Anke Arentsen; Sarah G. Kane; Vasily Belokurov; Tadafumi Matsuno; Martin Montelius; Stephanie Monty; Jason L. Sanders
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT Carbon-rich (C-rich) stars can be found at all metallicities and evolutionary stages. They are often the result of mass transfer from a companion, but some of the most metal-poor C-rich objects are likely carrying the imprint of the metal-free First Stars from birth. In this work, we employ a neural network to predict metallicities and carbon abundances for over 10 million stars with Gaia low-resolution XP spectra, down to $\rm {[Fe/H]} = -3.0$ and up to $\rm {[C/Fe]} \approx +2$. We identify ${\sim} 2000$ high-confidence bright ($G\lt 16$) carbon-enhanced metal-poor stars with $\rm {[Fe/H]} \lt -2.0$ and $\rm {[C/Fe]} \gt +0.7$. The majority of our C-rich candidates have $\rm {[Fe/H]} \gt -2.0$ and are expected to be binary mass-transfer products, supported by high barium abundances in the GALAH (GALactic Archaeology with HERMES) survey and/or their Gaia Renormalised Unit Weight Error (RUWE) and radial velocity variations. We confirm previous findings of an increase in C-rich stars with decreasing metallicity, adopting a definition of $3\sigma$ outliers from the [C/Fe] distribution, although our frequency appears to flatten for $-3.0 \lt \rm {[Fe/H]} \lt -2.0$ at a level of $6\!\!-\!\!7{{\ \rm per\, cent}}$. We also find that the fraction of C-rich stars is low among globular cluster stars (connected to their lower binary fraction), and that it decreases for field stars more tightly bound to the Milky Way. We interpret these last results as evidence that disrupted globular clusters contribute more in the inner Galaxy, supporting previous work. Homogeneous samples such as these are key to understanding the full population properties of C-rich stars, and this is just the beginning.
Tristan Whitmarsh; Wei Cope; Julia Carmona-Bozo; Roido Manavaki; Stephen‐John Sammut; Ramona Woitek; Elena Provenzano; Emma Brown; Sarah E. Bohndiek; Ferdia A. Gallagher; Carlos Caldas; Fiona J. Gilbert; Florian Markowetz
Breast Cancer Research · DOI ↗
BACKGROUND: Tumour vascular density assessed from CD-31 immunohistochemistry (IHC) images has previously been shown to have prognostic value in breast cancer. Current methods to measure vascular density, however, are time-consuming, suffer from high inter-observer variability and are limited in describing the complex tumour vasculature morphometry. METHODS: We propose a method for automatically measuring a range of vascular parameters from CD-31 IHC images, which together provide a detailed description of the vasculature morphology. We first used a U-Net based convolutional neural network, trained and validated using 36 partially annotated whole slide images from 27 patients, to segment vessel structures and tumour regions from which the measurements are taken. The model also segments the vascular smooth muscle, benign epithelium, adipose tissue, stroma, lymphocyte clusters, nerves and CD-31 positive leukocytes, and we applied it to an additional 21 images from 15 patients. Using these segmentations, we investigated the relationship between the various tissue types and the vasculature and studied the relationship of various vascular parameters with clinical parameters. We also performed a 3D histology analysis on a separate tumour sample as a proof of principle, providing a more comprehensive visualization of vasculature morphology compared to the standard 2D cross-section of a tissue sample. RESULTS: ) and significant (p<0.001) correlations with measurements taken from the manual ground truth vessel segmentations. A significant relationship between the major/minor axis ratio, a measure of elongation, and the tumour grade was found. CONCLUSION: Our proposed method shows promise as a tool for studying the tumour vasculature and its relationship with surrounding cells and tissue types. Furthermore, the correlation with tumour grade highlights the clinical relevance of our approach. These findings suggest that our method could have substantial implications for improving prognostic assessments and personalizing therapeutic strategies in breast cancer treatment.
Melis O Irfan; E. A. González-Solares; Tristan Whitmarsh; Alireza Molaeinezhad; Mohammad Al Sa’d; Claire M. Mulvey; Marta Páez Ribes; Atefeh Fatemi; Dario Bressan; N. A. Walton
Frontiers in Genetics · DOI ↗
Cell segmentation is a crucial step in numerous biomedical imaging endeavors-so much so that the community is flooded with publicly available, state-of-the-art segmentation techniques ready for out-of-the-box use. Assessing the strengths and limitations of each method on a tissue sample set and then selecting the optimal method for each research objective and input image are time-consuming and exacting tasks that often monopolize the resources of biologists, biochemists, immunologists, and pathologists, despite not being the primary goal of their research projects. In this work, we present a segmentation software wrapper, coined CellSampler, which runs a selection of established segmentation methods and then combines their individual segmentation masks into a single optimized mask. This so-called "uber mask" selects the best of the established masks across local neighborhoods within the image, where both the neighborhood size and the statistical measure used to define what qualifies as "best" are user-defined.
