N. Rowell; M. Davidson; N. C. Hambly; L. Lindegren; J. Castañeda; C. Fabricius; J. Hernández; D. W. Evans
Astronomy and Astrophysics · DOI
Context . An accurate model of the point spread function (PSF) is required in order to estimate positions and brightnesses of stars in digitised images. The PSF of the Gaia space telescope is unusual due to the use of drift-scan mode and time-delayed integration (TDI), in which the satellite spins and precesses while images are captured. This induces several systematic and periodic distortions in the PSF that are unique to Gaia . Aims . We identify several effects that distort Gaia ’s PSF. These include systematic variations in the stellar image drift rate with respect to the charge transfer rate, and spatial variations in the detector response that are, contrary to expectations, not marginalised by the use of TDI mode. These must be incorporated into the PSF model in order to reduce systematic errors in Gaia ’s data products. Methods . We developed a semi-analytic model of the PSF, in which the blurring effects of along- and across-scan stellar image motion are modelled analytically, and dependences of the PSF shape on source colour and position within the detector are calibrated empirically. We introduced constraints on the PSF origin in order to break a degeneracy with the geometric instrument calibration. Results . Our PSF model successfully reproduces several drift-scan-related effects and leads to significant improvements in the modelling of observations, particularly around the 11-13 magnitude range in Gaia ’s G band. This will contribute to reductions in the astrometric and photometric uncertainties in the derived data products. Conclusions . Our PSF model represents a significant advance over earlier models applied to Gaia data. It was deployed in the Gaia cyclic data processing systems and used in the production of the forthcoming Data Release 4. The linear part of Gaia ’s PSF is now well understood. Future development work will focus on optimised configuration of the model, and the handling of several non-linear effects that depend on the signal level, including charge transfer inefficiency and the brighter-fatter effect. This work provides a useful reference for users of Gaia data and for other missions that use the same observing principles, in particular the proposed GaiaNIR mission.
Alex G. Markowitz; M. Krumpe; D. Homan; Bożena Czerny; Mariusz Gromazdki; Hartmut Winkler; Joern Wilms; Steven Hämmerich; G. Lamer; T. Saha; David A. H. Buckley; Malte Schramm; Daniel E. Reichart; Mara Salvato; P. Baldini
Springer Link (Chiba Institute of Technology) · DOI
Context. Extreme sudden changes in the flow of accreting gas onto supermassive black holes manifest themselves via large-amplitude multiband continuum variability, as well as changes to broad Balmer emission profiles, driving changing-look active galactic nuclei (AGN). Aims. X-ray flux monitoring with Spectrum Roentgen Gamma (SRG)/eROSITA revealed that in the Seyfert AGN HE 1237−2252 the soft X-ray flux dipped abruptly, by a factor of 17 within 18 months. We initiated a follow-up campaign that caught the luminosity recovery after the dip, and enabled us to study how the various accretion components, including the broad-line region (BLR) and X-ray-emitting coronae, responded during this flux recovery. Methods. Our campaign included multiband photometry, X-ray spectroscopy, and optical spectroscopy. We tracked as the accretion rate relative to Eddington increased by a factor of 7 in 3 years. Results. Based on broad Hβ variability, HE 1237−2252 was subtype 1.0–1.2 in 2002, transitioned to subtype 1.8 by the time of the luminosity dip, and then transitioned back to subtype 1.0 within 3 months as luminosity recovered. Both transitions saw broad Hβ integrated line flux change by factors of 4–6. The broad Balmer profile is decomposed into a broad Gaussian consistent with virialized gas at 27 ± 3 lt-dy, plus a double-peaked profile, consistent with a diskline structure at ≳5 lt-dy. The diskline component’s relative contribution to the total profile increases as continuum flux rises. Conclusions. The lack of significant obscuration in the X-ray spectra, as well as the IR continuum dip, point to an intrinsic pause in the accretion rate as opposed to variable line-of-sight obscuration. Candidates for the underlying mechanisms include propagating cold and warm fronts in the accretion disk. The increased prominence of the diskline BLR component’s emission could be due to evolution in the physical extent of the X-ray corona, and in the fraction of > 13.6 eV photons intercepted by the diskline, as the accretion rate increases.
