The scarcity of high-fidelity extinction measurements remains a bottleneck in deriving accurate stellar properties from Gaia parallaxes. In this work, we aim to derive precise extinction estimates for Apache Point Observatory Galactic Evolution Experiment (APOGEE) data release 19 stars, establishing a new benchmark for Galactic stellar population studies. We first determine reddening by comparing observed colours-retrieved from photometric surveys or standardized synthetic magnitudes from Gaia low-resolution blue and red photometer (BP/RP) spectra-to intrinsic colours predicted via an XGBOOST model. The model is trained on minimally reddened stars to infer intrinsic colours and their associated uncertainties, using APOGEE stellar parameters (T-eff, log(g), [Fe/H], and [alpha/Fe]). The derived reddening values are then converted into extinctions using an anchor ratio of A(BP) /A(RP) = 1 . 694 +/- 0.004 , derived from red-clump-like stars. Here, we provide extinction measurements in 39 filters across 10 photometric systems and introduce a new empirical extinction curve optimized for broadband passbands. Our extinction estimates ( A(V) ) outperform existing results (Bayestar19, StarHorse, SEDEX), achieving a typical precision of similar to 0.03 mag in A(V) . Notably, we identify systematic deviations of up to 30 per cent between monochromatic and passband-integrated extinction ratios at wavelengths lambda > 700 nm. This result highlights the necessity of adopting passband-specific coefficients when correcting extinction to derive stellar parameters. The derived extinction and reddening data are available to the community for download.

The extremely metal-poor nature of the C-19 stream indicates that its progenitor was a primordial stellar system born in the very early Universe. Current observations show that it has a small metallicity dispersion (0.18 at the 95% confidence level), which is the signature of a globular cluster origin, while at the same time displaying an unusually large velocity dispersion (similar to 10 km s-1), typical of dwarf galaxies. To reconcile this conflicting observational evidence, previous simulations have focused on potential interactions with dark matter subhalos, which can efficiently make a cluster stream dynamically hot. In this work, we explore internal dynamical processes in star cluster formation, focusing on initial conditions shaped by gas expulsion and a top-heavy initial mass function. We find that the large observed velocity dispersion and broad stream morphology can be reproduced by a cluster that underwent severe gas expulsion and expansion during its birth phase, which is potentially a typical formation scenario of extremely metal-poor star clusters. A top-heavy initial mass function and binaries can also increase the velocity dispersion. The formation of C-19 may involve a combination of these effects.

The Galactic halo preserves a record of the Milky Way's earliest assembly and contains both in-situ stars and stars accreted from dwarf galaxies. Possible planets around these stars, therefore, probe formation in ancient, metal-poor environments, including systems of extragalactic origin. We present a search for short-period transiting planets around kinematically selected halo dwarfs using Gaia DR3 and TESS, focusing on planets with periods of 1 < P < 10 days. We identify two hot-Jupiter (HJ) candidates, one in the in-situ and one in the accreted halo, although the latter is highly grazing and excluded from the occurrence analysis. The accreted candidate, if confirmed, would orbit the most metal-poor HJ host known ([Fe/H] ≈ -1). Using injection–recovery tests and automated vetting, we constrain occurrence in the full halo, in-situ, and accreted samples. In the HJ regime (8 R_⊕ < R_ p < 22 R_⊕, 1 day < P < 10 days), the non-grazing candidate implies an overall halo occurrence rate of 0.13^+0.12_-0.07% if planetary, while the absence of confirmed detections gives a corresponding 1σ upper limit of <0.14%. For the in-situ halo, we infer 0.17^+0.17_-0.10% (or <0.19% assuming no detections), while for the accreted halo we derive an upper limit of <0.56%. These rates lie well below the corresponding short-period giant-planet occurrence measured in the Galactic disc. A forward model assuming Kepler-like occurrence also predicts 10 ± 3 detections compared with at most one observed. We find no significant occurrence difference between the in-situ and accreted halo populations, strengthening the evidence that close-in giant planets are rare across the old, metal-poor halo.

