Abstract
It has been suggested that the oldest stellar populations in the Milky Way are tightly bound and confined to the central regions of the Galaxy. This is one of the reasons why a handful of ...globular clusters located in the bulge region are thought to be remnants of the primeval formation stages of the Milky Way. The globular cluster, ESO 456-SC38 (Djorgovski 2), is one such cluster; it has a blue horizontal branch, is projected very close to the center of the Galaxy, and has an orbit confining it to the bulge/bar region. The first
α
abundances of seven stars in this heavily reddened cluster are presented using Apache Point Observatory Galaxy Evolution Experiment Data Release 16. A significant spread in the abundances of N, C, Na, and Al indicates the presence of multiple stellar populations in this cluster. Using Gaia DR2 proper motions and radial velocities from the Bulge Radial Velocity Assay for RR Lyrae stars, we confirm that RR Lyrae stars belong to this globular cluster.
We present radial velocities and chemical abundances of O, Na, Mg, Al, Si, Ca, Cr, Fe, Co, Ni, and Cu for a sample of 156 red giant branch stars in two Galactic bulge fields centered near (l, b) = (+ ...5.25,-3.02) and (0,-12). The (+ 5.25,-3.02) field also includes observations of the bulge globular cluster NGC 6553. However, we only selected a subset of the original observations that included spectra with both high S/N and that did not show strong TiO absorption bands. This work extends previous analysis of this data set beyond Fe and the alpha -elements Mg, Si, Ca, and Ti. For most elements, the NGC 6553 stars exhibit abundance trends nearly identical to comparable metallicity bulge field stars. However, the star-to-star scatter and mean Na/Fe ratios appear higher in the cluster, perhaps indicating additional self-enrichment.
RR Lyrae stars are recognized as some of the oldest stars in the Universe. In addition, they are some of the few old celestial objects for which distances can be reliably inferred. As such, these ...stars are excellent tracers of the oldest structures that exist in the inner Galaxy. Although the inner Galaxy is where the oldest structures in the Milky Way are thought to be hidden, it is also a region notoriously difficult to study due to high extinction and crowding. Here, I will summarize how RR Lyrae stars have been used to obtain a more complete picture of the inner Galaxy. In particular, recently, a large sample of RR Lyrae star motions through space have been obtained and compared to younger, more metal-rich stars in the bulge/bar. It is seen that the inner Galaxy RR Lyrae star kinematics are complicated by a mix of a variety of Galactic components. After isolating only those RR Lyrae stars that are confined to the bulge, a subsample of these stars have slower rotation and are less barred than the dominant bar/bulge. Curiously, there is no discernible metallicity Fe/H difference between these two subsamples. Old, metal-poor stars in the inner Galaxy need to be properly accounted for when discussing processes that gave rise to the formation of the inner Galaxy and the Galactic bar/bulge.
This paper presents the detailed abundances and r-process classifications of 126 newly identified metal-poor stars as part of an ongoing collaboration, the R-Process Alliance. The stars were ...identified as metal-poor candidates from the RAdial Velocity Experiment (RAVE) and were followed up at high spectral resolution (R ∼ 31,500) with the 3.5 m telescope at Apache Point Observatory. The atmospheric parameters were determined spectroscopically from Fe i lines, taking into account non-LTE corrections and using differential abundances with respect to a set of standards. Of the 126 new stars, 124 have Fe/H < −1.5, 105 have Fe/H < −2.0, and 4 have Fe/H < −3.0. Nine new carbon-enhanced metal-poor stars have been discovered, three of which are enhanced in r-process elements. Abundances of neutron-capture elements reveal 60 new r-I stars (with +0.3 ≤ Eu/Fe ≤ +1.0 and Ba/Eu < 0) and 4 new r-II stars (with Eu/Fe > +1.0). Nineteen stars are found to exhibit a "limited-r" signature (Sr/Ba > +0.5, Ba/Eu < 0). For the r-II stars, the second- and third-peak main r-process patterns are consistent with the r-process signature in other metal-poor stars and the Sun. The abundances of the light, , and Fe-peak elements match those of typical Milky Way (MW) halo stars, except for one r-I star that has high Na and low Mg, characteristic of globular cluster stars. Parallaxes and proper motions from the second Gaia data release yield UVW space velocities for these stars that are consistent with membership in the MW halo. Intriguingly, all r-II and the majority of r-I stars have retrograde orbits, which may indicate an accretion origin.
