bluuebunny/crossref_metadata_2025_split huggingface dataset:
A linear stability study of stellar rotating spheres
Authors: Rozier Simon , Fouvry Jean-Baptiste , Breen Philip G. , Varri Anna Lisa , Pichon Christophe , Heggie Douglas C. 
Published: March 2020

AbstractRecent observations of globular clusters imposed major revisions to the previous paradigm, in which they were considered to be isotropic in velocity space and non-rotating. However, the theory of collisionless spheroids with some kinematic richness has seldom been studied. We present here a first step in this direction, owing to new results regarding the linear stability of rotating Plummer spheres, with varying anisotropy in velocity space and total amount of angular momentum. We extend the well-known radial orbit instability to rotating systems, and discover a new regime of instability in fast rotating, tangentially anisotropic systems.
Black holes and rotation: Internal kinematics of star clusters with MUSE
Authors: Kamann Sebastian 
Published: March 2020

AbstractOver the last decade, our abilities to observe the internal kinematics of star clusters have drastically increased. Where a few years back only small numbers of bright stars with radial velocity measurements were available, we can nowadays study the three-dimensional motions of large stellar samples, thanks to the combined datasets gathered by state-of-art spectrographs and astrometric satellites. In this work, I summarise the contribution of integral-field spectrographs, in particular MUSE, to this paradigm change. Using dedicated software tools, we were able to overcome a fundamental limitation of spectroscopy and advance to the crowded cluster centres. This allowed us to study the central kinematics in unprecedented detail and to start uncovering the populations of black holes that reside in massive star clusters.
3 things they don’t tell you about star clusters
Authors: Renaud Florent 
Published: March 2020

AbstractDense stellar systems in general and star clusters in particular have recently regained the interest of the extragalactic and even cosmology communities, due to the role they could play as actors and probes of re-ionization, galactic archeology and the dark matter content of galaxies, among many others. In the era of the exploitation and the preparation of large stellar surveys (Gaia, APOGEE, 4MOST, WEAVE), of the detection of gravitational waves mostly originating from dense regions like the cores of clusters (Ligo, LISA), and in an always more holistic view of galaxy formation (HARMONI, Euclid, LSST†), a complete theory on the formation and evolution of clusters is needed to interpret the on-going and forthcoming data avalanche. In this context, the community carries an effort to model the aspects of star cluster formation and evolution in galactic and even cosmological context. However, it is not always easy to understand the caveats and the shortcuts taken in theories and simulations, and their implications on the conclusions drawn. I take the opportunity of this document to highlight three of these topics and discuss why some shortcuts taken by the community are or could be misleading.
RR Lyrae analysis in the Local Group globular clusters and dwarf galaxies
Authors: Benkortem Saruta , Tanakul Nahathai , Suwannajak Chutipong 
Published: March 2020

AbstractRR Lyrae variables are powerful tools to study their host stellar populations. Globular clusters and dwarf galaxies are old and usually host this type of variables. With a growing number of low luminosity objects discovered in the halo of the Milky Way, classifying stars clusters and galaxies has become more challenging. In this study, we examine the properties of RR Lyrae stars in globular clusters and dwarf galaxies in the Local Group. We construct a catalog of RR Lyrae variables in the Local Group globular clusters and dwarf galaxies from previously published data and compare the properties of RR Lyrae variables between those two types of stellar systems. Our goal is to search for a physical difference in the properties of RR Lyrae variables in those two classes of stellar systems. We also analyze the global trend of RRLs in these systems to understand more about their formation and evolution history.
Detecting the dark matter halos with star clusters in M31/M33 with PFS, SDSS-V and LAMOST
Authors: Fan Zhou , Haysahi Kohei , Zhao Jingkun , Zhao Gang 
Published: March 2020

AbstractSince a great number of star stream and substructures near M31/M33 have been discovered in Pan-Andromeda Archaeological Survey (PAndAS) and variations of star stream density may trace the dark matter sub-halos, it is good opportunity to study the dark matter sub-halos with the star streams. Further it has been proved that dozens of halo star clusters have the relations with the star stream. As Prime Focus Spectroscopy (PFS) of the 8.2-m Subaru telescope have the powerful ability (I ∼ 22.3 mag) to observe ∼ 2400 objects at a time, it can be used to observe the giant star streams, faint halo star clusters and dwarf galaxies, which provides excellent opportunity to investigate the sub-halos of M31. In addition, we are involved with the Local Volume Mapper (LVM) of SDSS-V program, which may also provide more informations for the star clusters of the Local Group, especially for M31. Finally since we have done series of work with Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), we will continue the spectroscopic observations for more star clusters and giant stars of M31/M33.
Abundance of zirconium in the atmospheres of red giants in Galactic globular cluster 47 Tuc
Authors: Kolomiecas Edgaras , Dobrovolskas Vidas , Kučinskas Arūnas 
Published: March 2020

