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Abstract The chemical abundances of Milky Way’s (MW's) satellites reflect their star formation histories (SFHs), yet, due to the difficulty of determining the ages of old stars, the SFHs of most satellites are poorly measured. Ongoing and upcoming surveys will obtain around 10 times more medium-resolution spectra for stars in satellites than are currently available. To correctly extract SFHs from large samples of chemical abundances, the relationship between chemical abundances and SFHs needs to be clarified. Here, we perform a high-resolution cosmological zoom-in simulation of a MW-like galaxy with detailed models of star formation, supernova (SN) feedback, and metal diffusion. We quantify SFHs, metallicity distribution functions, and theα-element (Mg, Ca, and Si) abundances in satellites of the host galaxy. We find that star formation in most simulated satellites is quenched before infalling to their host. Star formation episodes in simulated satellites are separated by a few hundred Myr owing to SN feedback; each star formation event produces groups of stars with similar [α/Fe] and [Fe/H]. We then perform a mock observation of the upcoming Subaru Prime Focus Spectrograph (PFS) observations. We find that Subaru PFS will be able to detect distinct groups of stars in [α/Fe] versus [Fe/H] space, produced by episodic star formation. This result means that episodic SFHs can be estimated from the chemical abundances of ≳1000 stars determined with medium-resolution spectroscopy. 

ABSTRACT We introduce the Sloan Digital Sky Survey (SDSS)/ Apache Point Observatory Galactic Evolution Experiment (APOGEE) value-added catalogue of Galactic globular cluster (GC) stars. The catalogue is the result of a critical search of the APOGEE Data Release 17 (DR17) catalogue for candidate members of all known Galactic GCs. Candidate members are assigned to various GCs on the basis of position in the sky, proper motion, and radial velocity. The catalogue contains a total of 7737 entries for 6422 unique stars associated with 72 Galactic GCs. Full APOGEE DR17 information is provided, including radial velocities and abundances for up to 20 elements. Membership probabilities estimated on the basis of precision radial velocities are made available. Comparisons with chemical compositions derived from the GALactic Archaeology with HERMES (GALAH) survey, as well as optical values from the literature, show good agreement. This catalogue represents a significant increase in the public data base of GC star chemical compositions and kinematics, providing a massive homogeneous data set that will enable a variety of studies. The catalogue in fits format is available for public download from the SDSS-IV DR17 value-added catalogue website. 

Abstract We created the APOGEE-GALEX-Gaia catalog to study white dwarf (WD) binaries. This database aims to create a minimally biased sample of WD binary systems identified from a combination of GALEX, Gaia, and APOGEE data to increase the number of WD binaries with orbital parameters and chemical compositions. We identify 3414 sources as WD binary candidates, with nondegenerate companions of spectral types between F and M, including main-sequence stars, main-sequence binaries, subgiants, sub-subgiants, red giants, and red clump stars. Among our findings are (a) a total of 1806 systems having inferred WD radii R < 25 R ⊕ , which constitute a more reliable group of WD binary candidates within the main sample; (b) a difference in the metallicity distribution function between WD binary candidates and the control sample of most luminous giants ( M H < −3.0); (c) the existence of a population of sub-subgiants with WD companions; (d) evidence for shorter periods in binaries that contain WDs compared to those that do not, as shown by the cumulative distributions of APOGEE radial velocity shifts; (e) evidence for systemic orbital evolution in a sample of 252 WD binaries with orbital periods, based on differences in the period distribution between systems with red clump, main-sequence binary, and sub-subgiant companions and systems with main-sequence or red giant companions; and (f) evidence for chemical enrichment during common envelope (CE) evolution, shown by lower metallicities in wide WD binary candidates ( P > 100 days) compared to post-CE ( P < 100 days) WD binary candidates. 