Alex G. Markowitz; M. Krumpe; D. Homan; Bożena Czerny; Mariusz Gromazdki; Hartmut Winkler; Joern Wilms; Steven Hämmerich; G. Lamer; T. Saha; D. A. H. Buckley; Malte Schramm; Daniel E. Reichart; Mara Salvato; P. Baldini
arXiv (Cornell University) · DOI
Extreme sudden changes in the flow of accreting gas onto SMBHs manifest themselves via large-amplitude continuum variability and changes to broad Balmer emission profiles, driving changing-look AGN. X-ray flux monitoring with SRG/eROSITA revealed that in the Seyfert AGN HE 1237-2252 the soft X-ray flux dipped abruptly, by a factor of 17 within 18 months. We initiated a follow-up campaign that caught the luminosity recovery after the dip, and enabled us to study how the various accretion components responded during this flux recovery. Our campaign included multiband photometry, X-ray spectroscopy, and optical spectroscopy. We tracked as the accretion rate relative to Eddington increased by a factor of 7 in 3 years. Based on broad Hbeta variability, HE 1237-2252 was subtype 1.0-1.2 in 2002, transitioned to subtype 1.8 by the time of the luminosity dip, and then transitioned back to subtype 1.0 within 3 months as luminosity recovered. Both transitions saw broad Hbeta integrated line flux change by factors of 4-6. The broad Balmer profile is decomposed into a broad Gaussian consistent with virialized gas at 27+/-3 lt-dy, plus a double-peaked profile, consistent with a diskline structure at more than roughly 5 lt-dy. The diskline component's relative contribution to the total profile increases as continuum flux rises. The lack of obscuration in the X-ray spectra, as well as the IR continuum dip, point to an intrinsic pause in the accretion rate as opposed to variable line-of-sight obscuration. Candidates for the underlying mechanisms include propagating cold and warm fronts in the accretion disk. The increased prominence of the diskline BLR component's emission could be due to evolution in the physical extent of the X-ray corona, and in the fraction of >13.6 eV photons intercepted by the diskline, as the accretion rate increases.
Alex G. Markowitz; M. Krumpe; D. Homan; Bożena Czerny; Mariusz Gromazdki; Hartmut Winkler; Joern Wilms; Steven Hämmerich; G. Lamer; T. Saha; David A. H. Buckley; Malte Schramm; Daniel E. Reichart; Mara Salvato; P. Baldini
arXiv (Cornell University)
Extreme sudden changes in the flow of accreting gas onto SMBHs manifest themselves via large-amplitude continuum variability and changes to broad Balmer emission profiles, driving changing-look AGN. X-ray flux monitoring with SRG/eROSITA revealed that in the Seyfert AGN HE 1237-2252 the soft X-ray flux dipped abruptly, by a factor of 17 within 18 months. We initiated a follow-up campaign that caught the luminosity recovery after the dip, and enabled us to study how the various accretion components responded during this flux recovery. Our campaign included multiband photometry, X-ray spectroscopy, and optical spectroscopy. We tracked as the accretion rate relative to Eddington increased by a factor of 7 in 3 years. Based on broad Hbeta variability, HE 1237-2252 was subtype 1.0-1.2 in 2002, transitioned to subtype 1.8 by the time of the luminosity dip, and then transitioned back to subtype 1.0 within 3 months as luminosity recovered. Both transitions saw broad Hbeta integrated line flux change by factors of 4-6. The broad Balmer profile is decomposed into a broad Gaussian consistent with virialized gas at 27+/-3 lt-dy, plus a double-peaked profile, consistent with a diskline structure at more than roughly 5 lt-dy. The diskline component's relative contribution to the total profile increases as continuum flux rises. The lack of obscuration in the X-ray spectra, as well as the IR continuum dip, point to an intrinsic pause in the accretion rate as opposed to variable line-of-sight obscuration. Candidates for the underlying mechanisms include propagating cold and warm fronts in the accretion disk. The increased prominence of the diskline BLR component's emission could be due to evolution in the physical extent of the X-ray corona, and in the fraction of >13.6 eV photons intercepted by the diskline, as the accretion rate increases.
