Multi-epoch radial velocity measurements of stars can be used to identify stellar, substellar, and planetary-mass companions. Even a small number of observation epochs can be informative about ...companions, though there can be multiple qualitatively different orbital solutions that fit the data. We have custom-built a Monte Carlo sampler (The Joker) that delivers reliable (and often highly multimodal) posterior samplings for companion orbital parameters given sparse radial velocity data. Here we use The Joker to perform a search for companions to 96,231 red giant stars observed in the APOGEE survey (DR14) with ≥3 spectroscopic epochs. We select stars with probable companions by making a cut on our posterior belief about the amplitude of the variation in stellar radial velocity induced by the orbit. We provide (1) a catalog of 320 companions for which the stellar companion's properties can be confidently determined, (2) a catalog of 4898 stars that likely have companions, but would require more observations to uniquely determine the orbital properties, and (3) posterior samplings for the full orbital parameters for all stars in the parent sample. We show the characteristics of systems with confidently determined companion properties and highlight interesting systems with candidate compact object companions.
We investigate aluminum abundance variations in the stellar populations of globular clusters using both literature measurements of sodium and aluminum and APOGEE measurements of nitrogen and aluminum ...abundances. For the latter, we show that the Payne is the most suitable of the five available abundance pipelines for our purposes. Our combined sample of 42 globular clusters spans approximately 2 dex in Fe/H and 1.5 dex in . We find no fewer than five globular clusters with significant internal variations in nitrogen and/or sodium with little to no corresponding variation in aluminum, and that the minimum present-day cluster mass for aluminum enrichment in metal-rich systems is . We demonstrate that the slopes of the Al/Fe versus Na/Fe and Al/Fe versus N/Fe relations for stars without field-like abundances are approximately log-linearly dependent on both the metallicity and the stellar mass of the globular clusters. In contrast, the relationship between Na/Fe and N/Fe shows no evidence of such dependencies. This suggests that there were (at least) two classes of non-supernova chemical polluters that were common in the early universe, and that their relative contributions within globular clusters somehow scaled with the metallicity and mass of globular clusters. The first of these classes is predominantly responsible for the CNO and NeNa abundance variations, and likewise the second for the MgAl abundance variations. Particularly striking examples of this dichotomy include 47 Tuc and M4. As an auxiliary finding, we argue that abundance variations among Terzan 5 stars are consistent with it being a normal globular cluster.
Aims. We attempt to constrain the kinematics of the thin and thick disks using the Besançon population synthesis model together with RAVE DR4 and Gaia first data release (TGAS). Methods. The RAVE ...fields were simulated by applying a detailed target selection function and the kinematics was computed using velocity ellipsoids depending on age in order to study the secular evolution. We accounted for the asymmetric drift computed from fitting a Stäckel potential to orbits. Model parameters such as velocity dispersions, mean motions, and velocity gradients were adjusted using an ABC-MCMC method. We made use of the metallicity to enhance the separation between thin and thick disks. Results. We show that this model is able to reproduce the kinematics of the local disks in great detail. The disk follows the expected secular evolution, in very good agreement with previous studies of the thin disk. The new asymmetric drift formula, fitted to our previously described Stäckel potential, fairly well reproduces the velocity distribution in a wide solar neighborhood. The U and W components of the solar motion determined with this method agree well with previous studies. However, we find a smaller V component than previously thought, essentially because we include the variation of the asymmetric drift with distance to the plane. The thick disk is represented by a long period of formation (at least 2 Gyr), during which, as we show, the mean velocity increases with time while the scale height and scale length decrease, very consistently with a collapse phase with conservation of angular momentum. Conclusions. This new Galactic dynamical model is able to reproduce the observed velocities in a wide solar neighborhood at the quality level of the TGAS-RAVE sample, allowing us to constrain the thin and thick disk dynamical evolution, as well as determining the solar motion.