AbstractWe determined zirconium abundance in the atmospheres of 327 red giant branch (RGB) stars in the globular cluster 47 Tuc. The 1D LTE abundances were obtained from the archival VLT GIRAFFE spectra, using 1D hydrostaticATLAS9 stellar model atmospheres and synthetic Zr I line profiles computed with theSYNTHE package. The average zirconium abundance determined in the sample of RGB stars, 〈[Zr/Fe]〉 = +0.38 ± 0.12, agrees well with zirconium abundances obtained at this metallicity in the Galactic field stars, as well as with those observed in other Galactic globular clusters.
Formation and evolution of globular clusters in cosmological simulations
Authors: Li Hui , Gnedin Oleg 
Published: March 2020

AbstractIn a series of three papers, we introduced a novel cluster formation model that describes the formation, growth, and disruption of star clusters in high-resolution cosmological simulations. We tested this model on a Milky Way-sized galaxy and found that various properties of young massive clusters, such as the mass function and formation efficiency, are consistent with observations in the local universe. Interestingly, most massive clusters – globular cluster candidates – are preferentially formed during major merger events. We follow the dynamical evolution of clusters in the galactic tidal field. Due to tidal disruption, the cluster mass function evolves from initial power law to a peaked shape. The surviving clusters at z = 0 show a broad range of metallicity [Fe/H] from -3 to -0.5. A robust prediction of the model is the age–metallicity relation, in which metal-rich clusters are systematically younger than metal-poor clusters by up to 3 Gyr.
Multiple populations in globular clusters: New insights from chemical evolution and horizontal-branch models
Authors: Lee Young-Wook , Kim Jenny J. , Jang Sohee , Chung Chul , Lim Dongwook , Hong Seungsoo 
Published: March 2020

AbstractIn order to investigate the origin of multiple populations in globular clusters (GCs), we have constructed new chemical evolution models for proto-GCs where the supernova blast waves undergo blowout without expelling the ambient gas. Chemical enrichments in our models are then dictated by the winds of massive stars together with the asymptotic-giant-branch stars ejecta. We find that the observed Na-O anti-correlation can be reproduced when multiple episodes of starburst and enrichment are allowed to continue in proto-GCs. The “mass budget problem” is mostly resolved by our models without ad-hoc assumptions on star formation efficiency, initial mass function, and significant loss of first-generation stars. Interestingly, ages and chemical abundances predicted by this chemical evolution model are in good agreements with those independently obtained from our stellar evolution model for the horizontal-branch. We also discuss observational evidence for the GC-like multiple populations in the Milky Way bulge.
Young massive clusters in Arp 299
Authors: Randriamanakoto Zara , Väisänen Petri 
Published: March 2020

AbstractBecause of their young ages and compact densities, young massive star clusters (YMCs) are widely considered as potential proto-globular clusters. They are ubiquitous in environments with ongoing star formation activity such as interacting luminous infrared galaxies. To determine the galactic environmental effects on the star cluster formation and evolution, we study the YMC population of Arp 299 (NGC 3690E/NGC 3690W) using data taken with the HST WFC3/UVIS camera. By fitting the multiband photometry with the Yggdrasil models, we derive the star cluster masses, ages and extinction. While the cluster mass-galactocentric radius relation of NGC 3690E indicates that there could be an influence of the gas density distribution on the cluster formation, the age distribution of the western component suggests that YMCs in that galaxy endure stronger disruption mechanisms. With a cluster formation efficiency of 19 percent, star formation happening in bound clusters in Arp 299 is 3–5 times higher than that of a typical normal spiral.
Multiple bursts of star formation in young star clusters: The case of the Orion Nebula Cluster
Authors: Jerabkova Tereza 
Published: March 2020

