Gemini/GMOS photometry of intermediate-age star clusters in the Large Magellanic Cloud

We present Gemini South GMOS g,i photometry of 14 intermediate-age Large Magellanic Cloud (LMC) star clusters, namely: NGC 2155, 2161, 2162, 2173, 2203, 2209, 2213, 2231, 2249, Hodge 6, SL 244, 505, 674, and 769, as part of a continuing project to investigate the extended Main Sequence Turnoff (EMSTO) phenomenon. Extensive artificial star tests were made over the observed field of view. These tests reveal the observed behaviour of photometric errors with magnitude and crowding. The cluster stellar density radial profiles were traced from star counts over the extent of the observed field. We adopt clus- ter radii and build colour-magnitude diagrams (CMDs) with cluster features clearly identified. We used the cluster (g,g-i) CMDs to estimate ages from the matching of theoretical isochrones. The studied LMC clusters are confirmed to be intermediate-age clusters, which range in age 9.10 < log(t) < 9.60. NGC 2162 and NGC 2249 look like new EMSTO candidates, in addition to NGC 2209, on the basis of having dual red clumps.Comment: MNRAS, accepte

Ultra-Low Amplitude Cepheids in the Large Magellanic Cloud

The MACHO variables of LMC Field 77 that lie in the vicinity of the Cepheid instability strip are reexamined. Among the 144 variables that we identify as Cepheids we find 14 that have Fourier amplitudes <0.05 mag in the MACHO red band, of which 7 have an amplitude <0.006 mag : we dub the latter group of stars ultra-low amplitude (ULA) Cepheids. The variability of these objects is verified by a comparison of the MACHO red with the MACHO blue lightcurves and with those of the corresponding OGLE LMC stars. The occurrence of ULA Cepheids is in agreement with theory. We have also discovered 2 low amplitude variables whose periods are about a factor of 5--6 smaller than those of F Cepheids of equal apparent magnitude. We suggest that these objects are Cepheids undergoing pulsations in a surface mode and that they belong to a novel class of Strange Cepheids (or Surface Mode Cepheids) whose existence was predicted by Buchler et al. (1997).Comment: 4 pages, 5 figures, slightly revised, to appear in ApJ Letter

SkyMapper Filter Set: Design and Fabrication of Large Scale Optical Filters

The SkyMapper Southern Sky Survey will be conducted from Siding Spring Observatory with u, v, g, r, i and z filters that comprise glued glass combination filters of dimension 309x309x15 mm. In this paper we discuss the rationale for our bandpasses and physical characteristics of the filter set. The u, v, g and z filters are entirely glass filters which provide highly uniform band passes across the complete filter aperture. The i filter uses glass with a short-wave pass coating, and the r filter is a complete dielectric filter. We describe the process by which the filters were constructed, including the processes used to obtain uniform dielectric coatings and optimized narrow band anti-reflection coatings, as well as the technique of gluing the large glass pieces together after coating using UV transparent epoxy cement. The measured passbands including extinction and CCD QE are presented.Comment: 9 pages, 2 tables, 7 figure

The Extended Main-Sequence Turn-off Clusters of the Large Magellanic Cloud - Missing links in Globular Cluster Evolution

Recent observations of intermediate age (1 - 3 Gyr) massive star clusters in the Large Magellanic Cloud (LMC) have revealed that the majority possess bifurcated or extended main-sequence turn-off (EMSTO) morphologies. This effect can be understood to arise from subsequent star formation amongst the stellar population with age differences between constituent stars amounting to 50 - 300 Myr. Age spreads of this order are similarly invoked to explain the light element abundance variations witnessed in ancient globular clusters. In this paper we explore the proposition that the clusters exhibiting the EMSTO phenomenon are a general phase in the evolution of massive clusters, one that naturally leads to the particular chemical properties of the ancient globular cluster population. We show that the isolation of EMSTO clusters to intermediate ages is the consequence of observational selection effects. In our proposed scenario, the EMSTO phenomenon is identical to that which establishes the light element abundance variations that are ubiquitous in the ancient globular cluster population. Our scenario makes a strong prediction: EMSTO clusters will exhibit abundance variations in the light elements characteristic of the ancient GC population.Comment: ApJ accepted. 33 pages, 5 figure

