arXiv subjects

Richard de Grijs

Publications and source records attributed to Richard de Grijs.

At least 19 recordsLinked to original sources

arXiv2026

Thirty years of primordial deuterium abundances: A provenance-aware statistical reanalysis

(ABRIDGED:) Primordial deuterium provides one of the most precise observational tests of Big Bang nucleosynthesis, yet the published literature is built on a comparatively small number of high-redshift absorption systems. We construct a provenance-aware database of 957 published primordial-D/H values from 247 publications spanning 1994--2026 and trace observational entries, wherever possible, to their underlying physical absorbers. Of the 795 observational entries, 80.1 percent represent reused individual or compilation values; only 11.4 percent correspond to new determinations of individual absorption systems. Although 52 distinct absorbers are identified overall, the eight most frequently represented systems account for 62.0 percent of all identifiable absorber mentions. An inverse Herfindahl--Hirschman measure applied to our full database gives an effective representation equivalent to only 16.28 equally represented absorbers, demonstrating that the published literature is strongly concentrated around a much smaller effective subset. Despite this strong internal dependence, the modern consensus value of $10^5({\rm D/H})\simeq2.5$ is robust to alternative absorber-level treatments and survives removal of the eight dominant systems. However, the apparent precision of literature-level compilations is more sensitive to repeated representation than a simple count of published values implies. We also identify a synchronised transition in the compilation literature around 2013--2014, associated with increasingly selective and homogeneous analyses while older individual values continued to circulate. The modern D/H consensus is therefore robust in central value, but the underlying literature is less statistically independent than its publication density suggests. This thus highlights the importance of provenance-aware analysis in precision cosmology.

astro-ph.CO↗

arXiv2026

Temporal rhythms of uncertainty: Evaluating Mars claims in the Australian colonial press

Favourable oppositions of Mars gave nineteenth-century astronomers recurring opportunities to test claims about the planet, while telegraphic news and newspaper reprinting carried those claims well beyond the professional observatories. Historians have established the importance of these events to the development of mass-media astronomy. Here, I examine a related question in the Australian colonial press: how did the standing of particular claims change as brief reports, local responses and fuller accounts appeared at different times? Drawing on colonial newspaper coverage from 1875 to 1899, I follow episodes surrounding the major Mars oppositions of 1892 and 1894. Reports of observations attributed to "Professor Pickering" in 1892 prompted both rapid circulation and immediate scrutiny. In 1894, a cable about William W. Campbell's spectroscopic work provoked local disagreement before more detailed accounts became available. These sequences show that a Mars opposition concentrated attention without imposing a uniform progression from anticipation to discovery and subsequent caution. Newspapers carried assessments and renewed speculation at the same time. The Australian case extends work on event astronomy by showing how the timing and form of information arriving in a colonial press network affected the public evaluation of astronomical claims.

physics.hist-ph↗

arXiv2026

Transients and Stellar Activity as Revealed by Ultraviolet Diagnostic Tracers

Ultraviolet (UV) observations offer unique insights into transient and variable astrophysical phenomena, from the Sun and nearby stars to supernovae and star-forming galaxies. Here, we summarise and review the diagnostic power of the UV spectrum for probing the physical conditions, dynamics and energetics of these events. We trace the historical development of UV astronomy from early satellite missions to the current landscape shaped by the Hubble Space Telescope, the GALaxy Evolution eXplorer, the Neil Gehrels Swift Observatory and AstroSat/UVIT. Particular emphasis is placed on resonance lines such as Mg II $h$ and $k$, C II, Si IV, C IV and N V, which probe the (solar and) stellar chromosphere and transition region, revealing magnetic heating, shocks and mass loss across stellar types. We examine UV diagnostics of stellar flares, pre-main-sequence activity and rotation--activity correlations, linking them to exoplanetary irradiation and habitability. We then explore the UV view of supernova shock breakout and early-time emission, as well as the far-UV mapping of young stellar populations and hierarchical star formation in the Magellanic Clouds. Together, these aspects illustrate how the UV connects small-scale plasma processes to galactic-scale star formation. Despite remarkable progress, UV transient astronomy remains limited by instrument availability and cadence. Forthcoming missions promise to transform this field by capturing the rapid, luminous phenomena that define the dynamic Universe.