Melis O Irfan; E. A. González-Solares; Tristan Whitmarsh; Alireza Molaeinezhad; Mohammad Al Sa’d; Claire M. Mulvey; Marta Ribes; Dario Bressan; N. A. Walton
bioRxiv (Cold Spring Harbor Laboratory) · DOI ↗
ABSTRACT Cell segmentation is a crucial step in numerous biomedical imaging endeavors; so much so that the community is flooded with publicly available, state-of-the-art segmentation techniques ready for out of the box use. Assessing the virtues and limitations of each method on a tissue sample set and then selecting the optimum method for each research objective and input image is a time consuming and exacting task that often monopolizes the resources of biologists, biochemists, immunologists and pathologists; despite not being their project primary research goal. In this work, we present a segmentation software wrapper, coined CellSampler , which runs a selection of established segmentation methods and then combines their individual segmentation masks into a single optimized mask. This, so called ‘uber mask’, selects the best of the established masks across local neighborhoods within the image, where the neighborhood size and the statistical measure which determines the qualitative term ‘best’ are both chosen by the user.
L. Delfini; Miguel Vioque; Álvaro Ribas; S. T. Hodgkin
Astronomy and Astrophysics · DOI ↗
Context. Accretion rates from protoplanetary discs onto forming stars are a key ingredient in star formation and protoplanetary disc evolution. Extensive efforts surveying different individual star-forming regions with spectroscopy and narrow-band photometry have been made to derive accretion rates on large populations of young stellar objects (YSOs). Aims. We use Gaia DR3 XP spectra to perform the first all-sky homogeneous analysis of YSO accretion properties within 500 pc. Methods. We characterise the H line emission of YSOs within 500 pc by using the H pseudo-equivalent widths and XP spectra provided by Gaia DR3. We derive accretion luminosities and mass accretion rates, together with stellar parameters, for 145 975 all-sky candidate YSO H emitters. We describe filtering strategies to select specific sub-samples of YSOs from this catalogue. Results. We identify a large population of low-accreting YSO candidates untraced by previous accretion rates surveys. We find previous surveys have mostly focused on YSO populations with significant infrared excess from disc emission. The population of low-accreting YSOs is mostly spatially dispersed, away from star-forming regions or the more clustered environments of star formation. Many YSOs appear entirely disconnected from young populations, and they are reminiscent of the long-lived ‘Peter Pan’ YSOs. We find L acc ∝ L ⋆ 1.41 ± 0.02 and Ṁ acc ∝ M ⋆ 2.4 ± 0.1 for the purest all-sky sample of YSO candidates. By fitting an exponential function to the fraction of accreting stars in clusters of different ages in the Sco-Cen complex, we obtain an accretion timescale of τ acc = 2.7 ± 0.4 Myr. The percentage of accretors found by fitting a power law function is 70% at 2 Myr and 2.8% at 10 Myr. Conclusions. With this new catalogue of H emitters, we significantly increase the number of YSO candidates with accretion rate estimations in the local neighbourhood. This allows us to study accretion timescales and the spatial and physical properties of YSO accretion from a large, all-sky, and homogeneous sample for the first time.
