6,105 research outputs found

    Standard Giant Branches in the Washington Photometric System

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    We have obtained CCD photometry in the Washington system C,T1 filters for some 850,000 objects associated with 10 Galactic globular clusters and 2 old open clusters. These clusters have well-known metal abundances, spanning a metallicity range of 2.5 dex from [Fe/H]~-2.25 to +0.25 at a spacing of ~0.2 dex. Analogous to the method employed by Da Costa and Armandroff (1990, AJ, 100, 162) for V,I photometry, we then proceed to construct standard giant branches for these clusters. The Washington system technique is found to have three times the metallicity sensitivity of the V,I technique. Thus, for a given photometric accuracy, metallicities can be determined three times more precisely with the Washington technique. We find a linear relationship between (C-T1)o (at M(T1)=-2) and metallicity (on the Zinn 1985, ApJ, 293, 424 scale) exists over the full metallicity range, with an rms of only 0.04 dex. We also derive methods to determine distance, reddening and metallicity simultaneously, and note that the Washington system holds great potential for deriving accurate ages as well.Comment: To be published in the 1999 AJ January issu

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

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    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

    Photometric Metallicities in Bootes I

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    We present new Stromgren and Washington data sets for the Bootes I dwarf galaxy, and combine them with the available SDSS photometry. The goal of this project is to refine a ground-based, practical, accurate method to determine age and metallicity for individual stars in Bootes I that can be selected in an unbiased imaging survey, without having to take spectra. We produce photometric metallicities from Stromgren and Washington photometry, for stellar systems with a range of −1.0>[Fe/H]>−3.5-1.0>[Fe/H]>-3.5. To avoid the decrease in sensitivity of the Stromgren metallicity index on the lower red-giant branch, we replace the Stromgren v-filter with the broader Washington C-filter; we find that CT1byCT_1by is the most successful filter combination, for individual stars with [Fe/H]<−2.0[Fe/H]<-2.0, to maintain ~0.2 dex [Fe/H][Fe/H]-resolution over the whole red-giant branch. We demonstrate that we can break the isochrones' age-metallicity degeneracy with these filters, using stars with log g=2.5-3.0, which have less than a 2% change in their (C−T1)(C-T_1)-colour due to age, over a range of 11-14 Gyr.Comment: 24 pages, 18 figures, accepted by MNRA

    Near-infrared photometry of globular clusters towards the Galactic bulge: Observations and photometric metallicity indicators

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    Indexación: Web of Science; Scopus.We present wide-field JHKS photometry of 16 Galactic globular clusters located towards the Galactic bulge, calibrated on the Two Micron All-Sky Survey photometric system. Differential reddening corrections and statistical field star decontamination are employed for all of these clusters before fitting fiducial sequences to the cluster red giant branches (RGBs). Observed values and uncertainties are reported for several photometric features, including the magnitude of the RGB bump, tip, the horizontal branch (HB) and the slope of the upper RGB. The latest spectroscopically determined chemical abundances are used to build distance- and reddening-independent relations between observed photometric features and cluster metallicity, optimizing the sample size and metallicity baseline of these relations by supplementing our sample with results from the literature.We find that the magnitude difference between the HB and the RGB bump can be used to predict metallicities, in terms of both iron abundance [Fe/H] and global metallicity [M/H], with a precision of better than 0.1 dex in all three near-IR bandpasses for relatively metal-rich ([M/H] ≳ -1) clusters. Meanwhile, both the slope of the upper RGB and the magnitude difference between the RGB tip and bump are useful metallicity indicators over the entire sampled metallicity range (-2 ≲ [M/H] ≲ 0) with a precision of 0.2 dex or better, despite model predictions that the RGB slope may become unreliable at high (near-solar) metallicities. Our results agree with previous calibrations in light of the relevant uncertainties, and we discuss implications for clusters with controversial metallicities as well as directions for further investigation.https://academic.oup.com/mnras/article-lookup/doi/10.1093/mnras/stw243

    Can Drug Court Results Be Predicted? Completion and Termination of Drug Court Participants

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    The substantial growth in Kentucky’s prison population since the 1980s has resulted in increased spending on corrections, both the total amount and as a percentage of total general fund spending. The sustained growth in corrections spending combined with shrinking budgetary realities has created an incentive to explore ways to reduce costs without compromising public safety. Community supervision programs are one alternative to addressing this problem. They are an attractive approach to dealing with certain types of criminals because the cost is significantly lower than incarceration. Drug courts are an example of community supervision that allows drug offenders to avoid imprisonment and receive treatment for their drug abuse while still being supervised by the courts. An assessment of whether drug court participants successfully complete or are prematurely terminated from the program can help policymakers evaluate the effectiveness of drug courts and make improvements. In this study, I sought to measure the impact specific drug or drug types had on completion and termination outcomes for individual participants. In addition, I examined the same explanatory variables’ effects on these outcomes based on the percentage of participants at the county-level. The findings for the individual participants suggest opiate and schedule II users are more likely to successfully complete the program, whereas oxycodone users are less likely. The county-level analysis does not generate any significant findings other than a slightly higher probability of completion in counties with a higher poverty rate. Termination among individuals appears to be less likely for methamphetamine and white participants. However, drug schedule I users seem to have a higher likelihood of being terminated. The greater the percentage of methamphetamine users within a county also decreases termination. Conversely, the higher the percentage of white participants results in a higher tendency for termination. The findings of this study are limited due to the relatively low number of participants who have completed the program and a lack of data regarding the individuals’ education level, employment status, and marital status. These factors have been found in other studies to impact drug court outcomes. The lack of information about how each jurisdiction operates and differences in judicial discretion are also limitations. I believe further study with attention to these limitations is warranted to better assess drug court outcomes in Kentucky. Continued study of drug courts should also be expanded to examine how these variables and outcomes of interest relate to recidivism

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

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    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
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