701 research outputs found
Searching for the extra-tidal stars of globular clusters using high-dimensional analysis and a core particle spray code
Three-body interactions can eject stars from the core of a globular cluster,
causing them to enter the Galactic halo as extra-tidal stars. While finding
extra-tidal stars is imperative for understanding cluster evolution, connecting
isolated extra-tidal field stars back to their birth cluster is extremely
difficult. In this work, we present a new methodology consisting of
high-dimensional data analysis and a particle spray code to identify
extra-tidal stars of any Galactic globular cluster using M3 as a case study.
Using the t-Stochastic Neighbour Embedding (t-SNE) and Uniform Manifold
Approximation and Projection (UMAP) machine learning dimensionality reduction
algorithms, we first identify a set of 103 extra-tidal candidates in the APOGEE
DR17 data catalogue with chemical abundances similar to M3 stars. To confirm
each candidate's extra-tidal nature, we introduce Corespray; a new Python-based
three-body particle spray code that simulates extra-tidal stars for any
Galactic globular cluster. Using Gaia EDR3 proper motions and APOGEE DR17
radial velocities, we apply multivariate Gaussian modelling and an extreme
deconvolution to identify the extra-tidal candidates that are more likely to be
associated with a distribution of Corespray-simulated M3 extra-tidal stars than
the field. Through these methods, we identify 13 new high-probability
extra-tidal stars of M3. Future applications of Corespray will yield better
understandings of core dynamics, star formation histories and binary fractions
in globular clusters.Comment: 15 pages, 8 figures, 2 tables. Submitted to Monthly Notices of the
Royal Astronomical Societ
The dominant mechanism(s) for populating the outskirts of star clusters with neutron star binaries
It has been argued that heavy binaries composed of neutron stars (NSs) and
millisecond pulsars (MSPs) can end up in the outskirts of star clusters via an
interaction with a massive black hole (BH) binary expelling them from the core.
We argue here, however, that this mechanism will rarely account for such
observed objects. Only for primary masses 100 M and a
narrow range of orbital separations should a BH-BH binary be both dynamically
hard and produce a sufficiently low recoil velocity to retain the NS binary in
the cluster. Hence, BH binaries are in general likely to eject NSs from
clusters. We explore several alternative mechanisms that would cause NS/MSP
binaries to be observed in the outskirts of their host clusters after a Hubble
time. The most likely mechanism is a three-body interaction involving the
NS/MSP binary and a normal star. We compare to Monte Carlo simulations of
cluster evolution for the globular clusters NGC 6752 and 47 Tuc, and show that
the models not only confirm that normal three-body interactions involving all
stellar-mass objects are the dominant mechanism for putting NS/MSP binaries
into the cluster outskirts, they also reproduce the observed NS/MSP binary
radial distributions without needing to invoke the presence of a massive BH
binary. Higher central densities and an episode of core-collapse can broaden
the radial distributions of NSs/MSPs and NS/MSP binaries due to three-body
interactions, making these clusters more likely to host NSs in the cluster
outskirts.Comment: 13 pages, 7 figures, 2 tables, submitted to MNRA
The evolution of kicked stellar-mass black holes in star cluster environments - II. Rotating star clusters
In this paper, we continue our study on the evolution of black holes (BHs) that receive velocity kicks at the origin of their host star cluster potential. We now focus on BHs in rotating clusters that receive a range of kick velocities in different directions with respect to the rotation axis. We perform N-body simulations to calculate the trajectories of the kicked BHs and develop an analytic framework to study their motion as a function of the host cluster and the kick itself. Our simulations indicate that for a BH that is kicked outside of the cluster's core, as its orbit decays in a rotating cluster the BH will quickly gain angular momentum as it interacts with stars with high rotational frequencies. Once the BH decays to the point where its orbital frequency equals that of local stars, its orbit will be circular and dynamical friction becomes ineffective since local stars will have low relative velocities. After circularization, the BH's orbit decays on a longer time-scale than if the host cluster was not rotating. Hence BHs in rotating clusters will have longer orbital decay times. The time-scale for orbit circularization depends strongly on the cluster's rotation rate and the initial kick velocity, with kicked BHs in slowly rotating clusters being able to decay into the core before circularization occurs. The implication of the circularization phase is that the probability of a BH undergoing a tidal capture event increases, possibly aiding in the formation of binaries and high-mass BHs
Comparative Genomics of Carriage and Disease Isolates of Streptococcus pneumoniae Serotype 22F Reveals Lineage-Specific Divergence and Niche Adaptation
Streptococcus pneumoniae is a major cause of meningitis, sepsis, and pneumonia worldwide. Pneumococcal conjugate vaccines have been part of the United Kingdom’s childhood immunization program since 2006 and have significantly reduced the incidence of disease due to vaccine efficacy in reducing carriage in the population. Here we isolated two clones of 22F (an emerging serotype of clinical concern, multilocus sequence types 433 and 698) and conducted comparative genomic analysis on four isolates, paired by Sequence Type (ST) with one of each pair being derived from carriage and the other disease (sepsis). The most compelling observation was of nonsynonymous mutations in pgdA, encoding peptidoglycan N-acetylglucosamine deacetylase A, which was found in the carriage isolates of both ST433 and 698. Deacetylation of pneumococcal peptidoglycan is known to enable resistance to lysozyme upon invasion. Althought no other clear genotypic signatures related to disease or carriage could be determined, additional intriguing comparisons between the two STs were possible. These include the presence of an intact prophage, in addition to numerous additional phage insertions, within the carriage isolate of ST433. Contrasting gene repertoires related to virulence and colonization, including bacteriocins, lantibiotics, and toxin-–antitoxin systems, were also observed
The polaroid image as photo-object
This article is part of a larger project on the cultural history of Polaroid photography and draws on research done at the Polaroid Corporate archive at Harvard and at the Polaroid company itself. It identifies two cultural practices engendered by Polaroid photography, which, at the point of its extinction, has briefly flared into visibility again. It argues that these practices are mistaken as novel but are in fact rediscoveries of practices that stretch back as many as five decades. The first section identifies Polaroid image-making as a photographic equivalent of what Tom Gunning calls the ‘cinema of attractions’. That is, the emphasis in its use is on the display of photographic technologies rather than the resultant image. Equally, the common practice, in both fine art and vernacular circles, of making composite pictures with Polaroid prints, draws attention from image content and redirects it to the photo as object
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