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.
This is an autobiographical account of my scientific career. My main research interest is the structure and assembly of galaxies. The assembly narrative has evolved from the monolithic and baryonic ...collapse picture of the early 1960s to the current hierarchical scenario underpinned by dark matter, and is still evolving. Technology has changed: CCDs replaced photographic plates and image tubes, large optical telescopes are much larger and instruments are much better, Galactic archaeology is supported by vast stellar surveys, and we have space astronomy and radio synthesis telescopes. The article describes the scientific areas in which I have worked and the colleagues who have influenced my progress. I have much to be grateful for: the people who have mentored and supported me over the years, the privilege of long-term collaborations, and the pleasure of advising many Ph.D. students and postdocs.
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
The characteristics of the stellar populations in the Galactic bulge inform and constrain the Milky Way’s formation and evolution. The metal-poor population is particularly important in ...light of cosmological simulations, which predict that some of the oldest stars in the Galaxy now reside in its centre. The metal-poor bulge appears to consist of multiple stellar populations that require dynamical analyses to disentangle. In this work, we undertake a detailed chemodynamical study of the metal-poor stars in the inner Galaxy. Using R ∼ 20 000 VLT/GIRAFFE spectra of 319 metal-poor (−2.55 dex ≤ Fe/H ≤ 0.83 dex, with $\overline{\rm {Fe/H}}$ = −0.84 dex) stars, we perform stellar parameter analysis and report 12 elemental abundances (C, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Zn, Ba, and Ce) with precisions of ≈0.10 dex. Based on kinematic and spatial properties, we categorize the stars into four groups, associated with the following Galactic structures: the inner bulge, the outer bulge, the halo, and the disc. We find evidence that the inner and outer bulge population is more chemically complex (i.e. higher chemical dimensionality and less correlated abundances) than the halo population. This result suggests that the older bulge population was enriched by a larger diversity of nucleosynthetic events. We also find one inner bulge star with a Ca/Mg ratio consistent with theoretical pair-instability supernova yields and two stars that have chemistry consistent with globular cluster stars.
ABSTRACT
Chemistry and kinematic studies can determine the origins of stellar population across the Milky Way. The metallicity distribution function of the bulge indicates that it comprises multiple ...populations, the more metal-poor end of which is particularly poorly understood. It is currently unknown if metal-poor bulge stars (Fe/H <−1 dex) are part of the stellar halo in the inner most region, or a distinct bulge population or a combination of these. Cosmological simulations also indicate that the metal-poor bulge stars may be the oldest stars in the Galaxy. In this study, we successfully target metal-poor bulge stars selected using SkyMapper photometry. We determine the stellar parameters of 26 stars and their elemental abundances for 22 elements using R∼ 47 000 VLT/UVES spectra and contrast their elemental properties with that of other Galactic stellar populations. We find that the elemental abundances we derive for our metal-poor bulge stars have lower overall scatter than typically found in the halo. This indicates that these stars may be a distinct population confined to the bulge. If these stars are, alternatively, part of the innermost distribution of the halo, this indicates that the halo is more chemically homogeneous at small Galactic radii than at large radii. We also find two stars whose chemistry is consistent with second-generation globular cluster stars. This paper is the first part of the Chemical Origins of Metal-poor Bulge Stars (COMBS) survey that will chemodynamically characterize the metal-poor bulge population.
ABSTRACT
M 31 has experienced a recent tumultuous merger history, as evidenced from the many substructures that are still present in its inner halo, particularly the G1-Clump, NE-, and W-shelves and ...the Giant Stream (GS). We present planetary nebulae (PNe) line-of-sight velocity (LOSV) measurements covering the entire spatial extent of these four substructures. We further use predictions for the satellite and host stellar particle phase space distributions for a major merger (mass ratio = 1:4) simulation to help interpret the data. The measured PN LOSVs for the two shelves and GS are consistent with those from red giant branch stars. Their projected radius versus LOSV phase space, links the formation of these substructures in a single unique event, consistent with a major merger. We find the G1-clump to be dynamically cold compared to the M 31 disc ($\rm \sigma _{LOS, PN}=27$ km s−1), consistent with pre-merger disc material. Such a structure can not form in a minor merger (mass ratio ∼1:20) and is therefore a smoking gun for the recent major merger event in M 31. The simulation also predicts the formation of a predominantly in situ halo from splashed-out pre-merger disc material, in qualitative agreement with observations of a metal-rich inner halo in M 31. Juxtaposed with previous results for its discs, we conclude that M 31 has had a recent (2.5–4 Gyr ago) ‘wet’ major merger with the satellite falling along the GS, heating the pre-merger disc to form the M 31 thicker disc, rebuilding the M 31 thin disc, and creating the aforementioned inner-halo substructures.
