The spread in CO absorption and effective temperature among the giants in omega Centauri

Infrared photometric observations of 82 stars on the upper giant branch of ω Centauri are presented. The data show that ω Cen differs markedly from other globular clusters studied in the infrared in two respects. First, at a given V - K color, there is a wide spread in CO absorption (≳ 0.1 mag) in the 3 mag interval below the red giant tip; this range is approximately 5 times that found for other clusters. Second, at a given luminosity, V — K has a spread of up to 1 mag; this range is also much larger than that found for other clusters. The latter result leads us to conclude, in agreement with recent findings by other authors, that there are star-to-star variations in heavy-metal abundance within ω Cen of a factor of 30 or more. Comparison of the spread in CO absorption with that in V — K reveals two sequences of stars, one which has “enhanced” CO absorption and one which has “normal” CO absorption when compared to the run of CO with V — K among stars in other globular clusters. The proportion of stars having “enhanced” CO exceeds 50%. Many of the strong CN stars in the cluster also have “enhanced” CO. Explanations for the origin of these sequences which involve primordial abundance variations as well as mixing phenomena are discussed briefly. Implications for the identification of the “second parameter” as the CNO abundance are also discussed. Effective temperatures and bolometric luminosities are given for the stars

Photometric studies of composite stellar systems. V - Infrared photometry of star clusters in the Magellanic clouds

The results of an infrared photometric study of the integrated light of 84 clusters in the Large and Small Magellanic Clouds (LMC and SMC) are presented. These clusters span nearly the complete range of cluster ages in the Clouds. In contrast to uvgr and UBV cluster colors which vary smoothly with age, the infrared colors display wide variations among the Searle, Wilkinson, and Bagnuolo groups IV-VI, i.e., in the "intermediate age" domain of ˜1-8 × 10^9 yr. Very red J - K and H - K colors for these clusters are shown to be due to the presence of luminous (M_(bol) < -4) carbon stars which are absent in the youngest and oldest clusters, and which have no effect upon the visible colors. An analysis of the CO and H - K data shows that on average half of the bolometric luminosity for 20 intermediate-age clusters comes from carbon stars on the asymptotic giant branch. This analysis agrees well with the recent carbon star surveys of Aaronson and Mould, Frogel and Cohen, and Lloyd-Evans. The effects of luminous carbon stars upon the infrared colors of the parent clusters are strong enough that metal-poor, intermediate-age stellar populations may be detectable in the integrated light of more distant galaxies. There is no difference, on average, between the clusters of the LMC and the SMC in the proportion of the light at 2 μm (or bolometrically) due to luminous carbon stars. This result is in apparent contrast to that of the Blanco et al. surveys of the carbon and M star populations in the general fields of the two galaxies; these surveys have revealed a sharp rise in the C/M star ratio going from the LMC to the SMC. The explanation appears to lie in the incompleteness of the Blanco et al. surveys for warm M stars in metal-poor populations. Carbon stars do not appear to be present in clusters ≤ 1 × 10^9 yr old; the infrared colors of these young clusters are dominated by M giants and supergiants which display strong CO band absorption at 2.3 μm. This lack of carbon stars agrees with the findings of Cohen et al. and Richer that a true paucity of massive, luminous (M_(bol) ≤ -6) carbon stars exists in the general fields of the Clouds. This situation is in conflict with current theories of stellar evolution on the asymptotic giant branch. The V - K colors of the youngest, i.e., 10^7 - 10^8 yr, clusters are compared with the single-burst model of an evolving stellar population due to Struck-Marcell and Tinsley. At a given U - V the observed V - K colors are up to 2 mag redder than the model predicts. The discrepancy is due to the neglect of red supergiants in the model; these luminous stars dominate the infrared colors and bolometric luminosities, and should be detectable in stellar populations like those in the arms of spiral galaxies. The infrared colors of the oldest clusters of the Magellanic Clouds resemble those of globular clusters in our galaxy and in M31

The spread in CO absorption and effective temperature among the giants in omega Centauri