The selective oxidation of glycerol to dihydroxyacetone (DHA) is an essential route to effectively utilize the byproduct glycerol of biodiesel, but the difficulty in balancing the activity and recycling stability of the catalyst severely limits the practical application of this process. Herein, we utilize the morphology engineering strategy of Au-loaded Cu-Zn composite oxide catalyst to optimize the catalytic performance. By regulating the calcination temperature, the Cu0.1Zn0.9O-T supports with morphologies such as microrod clusters, microrods, microspheres and yolk shells are obtained, and a series of Au/Cu0.1Zn0.9O-T catalysts are synthesized by loading Au NPs prepared through the plant-mediated method. The glycerol oxidation experiments reveal that catalyst morphology exerts a significant influence on efficacy. Among the tested catalysts, the microrod-structured Au/ Cu0.1Zn0.9O MR exhibited the best performance, achieving complete glycerol conversion (100 %) and a DHA selectivity of 82.3 %. Particularly, Au/Cu0.1Zn0.9O MR exhibits excellent cycling stability that outshines most current catalysts, while maintaining 68.8% glycerol conversion and 78.2 % DHA selectivity after five runs. The underlying mechanism of the influence of catalyst morphology on the glycerol conversion performance is further revealed by a series of characterizations and density functional theory calculations.

The Chinese Space Station Survey Telescope (CSST) is an upcoming Stage-IV sky survey telescope, distinguished by its large field of view (FoV), high image quality, and multi-band observation capabilities. It can simultaneously conduct precise measurements of the Universe by performing multi-color photometric imaging and slitless spectroscopic surveys. The CSST is equipped with five scientific instruments, i.e., Multi-band Imaging and Slitless Spectroscopy Survey Camera (SC), Multi-Channel Imager (MCI), Integral Field Spectrograph (IFS), Cool Planet Imaging Coronagraph (CPI-C), and THz Spectrometer (TS). Using these instruments, CSST is expected to make significant contributions and discoveries across various astronomical fields, including cosmology, galaxies and active galactic nuclei (AGN), the Milky Way and nearby galaxies, stars, exoplanets, Solar System objects, astrometry, and transients and variable sources. This review aims to provide a comprehensive overview of the CSST instruments, observational capabilities, data products, and scientific potential.

The Böotes III (Boo3) dwarf galaxy has long been suspected of being the progenitor of Styx, a 50°-long stellar stream that was simultaneously discovered in the same region of sky. Boo3's diffuse morphology, large velocity dispersion, small pericenter, and excess of candidate stars at large radii suggest it is undergoing active tidal disruption. A link to Styx is therefore logical; however, a clear connection between these structures has not yet been clearly demonstrated. Here, we re-examine the Boo3-Styx association by searching for Boo3's tidal debris using a combination of Gaia-selected members, new CaHK narrow-band imaging with CFHT/MegaCam, and stellar tracer catalogues of blue horizontal branch and red giant branch stars. We also conduct a broad search for a putative stream using matched filter techniques applied to SDSS DR17 and DELVE DR2. Despite our extensive search, we find no observational evidence directly linking Boo3 to Styx. Furthermore, our results suggest that either Boo3's extended substructure is too diffuse to be detected with current data, or that its particular orbit may have erased a coherent tidal signature. Boo3 thus remains an enigmatic system, and exemplifies the need for spectroscopic follow-up to properly disentangle the nature between this faint Milky Way satellite and nearby stream.

