176 research outputs found
Exotica in the Globular Cluster M4, Studied with Chandra, HST, and the VLA
No full textUsing the Hubble Ultraviolet Globular Cluster Survey (HUGS) and additional
HST archival data, we have carried out a search for optical counterparts to the
low-luminosity Chandra X-ray sources in the globular cluster M4 (NGC 6121). We
have also searched for optical or X-ray counterparts to radio sources detected
by the VLA. We find 24 new confident optical counterparts to Chandra sources
for a total of 40, including the 16 previously identified. Of the 24 new
identifications, 18 are stellar coronal X-ray sources (active binaries, ABs),
the majority located along the binary sequence in a V-I colour-magnitude
diagram and generally showing an H-alpha excess. In addition to confirming the
previously detected cataclysmic variable (CV, CX4), we identify one confident
new CV (CX76), and two candidates (CX81 and CX101). One MSP is known in M4
(CX12), and another strong candidate has been suggested (CX1); we identify some
possible MSP candidates among optical and radio sources, such as VLA20, which
appears to have a white dwarf counterpart. One X-ray source with a sub-subgiant
optical counterpart and a flat radio spectrum (CX8, VLA31) is particularly
mysterious. The radial distribution of X-ray sources suggests a relaxed
population of average mass ~ 1.2 - 1.5 Msun. Comparing the numbers of ABs,
MSPs, and CVs in M4 with other clusters indicates that AB numbers are
proportional to cluster mass (primordial population), MSPs to stellar encounter
rate (dynamically formed population), while CVs seem to be produced both
primordially and dynamically.Comment: 30 pages, 12 figures, 2 pages of supplementary material containing
finding chart
Searching for exotic object companions in the dense core of NGC 362
No full textThe dense cores of globular clusters (GCs) are efficient environments for the production of exotic stellar populations, including millisecond pulsars (MSPs), low-mass X-ray binaries (LMXBs), and cataclysmic variables (CVs). Most of these objects likely form through two- and three-body interactions and are useful tracers of the cluster’s dynamical evolution. In this work, we explore the exotic object population in the galactic GC NGC 362, searching for the optical counterpart of 33 X-ray sources identified within 1′ from the cluster centre. To this end, we exploited a large Hubble Space Telescope dataset obtained in eight different epochs and covering a wavelength range from the near UV to the optical I band. To identify the most promising counterparts, we followed a multi-step analysis based on four main ingredients, namely, positional coincidence, position in the colour–magnitude diagrams, Hα excess, and photometric variability. In addition, we complemented the photometric analysis with spectroscopic information coming from the analysis of MUSE radial velocity curves. Thanks to this multi-diagnostic approach, we were able to identify 28 high-confidence optical counterparts, including several candidate MSPs, active binaries, and CVs. The most intriguing counterparts include a candidate black widow system, an eclipsing binary blue straggler, and a system in outburst, potentially representing either an LMXB or a nova eruption from a CV. The candidate MSPs proposed in this work will contribute to ongoing radio analyses with MeerKAT for the identification and detailed study of MSPs in NGC 362
Limited Proteolysis in Microorganisms
No full textPhyllis Braun (with R.A. Calderone) is a contributing author, Proteolytic regulation of chitin synthetase in hyphal and yeast forms of Candida albicans , pp. 135-138.https://digitalcommons.fairfield.edu/biology-books/1010/thumbnail.jp
Communography in Phyllis Naidoo’s “Charlie and Jo”
No full textPhyllis Naidoo’s Footprints beyond Grey Street (2007) adjusts conventional boundaries of the autobiographical genre: it is written by Naidoo but appears not to be principally concerned with the author’s life. It is written largely about her comrades in the African National Congress who were in exile in African countries. Of the stories in Naidoo’s “autobiography”, “Charlie and Jo” in particular epitomises the absence of the author: a stylistic and generic anomaly which merits particular attention and thus forms the focus of this article. This memory-tale of social recollection evidences autobiographical self-displacement: the privileging of collective memory as opposed to an individual’s nostalgic journey towards self-definition. This foregrounding of a collective identity has been identified and termed communography in the writings of comparable political groups such as the Irish Republican Army.