Alex G. Markowitz; M. Krumpe; D. Homan; Bożena Czerny; Mariusz Gromazdki; Hartmut Winkler; Joern Wilms; Steven Hämmerich; G. Lamer; T. Saha; D. A. H. Buckley; Malte Schramm; Daniel E. Reichart; Mara Salvato; P. Baldini
Astronomy and Astrophysics · DOI
Context. Extreme sudden changes in the flow of accreting gas onto supermassive black holes manifest themselves via large-amplitude multiband continuum variability, as well as changes to broad Balmer emission profiles, driving changing-look active galactic nuclei (AGN). Aims. X-ray flux monitoring with Spectrum Roentgen Gamma (SRG)/eROSITA revealed that in the Seyfert AGN HE 1237−2252 the soft X-ray flux dipped abruptly, by a factor of 17 within 18 months. We initiated a follow-up campaign that caught the luminosity recovery after the dip, and enabled us to study how the various accretion components, including the broad-line region (BLR) and X-ray-emitting coronae, responded during this flux recovery. Methods. Our campaign included multiband photometry, X-ray spectroscopy, and optical spectroscopy. We tracked as the accretion rate relative to Eddington increased by a factor of 7 in 3 years. Results. Based on broad H β variability, HE 1237−2252 was subtype 1.0–1.2 in 2002, transitioned to subtype 1.8 by the time of the luminosity dip, and then transitioned back to subtype 1.0 within 3 months as luminosity recovered. Both transitions saw broad H β integrated line flux change by factors of 4–6. The broad Balmer profile is decomposed into a broad Gaussian consistent with virialized gas at 27 ± 3 lt-dy, plus a double-peaked profile, consistent with a diskline structure at ≳5 lt-dy. The diskline component’s relative contribution to the total profile increases as continuum flux rises. Conclusions. The lack of significant obscuration in the X-ray spectra, as well as the IR continuum dip, point to an intrinsic pause in the accretion rate as opposed to variable line-of-sight obscuration. Candidates for the underlying mechanisms include propagating cold and warm fronts in the accretion disk. The increased prominence of the diskline BLR component’s emission could be due to evolution in the physical extent of the X-ray corona, and in the fraction of > 13.6 eV photons intercepted by the diskline, as the accretion rate increases.
Subo Dong; Zexuan Wu; Yoon-Hyun Ryu; Andrzej Udalski; P Mróz; Krzysztof A. Rybicki; S. T. Hodgkin; Ł. Wyrzykowski; L. Eyer; T. Bensby; Ping Chen; Sharon Xuesong Wang; Andrew P. Gould; Hongjing Yang; Michael D. Albrow; Sun‐Ju Chung; Cheongho Han; Kyu-Ha Hwang; Youn Kil Jung; In-Gu Shin; Yossi Shvartzvald; Jennifer C. Yee; Weicheng Zang; Dong-Jin Kim; Chung‐Uk Lee; Byeong-Gon Park; R. Poleski; J. Skowron; Michał K. Szymański; I. Soszyński; Paweł Pietrukowicz; S Kozłowski; D. M. Skowron; Krzysztof Ulaczyk; Mariusz Gromadzki; M. Ratajczak; Patryk Iwanek; Marcin Wrona; Mateusz J. Mróz; Guy Rixon; Diana L. Harrison; E. Breedt
Science · DOI
A population of free-floating planets is known from gravitational microlensing surveys. None have a directly measured mass, owing to a degeneracy with the distance, but the population statistics indicate that many are less massive than Jupiter. We report a microlensing event-KMT-2024-BLG-0792/OGLE-2024-BLG-0516, which was observed from both ground- and space-based telescopes-that breaks the mass-distance degeneracy. The event was caused by an object with [Formula: see text] Jupiter masses that is either gravitationally unbound or on a very wide orbit. Through comparison with the statistical properties of other observed microlensing events and predictions from simulations, we infer that this object likely formed in a protoplanetary disk (like a planet), not in isolation (like a brown dwarf). Dynamical processes then ejected it from its birthplace, producing a free-floating object.