Elisabeth Sola; David Chemaly; Vasily Belokurov; Oliver Müller; Anke Arentsen; Elliot Y Davies; Júlia Laguna-Miralles; GyuChul Myeong; Konstantinos Panagiotakis; Hanyuan Zhang; Denis Erkal; S. E. Koposov; Dustin Lang; Jacob Nibauer
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT Tidal features from galaxy mergers, particularly stellar streams, offer valuable insights into galaxy assembly and dark matter halo properties. This paper aims to identify a large sample of nearby stellar streams suitable for detailed modelling and comparison with simulations to enable population-level constraints on halo properties. We visually inspect and compile a tidal feature catalogue for 19 387 galaxies with redshift $z \le 0.02$ from the Siena Galaxy Atlas 2020 using original, model, and residual images from the Dark Energy Spectroscopic Instrument Legacy Imaging Surveys. Residual images, produced by subtracting models of all sources, enhance the detectability of faint asymmetries such as tidal features. We find that $11.9 \pm 0.2{{\ \rm per\ cent}}$ of galaxies host detectable tidal features, more frequently around early- than late-type galaxies. The tidal feature fraction increases with stellar mass, from $2.4 \pm 0.4{{\ \rm per\ cent}}$ at $\sim 10^8\, \mathrm{M}_\odot$ to $36.5 \pm 1.2{{\ \rm per\ cent}}$ at $\sim 5\times 10^{11}\, \mathrm{M}_\odot$. From this, we present the first release of STRRINGS: STReams in Residual Images of Nearby GalaxieS, a subsample of 35 galaxies with long, narrow streams suitable for modelling. We segment these streams and derive their geometry, surface brightness, colours, and stellar masses. The median g-band surface brightness is 26.8 mag arcsec$^{-2}$, reaching 27.5 mag arcsec$^{-2}$ for the faintest stream. Mass ratios are consistent with minor mergers, and we identify five potential dwarf galaxy progenitors. Our streams are typically longer (median 124 kpc) than the literature, with comparable widths. Stream mass correlates with length and colour, and wider streams lie at larger galactocentric radii. STRRINGS will be expanded and used to constrain halo properties in future work.
M. Montelius; Else Starkenburg; Hanneke C. Woudenberg; A. Angrilli Muglia; Anke Arentsen; Anand Viswanathan; Amanda Byström; A. Helmi; N. Martin; Tadafumi Matsuno; Camila Navarrete; Julio F. Navarro
Astronomy and Astrophysics · DOI ↗
Context. The most metal-poor stars in our Galaxy contain important clues of its earliest history, particularly those occupying the inner regions of the Galaxy. In the search for such metal-poor stars, large spectroscopic surveys are an invaluable tool. However, the spectra of metal-poor stars can be difficult to analyse because of the relative lack of available lines, which can also lead to misclassification. Aims. We aim to identify the stars observed by the APOGEE survey that are below the metallicity limit of APOGEE’s analysis. For the highest confidence candidates, we classify the orbital properties of the stars to investigate whether their orbital distribution matches what we would expect for stars that are this metal poor and to select especially interesting targets for spectroscopic follow-up purposes. Methods. We examined the properties derived by APOGEE for metal-poor stars from the literature to find signatures of stars with a metallicity below the range of the grid used for spectral analysis. Once identified within APOGEE, we computed the orbits of our metal-poor candidates using AGAMA. Results. The calibrated APOGEE stellar parameters provide a clear signature of the most metal-poor stars in the survey, indicated by null values for their metallicities while having effective temperatures and surface gravities determined by the pipeline. From comparison with the literature, we find that, within a temperature range of 3700–6700 K and above a threshold of S/N &gt; 30, the vast majority of APOGEE stars without calibrated metallicities are very metal poor. Additional cleaning by visual inspection of the spectra improved the purity of the sample further. The radial velocities provided by APOGEE, Gaia DR3 positions and astrometry along with spectrophotometric distances derived in this work allowed for the computation of their orbits. In this work, we carefully selected 289 very metal-poor red giant stars (likely below [Fe / H] = −2.5) from the APOGEE results. Our sample contains 16 very metal-poor member candidates of the Magellanic Clouds, 14 very metal-poor stars with orbits confined to the inner Galaxy, and 13 inner Galaxy halo interlopers. These samples significantly add to the very metal-poor stars known in these regions and allow for a more detailed picture of early chemical evolution across different environments.
