Uncovering Multiple Populations with Washington Photometry: I. The Globular Cluster NGC 1851

The analysis of multiple populations (MPs) in globular clusters (GCs) has become a forefront area of research in astronomy. Multiple red giant branches (RGBs), subgiant branches (SGBs), and even main sequences (MSs) have now been observed photometrically in many GCs. UV photometry has been crucial in discovering and analyzing these MPs, but the Johnson U and the Stromgren and Sloan u filters that have generally been used are relatively inefficient and very sensitive to reddening and atmospheric extinction. In contrast, the Washington C filter is much broader and redder than these competing UV filters. Here we investigate the use of the Washington system to uncover MPs using only a 1-meter telescope. Our analysis of the well-studied GC NGC 1851 finds that the C filter is both very efficient and effective at detecting its previously discovered MPs in the RGB and SGB. Remarkably, we have also detected an intrinsically broad MS best characterized by two distinct but heavily overlapping populations that cannot be explained by binaries, field stars, or photometric errors. The MS distribution is in very good agreement with that seen on the RGB, with ~30% of the stars belonging to the second population. There is also evidence for two sequences in the red horizontal branch, but this appears to be unrelated to the MPs in this cluster. Neither of these latter phenomena have been observed previously in this cluster. The redder MS stars are also more centrally concentrated than the blue MS. This is the first time MPs in a MS have been discovered from the ground, and using only a 1-meter telescope. The Washington system thus proves to be a very powerful tool for investigating MPs, and holds particular promise for extragalactic objects where photons are limited.Comment: 25 pages, 10 figure

A study of soil topo-sequences in the Steese and White Mountains of Alaska

Thesis (M.S.) University of Alaska Fairbanks, 2018The Steese Mountains of Alaska present a complex landscape on which to study soil formation and characteristics in relation to topographic position. The White and Steese Mountains of Alaska are located approximately 70 to 220 km northeast of Fairbanks. Ten toposequences with 3 or 4 sites each were described in the field, sampled, and analyzed in the laboratory in order to determine the relationship between soil morphology and soil-forming factors. Permafrost is discontinuous within the study area and vegetation ranges from tundra on summits to boreal stands of resin birch, quaking aspen, black spruce and white spruce along the lower elevations. There have been many wildfires over time that may have altered the soils and affected the vegetation successional patterns. The processes through which various soil patterns have formed and the unique characteristics of the soils are described here based on field data obtained from both burned and unburned sites. The analysis includes biophysical settings, parent material, texture and nutrient concentrations. Organic horizons were common on most of the transects and play a key role in the depth of the active layer where they exist. Nutrient concentrations are also closely tied to the presence and depth of the organic horizons. Some patterns described in other areas of the boreal region were not observed in this study. There were some soil properties that are not readily described under the current taxonomy protocols which are suggested to be added in a future revision of Soil Taxonomy

Spectroscopy of blue horizontal branch stars in NGC 6656 (M22)

Recent investigations revealed very peculiar properties of blue horizontal branch (HB) stars in \omega Centauri, which show anomalously low surface gravity and mass compared to other clusters and to theoretical models. \omega Centauri, however, is a very unusual object, hosting a complex mix of multiple stellar populations with different metallicity and chemical abundances. We measured the fundamental parameters (temperature, gravity, and surface helium abundance) of a sample of 71 blue HB stars in M22, with the aim of clarifying if the peculiar results found in \omega Cen are unique to this cluster. M22 also hosts multiple sub-populations of stars with a spread in metallicity, analogous to \omega Cen. The stellar parameters were measured on low-resolution spectra fitting the Balmer and helium lines with a grid of synthetic spectra. From these parameters, the mass and reddening were estimated. Our results on the gravities and masses agree well with theoretical expectations, matching the previous measurements in three "normal" clusters. The anomalies found in \omega Cen are not observed among our stars. A mild mass underestimate is found for stars hotter than 14\,000 K, but an exact analogy with \omega Cen cannot be drawn. We measured the reddening in the direction of M22 with two independent methods, finding E(B-V)=0.35 \pm 0.02 mag, with semi-amplitude of the maximum variation \Delta(E(B-V))=0.06 mag, and an rms intrinsic dispersion of \sigma(E(B-V))=0.03 mag.Comment: 11 pages, 9 Postscript figure

Ecology and conditions of breeding of the cardinal-tetra Paracheirodon axelrodi (Pisces, Characoidea) in the area of the Rio Negro/Brazil

This paper covers the ecological development of the major ornamental fish Paracheirodon axelrodi found in rain forest streams (almost "clear-water") in the region of the middle and upper Rio Negro. Limnochemical conditions in these extremely nutrient-poor waters during both the low and high water seasons over the spawning period, as well as breeding conditions in captivity, are described. A comparison is made between the very slow rate of growth and limited age reached as a result of a food deficiency in its natural habitat, and the potential growth if bred under optimum feeding conditions

