Blue Stragglers in Low-Luminosity Star Clusters

We examine the blue straggler populations of 13 low-luminosity (M_V_t >~ -6) globular clusters and 2 old open clusters. These clusters test blue straggler formation in environments intermediate between higher luminosity (and usually higher density) clusters and the Galactic field. The anti-correlation between the relative frequency of blue stragglers (F_BSS = N_BSS / N_HB) and cluster luminosity continues to the lowest luminosity clusters, which have frequencies meeting or exceeding that of field stars. In addition we find that the anti-correlation between straggler frequency and central density disappears for clusters with density less than about 300 L_V,sun pc^-3, although this appears to be an artifact of the correlation between cluster luminosity and central density. We argue on observational (wide, eccentric binaries containing blue stragglers in M67, and the existence of very bright stragglers in most of the clusters in our sample) and theoretical grounds that stellar collisions still produce a significant fraction of the blue stragglers in low luminosity star clusters due to the long-term survival of wide binaries.Comment: 13 pages, 3 figures, accepted to ApJ Letter

Exploiting the open clusters in the Kepler and CoRoT fields

The open clusters in the Kepler and CoRoT fields potentially provide tight constraints for tests of stellar models and observational methods because they allow a combination of complementary methods. We are in the process of identi- fying and measuring parameters for detached eclipsing binaries (dEBs) in the open clusters in the Kepler and CoRoT fields. We make use of measurements of dEBs in the clusters to test the accuracy of asteroseismic scaling relations for mass. We are able to provide strong indications that the asteroseismic scaling relations over- estimate the stellar mass, but we are not yet able to distinguish between different proposed corrections from the literature. We argue how our ongoing measurements of more dEBs in more clusters, complemented by dEBs in the field, should be able to break the degeneracy. We also briefly describe how we can identify cluster stars that have evolved through non-standard evolution by making use of ensemble asteroseismology.Comment: Proc. of the workshop "Asteroseismology of stellar populations in the Milky Way" (Sesto, 22-26 July 2013), Astrophysics and Space Science Proceedings, (eds. A. Miglio, L. Girardi, P. Eggenberger, J. Montalban

Bright Variable Stars in NGC 6819 - An Open Cluster in the Kepler Field

We describe a variability study of the moderately old open cluster NGC 6819. We have detected 4 new detached eclipsing binaries near the cluster turnoff (one of which may be in a triple system). Several of these systems should be able to provide mass and radius information, and can therefore constrain the age of the cluster. We have also newly detected one possible detached binary member about 3.5 magnitudes below the turnoff. One EW-type binary (probably not a cluster member) shows unusually strong night-to-night light curve variations in sets of observations separated by 8 years. According to the best current information, the three brightest variables we detected (2 of them new) are cluster members, making them blue stragglers. One is a delta Scu pulsating variable, one is a close but detached binary, and the third contains a detached short period binary that shows total eclipses. In each case, however, there is evidence hinting that the system may have been produced through the interaction of more than two stars.Comment: 33 pages, 15 figures, accepted to A

The provision of education and training for healthcare professionals through the medium of the internet

This paper describes a new initiative to provide Internet based courses to student and professional occupational therapists in four centres in the UK, Belgium the Netherlands and Sweden. The basis of this collaborative Occupational Therapy Internet School (OTIS) is the concept of the “Virtual College”. This comprises the design and implementation of a sophisticated Internet-based system through which courses can be managed, prepared and delivered online in an effective fashion, and where students can communicate both with the staff and their peers. The aim is to support and facilitate the whole range of educational activities within a remote electronic environment. A major feature of the course organisation is the adoption of a problem-based approach in which students will collaborate internationally to propose effective intervention in given case study scenarios. The paper outlines the rationale for OTIS, the content and structure of the courseware, the technical specification of the system and evaluation criteria. In addition to the more conventional web-based learning facilities generally offered, a number of agent-based approaches are being adopted to assist in the management of the course by ensuring the proper delivery of course materials and to assist the functioning of project groups. </p

The non-segregated population of blue straggler stars in the remote globular cluster Palomar 14

We used deep wide-field observations obtained with the Canada-France-Hawaii Telescope to study the blue straggler star (BSS) population in the innermost five arcminutes of the remote Galactic globular cluster Palomar 14. The BSS radial distribution is found to be consistent with that of the normal cluster stars, showing no evidence of central segregation. Palomar 14 is the third system in the Galaxy (in addition to OmegaCentauri and NGC 2419) showing a population of BSS not centrally segregated. This is the most direct evidence that in Palomar 14 two-body relaxation has not fully established energy equipartition yet, even in the central regions (in agreement with the estimated half-mass relaxation time, which is significantly larger than the cluster age). These observational facts have important implications for the interpretation of the shape of the mass function and the existence of the tidal tails recently discovered in this cluster.Comment: 5 pages, 4 figures, accepted for publication in ApJ Letter

Evolved Stars in the Core of the Massive Globular Cluster NGC 2419

We present an analysis of optical and ultraviolet Hubble Space Telescope photometry for evolved stars in the core of the distant massive globular cluster NGC 2419. We characterize the horizontal branch (HB) population in detail including corrections for incompleteness on the long blue tail. We present a method for removing (to first order) lifetime effects from the distribution of HB stars to facilitate more accurate measurements of helium abundance for clusters with blue HBs and to clarify the distribution of stars reaching the zero-age HB. The population ratio R = N_HB / N_RGB implies there may be slight helium enrichment among the EHB stars in the cluster, but that it is likely to be small (dY < 0.05). An examination of the upper main sequence does not reveal any sign of multiple populations. Through comparisons of optical CMDs, we present evidence that the EHB clump in NGC 2419 contains the end of the canonical horizontal branch, and that the boundary between the normal HB stars and blue hook stars shows up as a change in the density of stars in the CMD. This corresponds to a spectroscopically-verified gap in NGC 2808 and an "edge" in omega Cen. The more clearly visible HB gap at V = 23.5 appears to be too bright.(Abridged)Comment: 27 pages, 25 figures (some bitmapped), uses emulateapj, accepted to Astronomical Journa