Sara Vitali; Á. Rojas-Arriagada; P. Jofré; Federico Sestito; Joshua Povick; V. Hill; Emma Fernández-Alvar; Anke Arentsen; P. Jablonka; Nicolas F. Martin; Else Starkenburg; David S. Aguado
Astronomy and Astrophysics · DOI ↗
Context . The Sagittarius dwarf spheroidal galaxy (Sgr dSph) is a satellite orbiting the Milky Way that has experienced multiple stripping events due to tidal interactions with our Galaxy. Its accretion history has led to a distinct stellar overdensity, which is the remnant of the core of the progenitor. Aims . We present a complete chemical analysis of 111 giant stars in the core of Sgr dSph to investigate the chemical evolution and enrichment history of this satellite. Methods . Employing the metallicity-sensitive Ca H&amp;K photometry from the Pristine Inner Galaxy Survey, we selected stars that span a wide metallicity range and obtained high-resolution spectra with the ESO FLAMES/GIRAFFE multiobject spectrograph. For the stellar sample covering − 2.13 &lt; [Fe/H] &lt; − 0.35, we derived abundances for up to 14 chemical elements with average uncertainties of ∼ 0.09 dex and a set of stellar ages that allowed us to build an age-metallicity relation (AMR) for the entire sample. Results . With the most comprehensive set of chemical species measured for the core of Sgr (Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ba, La, and Eu), we studied several [X/Fe] ratios. Most trends align closely with Galactic chemical trends, but notable differences emerge in the heavy n -capture elements, which offer independent insights into the star formation history of a stellar population. Conclusions . The deficiency in α elements with respect to the Milky Way suggests a slower, less efficient early star formation history, similar to other massive satellites. S -process element patterns indicate significant enrichment from Asymptotic giant branch stars over time. The AMR and chemical ratios point to an extended star formation history, with a rapid early phase in the first gigayears, followed by declining activity and later star-forming episodes. These findings are consistent with Sgr hosting multiple stellar populations, from young (∼4 Gyr) to old, metal-poor stars (∼10 Gyr).
Adam C. Schneider; F. J. Vrba; Justice Bruursema; Jeffrey A. Munn; M. J. Irwin; Mike Read; W. P. Varricatt; Tom Kerr; K. W. Hodapp; S. Dye; Stephen J. Williams; Andrew T. Cenko; T. Tilleman; Marc A. Murison; Barry Rothberg; S. E. Dahm; Bryan N. Dorland; A. Lawrence; K. C. Chambers
The Astronomical Journal · DOI ↗
Abstract This paper describes the second and third data releases (DR2 and DR3, respectively) from the ongoing United Kingdom Infrared Telescope Hemisphere Survey (UHS). DR2 is primarily comprised of the K -band portion of the UHS survey, and was released to the public on 2023 June 1. DR3 mainly includes the H -band portion of the survey, with a public release scheduled for September 2025. The H - and K -band data releases complement the previous J -band data release (DR1) from 2018. The survey covers approximately 12,700 square degrees between declinations of 0° and +60° and achieves median 5 σ point source sensitivities of 19.0 mag and 18.0 mag (Vega) for H and K , respectively. The data releases include images and source catalogs, which include ∼581 million H -band detections and ∼461 million K -band detections. DR2 and DR3 also include merged catalogs, created by combining J - and K -band detections (DR2) and J -, H -, and K -band detections (DR3). The DR2 merged catalog has a total of ∼513 million sources, while the DR3 merged catalog contains ∼560 million sources.
Thomas Hajnik; N. A. Walton; G. D’Ago; P. Bonifacio; Gavin Dalton; Lilian Domínguez-Palmero; E. Gafton; Irwin, Mike J.; Sergio Picó; David Terrett; Anke Arentsen; Rubén Sánchez-Janssen; David S. Aguado; J. A. L. Aguerri; Carlos Allende Prieto; M. Balcells; Chris Benn; A. Bragaglia; E. Caffau; Esperanza Carrasco; R. Carrera; S. Desidera; B. T. Gänsicke; Sarah Hughes; Shoko Jin; Ian Lewis; Alireza Molaeinezhad; D. N. A. Murphy; Ellen Schallig; S. C. Trager; A. Vallenari
arXiv (Cornell University) · DOI ↗
Current-day multi-object spectroscopic surveys are often limited in their ability to observe bright stars due to their low surface densities, resulting in increased observational overheads and reduced efficiency. Addressing this, we have developed a novel observing mode for WEAVE (William Herschel Telescope Enhanced Area Velocity Explorer) that enables efficient observations of low-surface-density target fields without incurring additional overheads from calibration exposures. As a pilot for the new mode, we introduce the WEAVE-TwiLight-Survey (WTLS), focusing on bright exoplanet-host stars and their immediate surroundings on the sky. High observational efficiency is achieved by superimposing multiple low-target-density fields and allocating the optical fibres in this configuration. We use a heuristic method to define fields relative to a central guide star, which serves as a reference for their superposition. Suitable guide fibres for each merged configuration are selected using a custom algorithm. Test observations have been carried out, demonstrating the feasibility of the new observing mode. We show that merged field configurations can be observed with WEAVE using the proposed method. The approach minimizes calibration times and opens twilight hours to WEAVE's operational schedule. WTLS is built upon the new observing mode and sourced from the ESA PLATO long-duration-phase fields. This survey will result in a homogeneous catalogue of approximately 6300 bright stars, including 62 known planet hosts, laying the groundwork for future elemental abundance studies tracing chemical patterns of planetary formation. This new observing mode (WEAVE-Tumble-Less) expands WEAVE's capabilities to rarely used on-sky time and low-density field configurations without sacrificing efficiency.
