554 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
Efficacy and Safety in Clinical Trials in Cardiovascular Disease
No full textMortality and morbid events are insensitive guides to the efficacy and safety of interventions in chronic cardiovascular disease (CVD). To enhance the ability to find new and effective long-term treatments, especially for the early stages of CVD, a revised strategy for clinical trials should emphasize efficacy on disease progression while monitoring symptoms and quality of life as guides to clinical benefit. Mortality, which is uncommon except in acute or advanced disease, provides at best a crude guide to net efficacy and safety. It must be monitored to support demonstrated efficacy on disease progression without adverse safety effects. This revised approach, made possible by our enhanced ability to monitor the progression of disease, should make it possible to study earlier disease and to improve cardiovascular health while reducing health care costs
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