astro-ph.SR↗

arXiv2026

Investigating the Young Stellar Populations and Hierarchies in Nearby Galaxies with the UVIT. III. Evidence for a Largest Scale of Correlated Stellar Structures and a Non-universal Fractal Dimension

Scale-free turbulent motions, gravitational collapse and galactic dynamics govern galactic-scale, hierarchical organization of star formation (SF) within galaxies. Past studies suggest that properties of SF hierarchies depend upon host galaxy properties and interstellar medium (ISM) conditions. To characterize SF hierarchies, we performed two-point correlation function analysis on ~25000 UV-selected star-forming clumps (SFCs) identified in a morphologically diverse sample of 8 classic spirals, 6 flocculent spirals and 3 dwarf irregulars. We found that SF hierarchies in galaxies exhibit a maximum spatial scale -- the correlation length ($l_{\rm corr}$) -- largest scale up to which SF is spatially correlated, presumably owing to ISM turbulence. The $l_{\rm corr}$ values range from ~100 pc to 3.4 kpc and exhibit strong dependence on the galaxy's stellar mass, morphology and nature of spiral arms. This suggests that a galaxy's gravitational potential and spiral structure place an upper limit on the sizes of the largest, hierarchically structured SF complexes. Connecting $l_{\rm corr}$ with turbulence injection sources suggests that stellar feedback in dwarf irregulars, whereas disk instabilities and spiral structure in classic/flocculent spirals dominate towards sustaining their SF hierarchies up to the $l_{\rm corr}$ scale. These hierarchies disperse to near-random distributions on timescales ($T_{\rm dis}$) ranging from 20-160 Myr. The broad range of derived $l_{\rm corr}$, projected fractal dimension ($D_2$ $\in$ 0.71$-$1.73), and $T_{\rm dis}$ indicates a non-universal, galaxy-specific nature of SF hierarchies. In this work, full coverage of each galaxy's star-forming extent with the AstroSat-UltraViolet Imaging Telescope uniquely enabled us to connect global parameters of SF hierarchies with large-scale galaxy properties.

astro-ph.GA↗

arXiv2026

The GALAH Survey: Neutron-Capture Elemental Abundances for 350,000 Gaia-RVS spectra and the Chemodynamics of Accreted Structures

We present a comprehensive data-driven spectroscopic analysis of 357,415 red giant stars using Gaia DR3 Radial Velocity Spectrometer (RVS) spectra (8460-8700 A; $R\approx11,500$), aimed at deriving homogenous stellar parameters and elemental abundances (collectively referred to as stellar labels). We employ The Cannon, a generative model based on 2747 giants in common with GALactic Archaeology with HERMES (GALAH) DR4, adopting GALAH labels ($R\approx28,000$) for training. The resulting model predicts 11 stellar labels for RVS giants: effective temperature ($T_{\rm eff}$), surface gravity ($\log g$), projected rotational velocity ($v\sin i$), and abundances of [Fe/H], [Ca/Fe], [Si/Fe], [Ni/Fe], [Ti/Fe], as well as the neutron-capture elements [Zr/Fe], [Ce/Fe], and [Nd/Fe]. Building on these results, we develop a probabilistic framework to chemically identify debris from the Gaia-Sausage-Enceladus (GSE) accretion event. A logistic regression classifier, optimized via Markov chain Monte Carlo sampling and trained on a small reference sample of GSE members and comparison stars, identifies stars with high GSE membership probabilities based solely on their chemical abundances, with the resulting candidates exhibiting distinctive abundance-ratio patterns, including [Ca/Ti], [Ti/Ce], and [Nd/Zr]. Applying independent kinematic constraints yields a robust sample of GSE candidates, demonstrating that the characteristic chemical signatures remain consistent after applying these constraints. This work demonstrates the potential of data-driven analysis techniques to extract detailed chemical information from medium-resolution spectra and establishes a framework for tracing Galactic accretion events using chemical abundances.