Infrared photometric observations of 82 stars on the upper giant branch of ω Centauri are presented. The data show that ω Cen differs markedly from other globular clusters studied in the infrared in two respects. First, at a given V - K color, there is a wide spread in CO absorption (≳ 0.1 mag) in the 3 mag interval below the red giant tip; this range is approximately 5 times that found for other clusters. Second, at a given luminosity, V — K has a spread of up to 1 mag; this range is also much larger than that found for other clusters. The latter result leads us to conclude, in agreement with recent findings by other authors, that there are star-to-star variations in heavy-metal abundance within ω Cen of a factor of 30 or more. Comparison of the spread in CO absorption with that in V — K reveals two sequences of stars, one which has “enhanced” CO absorption and one which has “normal” CO absorption when compared to the run of CO with V — K among stars in other globular clusters. The proportion of stars having “enhanced” CO exceeds 50%. Many of the strong CN stars in the cluster also have “enhanced” CO. Explanations for the origin of these sequences which involve primordial abundance variations as well as mixing phenomena are discussed briefly. Implications for the identification of the “second parameter” as the CNO abundance are also discussed. Effective temperatures and bolometric luminosities are given for the stars

Photometric studies of composite stellar systems. V - Infrared photometry of star clusters in the Magellanic clouds

The results of an infrared photometric study of the integrated light of 84 clusters in the Large and Small Magellanic Clouds (LMC and SMC) are presented. These clusters span nearly the complete range of cluster ages in the Clouds. In contrast to uvgr and UBV cluster colors which vary smoothly with age, the infrared colors display wide variations among the Searle, Wilkinson, and Bagnuolo groups IV-VI, i.e., in the "intermediate age" domain of ˜1-8 × 10^9 yr. Very red J - K and H - K colors for these clusters are shown to be due to the presence of luminous (M_(bol) < -4) carbon stars which are absent in the youngest and oldest clusters, and which have no effect upon the visible colors. An analysis of the CO and H - K data shows that on average half of the bolometric luminosity for 20 intermediate-age clusters comes from carbon stars on the asymptotic giant branch. This analysis agrees well with the recent carbon star surveys of Aaronson and Mould, Frogel and Cohen, and Lloyd-Evans. The effects of luminous carbon stars upon the infrared colors of the parent clusters are strong enough that metal-poor, intermediate-age stellar populations may be detectable in the integrated light of more distant galaxies. There is no difference, on average, between the clusters of the LMC and the SMC in the proportion of the light at 2 μm (or bolometrically) due to luminous carbon stars. This result is in apparent contrast to that of the Blanco et al. surveys of the carbon and M star populations in the general fields of the two galaxies; these surveys have revealed a sharp rise in the C/M star ratio going from the LMC to the SMC. The explanation appears to lie in the incompleteness of the Blanco et al. surveys for warm M stars in metal-poor populations. Carbon stars do not appear to be present in clusters ≤ 1 × 10^9 yr old; the infrared colors of these young clusters are dominated by M giants and supergiants which display strong CO band absorption at 2.3 μm. This lack of carbon stars agrees with the findings of Cohen et al. and Richer that a true paucity of massive, luminous (M_(bol) ≤ -6) carbon stars exists in the general fields of the Clouds. This situation is in conflict with current theories of stellar evolution on the asymptotic giant branch. The V - K colors of the youngest, i.e., 10^7 - 10^8 yr, clusters are compared with the single-burst model of an evolving stellar population due to Struck-Marcell and Tinsley. At a given U - V the observed V - K colors are up to 2 mag redder than the model predicts. The discrepancy is due to the neglect of red supergiants in the model; these luminous stars dominate the infrared colors and bolometric luminosities, and should be detectable in stellar populations like those in the arms of spiral galaxies. The infrared colors of the oldest clusters of the Magellanic Clouds resemble those of globular clusters in our galaxy and in M31

UV-Optical Pixel Maps of Face-On Spiral Galaxies -- Clues for Dynamics and Star Formation Histories