Milky Way halo substructures identified in dynamical space are known to suffer from contamination from the Milky Way in situ stars, which makes their accreted origins uncertain. We present detailed chemical abundances of 35 stars belonging to two sets of dynamically tagged groups, Rg8 and Rg9, to investigate their accreted nature. Both groups are composed of stars with low orbital energy and very retrograde orbits. We find that Rg8 and Rg9 are chemically indistinguishable across 20 elements, from C to Eu, strongly indicating that they belong to the same structure. The iron-abundance distribution of this low- E retrograde group has a prominent peak at [Fe/H] ≈ –2.1, revealing that its main population is very metal-poor (VMP), and a secondary peak at [Fe/H] ≈ –1.5, very likely due to contamination from Milky Way in situ stars. These groups also heavily overlap with the Thamnos substructure in dynamical space, and we thus use them to investigate the chemical properties of Thamnos. The dominant, low-metallicity population provides strong evidence for the ex situ origin of Thamnos, as does its VMP nature. We do not see any evidence of an α -knee in our sample, which is consistent with previous studies. Comparison with the Cetus-Palca stream in the chemical space shows similar abundance distributions, and thus it suggests that the Thamnos progenitor dwarf galaxy had a truncated star formation history due to its early merger with the Milky Way.

Stellar streams, remnants of compact star systems stretched out by the tidal forces of the Milky Way, offer a unique way to study stellar populations that formed billions of years ago. A particularly unique stream is C-19, the most metal-poor stellar stream known at less than a thousandth of the Sun's metallicity. The nature of C-19 is not yet clear, with properties that resemble both star clusters and ultra faint dwarf galaxies, yet in either case its extremely low metallicity indicates very early star formation, <1 Gyr after the Big Bang. Here, we present the first detailed study on the nature of C-19 based on the chemical abundances of 14 member stars from high-resolution spectroscopy. These reveal that C-19 formed stars in an early, rapid, and prolific star formation event, with mild inhomogeneous mixing of elements produced in massive stars. There is otherwise no evidence for subsequent star formation, multiple stellar populations, nor chemical evolution. Although C-19 is currently disrupted in the Milky Way halo, it offers a rare and complementary window into the details of star formation and chemical evolution in the early universe, ideal for comparisons with current studies of primordial star formation in the high-redshift universe.

Spectroscopic surveys have identified significant numbers of metal-poor nitrogen-rich (N-rich) field stars. These stars are strong candidates for escapees from globular clusters (GCs), as their distinctive nitrogen enhancement mirrors the chemical patterns observed in some of the members of GCs. As part of the effort to characterize their chemodynamical properties, we derived abundances for up to 25 elements in a sample of 33 N-rich field giant stars (18 of them are studied for the first time) using high-resolution optical spectroscopy. We confirm their elevated abundances of N, Na, and Al, strongly supporting a GC origin. Given that Galactic GCs themselves formed within diverse progenitor galaxies, we sought to identify the ancestral systems of these N-rich field stars. By analyzing their dynamical parameters, we separated the sample into high-energy (HE) and low-energy (LE) groups. The HE group exhibits lower [alpha/Fe] and enhanced r-process abundances compared to the LE group. This indicates that the HE stars likely escaped from GCs accreted from massive dwarf galaxies (e.g., Gaia-Sausage-Enceladus), while the LE stars probably originated from in situ GCs. We also find that the chemical pattern of these N-rich stars with [Fe/H] (sic) -1.0 is similar to that of the high-redshift "N-emitters." Furthermore, orbital integrations revealed a close encounter between one N-rich field star and the GC NGC 6235. Our work demonstrates the potential of using chemodynamical analyses to trace Galactic assembly through chemical peculiar stars, while highlighting that larger samples and more precise data in the future are crucial to establish definitive origins.

As an effective strategy to improve photocatalytic hydrogen evolution, S-scheme heterojunctions face the fundamental challenge of inefficient photogenerated charge separation. This study constructs a NiPS3/CdS (NPS/ CS) S-scheme system and systematically investigates the influence of different defect engineering approaches on interfacial charge transfer. Characterization reveals that nickel vacancy-modified NiPS3/CdS (VNi-NPS/CS) disrupts the original heterojunction structure, while sulfur/phosphorus vacancy-regulated NiPS3/CdS (NPS-VPS/CS) maintains the S-scheme band alignment while significantly enhancing charge separation through defect engineering. Under simulated solar irradiation, NPS-VPS/CS exhibits exceptional photocatalytic hydrogen evolution activity (18.24 mmol/g) with an apparent quantum efficiency of 12.11 %, demonstrating excellent broadspectrum responsiveness. Mechanistic studies indicate that the introduced P/S vacancies in NPS-VPS/CS not only serve as electron traps to suppress charge recombination but more importantly, establish intermediate energy levels that accelerate interfacial charge transfer while preserving the S-scheme band structure, thereby remarkably improving hydrogen evolution kinetics. This work provides new insights into the regulatory mechanisms of cation/anion vacancies on heterojunction interface engineering.