Thomas Hajnik; N. A. Walton; G. D’Ago; P. Bonifacio; Gavin Dalton; Lilian Domínguez-Palmero; E. Gafton; M. J. Irwin; Sergio Picó; David Terrett; Anke Arentsen; Rubén Sánchez-Janssen; David S. Aguado; J. A. L. Aguerri; Carlos Allende Prieto; Marc Balcells; Chris Benn; A. Bragaglia; E. Caffau; E. Carrasco; R. Carrera; S. Desidera; B. T. Gänsicke; Sarah Hughes; Shoko Jin; Ian Lewis; Alireza Molaeinezhad; D. N. A. Murphy; Ellen Schallig; S. C. Trager; A. Vallenari
RAS Techniques and Instruments · DOI ↗
ABSTRACT Current-day multi-object spectroscopic surveys are often limited in their ability to observe bright stars due to their low surface densities, resulting in increased observational overheads and reduced efficiency. Addressing this, we have developed a novel observing mode for WEAVE (William Herschel Telescope Enhanced Area Velocity Explorer) that enables efficient observations of low-surface-density target fields without incurring additional overheads from calibration exposures. As a pilot for the new mode, we introduce the WEAVE-TwiLight-Survey (WTLS), focusing on bright exoplanet-host stars and their immediate surroundings on the sky. High observational efficiency is achieved by superimposing multiple low-target-density fields and allocating the optical fibres in this configuration. We use a heuristic method to define fields relative to a central guide star, which serves as a reference for their superposition. Suitable guide fibres for each merged configuration are selected using a custom algorithm. Test observations have been carried out, demonstrating the feasibility of the new observing mode. We show that merged field configurations can be observed with WEAVE using the proposed method. The approach minimizes calibration times and opens twilight hours to WEAVE’s operational schedule. WTLS is built upon the new observing mode and sourced from the ESA PLATO long-duration-phase fields. This survey will result in a homogeneous catalogue of ∼6300 bright stars, including 62 known planet hosts, laying the groundwork for future elemental abundance studies tracing chemical patterns of planetary formation. This new observing mode (WEAVE-Tumble-Less) expands WEAVE’s capabilities to rarely used on-sky time and low-density field configurations without sacrificing efficiency.
Akshara Viswanathan; Else Starkenburg; Tadafumi Matsuno; Kim A. Venn; Nicolas F. Martin; Nicolas Longeard; Anke Arentsen; R. G. Carlberg; S. Fabbro; G. Kordopatis; Martin Montelius; Federico Sestito; Zhen Yuan
Astronomy and Astrophysics · DOI ↗
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 ∼0.15 dex. The purity of this sample in the VMP regime is ∼80%, with outliers representing a mere ∼3%. Conclusions. We have built an all-sky catalogue of ∼1500 stars available, featuring reliable spectroscopic metallicities down to [Fe/H] ∼ −4.0, of which ∼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 &lt; 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.
S. Lalitha; Thomas A Baycroft; I. Boisse; N. Heidari; A. Santerne; A. H. M. J. Triaud; Gavin A. L. Coleman; Yasmin Davis; M. Deleuil; G. Hébrard; David V. Martin; P. F. L. Maxted; Richard P. Nelson; Daniel Sebastian; Owen J Scutt; Matthew R. Standing
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT Circumbinary planets, orbiting both stars in a binary system, offer the opportunity to study planet formation and orbital migration in an environment different from that around single stars. However, despite the fact that $\gt 90~\% $ of binary systems in the solar neighbourhood are spectrally resolved double-lined binaries, there has been only one detection of a circumbinary planet orbiting a double-lined binary using the radial velocity method so far. Spectrally disentangling binary components is challenging due to blending of spectral lines and inaccuracies in spectral modelling. These inaccuracies add scatter to the measurements, which can hide the weak radial velocity signature of circumbinary exoplanets. We have obtained new high signal-to-noise, high-resolution spectra with the SOPHIE spectrograph, mounted on the 193 cm telescope at Observatoire de Haute-Provence (OHP), for six bright, double-lined binaries for which circumbinary exoplanet detection has been attempted in the past. To extract radial velocities, we use the DOLBY code, a recent method of spectral disentangling using Gaussian processes to model the time-varying components. We analyse the resulting radial velocities with a diffusive nested sampler to seek planets, and compute sensitivity limits. We do not detect any new circumbinary planet. However, we show that the combination of new data, new radial velocity extraction methods, and improved statistical methods to determine a data set’s sensitivity to planets leads to an approximately one order of magnitude improvement compared to previous results. This improvement brings us into the range of known circumbinary exoplanets and paves the way for future observation campaigns targeting double-lined binaries.