Abstract We report the first 3D kinematical measurements of 88 stars in the direction of several recently discovered substructures in the southern periphery of the Large Magellanic Cloud (LMC) using a combination of Gaia proper motions and radial velocities from the APOGEE-2 survey. More specifically, we explore stars in assorted APOGEE-2 pointings in a region of the LMC periphery where various overdensities of stars have previously been identified in maps of stars from Gaia and DECam. By using a model of the LMC disk rotation, we find that a sizable fraction of the APOGEE-2 stars have extreme space velocities that are distinct from, and not a simple extension of, the LMC disk. Using N -body hydrodynamical simulations of the past dynamical evolution and interaction of the LMC and Small Magellanic Cloud (SMC), we explore whether the extreme-velocity stars may be accounted for as tidal debris created in the course of that interaction. We conclude that the combination of LMC and SMC debris produced from their interaction is a promising explanation, although we cannot rule out other possible origins, and that these new data should be used to constrain future simulations of the LMC–SMC interaction. We also conclude that many of the stars in the southern periphery of the LMC lie outside of the LMC plane by several kiloparsecs. Given that the metallicity of these stars suggests that they are likely of Magellanic origin, our results suggest that a wider exploration of the past interaction history of the Magellanic Clouds is needed. 

Abstract We present a search for close, unresolved companions in a subset of spatially resolved Gaia wide binaries containing main-sequence stars within 200 pc of the Sun, utilizing the APOGEE–Gaia Wide Binary Catalog. A catalog of 37 wide binaries was created by selecting pairs of stars with nearly identical Gaia positions, parallaxes, and proper motions, and then confirming candidates to be gravitationally-bound pairs using APOGEE radial velocities. We identify close, unresolved stellar and substellar candidate companions in these multiple systems using (1) the Gaia binary main-sequence and (2) observed periodic radial velocity variations in APOGEE measurements due to the influence of a close substellar-mass companion. The studied wide binary pairs reveal a total of four stellar-mass close companions in four different wide binaries, and four substellar-mass close companion candidates in two wide binaries. The latter are therefore quadruple systems, with one substellar mass companion orbiting each wide binary component in an S-type orbit. Taken at face value, these candidate systems represent an enhancement of an order of magnitude over the expected occurrence rate of ∼2 per cent of stars having substellar companions >2 MJup within ∼100 day orbits; we discuss implications and possible explanations for this result. Finally, we compare chemical differences between the components of the wide binaries and the components of the candidate higher-order systems and find that any chemical influence or correlation due to the presence of close companions to wide binary stars is not discernible. 

ABSTRACT We measure rotational broadening in spectra taken by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey to characterize the relationship between stellar multiplicity and rotation. We create a sample of 2786 giants and 24 496 dwarfs with stellar parameters and multiple radial velocities from the APOGEE pipeline, projected rotation speeds vsin i determined from our own pipeline, and distances, masses, and ages measured by Sanders & Das. We use the statistical distribution of the maximum shift in the radial velocities, ΔRVmax, as a proxy for the close binary fraction to explore the interplay between stellar evolution, rotation, and multiplicity. Assuming that the minimum orbital period allowed is the critical period for Roche Lobe overflow and rotational synchronization, we calculate theoretical upper limits on expected vsin i and ΔRVmax values. These expectations agree with the positive correlation between the maximum ΔRVmax and vsin i values observed in our sample as a function of log(g). We find that the fast rotators in our sample have a high occurrence of short-period [log(P/d) ≲ 4] companions. We also find that old, rapidly rotating main-sequence stars have larger completeness-corrected close binary fractions than their younger peers. Furthermore, rapidly rotating stars with large ΔRVmax consistently show differences of 1–10 Gyr between the predicted gyrochronological and measured isochronal ages. These results point towards a link between rapid rotation and close binarity through tidal interactions. We conclude that stellar rotation is strongly correlated with stellar multiplicity in the field, and caution should be taken in the application of gyrochronology relations to cool stars. 

Abstract We use time-resolved spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) to examine the distribution of radial velocity (RV) variations in 249 stars identified as members of the Sagittarius (Sgr) dwarf spheroidal (dSph) galaxy by Hayes et al. We select Milky Way (MW) stars that have stellar parameters ( $\log \left(g\right)$,T_eff, and [Fe/H] ) similar to those of the Sagittarius members by means of a k-d tree of dimension 3. We find that the shape of the distribution of RV shifts in Sgr dSph stars is similar to that measured in their MW analogs, but the total fraction of RV variable stars in the Sgr dSph is larger by a factor of ∼2. After ruling out other explanations for this difference, we conclude that the fraction of close binaries in the Sgr dSph is intrinsically higher than in the MW. We discuss the implications of this result for the physical processes leading to the formation of close binaries in dwarf spheroidal and spiral galaxies.