Search for: All records

ABSTRACT There has been a concerted effort in recent years to identify the astrophysical sites of the r-process that can operate early in the galaxy. The discovery of many r-process-enhanced (RPE) stars (especially by the R-process Alliance collaboration) has significantly accelerated this effort. However, only limited data exist on the detailed elemental abundances covering the primary neutron-capture peaks. Subtle differences in the structure of the r-process pattern, such as the relative abundances of elements in the third peak, in particular, are expected to constrain the r-process sites further. Here, we present a detailed elemental-abundance analysis of four bright RPE stars selected from the HESP–GOMPA survey. Observations were carried out with the 10-m class telescope Gran Telescopio Canarias (GTC), Spain. The high spectral signal-to-noise ratios obtained allow us to derive abundances for 20 neutron-capture elements, including the third r-process peak element osmium (Os). We detect thorium (Th) in two stars, which we use to estimate their ages. We discuss the metallicity evolution of Mg, Sr, Ba, Eu, Os, and Th in r-II and r-I stars, based on a compilation of RPE stars from the literature. The strontium (Sr) abundance trend with respect to europium (Eu) suggests the need for an additional production site for Sr (similar to several earlier studies); this requirement could be milder for yttrium (Y) and zirconium (Zr). We also show that there could be some time delay between r-II and r-I star formation, based on the Mg/Th abundance ratios. 

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. 

We present new maps of the Milky Way disk showing the distribution of metallicity ([Fe/H]),α-element abundances ([Mg/Fe]), and stellar age, using a sample of 66,496 red giant stars from the final data release (DR17) of the Apache Point Observatory Galactic Evolution Experiment survey. We measure radial and vertical gradients, quantify the distribution functions for age and metallicity, and explore chemical clock relations across the Milky Way for the low-αdisk, high-αdisk, and total population independently. The low-αdisk exhibits a negative radial metallicity gradient of −0.06 ± 0.001 dex kpc⁻¹, which flattens with distance from the midplane. The high-αdisk shows a flat radial gradient in metallicity and age across nearly all locations of the disk. The age and metallicity distribution functions shift from negatively skewed in the inner Galaxy to positively skewed at large radius. Significant bimodality in the [Mg/Fe]–[Fe/H] plane and in the [Mg/Fe]–age relation persist across the entire disk. The age estimates have typical uncertainties of ∼0.15 in log(age) and may be subject to additional systematic errors, which impose limitations on conclusions drawn from this sample. Nevertheless, these results act as critical constraints on galactic evolution models, constraining which physical processes played a dominant role in the formation of the Milky Way disk. We discuss how radial migration predicts many of the observed trends near the solar neighborhood and in the outer disk, but an additional more dramatic evolution history, such as the multi-infall model or a merger event, is needed to explain the chemical and age bimodality elsewhere in the Galaxy.

 

The Opiliones superfamily Triaenonychoidea currently includes two families, the monogeneric New Zealand–endemic Synthetonychiidae Forster, 1954 and Triaenonychidae Sørensen, 1886, a diverse family distributed mostly throughout the temperate Gondwanan terranes, with ~110 genera and ~500 species and subspecies currently described. Traditionally, Triaenonychidae has been divided into subfamilies diagnosed by very few morphological characters largely derived from the troublesome ‘Roewerian system’ of morphology, and classifications based on this system led to many complications. Recent research within Triaenonychoidea using morphology and traditional multilocus data has shown multiple deeply divergent lineages, non-monophyly of Triaenonychidae, and non-monophyly of subfamilies, necessitating a revision based on phylogenomic data. We used sequence capture of ultraconserved elements across 164 samples to create a 50% taxon occupancy matrix with 704 loci. Using phylogenomic and morphological examinations, we explored family-level relationships within Triaenonychoidea, including describing two new families: (1) Lomanellidae Mendes & Derkarabetian, fam. nov., consisting of Lomanella Pocock, 1903, and a newly described genus Abaddon Derkarabetian & Baker, gen. nov. with one species, A. despoliator Derkarabetian, sp. nov.; and (2) the elevation to family of Buemarinoidae Karaman, 2019, consisting of Buemarinoa Roewer, 1956, Fumontana Shear, 1977, Flavonuncia Lawrence, 1959, and a newly described genus Turonychus Derkarabetian, Prieto & Giribet, gen. nov., with one species, T. fadriquei Derkarabetian, Prieto & Giribet, sp. nov. With our dataset we also explored phylogenomic relationships within Triaenonychidae with an extensive taxon set including samples representing ~80% of the genus-level diversity. Based on our results we (1) discuss systematics of this family including the historical use of subfamilies, (2) reassess morphology in the context of our phylogeny, (3) hypothesise placement for all unsampled genera, (4) highlight lineages most in need of taxonomic revision, and (5) provide an updated species-level checklist. Aside from describing new taxa, our study provides the phylogenomic context necessary for future evolutionary and systematic research across this diverse lineage.ZooBank Registration: urn:lsid:zoobank.org:pub:81683834-98AB-43AA-B25A-C28C6A404F41 