Tristan Whitmarsh; Mohammad Al Sa’d; E. González-Solares; Alireza Molaeinezhad; Melis O Irfan; Claire M. Mulvey; Marta Paez-Ribes; Atefeh Fatem; Wei Cope; Kui Hua; Gregory J. Hannon; Dario Bressan; Nicholas Walton
Frontiers in Bioinformatics · DOI
Multiplex imaging provides valuable insights into the functional and spatial organization of cells and tissues. However, traditional brightfield histopathology imaging remains important and may be required alongside multiplex imaging. We introduce a generalized framework to generate virtual brightfield images from multiplexed data, thereby reducing the need for additional tissue preparation and alignment with the multiplex images. Our approach uses a physically based stain model that simulates the light absorption of stains through the tissue. A channel selection strategy, using a lookup table or Large Language Model (LLM), allows for the mapping of molecular markers to their corresponding stain colors. To further enhance image quality, we integrate a deep learning-based upsampling and denoising model, trained on real brightfield images. We evaluated the methods on several modalities including mass-spectrometry based imaging mass cytometry and fluorescence based multiplex imaging. The results demonstrate that our method produces virtual brightfield images that are of similar quality as real brightfield images, are quantifiable and of diagnostic quality. We also show that LLMs are able to consistently determine appropriate channels in the multiplex image.
Delfini L; Miguel Vioque; Álvaro Ribas; S. T. Hodgkin
Strasbourg Astronomical Data Center · DOI
Qi Jia; Mingjie Jian; Gang Li; Qian Cui; Cheng Li
Monthly Notices of the Royal Astronomical Society · DOI
Abstract We present an all-sky catalogue of classical Be stars undergoing transitions between quiescent B-type and active Be-star phases, based on Gaia DR3 astrometry and multi-epoch mid-infrared photometry from WISE and NEOWISE-R. From a Gaia-selected parent sample of 4.2 million candidate OBA stars, we identify Be transition stars through correlated variability in W1 magnitude and W1 − W2 colour, which traces circumstellar disk formation and dissipation. The final catalogue contains 3,300 Be transition stars, including 2,743 newly identified objects, and provides a large, homogeneous sample for studying Be outburst activity across the sky. The median durations of the measured outburst and decay phases are 459 and 478 days, respectively, consistent with previous WISE-based measurements and compatible with the long disk-evolution timescales expected in the viscous decretion disk framework. As an initial application, we use TESS photometry for 3,017 targets to identify 63 eclipsing binary systems hosting Be transition stars, including 33 Algol-type, 17 Beta Lyrae-type, and 13 W Ursae Majoris-type systems. Among the multi-epoch LAMOST spectra, two sources show candidate radial-velocity shifts exceeding 20 km s −1; their line-profile behaviour suggests that RV variability in active Be transition stars may be influenced by outburst-related line-profile changes rather than being an unambiguous indicator of binary motion. This catalogue provides a basis for future statistical studies of Be outbursts, disk evolution, and their connection with binarity and spectroscopic variability.
Amy L. Rankine; D. Homan; James Aird; Pranavi Hiremath; Scott F. Anderson; Roberto J. Assef; F. E. Bauer; W N Brandt; M. Brusa; Johannes Buchner; Maria Chira; Y. Díaz; Patrick B. Hall; Anton M. Koekemoer; M. Krumpe; G. Lamer; Teng Liu; Sean Morrison; B. Musiimenta; Castalia Alenka Negrete; Qingling Ni; Paola Rodríguez Hidalgo; Mara Salvato; Donald P. Schneider; Yue Guo Shen; Matthew J. Temple; D. Tubín-Arenas; Dominika Wylezalek
Monthly Notices of the Royal Astronomical Society · DOI
ABSTRACT We present an investigation of the rest-frame optical/UV and X-ray properties for a sample of 3027 X-ray selected quasars between $1.5 \le z \le 3.5$ detected in the deepest Spectrum Roentgen Gamma/eROSITA data available and observed by the fifth iteration of the Sloan Digital Sky Survey (SDSS-V). We parametrize the C iv $\lambda 1549$ emission line to infer the strength of accretion disc winds and perform X-ray spectral fitting. The X-ray spectral properties – namely, the 2 keV monochromatic luminosity ($L_{2\, \text{keV}}$) and spectral slope – are not strongly correlated with wind strength. Despite this result, the X-ray selected sample is shifted towards lower C iv blueshifts and higher equivalent widths than the optically selected sample observed in previous SDSS surveys, and matching in optical luminosity, redshift, and Eddington ratio does not reduce these differences. We estimate the far-UV luminosity using the He ii $\lambda 1640$ line luminosity and define the slopes between this and the 2500 Å monochromatic luminosity ($L_{2500}$) and $L_{2\, \text{keV}}$ ($\alpha _\text{ouv}$ and $\alpha _\text{uvx}$, respectively) in a similar manner to the familiar $\alpha _\text{ox}$ parameter, which tracks the spectral slope between $L_{2500}$ and $L_{2\, \text{keV}}$. The quantity $\alpha _\text{ouv}$ is more strongly correlated with wind strength in our sample than $\alpha _\text{ox}$. We show that the correlation between $\alpha _\text{ox}$ and wind strength is driven by the relationship between the optical luminosity and wind strength. Our results are consistent with a radiation line-driven wind, whereby the ionizing far-UV photons must not over-ionize the gas. The hard X-ray photons are few enough in number to have a negligible effect on the ionization state of the material.