AbstractYoung star clusters (YSCs) with resolved stellar populations are well suited for studying star-cluster formation. In most cases, the (pre-main-sequence) stellar populations found in the YSCs are coeval with an intrinsic age spread of up to 1Myr. Such observations can be understood as the YSCs having formed in one burst, which star formation was truncated by stellar feedback. The recent discovery that the colour-magnitude diagram of the Orion Nebula Clusters (ONC) contains three well defined age-separated populations appears to shatter this model. The implication is that the ONC formed in three bursts, with star formation still on-going in the last burst. We present new observational results focusing on the three populations in the ONC using OmegaCAM photometry and Gaia DR2 measurements. We also describe a theoretical model which may explain these observations by an interplay between stellar feedback and cluster dynamics.
Spectroscopic studies of stellar populations in globular clusters and field stars: Implications for globular cluster and Milky Way halo formation
Authors: Gratton Raffaele 
Published: March 2020

AbstractWe review spectroscopic results concerning multiple stellar populations in globular clusters. The cluster initial mass is the most important parameter determining the fraction of second generation stars. The threshold for the onset of the multiple population phenomenon is 1–3×105 M⊙. Nucleosynthesis is influenced by metallicity: Na/O and Mg/Al anti-correlations are more extended in metal-poor than in metal-rich clusters. Massive clusters are more complex systems than the smaller ones, with several populations characterized by different chemical compositions. The high Li abundance observed in the intermediate second generation stars strongly favours intermediate mass AGB stars as polluters for this class of stars; however, it is well possible that the polluters of extreme second generation stars, that often do not have measurable Li, may be fast rotating massive stars or super-massive stars. The mass budget factor should be a function of the cluster mass, and needs to be large only in massive clusters.
Intra-cluster GC-LMXB in the Fornax galaxy cluster
Authors: Riccio G. , Paolillo M. , D’Abrusco R. , Cantiello M. , Jin X. , Li Z. , Venhola A. , D’Ago G. , Puzia Thomas H. , Iodice E. , Pota V. , Napolitano N. , Hilker M. , Mieske S. , Spavone M. , Peletier R. , Eigenthaler P. 
Published: March 2020

AbstractThe formation of Low mass X-ray binaries (LMXB) is favored within dense stellar systems such as Globular Clusters (GCs). The connection between LMXB and Globular Clusters has been extensively studied in the literature, but these studies have always been restricted to the innermost regions of galaxies. We present a study of LMXB in GCs within the central 1.5 deg2 of the Fornax cluster with the aim of confirming the existence of a population of LMXB in intra-cluster GCs and understand if their properties are related to the host GCs, to the environment or/and to different formation channels.
A deep view into the nucleus of the Sagittarius dwarf spheroidal galaxy: M54
Authors: Alfaro-Cuello M. , Kacharov N. , Neumayer N. , Mastrobuono-Battisti A. , Lützgendorf N. , Seth Anil C. , Böker T. , Kamann S. , Leaman R. , van de Ven G. , Bianchini P. , Watkins L. L. , Lyubenova M. 
Published: March 2020

AbstractNuclear star clusters hosted by dwarf galaxies exhibit similar characteristics to high-mass, metal complex globular clusters. This type of globular clusters could, therefore, be former nuclei from accreted galaxies. M54 resides in the photometric center of the Sagittarius dwarf galaxy, at a distance where resolving stars is possible. M54 offers the opportunity to study a nucleus before the stripping of their host by the tidal field effects of the Milky Way. We use a MUSE data set to perform a detailed analysis of over 6600 stars. We characterize the stars by metallicity, age, and kinematics, identifying the presence of three stellar populations: a young metal-rich (YMR), an intermediate-age metal-rich (IMR), and an old metal-poor (OMP). The evidence suggests that the OMP population is the result of accretion of globular clusters in the center of the host, while the YMR population was born in-situ in the center of the OMP population.
The contribution of Globular Clusters to the stellar halo using APOGEE and GAIA
Authors: Horta Danny , Ted Mackereth J. , Schiavon Ricardo P. ,   SDSS-IV/APOGEE Collaboration
Published: March 2020