Detailed elemental-abundance patterns of giant stars in the Galactic halo measured by the Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) have revealed the existence of a unique and ...significant stellar subpopulation of silicon-enhanced (Si/Fe ≳ +0.5) metal-poor stars, spanning a wide range of metallicities (−1.5 ≲ Fe/H ≲ −0.8). Stars with over-abundances in Si/Fe are of great interest because these have very strong silicon (
28
Si) spectral features for stars of their metallicity and evolutionary stage, offering clues about rare nucleosynthetic pathways in globular clusters (GCs). Si-rich field stars have been conjectured to have been evaporated from GCs, however, the origin of their abundances remains unclear, and several scenarios have been offered to explain the anomalous abundance ratios. These include the hypothesis that some of them were born from a cloud of gas previously polluted by a progenitor that underwent a specific and peculiar nucleosynthesis event or, alternatively, that they were due to mass transfer from a previous evolved companion. However, those scenarios do not simultaneously explain the wide gamut of chemical species that are found in Si-rich stars. Instead, we show that the present inventory of such unusual stars, as well as their relation to known halo substructures (including the in situ halo,
Gaia
-Enceladus, the Helmi Stream(s), and Sequoia, among others), is still incomplete. We report the chemical abundances of the iron-peak (Fe), the light- (C and N), the
α
- (O and Mg), the odd-
Z
(Na and Al), and the
s
-process (Ce and Nd) elements of 55 newly identified Si-rich field stars (among more than ∼600 000 APOGEE-2 targets), which exhibit over-abundances of Si/Fe as extreme as those observed in some Galactic GCs, and they are relatively well distinguished from other stars in the Si/Fe−Fe/H plane. This new census confirms the presence of a statistically significant and chemically-anomalous structure in the inner halo:
Jurassic
. The chemo-dynamical properties of the
Jurassic
structure is consistent with it being the tidally disrupted remains of GCs, which are easily distinguished by an over-abundance of Si/Fe among Milky Way populations or satellites.
We present an analysis of spectroscopic and astrometric data from APOGEE-2 and Gaia DR2 to identify structures toward the Orion Complex. By applying a hierarchical clustering algorithm to the ...six-dimensional stellar data, we identify spatially and/or kinematically distinct groups of young stellar objects with ages ranging from 1 to 12 Myr. We also investigate the star-forming history within the Orion Complex and identify peculiar subclusters. With this method we reconstruct the older populations in the regions that are currently largely devoid of molecular gas, such as Orion C (which includes the Ori cluster) and Orion D (the population that traces Ori OB1a, OB1b, and Orion X). We report on the distances, kinematics, and ages of the groups within the Complex. The Orion D group is in the process of expanding. On the other hand, Orion B is still in the process of contraction. In λ Ori the proper motions are consistent with a radial expansion due to an explosion from a supernova; the traceback age from the expansion exceeds the age of the youngest stars formed near the outer edges of the region, and their formation would have been triggered when they were halfway from the cluster center to their current positions. We also present a comparison between the parallax and proper-motion solutions obtained by Gaia DR2 and those obtained toward star-forming regions by the Very Long Baseline Array.
Abstract
We present the first high-resolution abundance analysis of the globular cluster VVV CL001, which resides in a region dominated by high interstellar reddening toward the Galactic bulge. Using
...H
-band spectra acquired by the Apache Point Observatory Galactic Evolution Experiment, we identified two potential members of the cluster, and estimated from their Fe
i
lines that the cluster has an average metallicity of Fe/H = −2.45 with an uncertainty due to systematics of 0.24 dex. We find that the light-(N),
α
-(O, Mg, Si), and Odd-
Z
(Al) elemental abundances of the stars in VVV CL001 follow the same trend as other Galactic metal-poor globular clusters. This makes VVV CL001 possibly the most metal-poor globular cluster identified so far within the Sun’s galactocentric distance and likely one of the most metal-deficient clusters in the Galaxy after ESO280-SC06. Applying statistical isochrone fitting, we derive self-consistent age, distance, and reddening values, yielding an estimated age of
11.9
−
4.05
+
3.12
Gyr at a distance of
8.22
−
1.93
+
1.84
kpc, revealing that VVV CL001 is also an old GC in the inner Galaxy. The Galactic orbit of VVV CL001 indicates that this cluster lies on a halo-like orbit that appears to be highly eccentric. Both chemistry and dynamics support the hypothesis that VVV CL001 could be an ancient fossil relic left behind by a massive merger event during the early evolution of the Galaxy, likely associated with either the Sequoia or the Gaia–Enceladus–Sausage structures.
The formation processes that led to the current Galactic stellar halo are still under debate. Previous studies have provided evidence for different stellar populations in terms of elemental ...abundances and kinematics, pointing to different chemical and star formation histories (SFHs). In the present work, we explore, over a broader range in metallicity ( ), the two stellar populations detected in the first paper of this series from metal-poor stars in DR13 of the Apache Point Observatory Galactic Evolution Experiment (APOGEE). We aim to infer signatures of the initial mass function (IMF) and the SFH from the two -to-iron versus iron abundance chemical trends for the most APOGEE-reliable -elements (O, Mg, Si, and Ca). Using simple chemical-evolution models, we infer the upper mass limit (Mup) for the IMF and the star formation rate, and its duration for each population. Compared with the low- population, we obtain a more intense and longer-lived SFH, and a top-heavier IMF for the high- population.
