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Principal Component Abundance Analysis of Microlensed Bulge Dwarf and Subgiant Stars

Andrews B. H., Weinberg D. H., Johnson J. A., Bensby T., Feltzing S.

Acta Astronomica

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2012

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Vol. 62, No. 3

269--279

EN

Elemental abundance patterns can provide vital clues to the formation and enrichment history of a stellar population. Here we present an investigation of the Galactic bulge, where we apply principal component abundance analysis (PCAA) - a principal component decomposition of relative abundances [X/Fe] - to a sample of 35 microlensed bulge dwarf and subgiant stars, characterizing their distribution in the 12-dimensional space defined by their measured elemental abundances. The first principal component PC1, which suffices to describe the abundance patterns of most stars in the sample, shows a strong contribution from α-elements, reflecting the relative contributions of Type II and Type Ia supernovae. The second principal component PC2 is characterized by a Na-Ni correlation, the likely product of metallicity-dependent Type II supernova yields. The distribution in PC1 is bimodal, showing that the bimodality previously found in the [Fe/H] values of these stars is robustly and independently recovered by looking at only their relative abundance patterns. The two metal-rich stars that are α-enhanced have outlier values of PC2 and PC3, respectively, further evidence that they have distinctive enrichment histories. Applying PCAA to a sample of local thin and thick disk dwarfs yields a nearly identical PC1. In PC1, the metal-rich and metal-poor bulge dwarfs track kinematically selected thin and thick disk dwarfs, respectively, suggesting broadly similar α-enrichment histories. However, the disk PC2 is dominated by a Y-Ba correlation, likely indicating a contribution of s-process enrichment from long-lived asymptotic giant branch stars that is absent from the bulge PC2 because of its rapid formation.

2

Total to Selective Extinction Ratios and Visual Extinctions from Ultraviolet Data

Geminale A., Popowski P.

Acta Astronomica

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2004

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Vol. 54, No. 4

375--390

EN

We present determinations of the total to selective extinction ratio RV and visual extinction AV values for Milky Way stars using ultraviolet color excesses. We extend the analysis of Gnaciński and Sikorski (1999) by using non-equal weights derived from observational errors. We present a detailed discussion of various statistical errors. In addition, we estimate the level of systematic errors by considering different normalization of the extinction curve adopted by Wegner (2002). Our catalog of 782 RV and AV values and their errors is available in the electronic form on the World Wide Web.

3

Extinction in the Galaxy from Surface Brightnesses of ESO-LV Galaxies: Testing ''Standard'' Extinction Maps

Chołoniewski J., Valentijn E. A.

Acta Astronomica

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2003

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Vol. 56, No. 3

265--280

EN

The relative extinction in the Galaxy computed with new method by Chołoniewski and Valentijn is compared with three patterns: Schlegel, Finkbeiner and Davis, Burstein and Heiles and the cosecans law. It is shown that extinction of SFD is more reliable than that of BH since it stronger correlates with our new extinction. The smallest correlation coefficient was obtained for the cosecans law. Linear regression analysis show that SFD overestimate the extinction by a factor of 1.4. Our results clearly indicate that there is non-zero extinction at the Galactic South pole and that the extinction near the Galactic equator (|b|<40°) is significantly larger in the Southern than in the Northern hemisphere.

4

Extinction in the Galaxy from Surface Brightnesses of ESO-LV Galaxies: Determination of AR/AB ratio

Chołoniewski J., Valentijn E. A.

Acta Astronomica

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2003

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Vol. 56, No. 3

249--264

EN

A new method for the determination of the extinction in the Galaxy is proposed. The method uses surface brightnesses of external galaxies in the B and R-bands. The observational data have been taken from the ESO-LV galaxy catalog. As a first application of our model we derive the ratio of R-band to B-band extinction. We introduce two methods for computing the ratio which give: 0.62±0.05 (the first method) and 0.64±0.06 (the second method) which is in agreement with the recent literature value of 0.61. This agreement confirms the validity and efficiency of our model and is an independent verification for the standard value of the "total to selective extinction". The method of extinction determination introduced in this paper will be explored in subsequent publication.