AbstractOver the last decade, much of the key questions in Galactic Archaeology have been asnwered by studying the Milky Way’s globular cluster (GC) system. Following on this, it has been shown that a substantial fraction of the Milky Way’s stellar halo field arises from GC dissolution. In this work, we make use of the latest data release fromn the APOGEE survey to study GC dissolution ratios in different spatial regions of the Galaxy. Our results will allow us to constrain many astrophysical questions, such as: the origin of N-Rich stars, the mass contribution from GCs to the stellar halo of the Galaxy, the origin of the Galactic GC system and the mass assembly of the Milky Way.
X-ray sources in Galactic globular clusters and old open clusters
Authors: van den Berg Maureen 
Published: March 2020

AbstractThe features and make up of the population of X-ray sources in Galactic star clusters reflect the properties of the underlying stellar environment. Cluster age, mass, stellar encounter rate, binary frequency, metallicity, and maybe other properties as well, determine to what extent we can expect a contribution to the cluster X-ray emission from low-mass X-ray binaries, millisecond pulsars, cataclysmic variables, and magnetically active binaries. Sensitive X-ray observations withXMM-Newton and certainlyChandra have yielded new insights into the nature of individual sources and the effects of dynamical encounters. They have also provided a new perspective on the collective X-ray properties of clusters, in which the X-ray emissivities of globular clusters and old open clusters can be compared to each other and to those of other environments. I will review our current understanding of cluster X-ray sources, focusing on star clusters older than about 1 Gyr, illustrated with recent results.
Self‐Consistent Ice Mass Balance and Regional Sea Level From Time‐Variable Gravity
Authors: Sutterley Tyler C. , Velicogna Isabella , Hsu Chia‐Wei 
Published: March 2020

AbstractMeasurements of time‐variable gravity from the Gravity Recovery and Climate Experiment (GRACE) and the GRACE Follow‐on (GRACE‐FO) missions are an invaluable tool for monitoring changes in the mass of the Earth's glaciated regions. We improve upon estimates of glacier and ice sheet mass balance from time‐variable gravity by including instantaneous spatiotemporal variations in sea level. Here, a least squares mascon technique is combined with solutions to the sea level equation to iteratively correct the GRACE/GRACE‐FO data for the induced sea level response on a monthly basis. We find that variations in regional sea level affect ice sheet mass balance estimates in Greenland by approximately 4% and in Antarctic by approximately 5%. Since 2002, the Greenland ice sheet has been losing mass at an average rate of 263 ± 23 Gt/yr, and the Antarctic ice sheet has been losing mass at average rates between 90 ± 52 and 122 ± 53 Gt/yr depending on the rate of glacial isostatic adjustment. The mass losses from both ice sheets represent an increase of 15.6 ± 2.0 mm to global mean sea levels since 2002.
Global K‐Pg Layer Deposited From a Dust Cloud
Authors: Artemieva Natalia , Morgan Joanna 
Published: March 2020

AbstractAlthough it is widely agreed that the distal K‐Pg clay layer contains ejecta from the Chicxulub impact site, no current models can explain how these ejecta travel from the impact site around the globe. A widely accepted hypothesis is that impact spherules and shocked minerals in the layer were ejected from an expanding impact plume and traveled to their final destination on a ballistic path. Shocked minerals, however, are ejected at too low a velocity to reach distal sites, and plausible ballistic ejection models cannot explain the observed ejecta distribution. Using a suite of numerical simulations, we find that intense interactions between the ejecta curtain and atmosphere generate a fast‐moving dust cloud traveling at speeds of a few kilometers per second, which carries a substantial fraction of ejecta, including shocked minerals, to distal sites. We conclude that ejecta curtain material must make a major contribution to the formation of the distal K‐Pg layer.
Comparing the Properties of ICME‐Induced Forbush Decreases at Earth and Mars
Authors: Freiherr von Forstner Johan L. , Guo Jingnan , Wimmer‐Schweingruber Robert F. , Dumbović Mateja , Janvier Miho , Démoulin Pascal , Veronig Astrid , Temmer Manuela , Papaioannou Athanasios , Dasso Sergio , Hassler Donald M. , Zeitlin Cary J. 
Published: March 2020

