V6 and V17 ([Fe/H] = -1.08, -1.06) exhibit silicate emission, while the five other stars with mid-infrared excess show only a featureless continuum which we argue is caused by metallic iron dust grains. We examine the metallicity of V42, and find it is likely part of the metal-rich population ([Fe/H] ~ -0.8). Aside from the post-AGB star V1, we find no star from the cluster's bulk, metal-poor ([Fe/H] < -1.5) population - including the carbon stars - to be producing detectable amounts of dust. We compare the dust production to the stars' H-alpha line profiles obtained at the Magellan/Clay telescope at Las Campanas Observatory, finding pulsation shocking in the strongest pulsators (V6, V17 and V42), but evidence of outflow in all other stars. We conclude that the onset of dust production does not signify a fundamental change in the material leaving the star. Our data add to a growing body of evidence that metallic iron dominates dust production in metal-poor, oxygen-rich stars, but that dust is probably not the primary accelerant of winds in this mass-metallicity regime., 13 pages, 10 figures, accepted MNRAS