We investigate interstellar extinction curve variations towards ∼4 deg2 of the inner Milky Way in VIJKs
photometry from the OGLE-III (third phase of the Optical Gravitational Lensing Experiment) and ...VVV (VISTA Variables in the Via Lactea) surveys, with supporting evidence from diffuse interstellar bands and F435W, F625W photometry. We obtain independent measurements towards ∼2000 sightlines of AI, E(V − I), E(I − J) and E(J − Ks
), with median precision and accuracy of 2 per cent. We find that the variations in the extinction ratios AI
/E(V − I), E(I − J)/E(V − I) and E(J − Ks
)/E(V − I) are large (exceeding 20 per cent), significant and positively correlated, as expected. However, both the mean values and the trends in these extinction ratios are drastically shifted from the predictions of Cardelli and Fitzpatrick, regardless of how RV
is varied. Furthermore, we demonstrate that variations in the shape of the extinction curve have at least two degrees of freedom, and not one (e.g. RV
), which we confirm with a principal component analysis. We derive a median value of 〈AV
/AKs
〉 = 13.44, which is ∼60 per cent higher than the ‘standard’ value. We show that the Wesenheit magnitude WI
= I − 1.61(I − J) is relatively impervious to extinction curve variations. Given that these extinction curves are linchpins of observational cosmology, and that it is generally assumed that RV
variations correctly capture variations in the extinction curve, we argue that systematic errors in the distance ladder from studies of Type Ia supernovae and Cepheids may have been underestimated. Moreover, the reddening maps from the Planck experiment are shown to systematically overestimate dust extinction by ∼100 per cent and lack sensitivity to extinction curve variations.
ABSTRACT
The Blanco DECam Bulge Survey (BDBS) imaged more than 200 sq deg of the Southern Galactic bulge using the ugrizY filters of the Dark Energy Camera, and produced point spread function ...photometry of approximately 250 million unique sources. In this paper, we present details regarding the construction and collation of survey catalogues, and also discuss the adopted calibration and dereddening procedures. Early science results are presented with a particular emphasis on the bulge metallicity distribution function and globular clusters. A key result is the strong correlation (σ ∼ 0.2 dex) between (u − i)o and Fe/H for bulge red clump giants. We utilized this relation to find that interior bulge fields may be well described by simple closed box enrichment models, but fields exterior to b ∼ −6° seem to require a secondary metal-poor component. Applying scaled versions of the closed box model to the outer bulge fields is shown to significantly reduce the strengths of any additional metal-poor components when compared to Gaussian mixture models. Additional results include: a confirmation that the u band splits the subgiant branch in M22 as a function of metallicity, the detection of possible extratidal stars along the orbits of M 22 and FSR 1758, and additional evidence that NGC 6569 may have a small but discrete He spread, as evidenced by red clump luminosity variations in the reddest bands. We do not confirm previous claims that FSR 1758 is part of a larger extended structure.