AbstractForbush decreases (FDs), which are short‐term drops in the flux of galactic cosmic rays, are caused by the shielding from strong and/or turbulent magnetic structures in the solar wind, especially interplanetary coronal mass ejections (ICMEs) and their associated shocks, as well as corotating interaction regions. Such events can be observed at Earth, for example, using neutron monitors, and also at many other locations in the solar system, such as on the surface of Mars with the Radiation Assessment Detector instrument onboard Mars Science Laboratory. They are often used as a proxy for detecting the arrival of ICMEs or corotating interaction regions, especially when sufficient in situ solar wind measurements are not available. We compare the properties of FDs observed at Earth and Mars, focusing on events produced by ICMEs. We find that FDs at both locations show a correlation between their total amplitude and the maximum hourly decrease, but with different proportionality factors. We explain this difference using theoretical modeling approaches and suggest that it is related to the size increase of ICMEs, and in particular their sheath regions, en route from Earth to Mars. From the FD data, we can derive the sheath broadening factor to be between about 1.5 and 1.9, agreeing with our theoretical considerations. This factor is also in line with previous measurements of the sheath evolution closer to the Sun.
Sea Surface Kinetic Energy as a Proxy for Phytoplankton Light Limitation in the Summer Pelagic Southern Ocean
Authors: Gradone J. C. , Oliver M. J. , Davies A. R. , Moffat C. , Irwin A. 
Published: March 2020

AbstractThe pelagic Southern Ocean is a high‐nutrient, low‐chlorophyll ecosystem. Here, phytoplankton growth is colimited by iron supply and light availability. This creates a general expectation that when light is available in the austral summer (shallow mixing depths), phytoplankton concentrations may be high or low depending on the delivery of iron to the surface layer. When light is not adequate (deep mixing depths), phytoplankton concentrations will likely be low, even if iron is available. Here we show that low surface kinetic energy behaves like a necessary but not sufficient condition for high chlorophyll concentrations. In high kinetic energy conditions, high chlorophyll concentrations are rare. Conversely, under low kinetic energy conditions, both high and low chlorophyll concentrations were observed. We show that higher kinetic energy conditions are related to deeper mixed layers, which is likely a proxy for local light conditions. Probabilistic models of chlorophyll based on surface kinetic energy were able to describe 30% of the spatial variability in monthly chlorophyll climatologies. This means that local light availability, proxied by mixing through kinetic energy, significantly shapes the spatial distribution of chlorophyll in the Southern Ocean. We suggest that regions with consistently higher kinetic energy may not be as sensitive to iron inputs compared to historic iron addition experiments, which were conducted in low surface kinetic energy conditions.
Dynamical Downscaling of CO2 in 2016 Over the Contiguous United States Using WRF‐VPRM, a Weather‐Biosphere‐Online‐Coupled Model
Authors: Hu Xiao‐Ming , Crowell Sean , Wang Qingyu , Zhang Yao , Davis Kenneth J. , Xue Ming , Xiao Xiangming , Moore Berrien , Wu Xiaocui , Choi Yonghoon , DiGangi Joshua P. 
Published: March 2020

AbstractEcosystem function (particularly CO2 fluxes and the subsequent atmospheric transport), synoptic‐scale weather (e.g., midlatitude cyclones), and interactions between ecosystems and the atmosphere can be investigated using a weather‐biosphere‐online‐coupled model. The Vegetation Photosynthesis and Respiration Model (VPRM) was coupled with the Weather Research and Forecasting (WRF) model in 2008 to simulate “weather‐aware” biospheric CO2 fluxes and subsequent transport and dispersion. The ability of the coupled WRF‐VPRM modeling system to simulate the CO2 structures within midlatitude cyclones, however, has not been evaluated due to the lack of data within these weather systems. In this study, VPRM parameters previously calibrated off‐line using eddy covariance tower data over North America are implemented into WRF‐VPRM. The updated WRF‐VPRM is then used to simulate spatiotemporal variations of CO2 over the contiguous United States at a horizontal grid spacing of 12 km for 2016 using an optimized downscaling configuration. The downscaled fields are evaluated using remotely sensed data from the Orbiting Carbon Observatory‐2, Total Carbon Column Observing Network, and in situ aircraft measurements from Atmospheric Carbon and Transport‐America missions. Evaluations show that WRF‐VPRM captures the monthly variation of column‐averaged CO2 concentrations (XCO2) and episodic variations associated with frontal passages. The downscaling also successfully captures the horizontal CO2 gradients across fronts and vertical CO2 contrast between the boundary layer and the free troposphere. WRF‐VPRM modeling results indicate that from May to September, biogenic fluxes dominate variability in XCO2 over most of the contiguous United States, except over a few metropolitan areas such as Los Angeles.