The C-19 star stream has the abundance characteristics of an unusually metal poor globular cluster but kinematically is uncharacteristically hot and wide for a cluster stream, having a line of sight velocity dispersion of 6 \kms\ and a 1-sigma width of 240 pc. We show that the tidal dissolution of an old, lower mass, globular cluster in a CDM galactic halo naturally creates a hot, wide stream currently near orbital apocenter. More generally, simulations show that hot streams, which are all near their orbital apocenter, become thin, cool streams near pericenter. Furthermore, the wide streams from a population of dissolved clusters in the simulations have a mean galactocentric radial velocity dispersion of 7.8$\pm$1.0 \kms\ in a CDM cosmology but only 4.1$\pm$1.6 \kms\ in a WDM (5.5 keV) simulation. A detailed C-19 model in a simplified Milky Way halo potential with a CDM subhalo population provides a lower bound to stream heating, finding that the stream develops a line of sight velocity dispersion of 4.1$\pm$1.1 \kms, whereas WDM (5.5 keV) subhalos give 3.1$\pm$0.1\kms. Known dwarf galaxies alone provide negligible heating. There are five other currently known streams wider than 200 pc that contain a globular cluster, all near their orbital apocenter.

The Pristine- Gaia synthetic catalogue of reliable photometric metallicities makes use of spectrophotometric information from Gaia DR3 XP spectra to calculate metallicity-sensitive CaHK magnitudes, which in turn provides photometric metallicities for ∼30 million FGK stars using the Pristine survey model and the survey's training sample. We performed the first low- to medium-resolution spectroscopic follow-up of bright (G<15) and distant (upto 35 kpc) very and extremely metal-poor (V/EMP Fe/H <-2.5) red giant branch stars from this catalogue--to evaluate the quality of the photometric metallicities and study the chemodynamics of these V/EMP stars. We used Isaac Newton Telescope/Intermediate Dispersion Spectrograph (INT/IDS) observations centred around the calcium triplet region ideal for V/EMP stars for this spectroscopic follow-up. We find that 76% of our stars indeed have Fe/H < -2.5 with these inferred spectroscopic metallicities, and only 3% are outliers with Fe/H > -2.0. We report a success rate of 77% and 38% in finding stars with Fe/H < -2.5 and -3.0, respectively. This is a huge improvement compared to the literature in the selection of V/EMP stars based on photometric metallicities and will allow for 10,000--20,000 homogeneously analysed EMP stars using the WEAVE survey follow-up of Pristine EMP candidates. Using kinematics, we categorised 20%, 46%, and 34% of the stars as being confined to the disc plane, or having inner and outer halo orbits, respectively. Based on their integrals-of-motion, we are able to associate these V/EMP stars with the metal-poor tail of the metallicity distribution functions of known accretion events such as the Gaia-Enceladus-Sausage, LMS-1/Wukong, Thamnos, Helmi streams, Sagittarius, Sequoia, and other retrograde mergers. For the stars that orbit close to the disc plane, we find that the prograde region with low vertical action is overdense with a significance of 4σ compared to its retrograde counterpart. We also find three new (brightest) members of the most metal-poor stellar stream, C-19, one of which is 50^∘ from the main body of the stream. This is the first member of C-19 found at positive height above the disc plane. Our measured mean metallicity, velocity dispersion, and stream width are consistent with the literature, but our results favour a slightly farther distance (∼21.5 kpc) for the stream. With this work, we publish a catalogue (and 1D spectra) of 215 V/EMP stars from this first spectroscopic follow-up of the Pristine- Gaia synthetic catalogue of photometric metallicities and showcase the power of chemokinematic analysis of bright and distant red giant stars in the V/EMP end.