Pavan Tanna; Simon Lock; Amy Bonsor; S. T. Hodgkin; Cathie J. Clarke
arXiv (Cornell University) · DOI
Giant impacts, collisions between planet-sized bodies, play an important role in planet and moon formation. As we enter a new era of large-scale surveys, such as \textit{Gaia} and LSST at the Vera C. Rubin observatory, there is potential to directly observe the remnants produced in such events and gain insights into the process of planet formation. Here, by modelling the emission and cooling of a series of giant impact remnants, we show that giant impacts are detectable as a sudden brightening followed by gradual dimming in the optical and near-infrared. Giant impacts between Earth-composition planets were simulated using the smoothed particle hydrodynamics code {\small SWIFT}, with total colliding masses ranging from 0.2 to 4 $M_{\oplus}$. By constraining the location of the photic surface of the post-impact bodies produced by the simulations, the initial luminosities of post-impact bodies were found to be between $5\times10^{-5}$ and $10^{-1}$ solar luminosities, with luminosity falling roughly exponentially on a timescale between 1 and 2000 days. Based on our results, along with estimates for planet and giant impact occurrence rates, we anticipate that between 0 and 14 terrestrial giant impacts will be observed in the full release of \textit{Gaia} epoch photometry in DR4, with at least a comparable number found by LSST. Identifying the remnants of multiple giant impacts will offer a powerful constraint on the frequency of giant impacts in the galaxy and hence the role of such collisions in planet formation.
Carolina Salgado; Sandro Notto Villanova; Doug Geisler; Nicolás Barrera; Anke Arentsen
Astronomy and Astrophysics · DOI
Context . The inner Milky Way hosts overlapping stellar populations (bar–bulge, inner thin and thick disks, and halo), thus complicating population assignments along the line of sight. A joint chemical–dynamical approach is required to isolate a clean field bulge sample. Metal-poor bulge stars are particularly valuable as they likely trace the earliest phases of chemical enrichment in the inner Galaxy. Aims . We characterize the α -element (Si, Mg) and selected Fe-peak abundances of a dynamically defined sample of bulge field stars, and contrast these trends with the inner-halo tail in the metal-poor regime. Methods . We analyzed metal-poor candidates from the Pristine Inner Galaxy Survey observed by the bulge Cluster APOGEE Survey. Using APOGEE/ASPCAP abundances (S/N ≥ 50), we integrated full 6D orbits in a barred Milky Way potential. Bulge membership was defined via orbital confinement using an apocenter cut and the high-density locus in the ( E J , L z ) plane, with uncertainties estimated using Monte Carlo simulations. We identified 98 stars as genuine bulge members. Results . The metallicity distribution spans −2.5 ≤ [Fe/H]≤−0.4, with a median [Fe/H] = −1.71, offset to higher metallicity than the inner halo (median [Fe/H] = −1.96). The sample follows a high- α sequence with slopes d[Si/Fe]/d[Fe/H] = −0.020 +0.012 −0.051 and d[Mg/Fe]/d[Fe/H] = −0.097 +0.062 −0.133 . Fe-peak tracers show [Ni/Fe]∼0, while [Mn/Fe] declines with [Fe/H] with a mild upturn at higher metallicity. We detect no significant [Si/Fe] gradients with R apo or Z max (+0.010 +0.018 0.000 and +0.006 +0.022 −0.011 dex kpc −1 , respectively). The results are insensitive to the assumed Ω p , yielding indistinguishable memberships. Conclusions . The chemo-orbital evidence favors an in situ origin within the inner Galaxy for the metal-poor bulge field, enriched at early times and later rearranged by secular bar evolution, with a minor contribution from halo stars at the most metal-poor end.