ABSTRACT
The latest edition of the APOGEE-2/DR14 survey catalogue and the first Payne data release of APOGEE abundance determinations by Ting et al. are examined. We identify 31 previously unremarked ...metal-poor giant stars with anomalously high levels of N/Fe abundances, which is not usually observed among metal-poor stars in the Milky Way. We made use of the Brussels Automatic Stellar Parameter (BACCHUS) code to re-derive manually the chemical abundances of 31 field stars in order to compile the main element families, namely the light elements (C, N), a-elements (O, Mg, Si), iron-peak element (Fe), s-process elements (Ce, Nd), and the light odd-Z element (Na, Al). We have found all these objects have a N/Fe ≳ +0.5, and are thus identified here as nitrogen-rich stars. An orbital analysis of these objects revealed that a handful of them shares the orbital properties of the bar/bulge, and possibly linked to tidal debris of surviving globular clusters trapped into the bar component. Three of the 31 stars are actually halo interlopers into the bulge area, which suggests that halo contamination is not insignificant when studying N-rich stars found in the inner Galaxy, whereas the rest of the N-rich stars share orbital properties with the halo population. Most of the newly identified population exhibits chemistry similar to the so-called second-generation globular cluster stars (enriched in aluminum, Al/Fe ≳ +0.5), whereas a handful of them exhibit lower abundances of aluminum, Al/Fe < +0.5, which are thought to be chemically associated with the first generation of stars, as seen in globular clusters, or compatible with origin from a tidally disrupted dwarf galaxy.
Stars with higher levels of aluminium and nitrogen enrichment are often key pieces in the chemical makeup of multiple populations in almost all globular clusters (GCs). There is also compelling ...observational evidence that some Galactic components could be partially built from dissipated GCs. The identification of such stars among metal-poor field stars may therefore provide insight into the composite nature of the Milky Way (MW) bulge and inner stellar halo, and could also reveal other chemical peculiarities. Here, based on APOGEE spectra, we report the discovery of 29 mildly metal-poor (Fe/H ≲ −0.7) stars with stellar atmospheres strongly enriched in aluminium (Al-rich stars: Al/Fe ≳ +0.5), well above the typical Galactic levels, located within the solar radius toward the bulge region, which lies in highly eccentric orbits (
e
≳ 0.6). We find many similarities for almost all of the chemical species measured in this work with the chemical patterns of GCs, and therefore we propose that they have likely been dynamically ejected into the bulge and inner halo from GCs formed in situ and/or GCs formed in different progenitors of known merger events experienced by the MW, such as the
Gaia
-Sausage-Enceladus and/or Sequoia.
The presence of nitrogen-enriched stars in globular clusters provides key evidence for multiple stellar populations (MPs), as has been demonstrated with globular cluster spectroscopic data towards ...the bulge, disk, and halo. In this work, we employ the VVV Infrared Astrometric Catalogue (VIRAC) and the DR16 SDSS-IV release of the APOGEE survey to provide the first detailed spectroscopic study of the bulge globular cluster UKS 1. Based on these data, a sample of six selected cluster members was studied. We find the mean metallicity of UKS 1 to be Fe/H = −0.98 ± 0.11, considerably more metal-poor than previously reported, and a negligible metallicity scatter, typical of that observed by APOGEE in other Galactic globular clusters. In addition, we find a mean radial velocity of 66.1 ± 12.9 km s
−1
, which is in good agreement with literature values, within 1
σ
. By selecting stars in the VIRAC catalogue towards UKS 1, we also measure a mean proper motion of (
μ
α
cos(
δ
),
μ
δ
) = (−2.77 ± 0.23, −2.43 ± 0.16) mas yr
−1
. We find strong evidence for the presence of MPs in UKS 1, since four out of the six giants analysed in this work have strong enrichment in nitrogen (N/Fe ≳ +0.95) accompanied by lower carbon abundances (C/Fe ≲ −0.2). Overall, the light- (C, N),
α
- (O, Mg, Si, Ca, Ti), Fe-peak (Fe, Ni), Odd-Z (Al, K), and the
s
-process (Ce, Nd, Yb) elemental abundances of our member candidates are consistent with those observed in globular clusters at similar metallicity. Furthermore, the overall star-to-star abundance scatter of elements exhibiting the multiple-population phenomenon in UKS 1 is typical of that found in other global clusters (GCs), and larger than the typical errors of some X/Fe abundances. Results from statistical isochrone fits in the VVV colour-magnitude diagrams indicate an age of 13.10
−1.29
+0.93
Gyr, suggesting that UKS 1 is a fossil relic in the Galactic bulge.
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