19 research outputs found
A Spitzer Space Telescope Atlas of omega Centauri: The Stellar Population, Mass Loss, and the Intracluster Medium
We present a Spitzer Space Telescope imaging survey of the most massive
Galactic globular cluster, omega Centauri, and investigate stellar mass loss at
low metallicity and the intracluster medium (ICM). The survey covers
approximately 3.2x the cluster half-mass radius at 3.6, 4.5, 5.8, 8, and 24
microns, resulting in a catalog of over 40,000 point-sources in the cluster.
Approximately 140 cluster members ranging 1.5 dex in metallicity show a red
excess at 24 microns, indicative of circumstellar dust. If all of the dusty
sources are experiencing mass loss, the cumulative rate of loss is estimated at
2.9 - 4.2 x 10^(-7) solar masses per year, 63% -- 66% of which is supplied by
three asymptotic giant branch stars at the tip of the Red Giant Branch (RGB).
There is little evidence for strong mass loss lower on the RGB. If this
material had remained in the cluster center, its dust component (> 1 x 10^(-4)
solar masses) would be detectable in our 24 and 70 micron images. While no dust
cloud located at the center of omega Cen is apparent, we do see four regions of
very faint, diffuse emission beyond two half-mass radii at 24 microns. It is
unclear whether these dust clouds are foreground emission or are associated
with omega Cen. In the latter case, these clouds may be the ICM in the process
of escaping from the cluster.Comment: 20 pages, 18 figures, 8 tables, accepted for publication in A
A Spitzer search for cold dust within globular clusters
Globular cluster stars evolving off the main sequence are known to lose mass,
and it is expected that some of the lost material should remain within the
cluster as an intracluster medium (ICM). Most attempts to detect such an ICM
have been unsuccessful. The Multiband Imaging Photometer for Spitzer on the
Spitzer Space Telescope was used to observe eight Galactic globular clusters in
an attempt to detect the thermal emission from ICM dust. Most clusters do not
have significant detections at 70 microns; one cluster, NGC 6341, has tentative
evidence for the presence of dust, but 90 micron observations do not confirm
the detection. Individual 70 micron point sources which appear in several of
the cluster images are likely to be background galaxies. The inferred dust mass
and upper limits are < 4e-4 solar masses, well below expectations for cluster
dust production from mass loss in red and asymptotic giant branch stars. This
implies that either globular cluster dust production is less efficient, or that
ICM removal or dust destruction is more efficient, than previously believed. We
explore several possibilities for ICM removal and conclude that present data do
not yet permit us to distinguish between them.Comment: AJ in press; 30 pages with 8 figure
Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial
Background
Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy
Correction to: Cluster identification, selection, and description in Cluster randomized crossover trials: the PREP-IT trials
An amendment to this paper has been published and can be accessed via the original article
Violent Police-Citizen Encounters: An Analysis of Major Newspaper Accounts
This paper investigates trends in police brutality using data found through the Lexis/Nexis system. Using the keywords police brutality, 15 newspapers classified as major papers by the Lexis/Nexis service were searched for descriptions of incidents of police misconduct against citizens that appeared from January 1, 1990 to May 31, 1992. One hundred and thirty distinct incidents of police brutality were analyzed based on the race and gender of the officers and of the victim, as well as issues of socioeconomic class. The situational characteristics surrounding the alleged assault were categorized and discussed. Minority citizens were involved in the vast majority of the incidents. The data also suggested a definite lack of penalties against the officers involved in abusive actions against citizens. Further, a citizen was equally likely to be assaulted for a disrespectful attitude towards a law enforcement officer than if the citizen had posed a serious bodily threat to the officer or another human being