Rodrigo Ibata; Khyati Malhan; Wassim Tenachi; Anke Arentsen; M. Bellazzini; Paolo Bianchini; P. Bonifacio; E. Caffau; Foivos I. Diakogiannis; Raphaël Errani; Benoît Famaey; Salvatore Ferrone; Nicolas F. Martin; P. Di Matteo; G. Monari; Florent Renaud; Else Starkenburg; Guillaume F. Thomas; Akshara Viswanathan; Zhen Yuan
The Astrophysical Journal · DOI ↗
Abstract We present an atlas and follow-up spectroscopic observations of 87 thin stream-like structures detected with the STREAMFINDER algorithm in Gaia DR3, of which 28 are new discoveries. Here, we focus on using these streams to refine mass models of the Galaxy. Fits with a double-power-law halo with the outer power-law slope set to − β h = −3 yield an inner power-law slope of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:mo>−</mml:mo> <mml:msub> <mml:mi>γ</mml:mi> <mml:mi>h</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>-</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:msubsup> <mml:mn>0.97</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.21</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.17</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mo stretchy="false">)</mml:mo> </mml:math> , a scale radius of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>r</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> <mml:mo>,</mml:mo> <mml:mi>h</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>14.7</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>4.7</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mi>kpc</mml:mi> </mml:math> , a halo density flattening q m , h = 0.75 ± 0.03, and a local dark matter density of ρ h ,⊙ = 0.0114 ± 0.0007 M ⊙ pc −3 . Freeing β yields <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:mi>β</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>2.53</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.16</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.42</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , but this value is heavily influenced by our chosen virial mass limit. The stellar disks are found to have a combined mass of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>4.20</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.53</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.44</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> , with the thick disk contributing 12.4% ± 0.7% to the local stellar surface density. The scale lengths of the thin and thick disks are <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:msubsup> <mml:mn>2.17</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.08</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.18</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>1.62</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.13</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.72</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em"/> <mml:mi>kpc</mml:mi> </mml:math> , respectively, while their scale heights are <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:msubsup> <mml:mn>0.347</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.010</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.007</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML&quot; overflow="scroll"> <mml:msubsup>
L. Venuti; Ann Marie Cody; G. Beccari; L. M. Rebull; M. J. Irwin; Apoorva Thanvantri; Sowmya Thanvantri; S. H. P. Alencar; Clara O. Leal; Geert Barentsen; J. E. Drew; Steve B. Howell
The Astronomical Journal · DOI ↗
Abstract Pre-main-sequence disk accretion is pivotal for determining the final stellar properties and the early conditions for close-in planets. We aim to establish the impact of internal (stellar mass) and external (radiation field) parameters on the disk evolution in the Lagoon Nebula massive star-forming region. We employ simultaneous u , g , r , i , H α time-series photometry, archival infrared data, and high-precision K2 light curves to derive the stellar, disk, and accretion properties for 1012 Lagoon Nebula members. We estimate that of all young stars in the Lagoon Nebula, 34%–37% have inner disks traceable down to ∼12 μ m, while 38%–41% are actively accreting. We detect disks ∼1.5 times more frequently around G, K, and M stars than around higher-mass stars, which appear to deplete their inner disks on shorter timescales. We find tentative evidence for a faster disk evolution in the central regions of the Lagoon Nebula, where the bulk of the O/B population is located. Conversely, disks appear to last longer at the nebula outskirts, where the measured fraction of disk-bearing stars tends to exceed that of accreting and disk-free stars. The derived mass accretion rates show a nonuniform dependence on stellar mass between ∼0.2 and 5 M ⊙ . In addition, the typical accretion rates appear to differ across the Lagoon Nebula extension, with values twice lower in the core region than at its periphery. Finally, we detect tentative radial density gradients in the surface accretion shocks, leading to lags in the appearance of light curve brightness features as a function of wavelength that can amount to ∼7%–30% of the rotation period.