Ca II TRIPLET SPECTROSCOPY OF SMALL MAGELLANIC CLOUD RED GIANTS. IV. ABUNDANCES FOR A LARGE SAMPLE OF FIELD STARS AND COMPARISON WITH THE CLUSTER SAMPLE

This paper represents a major step forward in the systematic and homogeneous study of Small Magellanic Cloud (SMC) star clusters and field stars carried out by applying the calcium triplet technique. We present in this work the radial velocity and metallicity of approximately 400 red giant stars in 15 SMC fields, with typical errors of about 7 km s-1 and 0.16 dex, respectively. We added to this information our previously determined metallicity values for 29 clusters and approximately 350 field stars using the identical techniques. Using this enlarged sample, we analyze the metallicity distribution and gradient in this galaxy. We also compare the chemical properties of the clusters and of their surrounding fields. We find a number of surprising results. While the clusters, taken as a whole, show no strong evidence for a metallicity gradient (MG), the field stars exhibit a clear negative gradient in the inner region of the SMC, consistent with the recent results of Dobbie et al. For distances to the center of the galaxy less than 4\ub0, field stars show a considerably smaller metallicity dispersion than that of the clusters. However, in the external SMC regions, clusters and field stars exhibit similar metallicity dispersions. Moreover, in the inner region of the SMC, clusters appear to be concentrated in two groups: one more metal-poor and another more metal-rich than field stars. Individually considered, neither cluster group presents an MG. Most surprisingly, the MG for both stellar populations (clusters and field stars) appears to reverse sign in the outer regions of the SMC. The difference between the cluster metallicity and the mean metallicity of the surrounding field stars turns out to be a strong function of the cluster metallicity. These results could be indicating different chemical evolution histories for these two SMC stellar populations. They could also indicate variations in the chemical behavior of the SMC in its internal and external regions

Recursive conditional means image denoising

Methods and composition for denoising digital camera images are provided herein. The method is based on directly measuring the local statistical structure of natural images in a large training set that has been corrupted with noise mimicking digital camera noise. The measured statistics are conditional means of the ground truth pixel value given a local context of input pixels. Each conditional mean is the Bayes optimal (minimum mean squared error) estimate given the specific local context. The conditional means are measured and applied recursively (e.g., the second conditional mean is measured after denoising with the first conditional mean). Each local context vector consists of only three variables, and hence the conditional means can be measured directly without prior assumptions about the underlying probability distributions, and they can be stored in fixed lookup tables.Board of Regents, University of Texas Syste

The peculiar Na-O anticorrelation of the bulge globular cluster NGC 6440

Context. Galactic Globular Clusters (GCs) are essential tools to understand the earliest epoch of the Milky Way, since they are among the oldest objects in the Universe and can be used to trace its formation and evolution. Current studies using high resolution spectroscopy for many stars in each of a large sample of GCs allow us to develop a detailed observational picture about their formation and their relation with the Galaxy. However, it is necessary to complete this picture by including GCs that belong to all major Galactic components, including the Bulge. Aims. Our aim is to perform a detailed chemical analyses of the bulge GC NGC 6440 in order to determine if this object has Multiple Populations (MPs) and investigate its relation with the Bulge of the Milky Way and with the other Galactic GCs, especially those associated with the Bulge, which are largely poorly studied. Methods. We determined the stellar parameters and the chemical abundances of light elements (Na, Al), iron-peak elements (Fe, Sc, Mn, Co, Ni), $\alpha$-elements (O, Mg, Si, Ca, Ti) and heavy elements (Ba, Eu) in seven red giant members of NGC 6440 using high resolution spectroscopy from FLAMES@UVES. Results. We found a mean iron content of [Fe/H]=-0.50$\pm$0.03 dex in agreement with other studies. We found no internal iron spread. On the other hand, Na and Al show a significant intrinsic spread, but the cluster has no significant O-Na anticorrelation nor exhibits a Mg-Al anticorrelation. The $\alpha$-elements show good agreement with the Bulge field star trend, although they are at the high alpha end and are also higher than those of other GCs of comparable metallicity. The heavy elements are dominated by the r-process, indicating a strong contribution by SNeII. The chemical analysis suggests an origin similar to that of the Bulge field stars.Comment: 12 pages, 13 figures, Accepted for publication in A&

A hot horizontal branch star with a close K-type main-sequence companion

Dynamical interactions in binary systems are thought to play a major role in the formation of extreme horizontal branch stars (EHBs) in the Galactic field. However, it is still unclear if the same mechanisms are at work in globular clusters, where EHBs are predominantly single stars. Here we report on the discovery of a unique close binary system (period ~1.61 days) in the globular cluster NGC6752, comprising an EHB and a main-sequence companion of 0.63+-0.05 Msun. Such a system has no counterpart among nearly two hundred known EHB binaries in the Galactic field. Its discovery suggests that either field studies are incomplete, missing this type of systems possibly because of selection effects, or that a particular EHB formation mechanism is active in clusters but not in the field