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To better understand the origin and evolution of the Milky Way bulge, we have conducted a survey of bulge red giant branch and clump stars using the High Efficiency and Resolution Multi-Element Spectrograph on the Anglo–Australian Telescope. We targeted ARGOS survey stars with predetermined bulge memberships, covering the full metallicity distribution function. The spectra have signal-to-noise ratios comparable to, and were analysed using the same methods as the GALAH survey. In this work, we present the survey design, stellar parameters, distribution of metallicity, and alpha-element abundances along the minor bulge axis at latitudes b  = −10°, − 7.5°, and −5°. Our analysis of ARGOS stars indicates that the centroids of ARGOS metallicity components should be located ≈0.09 dex closer together. The vertical distribution of α-element abundances is consistent with the varying contributions of the different metallicity components. Closer to the plane, alpha abundance ratios are lower as the metal-rich population dominates. At higher latitudes, the alpha abundance ratios increase as the number of metal-poor stars increases. However, we find that the trend of alpha-enrichment with respect to metallicity is independent of latitude. Comparison of our results with those of GALAH DR2 revealed that for [Fe/H] ≈ −0.8, the bulge shares the same abundance trend as the high-α disc population. However, the metal-poor bulge population ([Fe/H] ≲ −0.8) show enhanced alpha abundance ratios compared to the disc/halo. These observations point to fairly rapid chemical evolution in the bulge, and that the metal-poor bulge population does not share the same similarity with the disc as the more metal-rich populations. [ABSTRACT FROM AUTHOR]

We present the first results of the EMBLA survey (Extremely Metal-poor BuLge stars with AAOmega), aimed at finding metal-poor stars in the Milky Way bulge, where the oldest stars should now preferentially reside. EMBLA utilizes SkyMapper photometry to pre-select metal-poor candidates, which are subsequently confirmed using AAOmega spectroscopy. We describe the discovery and analysis of four bulge giants with −2.72 ≤ [Fe/H] ≤ −2.48, the lowest metallicity bulge stars studied with high-resolution spectroscopy to date. Using FLAMES/UVES spectra through the Gaia-ESO Survey we have derived abundances of twelve elements. Given the uncertainties, we find a chemical similarity between these bulge stars and halo stars of the same metallicity, although the abundance scatter may be larger, with some of the stars showing unusual [α/Fe] ratios. [ABSTRACT FROM AUTHOR]

We demonstrate that failure to properly account for stellar evolution can bias results in determinations of the spatial morphology of Galactic bulge stars, focusing on the question of whether or not the X-shape is more pronounced among the more metal-rich stars than among the metal-poor stars. We argue that this trend, a result recently claimed by three separate groups, may have been overestimated as it is relatively easier to detect a bimodality in the distance distribution function at higher metallicities. This is due to three factors. First, the intrinsic colour of red clump and red giant stars varies with metallicity, at the level d(V - I)RC/d[M/H] ≈ 0.25 mag dex−1, and thus the ratio of red clump to red giant stars within a spectroscopic sample will depend on the photometric selection of any investigation. Secondly, the duration of ascent of the red giant branch goes down and the red clump lifetime goes up as metallicity increases, which has the effect of increasing the ratio of red clump to red giant stars by as much as ∼33 per cent over the range of the bulge metallicity distribution function. Finally, over the same metallicity interval, the effective number of red giant branch bump stars is predicted to increase by ∼200 per cent, and their presence becomes degenerate with the observational parameters of the two red clumps, creating an illusory increase in signal to noise for a second peak in the distance modulus distribution. [ABSTRACT FROM AUTHOR]

Context. Caustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the companion signal to be extracted. Aims. MOA 2009-BLG-411 was detected on August 5, 2009 by the MOA-Collaboration. Alerted as a high-magnification event, it was sensitive to planets. Suspected anomalies in the light curve were not confirmed by a real-time model, but further analysis revealed small deviations from a single lens extended source fit. Methods. Thanks to observations by all the collaborations, this event was well monitored. We first decided to characterize the source star properties by using a more refined method than the classical one: we measure the interstellar absorption along the line of sight in five different passbands (VIJHK). Secondly, we model the lightcurve by using the standard technique: make (s, q, α) grids to look for local minima and refine the results by using a downhill method (Markov chain Monte Carlo). Finally, we use a Galactic model to estimate the physical properties of the lens components. Results. We find that the source star is a giant G star with radius 9 R☉. The grid search gives two local minima, which correspond to the theoretical degeneracy s ≡ s-1. We find that the lens is composed of a brown dwarf secondary of mass MS = 0.05 M☉ orbiting a primary M-star of mass MP = 0.18 M☉. We also reveal a new mass-ratio degeneracy for the central caustics of close binaries. Conclusions. As far as we are aware, this is the first detection using the microlensing technique of a binary system in our Galaxy composed of an M-star and a brown dwarf [ABSTRACT FROM AUTHOR]