astro-ph.GA↗

arXiv2026

Star Clusters in the Ultraviolet

Ultraviolet (UV) observations provide a powerful window into the hot and evolved stellar populations that shape the structure, evolution and integrated light of star clusters. Because UV wavelengths are highly sensitive to massive main-sequence stars, blue straggler stars (BSS), extreme-horizontal branch (HB) stars, post-HB stars, interacting binaries and compact remnants, they probe key evolutionary processes that are inaccessible at optical and infrared wavelengths. This review synthesises five decades of UV studies of star clusters across the Milky Way, the Magellanic Clouds (MCs) and nearby galaxies, drawing on results from early space missions, wide-field surveys, and high-resolution imaging. In Galactic open clusters, UV studies have revealed compact companions$-$including white dwarfs, hot subdwarfs and stripped stars$-$and have established the mass-transfer origins of BSS, Blue Lurkers and yellow stragglers. In globular clusters, UV imaging has identified multiple stellar populations through UV-sensitive molecular bands, probed helium enrichment and mapped HB morphologies. Wide-field UVIT surveys have extended HST studies with homogeneous catalogues of HB and post-HB stars across entire clusters. In the MCs, UV observations have transformed our understanding of multiple populations, rotation-driven extended main-sequence turn-offs and the UV-dim phenomenon, while spectroscopic surveys have constrained massive-star evolution, stellar winds and binarity at low metallicity. UV mapping of the Magellanic Bridge has revealed ongoing massive-star formation in low-density tidal environments. Beyond the Local Group, UV studies of extragalactic clusters constrain star-formation histories, stellar feedback and population synthesis across galactic environments. Collectively, UV observations now form a cornerstone of star cluster astrophysics and will continue to do so with upcoming missions.

astro-ph.GA↗

arXiv2026

Fifty years of primordial helium abundances: A statistical reanalysis

The primordial helium mass fraction, $Y_\mathrm{p}$, is a key observational pillar of Big Bang nucleosynthesis and a sensitive probe of early-Universe physics. Over the past several decades, numerous observational $Y_\mathrm{p}$ determinations have been published using a wide range of astrophysical tracers and cosmological techniques. Although recent measurements exhibit striking convergence and increasingly small uncertainties, the statistical and historical context of this consensus has not been examined systematically. Here, we compile and analyse a comprehensive dataset of observational $Y_\mathrm{p}$ determinations published between the late-1960s and 2022. The final sample comprises 143 reported values spanning multiple tracers. We find clear evidence for long-term convergence in published $Y_\mathrm{p}$ values, punctuated by statistically significant change points in the mid-2000s and early 2010s. Careful examination reveals that many extragalactic H{\sc ii}-region determinations are not fully independent, relying on re-analyses or partial reuse of a limited number of observational datasets. This reduces the effective number of independent constraints and provides important context for interpreting the precision of recent results. Our findings do not challenge the overall consistency of modern $Y_\mathrm{p}$ determinations with standard cosmology, but they underscore the importance of accounting for data dependence, methodological homogeneity and historical evolution when synthesising measurements.