Identifying dwarf galaxies within the Local Volume is crucial for constraining the luminosity function of satellite galaxies in the nearby universe. We report the detection capabilities of dwarf galaxies within the Local Volume using the Chinese Space Station Telescope (CSST). Based on the simulated imaging data of CSST, we present VIDA, a ViT-based dwarf galaxy identification Algorithm designed for detecting Local Volume dwarf galaxies. The simulated Local Volume dwarf galaxies can be identified using a pre-processing method for 'extended source detection', followed by classification with a pretrained ViT-Base model. This pipeline achieves a true positive rate exceeding 85 percent with a false positive rate of only 0.1 percent. We quantify the detection completeness of Local Volume dwarf galaxies across a three-dimensional parameter space defined by absolute magnitude ( M-V ), half-light radius ( Rh ), and heliocentric distance, based on simulated single-exposure CSST wide-field imaging survey data. For unresolved or semiresolved dwarf galaxies, our method achieves a significantly deeper absolute magnitude detection limit compared to catalogue-based approaches, reaching M-V = -7 within 10 Mpc with a surface brightness threshold mu similar to 25 mag/arcsec(2) at 2-5 Mpc and similar to 26 mag/arcsec(2) at 5-10 Mpc. While traditional matched-filter techniques based on stellar catalogues remain more effective for detecting fully resolved, extremely low surface brightness galaxies within 5 Mpc, our approach offers complementary strengths-particularly in identifying compact or more distant systems-making it a valuable tool for expanding the census of Local Volume dwarf galaxies.

The discovery of the most metal-poor stream, C-19, provides us with a fossil record of a stellar structure born very soon after the big bang. In this work, we search for new C-19 members throughout the sky by combining two complementary stream-searching algorithms, STREAMFINDER and StarGO, and utilizing low-metallicity star samples from the Pristine survey, as well as Gaia BP and RP spectrophotometric catalogs. We confirm 13 new members, spread over more than 100 degrees, using velocity and metallicity information from a set of spectroscopic follow-up programs that targeted a quasi-complete sample of our bright candidates (G less than or similar to 16.0). From the updated set of stream members, we confirm that the stream is wide, with a stream width of similar to 200 pc, and dynamically hot, with a derived velocity dispersion of 10.9(-1.5)(+2.1) km s(-1). The tension remains between these quantities and a purely baryonic scenario in which the relatively low-mass stream (even updated to a few 10(4) M-circle dot) stems from a globular cluster progenitor, as suggested by its chemical abundances. Some heating mechanism, such as preheating of the cluster in its own dark matter halo or through interactions with halo substructures, appears necessary to explain the tension. The impact of binaries on the measured dispersion also remains unknown. Detailed elemental abundances of more stream members, as well as multi-epoch radial velocities from spectroscopic observations, are therefore crucial to fully understanding the nature and past history of the most metal-poor stream of the Milky Way.

The most metal-poor stars (e.g. [Fe/H] ≤-2.5) are the ancient fossils from the early assembly epoch of our Galaxy, very likely before the formation of the thick disc. Recent studies have shown that a non-negligible fraction of them have prograde planar orbits, which makes their origin a puzzle. It has been suggested that a later-formed rotating bar could have driven these old stars from the inner Galaxy outward, and transformed their orbits to be more rotation-dominated. However, it is not clear if this mechanism can explain these stars as observed in the solar neighborhood. In this paper, we explore the possibility of this scenario by tracing these stars backwards in an axisymmetric Milky Way potential with a bar perturber. We integrate their orbits backward for 6 Gyr under two bar models: one with a constant pattern speed and another one with a decelerating speed. Our experiments show that, under the constantly-rotating bar model, the stars of interest are little affected by the bar and cannot have been shepherded from a spheroidal inner Milky Way to their current orbits. In the extreme case of a rapidly decelerating bar, some of the very metal-poor stars on planar and prograde orbits can be brought from the inner Milky Way, but ∼90% of them were nevertheless already rotation-dominated (J_ϕ ≥ 1000 km s^-1 kpc) 6 Gyr ago. The chance of these stars having started with spheroid-like orbits with small rotation (J_ϕ ≲ 600 km s^-1 kpc) is very low (< 3%). We therefore conclude that, within the solar neighborhood, the bar is unlikely to have shepherded a significant fraction of inner Galaxy spheroid stars to produce the overdensity of stars on prograde, planar orbits that is observed today.

