Richard de Grijs
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View article: The GALAH survey: Improving chemical abundances using star clusters
The GALAH survey: Improving chemical abundances using star clusters Open
Large spectroscopic surveys aim to consistently compute stellar parameters of very diverse stars, while minimizing systematic errors. We explore the use of stellar clusters as benchmarks to verify the precision of spectroscopic parameters …
UVIT Study of the Magellanic Clouds (U-SMAC). III. Hierarchical Star Formation in the Small Magellanic Cloud Regulated by Turbulence Open
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 yo…
View article: The VMC survey
The VMC survey Open
Context. The study of the internal kinematics of galaxies provides insights into their past evolution, current dynamics, and future trajectory. The Large Magellanic Cloud (LMC), as the largest and one of the nearest satellite galaxies of t…
View article: The MALATANG survey: Dense gas distribution on sub-kiloparsec scales across the disk of M82
The MALATANG survey: Dense gas distribution on sub-kiloparsec scales across the disk of M82 Open
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 stud…
View article: The VMC Survey
The VMC Survey Open
Context. Anomalous Cepheids (ACs) are pulsating variable stars, and are less studied compared to the well-known Classical Cepheids (CCs) and RR Lyrae stars. The ACs are metal poor ([Fe/H] < 1.5) and follow distinct period-luminosity (PL) a…
View article: The VMC survey
The VMC survey Open
Context. The near-infrared YJK s Visual and Infrared Survey Telescope for Astronomy (VISTA) survey of the Magellanic Clouds (VMC) is complete, along with data from additional programmes contributing to the enhancement of its quality over t…
UVIT Study of the Magellanic Clouds (U-SMAC). III. Hierarchical Star Formation in the Small Magellanic Cloud Regulated by Turbulence Open
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 yo…
View article: Optical spectroscopic signatures of the red giant evolutionary state
Optical spectroscopic signatures of the red giant evolutionary state Open
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…
View article: Optical spectroscopic signatures of the red giant evolutionary state
Optical spectroscopic signatures of the red giant evolutionary state Open
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 …
Photometric activity cycles in fast-rotating stars: revisiting the reality of stellar activity cycle branches Open
We aim to detect activity cycles in young main-sequence stars, analogous to the 11-yr solar cycle, using combined photometric survey data. This research will enhance our understanding of how cycle periods relate to rotation rates in fast-r…
View article: The HASHTAG project II. Giant molecular cloud properties across the M31 disc
The HASHTAG project II. Giant molecular cloud properties across the M31 disc Open
We present a study of giant molecular cloud (GMC) properties in the Andromeda galaxy (M31) using CO(3-2) data from the James Clerk Maxwell Telescope (JCMT) in selected regions across the disc and in the nuclear ring, and comparing them wit…
View article: The GALAH Survey: Stellar parameters and abundances for 800 000 <i>Gaia</i> RVS spectra using GALAH DR4 and <i>The Cannon</i>
The GALAH Survey: Stellar parameters and abundances for 800 000 <i>Gaia</i> RVS spectra using GALAH DR4 and <i>The Cannon</i> Open
Analysing stellar parameters and abundances from nearly one million Gaia Data Release 3 (DR3) Radial Velocity Spectrometer (RVS) spectra poses challenges due to the limited spectral coverage (restricted to the infrared Ca ii triplet) and v…
View article: The VMC Survey – LI. Classifying extragalactic sources using a probabilistic random forest supervised machine learning algorithm
The VMC Survey – LI. Classifying extragalactic sources using a probabilistic random forest supervised machine learning algorithm Open
We used a supervised machine learning algorithm (probabilistic random forest) to classify ∼130 million sources in the VISTA Survey of the Magellanic Clouds (VMC). We used multi-wavelength photometry from optical to far-infrared as features…
View article: The VMC Survey : LI. Classifying extragalactic sources using a probabilistic random forest supervised machine learning algorithm
The VMC Survey : LI. Classifying extragalactic sources using a probabilistic random forest supervised machine learning algorithm Open
We used a supervised machine learning algorithm (probabilistic random forest) to classify ~130 million sources in the VISTA Survey of the Magellanic Clouds (VMC). We used multi-wavelength photometry from optical to far-infrared as features…
View article: The GALAH survey: Improving chemical abundances using star clusters
The GALAH survey: Improving chemical abundances using star clusters Open
Large spectroscopic surveys aim to consistently compute stellar parameters of very diverse stars while minimizing systematic errors. We explore the use of stellar clusters as benchmarks to verify the precision of spectroscopic parameters i…
View article: The GALAH survey: Data release 4
The GALAH survey: Data release 4 Open
The stars of the Milky Way carry the chemical history of our Galaxy in their atmospheres as they journey through its vast expanse. Like barcodes, we can extract the chemical fingerprints of stars from high-resolution spectroscopy. The four…