Recent results from chemical tagging studies using Apache Point Observatory Galactic Evolution Experiment data suggest a strong link between the chemical abundance patterns of stars found within globular clusters (GC), and chemically peculiar populations in the Galactic halo field. In this paper, we analyse the chemical compositions of stars within the cluster body and tidal streams of Palomar 5, a GC that is being tidally disrupted by interaction with the Galactic gravitational potential. We report the identification of nitrogen-rich (N-rich) stars both within and beyond the tidal radius of Palomar 5, with the latter being clearly aligned with the cluster tidal streams; this acts as confirmation that N-rich stars are lost to the Galactic halo from GCs, and provides support to the hypothesis that field N-rich stars identified by various groups have a GC origin.

 

Abstract The S2 stream is a kinematically cold stream that is plunging downwards through the Galactic disc. It may be part of a hotter and more diffuse structure called the Helmi stream. We present a multi-instrument chemical analysis of the stars in the metal-poor S2 stream using both high- and low-resolution spectroscopy, complemented with a re-analysis of the archival data to give a total sample of 62 S2 members. Our high-resolution program provides α-elements (C, Mg, Si, Ca and Ti), iron-peak elements (V, Cr, Mn, Fe, Ni), n-capture process elements (Sr, Ba) and other elements such as Li, Na, Al, and Sc for a subsample of S2 objects. We report coherent abundance patterns over a large metallicity spread (∼1 dex) confirming that the S2 stream was produced by a disrupted dwarf galaxy. The combination of S2’s α-elements displays a mildly decreasing trend with increasing metallicity which can be tentatively interpreted as a “knee” at [Fe/H]<−2. At the low metallicity end, the n-capture elements in S2 may be dominated by r-process production however several stars are Ba-enhanced, but unusually poor in Sr. Moreover, some of the low-[Fe/H] stars appear to be carbon-enhanced. We interpret the observed abundance patterns with the help of chemical evolution models that demonstrate the need for modest star-formation efficiency and low wind efficiency confirming that the progenitor of S2 was a primitive dwarf galaxy. 

ABSTRACT We report evidence from APOGEE for the presence of a new metal-poor stellar structure located within ∼4 kpc of the Galactic Centre. Characterized by a chemical composition resembling those of low-mass satellites of the Milky Way, this new inner Galaxy structure (IGS) seems to be chemically and dynamically detached from more metal-rich populations in the inner Galaxy. We conjecture that this structure is associated with an accretion event that likely occurred in the early life of the Milky Way. Comparing the mean elemental abundances of this structure with predictions from cosmological numerical simulations, we estimate that the progenitor system had a stellar mass of ∼5 × 108 M⊙, or approximately twice the mass of the recently discovered Gaia-Enceladus/Sausage system. We find that the accreted:in situ ratio within our metal-poor ([Fe/H] < –0.8) bulge sample is somewhere between 1:3 and 1:2, confirming predictions of cosmological numerical simulations by various groups.