Alireza Molaeinezhad; Nicholas Walton; M. Riello; Eduardo González Solares; Leigh Smith; G. D’Ago; D. Homan
Zenodo (CERN European Organization for Nuclear Research) · DOI
A standalone, read-only toolkit of 46 astronomy tools (literature, public archives, offline calculators) exposed as a Python API, a command line and a Model Context Protocol server, with a generated tool catalogue and a seed benchmark (CASPER AstroToolBench) for tool-using language models. It is the open, public part of CASPER, the assistant platform of CAMCEAD at the Institute of Astronomy, University of Cambridge.
Amy L. Rankine; D. Homan; James Aird; Pranavi Hiremath; Scott F. Anderson; Roberto J. Assef; Franz E. Bauer; William Nielsen Brandt; M. Brusa; Johannes Buchner; Maria Chira; Y. Díaz; Patrick B. Hall; Anton M. Koekemoer; M. Krumpe; G. Lamer; Teng Liu; Sean Morrison; B. Musiimenta; Castalia Alenka Negrete; Qingling Ni; Paola Rodríguez Hidalgo; Mara Salvato; Donald P. Schneider; Yue Shen; Matthew J. Temple; D. Tubín-Arenas; Dominika Wylezalek
Apollo (University of Cambridge) · DOI
We present an investigation of the rest-frame optical/UV and X-ray properties for a sample of 3027 X-ray selected quasars between $1.5 \leq z \leq 3.5$ detected in the deepest Spectrum Roentgen Gamma/eROSITA data available and observed by the fifth iteration of the Sloan Digital Sky Survey (SDSS-V). We parametrize the CIV$\lambda1549$ emission line to infer the strength of accretion disc winds and perform X-ray spectral fitting. The X-ray spectral properties -- namely, the 2keV monochromatic luminosity (L$_\text{2keV}$) and spectral slope -- are not strongly correlated with wind strength. Despite this result, the X-ray selected sample is shifted towards lower CIV blueshifts and higher equivalent widths than the optically selected sample observed in previous SDSS surveys, and matching in optical luminosity, redshift, and Eddington ratio does not reduce these differences. We estimate the far-UV luminosity using the HeII$\lambda1640$ line luminosity and define the slopes between this and the 2500A monochromatic luminosity ($L_{2500}$) and L$_\text{2keV}$ ($α_\text{ouv}$ and $α_\text{uvx}$, respectively) in a similar manner to the familiar $α_\text{ox}$ parameter, which tracks the spectral slope between $L_{2500}$ and L$_\text{2keV}$. The quantity $α_\text{ouv}$ is more strongly correlated with wind strength in our sample than $α_\text{ox}$. We show that the correlation between $α_\text{ox}$ and wind strength is driven by the relationship between the optical luminosity and wind strength. Our results are consistent with a radiation line-driven wind, whereby the ionising far-UV photons must not over-ionise the gas. The hard X-ray photons are few enough in number to have a negligible effect on the ionisation state of the material.
David Chemaly; Elisabeth Sola; Vasily A Belokurov; Sergey E. Koposov; GyuChul Meyong; Hanyuan Zhang; Denis Erkal
Monthly Notices of the Royal Astronomical Society · DOI
ABSTRACT Stellar streams, the debris of tidally disrupted satellites, trace their host’s gravitational potential and thus probe dark matter halo structure. While six-dimensional phase-space data of Galactic streams enable precise dark matter halo modelling in the Milky Way, streams around external galaxies are typically available only as low surface brightness features without kinematics (i.e. two-dimensional photometric data), providing only weak constraints when considered individually. We present a hierarchical Bayesian framework that infers the population distribution of halo flattening using only projected stream tracks. Streams are forward-modelled in StreaMAX1, a new JAX-accelerated particle-spray package that achieves orders of magnitude faster stream generation when compared to traditional methods. For each stream, we fit an axisymmetric dark matter halo model and obtain a posterior on the flattening. These posteriors are then combined through hierarchical reweighting to constrain the population distribution. Using mock data, we show that individual fits recover the correct flattening with modest precision and exhibit projection-induced multi-modalities. Nevertheless, aggregating these fits yields accurate and confident constraints on the underlying population distribution of dark matter halo morphologies, clearly distinguishing between oblate, spherical, and prolate populations. The total computational cost scales linearly with sample size. Our results demonstrate that ensembles of purely photometric streams carry sufficient information to constrain dark matter halo shapes in external galaxies at the population level. With the forthcoming samples from Euclid and Rubin/LSST, this approach offers a practical path to population-level inferences of halo morphology without any kinematic measurements.