View article: An automated method to detect and characterise semi-resolved star clusters
An automated method to detect and characterise semi-resolved star clusters Open
We present a novel method for automatically detecting and characterising semi-resolved star clusters: clusters where the observational point-spread function (PSF) is smaller than the cluster's radius, but larger than the separations betwee…
View article: The GALAH Survey: Stellar parameters and abundances for 800,000 Gaia RVS spectra using GALAH DR4 and The Cannon
The GALAH Survey: Stellar parameters and abundances for 800,000 Gaia RVS spectra using GALAH DR4 and The Cannon Open
Analysing stellar parameters and abundances from nearly one million Gaia Data Release 3 (DR3) Radial Velocity Spectrometer (RVS) spectra poses challenges due to the limited spectral coverage (restricted to the infrared Ca II triplet) and v…
All roads lead to (New) Rome: Byzantine astronomy and geography in a rapidly changing world Open
During the first few centuries CE, the centre of the known world gradually shifted from Alexandria to Constantinople. Combined with a societal shift from pagan beliefs to Christian doctrines, Antiquity gave way to the Byzantine era. While …
View article: The GALAH Survey: Data Release 4
The GALAH Survey: Data Release 4 Open
The stars of the Milky Way carry the chemical history of our Galaxy in their atmospheres as they journey through its vast expanse. Like barcodes, we can extract the chemical fingerprints of stars from high-resolution spectroscopy. The four…
The Origin of Young Stellar Populations in NGC 1783: Accretion of External Stars Open
The presence of young stellar populations in the Large Magellanic Cloud cluster NGC 1783 has caught significant attention, with suggestions ranging from it being a genuine secondary stellar generation to a population of blue straggler star…
View article: The GALAH survey: tracing the Milky Way’s formation and evolution through RR Lyrae stars
The GALAH survey: tracing the Milky Way’s formation and evolution through RR Lyrae stars Open
Stellar mergers and accretion events have been crucial in shaping the evolution of the Milky Way (MW). These events have been dynamically identified and chemically characterized using red giants and main-sequence stars. RR Lyrae (RRL) vari…
View article: New quasars behind the Magellanic Clouds
New quasars behind the Magellanic Clouds Open
Context. Quasi-stellar objects (QSOs) are a basis for an absolute reference system for astrometric studies. A system like this at the far side of nearby galaxies is required to facilitate measuring of the proper motions of these galaxies. …
View article: New quasars behind the Magellanic Clouds. II. Spectroscopic confirmation of 136 near-infrared selected candidates
New quasars behind the Magellanic Clouds. II. Spectroscopic confirmation of 136 near-infrared selected candidates Open
Quasi-stellar objects (QSOs) are a basis for an absolute reference system for astrometric studies. There is a need for creating such system behind nearby galaxies, to facilitate the measuring of the proper motions of these galaxies. Howeve…
View article: The GALAH survey: elemental abundances in open clusters using joint effective temperature and surface gravity photometric priors
The GALAH survey: elemental abundances in open clusters using joint effective temperature and surface gravity photometric priors Open
The ability to measure precise and accurate stellar effective temperatures (Teff) and surface gravities (log (g)) is essential in determining accurate and precise abundances of chemical elements in stars. Measuring log (g) from isochrones …
View article: The GALAH survey: Elemental abundances in open clusters using joint effective temperature and surface gravity photometric priors
The GALAH survey: Elemental abundances in open clusters using joint effective temperature and surface gravity photometric priors Open
The ability to measure precise and accurate stellar effective temperatures ($T_{\rm{eff}}$) and surface gravities ($\log(g)$) is essential in determining accurate and precise abundances of chemical elements in stars. Measuring $\log(g)$ fr…
View article: The VMC survey
The VMC survey Open
Context. Type II Cepheids (T2Cs) are the less frequently used counterparts of classical or type I Cepheids (CCs) which provide the primary calibration of the distance ladder for measuring the Hubble constant in the local Universe. In the e…
View article: The VMC Survey -- L. Type II Cepheids in the Magellanic Clouds
The VMC Survey -- L. Type II Cepheids in the Magellanic Clouds Open
Type II Cepheids (T2C) are less frequently used counterparts of classical Cepheids which provide the primary calibration of the distance ladder for measuring $H_0$ in the local Universe. In the era of the Hubble Tension, T2C variables with…
Extended main sequences in star clusters Open
Extended main sequences (eMSs) and extended main-sequence turn-offs (eMSTOs) are fascinating phenomena that are routinely observed in star clusters. These phenomena strongly challenge the current canonical "simple stellar population" pictu…
DIFFERENT DYNAMICAL AGES FOR THE TWO YOUNG AND COEVAL LMC STAR CLUSTERS, NGC 1805 AND NGC 1818, IMPRINTED ON THEIR BINARY POPULATIONS Open
The two Large Magellanic Cloud star clusters, NGC 1805 and NGC 1818, are approximately the same chronological age (~30 Myr), but show different radial trends in binary frequency. The F-type stars (1.3–2.2 M⊙) in NGC 1818 have a binary freq…