UV and optical images of the face-on spiral galaxies NGC 6753 and NGC 6782 reveal regions of strong on-going star formation that are associated with structures traced by the old stellar populations. We make NUV--(NUV-I) pixel color-magnitude diagrams (pCMDs) that reveal plumes of pixels with strongly varying NUV surface brightness and nearly constant I surface brightness. The plumes correspond to sharply bounded radial ranges, with (NUV-I) at a given NUV surface brightness being bluer at larger radii. The plumes are parallel to the reddening vector and simple model mixtures of young and old populations, thus neither reddening nor the fraction of the young population can produce the observed separation between the plumes. The images, radial surface-brightness, and color plots indicate that the separate plumes are caused by sharp declines in the surface densities of the old populations at radii corresponding to disk resonances. The maximum surface brightness of the NUV light remains nearly constant with radius, while the maximum I surface brightness declines sharply with radius. An MUV image of NGC 6782 shows emission from the nuclear ring. The distribution of points in an (MUV-NUV) vs. (NUV-I) pixel color-color diagram is broadly consistent with the simple mixture model, but shows a residual trend that the bluest pixels in (MUV-NUV) are the reddest pixels in (NUV-I). This may be due to a combination of red continuum from late-type supergiants and [SIII] emission lines associated with HII regions in active star-forming regions. We have shown that pixel mapping is a powerful tool for studying the distribution and strength of on-going star formation in galaxies. Deep, multi-color imaging can extend this to studies of extinction, and the ages and metallicities of composite stellar populations in nearby galaxies.Comment: LaTeX with AASTeX style file, 29 pages with 12 figures (some color, some multi-part). Accepted for publication in The Astrophysical Journa

Design, construction, and characterization of a compact DD neutron generator designed for 40Ar/39Ar geochronology

A next-generation, high-flux DD neutron generator has been designed, commissioned, and characterized, and is now operational in a new facility at the University of California Berkeley. The generator, originally designed for 40Ar/39Ar dating of geological materials, has since served numerous additional applications, including medical isotope production studies, with others planned for the near future. In this work, we present an overview of the High Flux Neutron Generator (HFNG) which includes a variety of simulations, analytical models, and experimental validation of results. Extensive analysis was performed in order to characterize the neutron yield, flux, and energy distribution at specific locations where samples may be loaded for irradiation. A notable design feature of the HFNG is the possibility for sample irradiation internal to the cathode, just 8 mm away from the neutron production site, thus maximizing the neutron flux (n/cm2/s). The generator's maximum neutron flux at this irradiation position is 2.58e7 n/cm2/s +/- 5% (approximately 3e8 n/s total yield) as measured via activation of small natural indium foils. However, future development is aimed at achieving an order of magnitude increase in flux. Additionally, the deuterium ion beam optics were optimized by simulations for various extraction configurations in order to achieve a uniform neutron flux distribution and an acceptable heat load. Finally, experiments were performed in order to benchmark the modeling and characterization of the HFNG.Comment: 31 pages, 20 figure

Serum Adiponectin in Relation to Body Mass Index and Other Correlates in Black and White Women

Adiponectin is a promising biomarker linking obesity and disease risk; however, limited data are available regarding adiponectin in black women among whom obesity is highly prevalent

Surgical Standards for Management of the Axilla in Breast Cancer Clinical Trials with Pathological Complete Response Endpoint.

Advances in the surgical management of the axilla in patients treated with neoadjuvant chemotherapy, especially those with node positive disease at diagnosis, have led to changes in practice and more judicious use of axillary lymph node dissection that may minimize morbidity from surgery. However, there is still significant confusion about how to optimally manage the axilla, resulting in variation among practices. From the viewpoint of drug development, assessment of response to neoadjuvant chemotherapy remains paramount and appropriate assessment of residual disease-the primary endpoint of many drug therapy trials in the neoadjuvant setting-is critical. Therefore decreasing the variability, especially in a multicenter clinical trial setting, and establishing a minimum standard to ensure consistency in clinical trial data, without mandating axillary lymph node dissection, for all patients is necessary. The key elements which include proper staging and identification of nodal involvement at diagnosis, and appropriately targeted management of the axilla at the time of surgical resection are presented. The following protocols have been adopted as standard procedure by the I-SPY2 trial for management of axilla in patients with node positive disease, and present a framework for prospective clinical trials and practice