Gender Differences in Stress and Coping Among Adults Living in Hawai`i

Background and purpose. Stress has been recognized as a public health problem. However, little research has been done on gender differences in sources of stress and coping strategies in Hawaii. In this study, we hypothesized that: 1) women will report higher levels of stress than men; 2) women will report being stressed by family and health related stressors while men will report stress related to finances and work-related issues; 3) women will report using adaptive coping strategies more frequently while men will report using maladaptive and avoidance strategies more frequently; 4) there will be no gender differences in the readiness to use stress management strategies. Method. A statewide cross-sectional telephone-survey of 1518 participants was conducted during the spring and summer of 2006. Results. Women reported higher overall perceived stress levels, but there was no difference in the experienced social stressors and health stressors between genders. Men perceived more stress from personal factors. There were no gender differences in the perceived ability to cope with stress. However, women were more likely to use adaptive coping strategies, whereas men were more likely to use maladaptive and avoidance coping strategies. There were no significant gender differences in stages of change for stress management. Conclusion. Based on this study, interventions can be developed to help people better cope with stress. Interventions for women may focus on increasing the use of adaptive strategies such as praying and talking to friends and family, while interventions for men may introduce the use of adaptive coping strategies such as exercise and actively fighting causes of stress. This study shows that gender differences in stress levels and coping in Hawaii are similar to previous studies conducted on the mainland. More research into specific stressors and coping strategies may help tailor interventions that are more effective and comprehensive

Anticoagulant rodenticides on our public and community lands: spatial distribution of exposure and poisoning of a rare forest carnivore.

Anticoagulant rodenticide (AR) poisoning has emerged as a significant concern for conservation and management of non-target wildlife. The purpose for these toxicants is to suppress pest populations in agricultural or urban settings. The potential of direct and indirect exposures and illicit use of ARs on public and community forest lands have recently raised concern for fishers (Martes pennanti), a candidate for listing under the federal Endangered Species Act in the Pacific states. In an investigation of threats to fisher population persistence in the two isolated California populations, we investigate the magnitude of this previously undocumented threat to fishers, we tested 58 carcasses for the presence and quantification of ARs, conducted spatial analysis of exposed fishers in an effort to identify potential point sources of AR, and identified fishers that died directly due to AR poisoning. We found 46 of 58 (79%) fishers exposed to an AR with 96% of those individuals having been exposed to one or more second-generation AR compounds. No spatial clustering of AR exposure was detected and the spatial distribution of exposure suggests that AR contamination is widespread within the fisher's range in California, which encompasses mostly public forest and park lands Additionally, we diagnosed four fisher deaths, including a lactating female, that were directly attributed to AR toxicosis and documented the first neonatal or milk transfer of an AR to an altricial fisher kit. These ARs, which some are acutely toxic, pose both a direct mortality or fitness risk to fishers, and a significant indirect risk to these isolated populations. Future research should be directed towards investigating risks to prey populations fishers are dependent on, exposure in other rare forest carnivores, and potential AR point sources such as illegal marijuana cultivation in the range of fishers on California public lands

Symmetries of perturbed conformal field theories

The symmetries of perturbed conformal field theories are analysed. We explain which generators of the chiral algebras of a bulk theory survive a perturbation by an exactly marginal bulk field. We also study the behaviour of D-branes under current-current bulk deformations. We find that the branes always continue to preserve as much symmetry as they possibly can, i.e. as much as is preserved in the bulk. We illustrate these findings with several examples, including permutation branes in WZW models and B-type D-branes in Gepner models.Comment: 30 pages, 3 figures. V2: Small error in eq. (2.14) correcte

Cepheid Mass-loss and the Pulsation -- Evolutionary Mass Discrepancy

I investigate the discrepancy between the evolution and pulsation masses for Cepheid variables. A number of recent works have proposed that non-canonical mass-loss can account for the mass discrepancy. This mass-loss would be such that a 5Mo star loses approximately 20% of its mass by arriving at the Cepheid instability strip; a 14Mo star, none. Such findings would pose a serious challenge to our understanding of mass-loss. I revisit these results in light of the Padova stellar evolutionary models and find evolutionary masses are ($17\pm5$)% greater than pulsation masses for Cepheids between 5<M/Mo<14. I find that mild internal mixing in the main-sequence progenitor of the Cepheid are able to account for this mass discrepancy.Comment: 15 pages, 3 figures, ApJ accepte

Young Clusters in the Magellanic Clouds II

We present the results of a quantitative study of the degree of extension to the boundary of the classical convective core within intermediate mass stars. The basis of our empirical study is the stellar population of four young populous clusters in the Magellanic Clouds which has been detailed in Keller, Bessell & Da Costa (2000). The sample affords a meaningful comparison with theoretical scenarios with varying degrees of convective core overshoot and binary star fraction. Two critical properties of the population, the main-sequence luminosity function and the number of evolved stars, form the basis of our comparison between the observed data set and that simulated from the stellar evolutionary models. On the basis of this comparison we conclude that the case of no convective core overshoot is excluded at a 2 sigma level.Comment: 27 pages, 12 figures, AJ accepte