astro-ph.CO↗

arXiv2026

Mars in the Australian Press, 1875-1899. 2. Circulation and Attribution

Between 1875 and 1899, Mars occupied a prominent and recurring position in newspaper reporting across Europe, North America and beyond. Although the scientific and cultural dimensions of this "Mars excitement" have been well studied in metropolitan contexts, far less attention has been paid to how planetary astronomy circulated through colonial press systems. This paper examines the Australian press as a case study in the global mediation of nineteenth-century astronomical knowledge. Drawing on a structured compilation of 1040 digitised newspaper articles accessed via the National Library of Australia, the study analyses patterns of first appearance, reprinting, attribution and temporal persistence in Australian Mars reporting. Mars-related news entered Australia primarily through international telegraphic networks and overseas syndication before circulating widely through metropolitan, regional and provincial newspapers. Distinguishing between novel reports and subsequent reprints reveals that apparent abundance often masked a small number of originating items that achieved extensive colonial reach. Attribution practices evolved over time, shifting from anonymous or institutional authority towards increasing reliance on named overseas figures such as Asaph Hall, William H. Pickering and, most notably, Percival Lowell. This shift reshaped both the form and longevity of Mars reporting, allowing interpretive and personality-driven material to persist independently of specific observational events. By emphasising circulation, attribution and temporal rhythm, this study situates Australian newspapers within international systems of scientific communication. Colonial journalism actively mediated astronomical knowledge rather than merely transmitting it, shaping how Mars became a durable object of public scientific attention in the late nineteenth century.

physics.hist-ph↗

arXiv2026

Mars in the Australian Press, 1875-1899. 1. Interpretation, Authority and Planetary Science

[Abridged] In the late nineteenth century, Mars emerged as one of the most intensively reported astronomical objects in the popular press, driven by favourable oppositions, improved telescopic capabilities and growing speculation regarding planetary habitability. I examine how Mars was interpreted in Australian newspapers between the 1870s and 1899, focusing on the ways in which astronomical knowledge was framed, contextualised and debated within a colonial media environment. Drawing on a large collection of digitised newspaper articles, I analyse how observational authority, instrumental credibility and individual expertise were harnessed in press reporting. The paper situates Australian Mars coverage within a global network of scientific communication dominated by metropolitan centres in Europe and North America, while highlighting the distinctive role played by southern-hemisphere visibility. Australian observatories and observers were frequently positioned as contributors of confirmatory observation rather than interpretive leadership, reinforcing a pattern of locally grounded but internationally oriented scientific engagement. The analysis traces a shift from early emphasis on disciplined observation and measurement to later periods characterised by contested interpretations, particularly surrounding the so-called Martian "canals" and the speculative claims advanced by personalities such as Percival Lowell in the USA. By examining how newspapers mediated between observational astronomy, engineering analogies and popular imagination, this study contributes to a broader understanding of how planetary science entered public discourse beyond metropolitan centres. In doing so, it underscores the active role of colonial newspapers in shaping scientific meaning and situates Australian Mars reporting within the wider history of nineteenth-century astronomical culture.

physics.hist-ph↗

arXiv2026

Mars excitement in Australian newspapers, 1877-1899: Humour and the public negotiation of astronomical knowledge

Speculation about Martian canals was a recurring feature of late nineteenth-century popular astronomy. This paper examines how colonial newspapers used humour to negotiate the epistemic uncertainty and interpretive excess associated with canal theory. Drawing on over one thousand metropolitan and regional Australian newspapers published between 1877 and 1899, we identify five overlapping modes of humour: imported metropolitan wit; satire of modern engineering culture; humour grounded in observational uncertainty; scale-based exaggeration and colonial self-comparison; and overt sceptical parody. These modes tracked shifting relationships between observation, interpretation and authority, allowing newspapers to entertain speculative ideas while marking the limits of scientific credibility. At the same time, humorous treatments positioned Australian readers within a global culture of science and modernity. Comparisons with projects such as the Suez and Panama Canals, and with European and American astronomers, aligned colonial audiences with metropolitan discourse, even as local experience with land, water and scale shaped the tone of satire. We demonstrate that Australian newspapers did not passively transmit overseas ideas but actively reworked them through humour, balancing fascination with restraint. More generally, this case suggests that humour could function as a cultural strategy through which historical newspaper audiences engaged with speculative scientific claims without abandoning trust in scientific authority.