Context. The presence of two stellar populations in the Milky Way bulge has been reported recently, based on observations of giant and dwarf stars in the inner and intermediate bulge. Aims. We aim at studying the abundances and kinematics of stars in the outer Galactic bulge, thereby providing additional constraints on formation models of the bulge. Methods. Spectra of 401 red giant stars in a field at (l,b) = (0°, −10°) were obtained with the FLAMES-GIRAFFE spectrograph at the VLT. Stars of luminosities down to below the two bulge red clumps are included in the data set. From these spectra we measured general metallicities, abundances of iron and the α-elements, and radial velocities of the stars. The abundances were derived from an interpolation and fitting procedure within a grid of COMARCS model atmospheres and spectra. These measurements as well as photometric data were compared to simulations with the Besançon and TRILEGAL models of the Galaxy. Results. We confirm the presence of two populations among our sample stars: i) a metal-rich one at [M/H] ~ +0.3, comprising about 30% of the sample, with low velocity dispersion and low α-abundance, and ii) a metal-poor population at [M/H] ~ −0.6 with high velocity dispersion and high α-abundance. The metallicity difference between the two populations, a systematically and statistically robust figure, is Δ [M/H] = 0.87 ± 0.03. The metal-rich population could be connected to the Galactic bar. We identify this population as the carrier of the double red clump feature. We do not find a significant difference in metallicity or radial velocity between the two red clumps, a small difference in metallicity being probably due to a selection effect and contamination by the metal-poor population. The velocity dispersion agrees well with predictions of the Besançon Galaxy model, but the metallicity of the “thick bulge” model component should be shifted to lower metallicity by 0.2 to 0.3 dex to well reproduce the observations. We present evidence that the metallicity distribution function depends on the evolutionary state of the sample stars, suggesting that enhanced mass loss preferentially removes metal-rich stars. We also confirm the decrease of α-element over-abundance with increasing metallicity. Conclusions. Our sample is consistent with the existence of two populations, one being a metal-rich bar, the second one being more like a metal-poor classical bulge with larger velocity dispersion. [ABSTRACT FROM AUTHOR]

We combine ground- and space-based photometry of the Galactic globular cluster 47 Tuc to measure four independent lines of evidence for a helium gradient in the cluster, whereby stars in the cluster outskirts would have a lower initial helium abundance than stars in and near the cluster core. For our first and second lines of evidence, we show that the red giant branch bump stars exhibit gradients in their number counts and brightness. With increased separation from the. cluster center, they become more numerous relative to the other red giant stars. They also become fainter. For our third and fourth lines of evidence, we show that the horizontal branch of the cluster becomes both fainter and redder for sightlines farther from the cluster center. These four results are respectively detected at the 2.3σ, 3.6σ, 7.7&sigma, and 4.1σ levels. Each of these independent lines of evidence is found to be significant in the cluster outskirts; closer in, the data are more compatible with uniform mixing. Our radial profile is qualitatively consistent with but quantitatively tighter than previous results based on CN absorption. These observations are qualitatively consistent with a scenario wherein a second generation of stars with enhanced helium formed deep within the gravitational potential of a cluster of previous generation stars having more canonical abundances. [ABSTRACT FROM AUTHOR]

Transplantation of B cells engineered ex vivo to secrete broadly neutralizing antibodies (bNAbs) has shown efficacy in disease models. However, clinical translation of this approach would require specialized medical centers, technically demanding protocols and major histocompatibility complex compatibility of donor cells and recipients. Here we report in vivo B cell engineering using two adeno-associated viral vectors, with one coding for Staphylococcus aureus Cas9 (saCas9) and the other for 3BNC117, an anti-HIV bNAb. After intravenously injecting the vectors into mice, we observe successful editing of B cells leading to memory retention and bNAb secretion at neutralizing titers of up to 6.8 µg ml -1 . We observed minimal clustered regularly interspaced palindromic repeats (CRISPR)-Cas9 off-target cleavage as detected by unbiased CHANGE-sequencing analysis, whereas on-target cleavage in undesired tissues is reduced by expressing saCas9 from a B cell-specific promoter. In vivo B cell engineering to express therapeutic antibodies is a safe, potent and scalable method, which may be applicable not only to infectious diseases but also in the treatment of noncommunicable conditions, such as cancer and autoimmune disease., (© 2022. The Author(s), under exclusive licence to Springer Nature America, Inc.)

HIV viremia can be controlled by chronic antiretroviral therapy. As a potentially single-shot alternative, B cells engineered by CRISPR/Cas9 to express anti-HIV broadly neutralizing antibodies (bNAbs) are capable of secreting high antibody titers. Here, we show that, upon immunization of mice, adoptively transferred engineered B cells home to germinal centers (GC) where they predominate over the endogenous response and differentiate into memory and plasma cells while undergoing class switch recombination (CSR). Immunization with a high affinity antigen increases accumulation in GCs and CSR rates. Boost immunization increases the rate of engineered B cells in GCs and antibody secretion, indicating memory retention. Finally, antibody sequences of engineered B cells in the spleen show patterns of clonal selection. Therefore, B cells can be engineered into what could be a living and evolving drug.

Oxygenic photosynthesis supports virtually all life forms on earth. Light energy is converted by two photosystems-photosystem I (PSI) and photosystem II (PSII). Globally, nearly 50% of photosynthesis takes place in the Ocean, where single cell cyanobacteria and algae reside together with their viruses. An operon encoding PSI was identified in cyanobacterial marine viruses. We generated a PSI that mimics the salient features of the viral complex, named PSI(PsaJF). PSI(PsaJF) is promiscuous for its electron donors and can accept electrons from respiratory cytochromes. We solved the structure of PSI(PsaJF) and a monomeric PSI, with subunit composition similar to the viral PSI, providing for the first time a detailed description of the reaction center and antenna system from mesophilic cyanobacteria, including red chlorophylls and cofactors of the electron transport chain. Our finding extends the understanding of PSI structure, function and evolution and suggests a unique function for the viral PSI. DOI: http://dx.doi.org/10.7554/eLife.01496.001.