Stellar Populations and Ages of M82 Super Star Clusters

We present high signal-to-noise optical spectra of two luminous super star clusters in the starburst galaxy M82. The data for cluster F and the nearby, highly reddened cluster L were obtained with the William Herschel Telescope (WHT) at a resolution of 1.6A. The blue spectrum (3250-5540A) of cluster F shows features typical of mid-B stars. The red spectra (5730-8790A) of clusters F and L show the Ca II triplet and numerous F and G-type absorption features. Strong Ca II and Na I interstellar absorption lines arising in M82 are also detected, and the 6283A diffuse interstellar band appears to be present. The quality of the WHT spectra allows us to considerably improve previous age estimates for cluster F. By comparing the blue spectrum with theoretical model cluster spectra using the PEGASE spectral synthesis code (Fioc & Rocca-Volmerange 1997), we derive an age of 60+/-20 Myr. The strength of the Ca II triplet is also in accord with this age. Cluster L appears to have a similar age, although this is much less certain. The measured radial velocities for the two clusters differ substantially, indicating that they are located in different regions of the M82 disk. Cluster F appears to be deep in M82, slightly beyond the main starburst region while the highly obscured cluster L lies near the outer edges of the disk. We derive an absolute V magnitude of -16.5 for F indicating that it is an extremely massive cluster. The presence of such a luminous super star cluster suggests that the M82 starburst experienced an episode of intense star formation approximately 60 Myr ago.Comment: 10 pages and 5 figures for publication in MNRA

Realistic Ionizing Fluxes for Young Stellar Populations from 0.05 to twice solar metallicity

We present a new grid of ionizing fluxes for O and Wolf-Rayet stars for use with evolutionary synthesis codes and single star H II region analyses. A total of 230 expanding, non-LTE, line-blanketed model atmospheres have been calculated for five metallicities (0.05, 0.2, 0.4, 1 and 2 solar) using the WM-basic code of Pauldrach et al. (2001) and the CMFGEN code of Hillier & Miller (1998). The stellar wind parameters are scaled with metallicity for both O and W-R stars. We incorporate the new models into Starburst99 (Leitherer et al. 1999) and compare the ionizing outputs with Schaerer & Vacca (1998) and Leitherer et al. (1999). The changes in the output ionizing fluxes are dramatic, particularly below 228 A. We also find lower fluxes in the He I continuum for Z > 0.4 solar and ages < 7 Myr because of the increased line blanketing. We test the accuracy of the new models by constructing photoionization models. We show that for the dwarf O star grid, He I 5876/H beta decreases between Z = 1 and twice solar in a similar manner to observations (e.g. Bresolin et al. 1999) due to the increased effect of line blanketing. We therefore suggest that a lowering of the upper mass limit at high abundances is not required to explain the observations. For the case of an instantaneous burst, we plot the softness parameter "eta prime" against the abundance indicator R_23. The new models are coincident with the data of Bresolin et al. (1999), particularly during the W-R phase, unlike previous models which over-predict the hardness of the ionizing radiation.Comment: 21 pages, 15 postscript colour figures, includes mn2e.cls. To be published in MNRAS. Revised version containing modifications to Tables 1-

Carbon changes in conterminous US forests associated with growth and major disturbances.

Abstract We estimated forest area and carbon changes in the conterminous United States using a remote sensing based land cover change map, forest fire data from the Monitoring Trends in Burn Severity program, and forest growth and harvest data from the USDA Forest Service, Forest Inventory and Analysis Program. Natural and human-associated disturbances reduced the forest ecosystems\u27 carbon sink by 36% from 1992 to 2001, compared to that without disturbances in the 48 states. Among the three identified disturbances, forest-related land cover change contributed 33% of the total effect in reducing the forest carbon potential sink, while harvests and fires accounted for 63% and 4% of the total effect, respectively. The nation\u27s forests sequestered 1.6 ± 0.1Pg (1015 petagram) carbon during the period, or 0.18PgCyr-1, with substantial regional variation. The southern region of the United States was a small net carbon source whereas the greater Pacific Northwest region was a strong net sink. Results of the approach fit reasonably well at an aggregate level with other related estimates of the current forest US greenhouse gas inventory, suggesting that further research using this approach is warranted

Chemical composition and origin of nebulae around Luminous Blue Variables

We use the analysis of the heavy element abundances (C, N, O, S) in circumstellar nebulae around Luminous Blue Variables to infer the evolutionary phase in which the material has been ejected. (1) We discuss the different effects that may have changed the gas composition of the nebula since it was ejected (2) We calculate the expected abundance changes at the stellar surface due to envelope convection in the red supergiant phase. If the observed LBV nebulae are ejected during the RSG phase, the abundances of the LBV nebulae require a significantly smaller amount of mass to be lost than assumed in evolutionary models. (3) We calculate the changes in the surface composition during the main sequence phase by rotation induced mixing. If the nebulae are ejected at the end of the MS-phase, the abundances in LBV nebulae are compatible with mixing times between 5 x 10^6 and 1 x 10^7 years. The existence of ON stars supports this scenario. (4) The predicted He/H ratio in the nebulae are significantly smaller than the current observed photospheric values of their central stars. Combining various arguments we show that the LBV nebulae are ejected during the blue SG phase and that the stars have not gone through a RSG phase. The chemical enhancements are due to rotation induced mixing, and the ejection is possibly triggered by near-critical rotation. During the ejection, the outflow was optically thick, which resulted in a large effective radius and a low effective temperature. This also explains the observed properties of LBV dust.Comment: 18 pages, 4 figures, to be published in The Astrophysical Journal, April 20, 200

AmeriCorps in the Field: Implementation of the National and Community Service Trust Act in Nine Study States

This report presents the results of P/PVs 30-month study of the implementation of AmeriCorps, the signature program of the National and Community Service Trust Act of 1993. In particular, it documents the federal-state relationship, the role that states played, and the individual challenges and successes of various sites as they developed their programs. The report concludes that AmeriCorps was successful in rapidly implementing high-quality programs while attracting a diverse group of participants. In addition, it frames some broader recommendations for the future of national service

News from Academy Bay

New Faces and New Projects in a New CDRS Department. International Workshop: Feral Goat Eradication Program. Geologists to Invade Galápagos. GIS in Galápagos. The Isabela Project: Off and Running. A Pig-Free Santiago: Is it a Dream or on the Horizon? The Special Law for Galápagos

Divergence or convergence? Health inequalities and policy in a devolved Britain

Since the advent of political devolution in the UK, it has been widely reported that markedly different health policies have emerged. However, most of these analyses are based on a comparison of health care policies and, as such, only tell part of a complex and evolving story. This paper considers official responses to a shared public health policy aim, the reduction of health inequalities, through an examination of national policy statements produced in England, Scotland and Wales respectively since 1997. The analysis suggests that the relatively consistent manner in which the ‘policy problem’ of health inequalities has been framed combined with the dominance of a medical model of health have constrained policy responses. Our findings differ from existing analyses, raising some important questions about the actuality of, and scope for, policy divergence since devolution