Dolev Bashi; Vasily Belokurov; S. T. Hodgkin
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT The study of binary stars in the Galactic halo provides crucial insights into the dynamical history and formation processes of the Milky Way. In this work, we aim to investigate the binary fraction in a sample of accreted and in situ halo stars, focusing on short-period binaries. Utilizing data from Gaia Data Release 3 (DR3), we analysed the radial velocity uncertainty $\sigma _{\mathrm{RV}}$ distribution of a sample of main-sequence stars. We used a novel Bayesian framework to model the dependence in $\sigma _{\mathrm{RV}}$ of single and binary systems allowing us to estimate binary fractions F in a sample of bright ($G_{\mathrm{RVS}}$ &amp;lt; 12) Gaia sources. We selected the samples of in situ and accreted halo stars based on estimating the 6D phase space information and affiliating the stars to the different samples on an action angle versus energy ($L_{\mathrm{z}}{\!-\!}E$) diagram. Our results indicate a higher, though not significant, binary fraction in accreted stars compared to the in situ halo sample. We further explore binary fractions using cuts in E and $L_z$, and find a higher binary fraction in both high-energy and prograde orbits that might be explained by differences in metallicity. By cross-matching our Gaia sample with APOGEE DR17 catalogue, we confirm the results of previous studies on higher binary fractions in metal-poor stars and find the fractions of accreted and in situ halo stars consistent with this trend. Our finding provides new insights into binary stars’ formation processes and dynamical evolution in the primordial Milky Way Galaxy and its accreted dwarf Galaxies.
Zhen Yuan; Chengdong Li; Nicolas F. Martin; G. Monari; Benoît Famaey; A. Siebert; Rimpei Chiba; Anke Arentsen; Federico Sestito; Guillaume F. Thomas; V. Hill; Rodrigo Ibata; G. Kordopatis; Else Starkenburg; Akshara Viswanathan
Astronomy and Astrophysics · DOI ↗
The most metal-poor stars (e.g., [Fe/H] ≤ –2.5) are the ancient fossils from the early assembly epoch of our Galaxy. They very likely formed before the the thick disk. Recent studies have shown that a non-negligible fraction of them have prograde planar orbits, which means that their origin is 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 so that they became more dominated by rotation. However, it is unclear whether this mechanism can explain these stars as observed in the solar neighborhood. We explore whether this scenario is feasible by tracing these stars backward in an axisymmetric Milky Way potential with a bar as perturber. We integrated their orbits backward for 6 Gyr under two bar models: one model with a constant pattern speed, and the other with a decelerating speed. Our experiments show that for the constantly rotating bar model, the stars of interest are little affected by the bar and cannot have been driven from a spheroidal inner Milky Way to their current orbits. In the extreme case of a 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 dominated by rotation ( J ϕ ≥ 1000 km s −1 kpc) 6 Gyr ago. The chance that these stars started with spheroid-like orbits with low rotation ( J ϕ ≲ 600 km s −1 kpc) is very low (&lt; 3%). We therefore conclude that within the solar neighborhood, the bar is unlikely to have shepherded a significant fraction of spheroid stars in the inner Galaxy to produce the overdensity of stars on prograde planar orbits that is observed today.
Hanyuan Zhang; Vasily Belokurov; N. W. Evans; Zhao‐Yu Li; Jason L. Sanders; Anke Arentsen
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT We present a novel method to constrain the formation time of the Milky Way disc using the chrono-kinematic signatures of the inner Galaxy. We construct an O-rich Mira variable sample from the Gaia long-period variable catalogue to study the kinematic behaviour of stars with different ages in the inner Galaxy. From the Auriga suite of cosmological zoom-in simulations, we find that the age of the oldest stellar population with imprints of the bar in density and kinematics matches the disc spin-up epoch. This is because stars born before the spin-up show insufficient rotation and are not kinematically cold enough to be efficiently trapped by the bar. We find that the bar kinematic signature disappears for Mira variables with a period shorter than 190 d. Using the period–age relation of Mira variables, we constrain the spin-up epoch of the Milky Way to be younger than $\sim 11{-}12$ Gyr (redshift $\sim 3$). We also discuss and compare our method and result to other evidence of the Milky Way spin-up epoch under the context of a realistic age uncertainty. Age uncertainty leads to an overestimation of the disc formation time when performing backward modelling. Our constrain of the spin-up epoch is independent from previous studies because it relies on the kinematics of the inner Galaxy instead of the solar vicinity.