Geert Jan Talens; Leigh C. Smith; Luca Malavolta; Lionel Garcia; S. T. Hodgkin; Suzanne Aigrain
arXiv (Cornell University) · DOI
Aims: Our goal is to test and compare transit search methodologies, and provide recommendations as to the best practices to be implemented by the upcoming ESA PLATO mission, in order to achieve its goal of detecting Earth-like planets in the habitable zones of Sun-like stars. Methods: We generate simulated two-year PLATO light curves with injected planets with sizes 0.5--2.0 $R_\oplus$, and compare the performance of the CETRA, umbra, and nuance transit search methods. CETRA and umbra require pre-filtered light curves and we test the biweight, Huber spline, Lowess, and YSD-Lowess filters. nuance uses a Gaussian process to model the stellar variability at all proposed transit parameters. Results: nuance achieves the best performance, recovering 61.2% signals using a simple harmonic oscillator Gaussian process kernel, and it performs especially well for both hot and fast-rotating stars. However, when multiple Huber spline filter windows are considered, both CETRA and umbra can match nuance's performance. CETRA matches nuance with four windows, recovering 61.3% of signals. umbra matches nuance with two windows, recovering 61.7% of signals. Recovery rates exceeding nuance are possible by using more windows. The computational cost of running nuance is so high that running CETRA or umbra on multiple windows is preferred. Conclusions: The PLATO pipeline should use the Huber spline with a range of window sizes as its primary light curve filter. CETRA should be updated to use the warped least-squares templates implemented in umbra. The use of nuance should be considered for hot, rapidly rotating stars.
Euclid Collaboration; Nathaniel Starkman; Jacob Nibauer; S. Pearson; S. Wu; Mike Walmsley; Lina Necib; Jo Bovy; Francine R. Marleau; Elisabeth Sola; et al.
arXiv (Cornell University) · DOI
Wide-field surveys like Euclid mark a new era of extragalactic stellar stream studies. With a large number of streams, it is now possible to constrain the dark matter halos of galaxies in a cosmological volume and draw comparisons to theoretical expectations for the geometry of dark matter halos. This study combines Euclid imaging with visual detection and segmentation annotations to analyse streams. We use projected stream morphologies to constrain the shape and centre-of-mass position (CoM) of each host galaxy's potential, jointly probing baryonic and dark matter distributions. These inferences complement weak lensing methods, with sensitivity to halo profile and geometry on sub-virial scales. The method enables both stacked, population-level constraints on halo flattening and CoM position, and constraints on these quantities for individual halos. We also present a novel method for transforming segmentation maps of stellar streams into smooth, curvature-preserving tracks optimised for fast and robust dynamical inference. This approach enables rapid modelling of stream morphology, supports a statistically rigorous combination of constraints across multiple streams within a single galaxy, and enables joint inference across galactic hosts. From our study of 13 galaxies with prominent tidal streams, we find agreement with spherical halos, albeit a mild preference for flattening with $q = 0.95^{+0.05}_{-0.10}$ at 68\% confidence. This is promising early agreement with $Λ$CDM predictions. With thousands more discovered streams expected across \Euclid's mission, our programme will enable precise measurements of halo shapes and CoM positions across large samples and redshifts, offering constraints on the geometry of dark matter halos.