physics.hist-ph↗

arXiv2026

Searching for and characterizing halo substructures with the GALAH DR4 survey

Recent studies show that the Milky Way stellar halo is composed of populations of different origins, shaped by multiple accretion events. To better understand the formation of the Milky Way and other spiral galaxies, we characterize the chemical and kinematic properties of halo substructures using GALAH DR4 and Gaia data. We apply wavelet transforms in the space of sqrt(J_r) and azimuthal action (L_z) to identify kinematic overdensities. Stars in the detected structures are analyzed in elemental abundance space to determine their origin. We further assess contamination using the unsupervised machine-learning algorithm t-distributed stochastic neighbor embedding (t-SNE), performing chemical tagging with 15 elemental abundances. We recover five structures: the Galactic disk, the Splash, Gaia-Sausage-Enceladus (GSE), Thamnos1, and Thamnos2. GSE shows two peaks; one at sqrt(J_r) ~ 25 kpc km s^-1 is due to disk contamination, while the other above sqrt(J_r) ~ 40 kpc km s^-1 represents the cleanest GSE population. Thamnos exhibits three peaks linked to Thamnos1 and Thamnos2. Thamnos2 shows higher [alpha/Fe], iron-peak elements are enhanced in the Splash, and halo groups retain a stronger r-process signature. The multiply peaked structures suggest that the splashed disk extends beyond prograde orbits. The distinct chemo-dynamical properties of the halo groups support their extragalactic origin.

astro-ph.GA↗

arXiv2026

Marking Noon: The Time Balls and Time Flaps of the Netherlands

In the nineteenth century, the Netherlands quickly adopted the time ball -- a British innovation for maritime chronometer calibration -- in its main naval ports (Nieuwediep/Den Helder, Vlissingen, Hellevoetsluis) and commercial centres (Amsterdam, Rotterdam). A large sphere dropped from a mast at a fixed time, the device enabled ships to verify their chronometers against a standard, essential for accurate longitude determination and safe navigation. Its ready acceptance was eased by indigenous Dutch traditions. Rural communities had long used visual time signals like the sjouw on Terschelling island, a wicker ball raised on a mast to mark the lunch hour and milking time for farmers, and the lawei, a basket or sack used in the peat bogs of Friesland to regulate labourers' hours. The Dutch time-signal system was distinguished by its strong institutional backing from the country's Royal Navy, its Hydrographic Service and by professional astronomers. Among the latter, Frederik Kaiser was a pivotal figure, vehemently defending the system's accuracy and pioneering technical improvements. He successfully advocated for replacing the traditional falling ball with a system of rotating flaps, which provided a more instantaneous and reliable visual signal. Beyond their practical role, time signals became civic spectacles and symbols of Dutch scientific modernity and imperial reach. Their decline began with the electric telegraph and was finalised by wireless radio, which allowed ships to calibrate chronometers at sea.

physics.hist-ph↗

arXiv2026

Dutch Colonial Time: Time Signals in Paramaribo and the Dutch Caribbean

In the nineteenth century, the Dutch established time signals in their Atlantic colonies to synchronise maritime navigation with European standards. In Paramaribo (Suriname), a sophisticated sequence of apparatus -- including time balls, noon guns, discs and flags -- operated from 1851 until World War I. Naval officers aboard guard ships used sextants equipped with artificial horizons to determine local noon, thus integrating the colony into the global Greenwich-based cartographic system. This infrastructure was not merely technical; it became a civic ritual, with the daily noon gun structuring urban life and becoming a point of political negotiation between naval commanders and the colonial governor. In contrast, the Dutch Caribbean islands employed simpler, pragmatic systems. Curaçao used a daily time flag, a cost-effective solution suited to its climate and harbour scale, while smaller islands like Aruba and St. Eustatius relied on occasional noon guns. This diversity reflected a decentralised colonial administration that adapted technologies to local conditions and budgets. The history of these time signals reveals a process of hybrid adaptation, not simply replication of European models. They were shaped by environmental challenges, fiscal constraints and local politics, functioning simultaneously as navigational aids and civic landmarks. Their eventual decline, owing to budgetary pressures and new technologies like wireless telegraphy, underscores the fragile and negotiated nature of colonial scientific infrastructures.