Opsomming
Phyllis Naidoo se Footprints beyond Grey Street (2007) verskuif die konvensionele grense van die outobiografie-genre: dit is deur Naidoo geskryf, maar dit kom voor asof dit nie primêr met die skrywer se lewe gemoeid is nie. Dit handel grotendeels oor haar comrades in die African National Congress wat in ballingskap in Afrika-lande was. Van al die stories in Naidoo se “outobiografie” staan “Charlie and Jo” veral uit wat betref die afwesigheid van die skrywer: ’n stilistiese en genre anomalie wat besondere aandag verdien en daarom die fokus van hierdie artikel vorm. Hierdie geheue-vertelling van sosiale terugroeping is ’n goeie voorbeeld van outobiografiese self-verplasing: die vooropstelling van kolletiewe geheue eerder as die nostalgiese reis van ’n individu na self-definiëring. Hierdie beklemtoning van ’n kollektiewe identiteit is geïdentifiseer en benoem as “communography” in die skryfwerk van vergelykbare politieke groepe soos die Ierse Republikeinse Leër
Improved mass and radius constraints for quiescent neutron stars in omega Cen and NGC 6397
No full textWe use Chandra and XMM-Newton observations of the globular clusters omega Cen and NGC 6397 to measure the spectrum of their quiescent neutron stars (NSs), and thus to constrain the allowed ranges of mass and radius for each. We also use Hubble Space Telescope photometry of NGC 6397 to identify a potential optical companion to the quiescent NS, and find evidence that the companion lacks hydrogen. We carefully consider a number of systematic problems, and show that the choices of atmospheric composition, interstellar medium abundances, and cluster distances can have important effects on the inferred NS mass and radius. We find that for typical NS masses, the radii of both NSs are consistent with the 10-13 km range favoured by recent nuclear physics experiments. This removes the evidence suggested by Guillot and collaborators for an unusually small NS radius, which relied upon the small inferred radius of the NGC 6397 NS
The Christian Right and US Foreign Policy in the Twenty-first Century
No full textThe thesis discusses the role of the Christian Right in the US foreign policy decision making process. The research revealed that the Christian Right has long been fascinated with some international issues in general and US foreign policy in particular. The Christian Right’s interest in international issues increased markedly during years of the George W. Bush presidency. It successfully widened its activities from domestic social conservative issues to foreign policy issues by participating in, articulating and lobbying for its religious version of American foreign policy. In assessing the role of the Christian Right in US foreign policy making, this dissertation examines three aspects of US foreign policy, namely Israel, international religious freedom and global humanitarianism. Based on these aspects, the Christian Right is seen as skilled in framing and defining issues. The Christian Right seems effective in selecting and prioritizing international issues that have a reasonable chance of being selected by foreign policy decision makers, especially in Congress. Moreover, the Christian Right has shown its maturity in seeking engagement and cooperation with other organizations, secular and religious, in order to advance its international goals. Finally, in pursuing and conveying its international agenda, the Christian Right has adopted a more moderate and less overtly religious approach. Instead of using its traditional religious rhetoric, the Christian Right has successfully projected its foreign policy preferences into the conventional realist discourse of American foreign policy that is largely based on the objective of national interest and national security. Nevertheless, this study does not, in any way, conclude that the Christian Right was able to influence or determine the direction of US foreign policy and its outcomes; however, it does suggest that the Christian Right did contribute and have an impact on the formulation of some US foreign policy. As such, the research contends that the role of the Christian Right is similar to other interest group lobbies and that its perceived influence on US foreign policy should not be exaggerated. Finally, the research suggests that the emergence of the Christian Right as an actor in asserting its global agenda through US foreign policy can possibly provide an example of how religious beliefs and values can become a potential source of “soft power”. Together with the “climate of opinion” of the American public during the Bush administration, the “soft power” at domestic level could serve as a valuable new explanatory variable in understanding how the US foreign policy was formulated in the early 21st century