ABSTRACT The oldest stars in the Milky Way (born in the first few billion years) are expected to have a high density in the inner few kpc, spatially overlapping with the Galactic bulge. We use spectroscopic data from the Pristine Inner Galaxy Survey (PIGS) to study the dynamical properties of ancient, metal-poor inner Galaxy stars. We compute distances using starhorse, and orbital properties in a barred Galactic potential. With this paper, we release the spectroscopic AAT/PIGS catalogue (13 235 stars). We find that most PIGS stars have orbits typical for a pressure-supported population. The fraction of stars confined to the inner Galaxy decreases with decreasing metallicity, but many very metal-poor stars (VMP; [Fe/H] <−2.0) stay confined ($\sim 60~{{\ \rm per \, cent}}$ stay within 5 kpc). The azimuthal velocity vϕ also decreases between [Fe/H] = −1.0 and −2.0, but is constant for VMP stars (at ∼+40 km s−1). The carbon-enhanced metal-poor (CEMP) stars in PIGS appear to have similar orbital properties compared to normal VMP stars. Our results suggest a possible transition between two spheroidal components – a more metal-rich, more concentrated, faster rotating component, and a more metal-poor, more extended and slower/non-rotating component. We propose that the former may be connected to pre-disc in-situ stars (or those born in large building blocks), whereas the latter may be dominated by contributions from smaller galaxies. This is an exciting era where large metal-poor samples, such as in this work (as well as upcoming surveys, e.g. 4MOST), shed light on the earliest evolution of our Galaxy.

Electrochemical reduction of carbon dioxide presents a promising pathway to tackle global energy and environmental challenges. Porous carbon materials from metal-organic frameworks exhibit high specific surface area, abundant active sites, and adjustable pore structure, demonstrating excellent electrocatalytic performance. With their abundant resources and tunability, copper-based catalysts are well-suited for efficient carbon dioxide conversion. However, the selectivity and stability of copper-based catalysts is poor. This study presents the preparation of the first Cu-doped ZIF-8-derived carbon materials and investigates their effect on electrocatalytic carbon dioxide reduction. At the optimal potential of -0.7 V vs. RHE, the CO Faradaic Efficiency (FE) of the Cu-0.5-N-C catalyst reaches 89 %. Furthermore, the electrochemical current density and CO FE of Cu-0.5-N-C catalyst remain nearly unchanged within 13 hours in 0.1 mol L-1 KHCO3 electrolyte. Compared to most of the reported copper-based catalysts, Cu-0.5-N-C exhibits better stability. Characterization results show that Cu-0.5-N-C has a larger Cu-N-4, higher pyridinic N content, larger specific surface area, and average pore size, which help promote CO2 adsorption and enhance catalyst stability. This work provides new insights and pathways for electrocatalytic carbon dioxide reduction, with enormous potential to contribute to the global energy transition and environmental protection.