physics.hist-ph↗

arXiv2026

Searching for White Dwarf Candidates Formed Through Binary evolution in Star Clusters

White dwarfs (WDs), the evolutionary endpoints of most stars, can form through both single-star and binary channels. While single-star evolutionary models enable reliable WD age estimates, binary evolution introduces interactions that can accelerate WD formation and result in a variety of exotic WDs, which may exhibit strong magnetic fields, rapid rotation, or even serve as potential gravitational wave sources. Such systems offer valuable insights into magnetic field generation, angular momentum evolution, and compact object physics. Star clusters, with their approximately coeval populations, allow precise age determination of member WDs. If a WD's total age derived from single-star evolution exceeds that of its host cluster, it likely indicates a binary origin. In this study, we use \textit{Gaia} 5D astrometry to identify 439 WD candidates in 117 open clusters, with 244 likely formed via binary evolution. We discuss the possibility of dynamical ejection for WDs meeting only 2D (proper motion space) membership criteria. Spectroscopic observations further reveal a subset with strong magnetic fields and rapid rotation, supporting their binary evolutionary origin.

astro-ph.SR↗

arXiv2025

The MALATANG survey: Dense gas distribution on sub-kiloparsec scales across the disk of M82

We present observations of HCN J=4-3 and HCO^+ J=4-3 lines obtained with the James Clerk Maxwell Telescope as part of the MALATANG survey, combined with archival HCN J=1-0 and HCO^+ J=1-0 data from the Green Bank Telescope, to study the spatial distribution and excitation conditions of dense molecular gas in the disk of M82. We detect HCN J=4-3 and HCO^+ J=4-3 emission within the central region (< 500 pc) of the galaxy, while the J=1-0 emission lines exhibit a more extended spatial distribution (> 700 pc). The dense gas shows a clear double-lobed structure in both spatial distribution and kinematics, with the HCN and HCO^+ J=4-3 lines in the southwest lobe blueshifted by ~ 40 km/s relative to the J=1-0 lines. The HCN J=4-3/1-0 and HCO^+ J=4-3/1-0 line-luminosity ratios range from 0.09 to 0.53 and from 0.14 to 0.87, respectively, with mean values of 0.18 +/- 0.04 and 0.36 +/- 0.06. The HCN ratio is lower than the typical average observed in nearby star-forming galaxies, whereas the HCO^+ ratio is comparatively higher, suggesting that the high-J HCN emission in M82 is significantly sub-thermally excited. Spatially, the peak values of the J=4-3/1-0 ratios are found in the northwest region of M82, coinciding with the galaxy-scale outflow. Elevated HCN/HCO^+ ratios are also detected in roughly the same area, potentially tracing local excitation enhancements driven by the outflow. The HCN/HCO^+ J=4-3 ratio across all detected regions ranges from 0.19 to 1.07 with a mean value of 0.41 +/- 0.11, which is significantly lower than the average J=1-0 ratio of 0.76 +/- 0.08. Both ratios are significantly lower than the average values observed in nearby star-forming galaxies, which could be related to the relatively low gas density and the presence of an extended photo-dissociation region in M82.

astro-ph.GA↗

arXiv2025

UVIT Study of the Magellanic Clouds (U-SMAC). III. Hierarchical Star Formation in the Small Magellanic Cloud Regulated by Turbulence

The Small Magellanic Cloud (SMC), a satellite galaxy of the Milky Way, is an irregular dwarf galaxy exhibiting evidence of recent and ongoing star formation. We performed a spatial clustering analysis of far-ultraviolet stars in the SMC younger than 150 Myr using data from the Ultra Violet Imaging Telescope onboard AstroSat. We identified 236 young stellar structures as surface overdensities at different significance levels. The sizes of these structures range from a few parsecs to several hundred parsecs. Their irregular morphologies are characterized by a perimeter-area dimension, derived from the projected boundaries of the young stellar structures, of Dp = 1.46 +/- 0.4. The 2D fractal dimensions obtained from, respectively, the number-size relation and the size distribution are D2 = 1.64 +/- 0.03 and D2 = 1.31 +/- 0.16. These values indicate significant lumpiness among the young stellar structures. In addition, the surface density distribution of the identified structures follows a log-normal distribution. These features are strikingly similar to those of the turbulent interstellar medium, thus supporting the scenario of hierarchical star formation regulated by supersonic turbulence.