The orbits, atmospheric parameters, chemical abundances, and ages of individual stars in the Milky Way provide the most comprehensive illustration of galaxy formation available. The Tycho-Gaia ...Astrometric Solution (TGAS) will deliver astrometric parameters for the largest ever sample of Milky Way stars, though its full potential cannot be realized without the addition of complementary spectroscopy. Among existing spectroscopic surveys, the RAdial Velocity Experiment (RAVE) has the largest overlap with TGAS ( 200,000 stars). We present a data-driven re-analysis of 520,781 RAVE spectra using The Cannon. For red giants, we build our model using high-fidelity APOGEE stellar parameters and abundances for stars that overlap with RAVE. For main sequence and sub-giant stars, our model uses stellar parameters from the K2/EPIC. We derive and validate effective temperature Teff, surface gravity log g, and chemical abundances of up to seven elements (O, Mg, Al, Si, Ca, Fe, and Ni). We report a total of 1,685,851 elemental abundances with a typical precision of 0.07 dex, a substantial improvement over previous RAVE data releases. The synthesis of RAVE-on and TGAS is the most powerful data set for chemo-dynamic analyses of the Milky Way ever produced.
Abstract
We present wide-field, high resolution maps of the color excess for 14 globular clusters toward the Southern Galactic bulge. The maps were derived using Gaia EDR3 astrometry and stellar ...photometry from the Blanco DECam Bulge Survey, which is a deep, wide-field
ugriz
Y photometric survey of the southern Galactic bulge. Comparisons with WISE 12
μ
m images of thermal continuum emission demonstrate that the maps presented here trace interstellar extinction by dust down to 5″ scales. We use the reddening-corrected photometry of proper motion-selected cluster stars to build color–magnitude diagrams for the target globular clusters, which show residual broadening in excess of that expected from the photometric errors alone. This residual broadening is likely to be driven by star-to-star elemental abundance variations.
Abstract
The Milky Way Bulge extra-tidal star survey is a spectroscopic survey with the goal of identifying stripped globular cluster stars from inner Galaxy clusters. In this way, an indication of ...the fraction of metal-poor bulge stars that originated from globular clusters can be determined. We observed and analyzed stars in and around BH 261, an understudied globular cluster in the bulge. From seven giants within the tidal radius of the cluster, we measured an average heliocentric radial velocity of 〈RV〉 = −61 ± 2.6 km s
−1
with a radial velocity dispersion of 〈
σ
〉 = 6.1 ± 1.9 km s
−1
. The large velocity dispersion may have arisen from tidal heating in the cluster’s orbit about the Galactic center, or because BH 261 has a high dynamical mass as well as a high mass-to-light ratio. From spectra of five giants, we measure an average metallicity of 〈Fe/H〉 = −1.1 ± 0.2 dex. We also spectroscopically confirm an RR Lyrae star in BH 261, which yields a distance to the cluster of 7.1 ± 0.4 kpc. Stars with 3D velocities and metallicities consistent with BH 261 reaching to ∼0.°5 from the cluster are identified. A handful of these stars are also consistent with the spatial distribution of potential debris from models focusing on the most recent disruption of the cluster.
Detailed elemental abundance patterns of metal-poor (Fe/H ∼ −1 dex) stars in the Galactic bulge indicate that a number of them are consistent with globular cluster (GC) stars and may be former ...members of dissolved GCs. This would indicate that a few per cent of the Galactic bulge was built up from destruction and/or evaporation of GCs. Here, an attempt is made to identify such presumptive stripped stars originating from the massive, inner Galaxy GC NGC 6441 using its rich RR Lyrae variable star (RRL) population. We present radial velocities of 40 RRLs centered on the GC NGC 6441. All 13 of the RRLs observed within the cluster tidal radius have velocities consistent with cluster membership, with an average radial velocity of 24 5 km s−1 and a star-to-star scatter of 11 km s−1. This includes two new RRLs that were previously not associated with the cluster. Eight RRLs with radial velocities consistent with cluster membership but up to three time the distance from the tidal radius are also reported. These potential extra-tidal RRLs also have exceptionally long periods, which is a curious characteristic of the NGC 6441 RRL population that hosts RRLs with periods longer than seen anywhere else in the Milky Way. As expected of stripped cluster stars, most are inline with the cluster's orbit. Therefore, either the tidal radius of NGC 6441 is underestimated and/or we are seeing dissolving cluster stars stemming from NGC 6441 that are building up the old spheroidal bulge.
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