ABSTRACT
We obtain a magnitude-limited sample of Andromeda (M 31) disc PNe with chemical abundance estimated through the direct detection of the O iii 4363 Å line. This leads to 205 and 200 PNe with ...oxygen and argon abundances, respectively. We find that high- and low-extinction M 31 disc PNe have statistically distinct argon and oxygen abundance distributions. In the radial range of 2−30 kpc, the older low-extinction disc PNe are metal-poorer on average with a slightly positive radial oxygen abundance gradient (0.006 ± 0.003 dex kpc−1) and slightly negative for argon (−0.005 ± 0.003 dex kpc−1), while the younger high-extinction disc PNe are metal-richer on average with steeper radial abundance gradients for both oxygen (−0.013 ± 0.006 dex kpc−1) and argon (−0.018 ± 0.006 dex kpc−1), similar to the gradients computed for the M 31 H ii regions. The M 31 disc abundance gradients are consistent with values computed from major merger simulations, with the majority of the low-extinction PNe being the older pre-merger disc stars in the thicker disc, and the majority of the high-extinction PNe being younger stars in the thin disc, formed during and after the merger event. The chemical abundance of the M 31 thicker disc has been radially homogenized because of the major merger. Accounting for disc scale lengths, the positive radial oxygen abundance gradient of the M 31 thicker disc is in sharp contrast to the negative one of the MW thick disc. However, the thin discs of the MW and M 31 have remarkably similar negative oxygen abundance gradients.
ABSTRACT
The metal-poor stars in the bulge are important relics of the Milky Way’s formation history, as simulations predict that they are some of the oldest stars in the Galaxy. In order to ...determine if they are truly ancient stars, we must understand their origins. Currently, it is unclear if the metal-poor stars in the bulge (Fe/H < −1 dex) are merely halo interlopers, a unique accreted population, part of the boxy/peanut-shaped bulge, or a classical bulge population. In this work, we use spectra from the VLT/FLAMES spectrograph to obtain metallicity estimates using the Ca-II triplet of 473 bulge stars (187 of which have Fe/H < −1 dex), targeted using SkyMapper photometry. We also use Gaia DR2 data to infer the Galactic positions and velocities along with orbital properties for 523 stars. We employ a probabilistic orbit analysis and find that about half of our sample has a >50 per cent probability of being bound to the bulge, and half are halo interlopers. We also see that the occurrence rate of halo interlopers increases steadily with decreasing metallicity across the full range of our sample (−3 < Fe/H < 0.5). Our examination of the kinematics of the confined compared to the unbound stars indicates the metal-poor bulge comprises at least two populations; those confined to the boxy/peanut bulge and halo stars passing through the inner galaxy. We conclude that an orbital analysis approach, as we have employed, is important to understand the composite nature of the metal-poor stars in the inner region.
Two mycobacteriophages were administered intravenously to a male with treatment-refractory Mycobacterium abscessus pulmonary infection and severe cystic fibrosis lung disease. The phages were ...engineered to enhance their capacity to lyse M. abscessus and were selected specifically as the most effective against the subject’s bacterial isolate. In the setting of compassionate use, the evidence of phage-induced lysis was observed using molecular and metabolic assays combined with clinical assessments. M. abscessus isolates pre and post-phage treatment demonstrated genetic stability, with a general decline in diversity and no increased resistance to phage or antibiotics. The anti-phage neutralizing antibody titers to one phage increased with time but did not prevent clinical improvement throughout the course of treatment. The subject received lung transplantation on day 379, and systematic culturing of the explanted lung did not detect M. abscessus. This study describes the course and associated markers of a successful phage treatment of M. abscessus in advanced lung disease.
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•Treatment-refractory M. abscessus pulmonary infection was eradicated in a person with CF•Specific mycobacteriophages lysed the bacteria over the course of a year•M. abscessus did not acquire resistance to the phages•M. abscessus eradication occurred despite a partial anti-phage antibody response
Phage treatment of an individual with cystic fibrosis, advanced lung disease, and M. abscessus infection enabled a subsequent successful lung transplant.
Abstract
The stellar velocity ellipsoid of the solar neighbour (d < 200 pc) is re-examined using intermediate-old mono-abundance stellar groups with high-quality chemistry data together with ...parallaxes and proper motions from Gaia DR1. We find the average velocity dispersion values for the three space velocity components for the thin and thick discs of (σU, σV, σW)thin = (33 ± 4, 28 ± 2, 23 ± 2) and (σU, σV, σW)thick = (57 ± 6, 38 ± 5, 37 ± 4) km s−1, respectively. The mean values of the ratio between the semi-axes of the velocity ellipsoid for the thin disc are found to be σV/σU = 0.70 ± 0.13 and σW/σU is 0.64 ± 0.08, while for the thick disc σV/σU = 0.67 ± 0.11 and σW/σU is 0.66 ± 0.11. Inputting these dispersions into the linear Strömberg relation for the thin disc groups, we find the Sun's velocity with respect to the Local Standard of Rest in Galactic rotation to be V⊙ = 13.9 ± 3.4 km s−1. A relation is found between the vertex deviation and the chemical abundances for the thin disc, ranging from −5 to +40° as iron abundance increases. For the thick disc we find a vertex deviation of luv ∼− 15°. The tilt angle (luw) in the U–W plane for the thin disc groups ranges from −10 to +15°, but there is no evident relation between luw and the mean abundances. However, we find a weak relation for luw as a function of iron abundances and α-elements for most of the groups in the thick disc, where the tilt angle decreases from −5 to −20° when Fe/H decreases and α/Fe increases. The velocity anisotropy parameter is independent of the chemical group abundances and its value is nearly constant for both discs (β ∼ 0.5), suggesting that the combined disc is dynamically relaxed.
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