astro-ph.GA↗

arXiv2025

The VMC Survey -- LIV. Anomalous Cepheids in the Magellanic Clouds Period-Luminosity relations in the near-infrared bands

Anomalous Cepheids (ACs) are less studied metal-poor pulsating stars ([Fe/H]<-1.5) compared to Classical Cepheids (CCs) and RR Lyrae stars. They follow distinct Period-Luminosity (PL) and Period-Wesenheit (PW) relations and pulsate in either the fundamental (F) or first overtone (1O) mode. Our goal is to assess the precision and accuracy of AC-based distances and evaluate their potential for establishing an independent distance scale. We derive new PL and PW relations for F-mode, 1O-mode, and, for the first time, combined F+1O ACs in the Magellanic Clouds. We study their wavelength dependence and apply the relations to estimate distances to Local Group stellar systems hosting ACs, while also confirming AC classifications. Our analysis is based on near-infrared time-series photometry in the Y, J, and Ks bands for about 200 ACs in the Magellanic Clouds from the VISTA survey of the Magellanic Clouds system (VMC, 2009-2018). VMC data are complemented with optical photometry from Gaia DR3 and OGLE-IV, which also provide periods and pulsation modes. Custom light-curve templates were used to derive precise intensity-averaged magnitudes for 118 ACs in the Large Magellanic Cloud (LMC) and 75 in the Small Magellanic Cloud. These data were used to derive multi-band PL and PW relations, calibrated using the geometric LMC distance from eclipsing binaries. We find that PL relation slopes increase and dispersions decrease with wavelength. Using Gaia parallaxes, we determine the LMC distance modulus and the LMC-SMC relative distance. We also confirm the AC nature of several new candidates in Galactic Globular Clusters and derive a distance modulus for the Draco dSph galaxy of 19.425+/-0.048 mag. A 0.1 mag discrepancy with RR Lyrae-based distances may reflect metallicity effects. Future spectroscopic surveys and Gaia DR4 will help refine the AC distance scale and quantify metallicity impacts.

astro-ph.SR↗

arXiv2025

Optical spectroscopic signatures of the red giant evolutionary state

Modern spectroscopic surveys output large data volumes. Theoretical models provide a means to transform the information encoded in these data to measurements of physical stellar properties. However, in detail the models are incomplete and simplified, and prohibit interpretation of the fine details in spectra. Instead, the available data provide an opportunity to use data-driven, differential analysis techniques, as a means towards understanding spectral signatures. We deploy such an analysis to examine core helium-fusing red clump (RC) and shell hydrogen-fusing red giant branch (RGB) stars, to uncover signatures of evolutionary state imprinted in optical stellar spectra. We exploit 786 pairs of RC and RGB stars from the GALAH survey, chosen to minimise spectral differences, with evolutionary state classifications from TESS and K2 asteroseismology. We report sub-percent residual, systematic spectral differences between the two classes of stars, and show that these residuals are significant compared to a reference sample of RC$-$RC and RGB$-$RGB pairs selected using the same criteria. First, we report systematic differences in the Swan ($\rm{C}_2$) band and CN bands caused by stellar evolution and a difference in mass, where RGB stars at similar stellar parameters have higher masses than RC stars. Secondly, we observe systematic differences in the line-width of the H$_α$ and H$_β$ lines caused by a difference in microturbulence, as measured by GALAH, where we measure higher microturbulence in RC stars than RGB stars. This work demonstrates the ability of large surveys to uncover the subtle spectroscopic signatures of stellar evolution using model-free, data-driven methods.

astro-ph.SR↗