C. Pagani; N. C. Hambly; M. Davidson; N. Rowell; Cian M. Crowley; R. Collins; Floor van Leeuwen; G. M. Seabroke; A. Holland; M. A. Barstow; Dafydd Wyn Evans
Astronomy and Astrophysics · DOI
During the course of its mission, ESA’s Gaia spacecraft has generated a map of the stars of the Galaxy of exquisite detail. While in its L2 orbit, the satellite has been exposed to high-energy cosmic rays and solar particles, which caused permanent damage to its CCDs. The main effect of radiation damage on Gaia data is the distortion of its images and spectra that is caused by the charge transfer inefficiency (CTI) of the CCDs during the readout process. When this is not taken into account, it can result in inaccurate measurements of a star’s location and flux. We analysed and modelled the effect of CTI on the serial readout direction, which is larger than in the parallel due to the presence of CCD manufacturing defects. A pixel-based physically motivated CTI model, CtiPixel , was developed to characterise the damage in Gaia CCDs. The model was calibrated using dedicated serial CTI diagnostic data, taken every three to four months over the course of the mission. The model is shown to be a good representation of the observed signatures of CTI in the calibration datasets, and its parameters reveal significant insights into the nature of the CCD defects generated by space irradiation. The damage in the serial direction slightly increases linearly over time in general, with sudden step changes after strong solar flares and coronal mass ejections directed towards Earth. The serial CTI showed a further step increase as a consequence of the engineering CCD annealing experiment that was carried out after the completion of Gaia science observations.
C. Pagani; N. C. Hambly; M. Davidson; N. Rowell; Cian M. Crowley; R. Collins; Floor van Leeuwen; G. M. Seabroke; A. Holland; M. A. Barstow; Dafydd Wyn Evans
arXiv (Cornell University) · DOI
During the course of its mission, ESA's Gaia spacecraft has generated a map of the stars of the Galaxy of exquisite detail. While in its L2 orbit, the satellite has been exposed to high energy cosmic rays and solar particles, that caused permanent damage to its CCDs. The main effect of radiation damage on Gaia data is the distortion of its images and spectra, caused by the CCDs charge transfer inefficiency (CTI) during the readout process, that, if not taken into account, can result in inaccurate measurements of a star's location and flux. In this work, the impact of CTI in the serial readout direction, larger than in the parallel due to the presence of CCDs manufacturing defects, has been analysed and modelled. A pixel-based, physically motivated CTI model, CtiPixel, has been developed to characterise the damage in Gaia CCDs. The model has been calibrated using dedicated serial CTI diagnostic data, taken every 3-4 months over the course of the mission. The model is shown to be a good representation of the observed signatures of CTI in the calibration datasets, and its parameters reveal significant insights into the nature of the CCD defects generated by space irradiation. The evolution of the damage in the serial direction shows a general small linear increase over time, with sudden step changes after strong solar flares and coronal mass ejections directed towards Earth. The serial CTI showed a further step increase as a consequence of the engineering CCD annealing experiment carried out after the completion of Gaia science observations.
Gang Li; Haotian Wang; Anuj Gautam; J. S. G. Mombarg; Simon J. Murphy; Mara Bernizzoni; Mingjie Jian; Saakshi Wadhwa; D. J. Fritzewski; F. D. Moyano; Prasad Mani; Chenyuan Li; T. R. Bedding; Conny Aerts
arXiv (Cornell University) · DOI
Coeval stellar populations offer a unique advantage for studying stellar physics because their members share a common age and broadly similar initial chemical composition, allowing the free parameters in stellar models to be constrained more efficiently. Meanwhile, asteroseismology, through the study of pulsation modes that propagate through stellar interiors, provides powerful constraints on internal structure and the physical processes operating beneath stellar atmospheres. The combination of coeval-population studies and asteroseismology therefore provides an unparalleled laboratory for testing and improving stellar evolutionary and structural models. Using light curves from the Kepler and TESS space missions, together with membership constraints based on Gaia astrometry, we identify g-mode period-spacing patterns in dozens of early-type ($T_{\rm eff} \gtrsim 7000\,\mathrm{K}$) main-sequence stars across 16 stellar groups. From these patterns, we infer near-core rotation rates $f_\mathrm{rot}$ and measure the asymptotic spacing $Π_0$ of g modes, tracing both angular-momentum transport and the evolution of the convective stellar cores. Using our homogeneous set of g-mode stellar-group members spanning a wide range of ages, we show that near-core rotation in early-type stars decreases with stellar evolution. We compare our results with existing model predictions. Our $Π_0$ measurements still show discrepancies with current stellar models for reasons that remain unclear, as reported in several previous studies. We also report two g-mode pre-main-sequence pulsators and three pulsating blue stragglers. Our sample provides a useful basis for calibrating stellar models in future ensemble asteroseismic studies of coeval stellar populations.