The Dynamics of the Merging Galaxy Cluster System A2256: Evidence for a New Subcluster
No full textWe present 236 new radial velocities of galaxies in the cluster A2256 measured with the WIYN Hydra Multi-Object Spectrograph. Combined with the previous work of Fabricant, Kent, & Kurtz, we have velocities for a total of 319 galaxies, of which 277 are cluster members. In addition to the new radial velocities, we present a 3 × 3 image mosaic in the R band of the central 19′ × 19′ region of A2256, from which we obtained photometry for 861 galaxies. These data provide strong evidence for a merger event between two groups. In addition, we present evidence for the presence of a third group, on the outer reaches of the system, that is just now beginning to merge with the system
FOKKER-PLANCK MODELS FOR M15 WITHOUT A CENTRAL BLACK HOLE: THE ROLE OF THE MASS FUNCTION
No full text
The dynamical evolution of poor clusters of galaxies: Growth and properties of the first-ranked galaxy
No full textWe report N-body simulations of the dynamical evolution of isolated clusters of 50 galaxies containing a dark matter component that comprises 90% of the cluster mass. For our adopted physical scaling, the line-of- sight velocity dispersion of the cluster is 310 km s^-1^ and the initial core radius is 250 kpc. Our results are applicable to (1) present-day poor clusters, (2) the small systems that may have merged to produce present-day rich clusters, and (3) virialized subclumps within larger systems, in between major substructure merger events. We have evolved a total of 10 cluster models, using N = 40,000 particles per model. The models are fully self-consistent in that each galaxy is represented as an extended structure containing many particles and the gravitational potential arises from the particles alone. Dark matter is apportioned between the galaxy halos and a smoothly distributed common group halo, the intracluster background (ICB). The percentage of cluster mass initially in the ICB, β, is chosen to be 50, 75, or 90. Increasing β has the effect of removing mass from dark halos around galaxies and distributing it throughout the cluster. The initial conditions were constructed by randomly sampling a King distribution with W_0_ = 6. The galaxies are also King models; the masses of the galaxies follow a Schechter distribution function. The five β = 50 models all followed a similar pattern of behavior. Galaxies experience dynamical friction and undergo orbital decay, leading to an enhanced encounter rate. In ~10 Gyr, merging has resulted in the formation of a dominant, centrally located galaxy. Almost all of the subsequent merging involves this dominant galaxy accreting the others. Mass segregation is apparent, leading the largest galaxies to preferentially engage in merging. Merging produces an extension of the galaxy mass distribution to higher masses, while at the same time it reduces the characteristic mass of the distribution owing to the overall depletion of bright galaxies. Once the first-ranked galaxy (FRG) has grown to twice the size of the initially largest galaxy, its velocity has typically decreased to less than half the cluster velocity dispersion and it remains within the cluster core. The distribution of FRG peculiar velocities at this point contains no values greater than the cluster dispersion; there are no high-velocity FRGs of the sort that have been observed in ~10% of clusters. The most evident change in the cluster space density profile occurs in the inner 200 kpc, where a rise in density causes the core to be erased. If the location of the FRG is taken to define the cluster center, then the density profile is even more strongly cusped and resembles a singular isothermal sphere. The FRG-centered surface density profile can be fit by both power-law and exponential profiles. Once the FRG has assumed a central position in the cluster, multiple nuclei are seen at least 20% of the time, roughly what is expected from the projected surface density distribution. The frequency rises above this to ~40% at ~11 Gyr. The additional nuclei are on orbits which bring them into contact with the FRG. After these satellites merge with the FRG, the frequency of multiple nuclei falls back to the value expected from projection. Observations of {DELTA}M_12_, FRG luminosity, and the number of multiple nuclei can best be fit by cluster models with ages ~11 Gyr; growth in luminosity of the FRG during this amount of time is consistent with only weak cannibalism. Fitting observations of the peculiar velocities of the FRG requires younger ages of ~8 Gyr. Increasing β to 75 slows the rate of merging, but otherwise causes little change in behavior For β = 90, the onset of merging can be delayed for over 13 Gyr; thus a dominant central galaxy is not created
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