We used the spectro-photometric information of similar to 219 million stars from Gaia's Data Release 3 (DR3) to calculate synthetic, narrowband, metallicity-sensitive CaHK magnitudes that mimic the observations of the Pristine survey, a survey of photometric metallicities of Milky Way stars that has been mapping more than 6500 deg(2) of the northern sky with the Canada-France-Hawaii Telescope since 2015. These synthetic magnitudes were used for an absolute recalibration of the deeper Pristine photometry and, combined with broadband Gaia information, synthetic and Pristine CaHK magnitudes were used to estimate photometric metallicities over the whole sky. The resulting metallicity catalogue is accurate down to [Fe/H]similar to-3.5 and is particularly suited for the exploration of the metalpoor Milky Way ([Fe/H] < -1.0). We make available here the catalogue of synthetic CaHKsyn magnitudes for all stars with BP/RP information in Gaia DR3, as well as an associated catalogue of more than similar to 30 million photometric metallicities for high signal-to-noise FGK stars. This paper further provides the first public data release of the Pristine catalogue in the form of higher quality recalibrated Pristine CaHK magnitudes and photometric metallicities for all stars in common with the BP/RP spectro-photometric information in Gaia DR3. We demonstrate that, when available, the much deeper Pristine data greatly enhance the quality of the derived metallicities, in particular at the faint end of the catalogue (G(BP) greater than or similar to 16). Combined, both photometric metallicity catalogues include more than two million metal-poor star candidates ([Fe/H](phot) < -1.0) as well as more than 200 000 and similar to 8000 very and extremely metal-poor candidates ([Fe/H](phot) < -2.0 and < -3.0, respectively). Finally, we show that these metallicity catalogues can be used efficiently, among other applications, for Galactic archaeology, to hunt for the most metal-poor stars, and to study how the structure of the Milky Way varies with metallicity, from the flat distribution of disk stars to the spheroid-shaped metal-poor halo.

Context. Gaia DR3 has offered the scientific community a remarkable dataset of approximately one million spectra acquired with the radial velocity spectrometer (RVS) in the calcium II triplet region, which is well suited to identify very metal-poor (VMP) stars. However, over 40% of these spectra have no released parameters by Gaia's GSP-Spec pipeline in the domain of VMP stars, whereas VMP stars are key tracers of early Galactic evolution. Aims. We aim to provide spectroscopic metallicities for VMP stars using Gaia RVS spectra, thereby producing a catalogue of bright VMP stars distributed over the full sky that can serve as the basis for studies of early chemical evolution throughout the Galaxy. Methods. We selected VMP stars using photometric metallicities from the literature and analysed the Gaia RVS spectra to infer spectroscopic metallicities for these stars. Results. The inferred metallicities agree very well with literature high-resolution metallicities, with a median systematic offset of 0.1 dex and standard deviation of similar to 0.15 dex. The purity of this sample in the VMP regime is similar to 80%, with outliers representing a mere similar to 3%. Conclusions. We have built an all-sky catalogue of similar to 1500 stars available, featuring reliable spectroscopic metallicities down to [Fe/H] similar to -4.0, of which similar to 1000 are VMP stars. More than 75% of these stars have either no spectroscopic metallicity value in the literature to date or have been flagged as unreliable in their literature spectroscopic metallicity estimates. This catalogue of bright (G < 13) VMP stars is three times larger than the current sample of well-studied VMP stars in the literature in this magnitude range, making it ideal for high-resolution spectroscopic follow-ups and studies of the properties of VMP stars in different parts of our Galaxy.

The most metal-poor tail of the Milky Way ([Fe/H] $\leq$ $-$2.5) contains a population of stars with very prograde planar orbits, which is puzzling in both their origin and evolution. A possible scenario is that they are shepherded by the bar from the inner Galaxy, where many of the old and low-metallicity stars in the Galaxy are located. To investigate this scenario, we use test-particle simulations with an axisymmetric background potential plus a central bar model. The test particles are generated by an extended distribution function (EDF) model based on the observational constraints of bulge stars. According to the simulation results, a bar with constant pattern speed cannot help bring stars from the bulge to the solar vicinity. In contrast, when the model includes a rapidly decelerating bar, some bulge stars can gain rotation and move outwards as they are trapped in the co-rotation regions of the bar. The resulting distribution of shepherded stars heavily depends on the present-day azimuthal angle between the bar and the Sun. The majority of the low-metallicity bulge stars driven outwards are distributed in the fourth quadrant of the Galaxy with respect to the Sun, and about 10$\%$ of them are within 6 kpc from us. Our experiments indicate that the decelerating bar perturbation can be a contributing process to explain part of the most metal-poor stars with prograde planar orbits seen in the Solar neighborhood but is unlikely to be the dominant one.