Federico Sestito; Christian R. Hayes; Kim A. Venn; Jaclyn Jensen; Alan W. McConnachie; John Pazder; Fletcher Waller; Anke Arentsen; P. Jablonka; Nicolas F. Martin; Tadafumi Matsuno; Julio F. Navarro; Else Starkenburg; Sara Vitali; John Bassett; Trystyn A. M. Berg; Rubén Díaz; Michael L. Edgar; V. Firpo; Manuel Gómez-Jiménez; V. M. Kalari; Sam Lambert; Jon Lawrence; Gordon L. Robertson; Roque Ruiz-Carmona; R. Salinas; Kim M. Sebo; Sudharshan Venkatesan
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT This study focuses on Pristine$\_180956.78$−294759.8 (hereafter P180956, [Fe/H] = −1.95 ± 0.02), a star selected from the Pristine Inner Galaxy Survey (PIGS), and followed-up with the recently commissioned Gemini High-resolution Optical SpecTrograph (GHOST) at the Gemini South telescope. The GHOST spectrograph’s high efficiency in the blue spectral region (3700−4800 Å) enables the detection of elemental tracers of early supernovae (e.g. Al, Mn, Sr, and Eu). The star exhibits chemical signatures resembling those found in ultrafaint dwarf (UFD) systems, characterized by very low abundances of neutron-capture elements (Sr, Ba, and Eu), which are uncommon among stars in the Milky Way halo. Our analysis suggests that P180956 bears the chemical imprints of a small number (2 or 4) of low-mass hypernovae ($\sim 10{-}15{\rm \, M_\odot }$), which are needed to mostly reproduce the abundance pattern of the light-elements (e.g. [Si, Ti/Mg, Ca] ∼0.6), and one fast-rotating intermediate-mass supernova ($\sim 300{\rm \, km \ s^{-1}}$, $\sim 80{-}120{\rm \, M_\odot }$), which is the main channel contributing to the high [Sr/Ba] (∼+1.2). The small pericentric ($\sim 0.7{\rm \, kpc}$) and apocentric ($\sim 13{\rm \, kpc}$) distances and its orbit confined to the plane ($\lesssim 2{\rm \, kpc}$) indicate that this star was likely accreted during the early Galactic assembly phase. Its chemo-dynamical properties suggest that P180956 formed in a system similar to a UFD galaxy accreted either alone, as one of the low-mass building blocks of the proto-Galaxy, or as a satellite of Gaia–Sausage–Enceladus. The combination of Gemini’s large aperture with GHOST’s high efficiency and broad spectral coverage makes this new spectrograph one of the leading instruments for near-field cosmology investigations.
Michalina Maksymowicz-Maciata; Chiara Spiniello; Ignacio Martín-Navarro; Anna Ferré-Mateu; Davide Bevacqua; Michele Cappellari; G. D’Ago; C. Tortora; M. Arnaboldi; Johanna Hartke; N. R. Napolitano; P. Saracco; Diana Scognamiglio
Monthly Notices of the Royal Astronomical Society · DOI ↗
ABSTRACT The INSPIRE project has built the largest sample of ultra-compact massive galaxies (UCMGs) at 0.1 &amp;lt; z &amp;lt; 0.4 and obtained their star formation histories (SFHs). Due to their preserved very old stellar populations, relics are the perfect systems to constrain the earliest epochs of mass assembly in the Universe and the formation of massive early-type galaxies. The goal of this work is to investigate whether a correlation exists between the degree of relicness (DoR), quantifying the fraction of stellar mass formed at z &amp;gt; 2, and the other stellar population parameters. We use the Full-Index-Fitting method to fit the INSPIRE spectra to single stellar population (SSP) models. This allows us to measure, for the first time, the slope of the IMF, as well as stellar metallicity [M/H], [Mg/Fe], [Ti/Fe], and [Na/Fe] ratios, and study correlations between them and the DoR. Similarly to normal-sized galaxies, UCMGs with larger stellar masses have overall higher metallicities. We found a correlation between the IMF slope and the DoR, that, however, breaks down for systems with a more extended SFH. An even stronger dependency is found between the IMF and the fraction of mass formed at high-z. At equal velocity dispersion and metallicity, galaxies with a higher DoR have a larger dwarf-to-giant ratio, i.e. a bottom heavy IMF, than that of low-DoR counterparts. This might indicate that the cosmic epoch and therefore different formation scenarios influence the fragmentation of the star formation cloud and hence might be the explanation for IMF variations detected in massive ETGs.