Abundances In Very Metal Poor Dwarf Stars

We discuss the detailed composition of 28 extremely metal-poor dwarfs, 22 of which are from the Hamburg/ESO Survey, based on Keck Echelle spectra. Our sample has a median [Fe/H] of -2.7 dex, extends to -3.5 dex, and is somewhat less metal-poor than was expected from [Fe/H](HK,HES) determined from low resolution spectra. Our analysis supports the existence of a sharp decline in the distribution of halo stars with metallicity below [Fe/H] = -3.0 dex. So far no additional turnoff stars with [Fe/H]}<-3.5 have been identified in our follow up efforts. For the best observed elements between Mg and Ni, we find that the abundance ratios appear to have reached a plateau, i.e. [X/Fe] is approximately constant as a function of [Fe/H], except for Cr, Mn and Co, which show trends of abundance ratios varying with [Fe/H]. These abundance ratios at low metallicity correspond approximately to the yield expected from Type II SN with a narrow range in mass and explosion parameters; high mass Type II SN progenitors are required. The dispersion of [X/Fe] about this plateau level is surprisingly small, and is still dominated by measurement errors rather than intrinsic scatter. The dispersion in neutron-capture elements, and the abundance trends for Cr, Mn and Co are consistent with previous studies of evolved EMP stars. Two dwarfs in the sample are carbon stars, while two others have significant C enhancements, all with C12/C13 ~ 7 and with C/N between 10 and 150. Three of these C-rich stars have large enhancements of the heavy neutron capture elements, including lead, which implies a strong s-process contribution, presumably from binary mass transfer; the fourth shows no excess of Sr or Ba.Comment: Accepted for publication in the Ap

Spectroscopic Analysis of Two Carbon Rich Post-AGB Stars

The chemical compositions of the C-rich pAGB stars IRAS 05113+1347 and IRAS 22272+5424 are determined from high-resolution optical spectra using standard LTE model atmosphere-based techniques. The stars are C, N, and $s$-process enriched suggesting efficient operation of the third-dredge up in the AGB star following a first dredge-up that increased the N abundance. Lithium is present with an abundance requiring Li manufacture. With this pair, abundance analyses are now available for 11 C-rich pAGBs. A common history is indicated and, in particular, the $s$-abundances, especially the relative abundances of light to heavy $s$-process elements, follow recent predictions for the third dredge-up in AGB stars.Comment: 41 pages (including 10 figs). 2001, ApJ, Accepte

Search for the standard model Higgs boson decaying to a bb pair in events with one charged lepton and large missing transverse energy using the full CDF data set

We present a search for the standard model Higgs boson produced in association with a W boson in sqrt(s) = 1.96 TeV p-pbar collision data collected with the CDF II detector at the Tevatron corresponding to an integrated luminosity of 9.45 fb-1. In events consistent with the decay of the Higgs boson to a bottom-quark pair and the W boson to an electron or muon and a neutrino, we set 95% credibility level upper limits on the WH production cross section times the H->bb branching ratio as a function of Higgs boson mass. At a Higgs boson mass of 125 GeV/c2 we observe (expect) a limit of 4.9 (2.8) times the standard model value.Comment: Submitted to Phys. Rev. Lett (v2 contains clarifications suggested by PRL

Search for the standard model Higgs boson decaying to a bbˉb\bar{b} pair in events with no charged leptons and large missing transverse energy using the full CDF data set

We report on a search for the standard model Higgs boson produced in association with a vector boson in the full data set of proton-antiproton collisions at $\sqrt{s} = 1.96$ TeV recorded by the CDF II detector at the Tevatron, corresponding to an integrated luminosity of 9.45 fb$^{-1}$. We consider events having no identified charged lepton, a transverse energy imbalance, and two or three jets, of which at least one is consistent with originating from the decay of a $b$ quark. We place 95% credibility level upper limits on the production cross section times standard model branching fraction for several mass hypotheses between 90 and $150 \mathrm{GeV}/c^2$. For a Higgs boson mass of $125 \mathrm{GeV}/c^2$, the observed (expected) limit is 6.7 (3.6) times the standard model prediction.Comment: Accepted by Phys. Rev. Let

Search for the standard model Higgs boson decaying to a bb pair in events with two oppositely-charged leptons using the full CDF data set

We present a search for the standard model Higgs boson produced in association with a Z boson in data collected with the CDF II detector at the Tevatron, corresponding to an integrated luminosity of 9.45/fb. In events consistent with the decay of the Higgs boson to a bottom-quark pair and the Z boson to electron or muon pairs, we set 95% credibility level upper limits on the ZH production cross section times the H -> bb branching ratio as a function of Higgs boson mass. At a Higgs boson mass of 125 GeV/c^2 we observe (expect) a limit of 7.1 (3.9) times the standard model value.Comment: To be submitted to Phys. Rev. Let

Chemical Abundances from Inversions of Stellar Spectra: Analysis of Solar-Type Stars with Homogeneous and Static Model Atmospheres

Spectra of late-type stars are usually analyzed with static model atmospheres in local thermodynamic equilibrium (LTE) and a homogeneous plane-parallel or spherically symmetric geometry. The energy balance requires particular attention, as two elements which are particularly difficult to model play an important role: line blanketing and convection. Inversion techniques are able to bypass the difficulties of a detailed description of the energy balance. Assuming that the atmosphere is in hydrostatic equilibrium and LTE, it is possible to constrain its structure from spectroscopic observations. Among the most serious approximations still implicit in the method is a static and homogeneous geometry. In this paper, we take advantage of a realistic three-dimensional radiative hydrodynamical simulation of the solar surface to check the systematic errors incurred by an inversion assuming a plane-parallel horizontally-homogeneous atmosphere. The thermal structure recovered resembles the spatial and time average of the three-dimensional atmosphere. Furthermore, the abundances retrieved are typically within 10% (0.04 dex) of the abundances used to construct the simulation. The application to a fairly complete dataset from the solar spectrum provides further confidence in previous analyses of the solar composition. There is only a narrow range of one-dimensional thermal structures able to fit the absorption lines in the spectrum of the Sun. With our carefully selected dataset, random errors are about a factor of two smaller than systematic errors. A small number of strong metal lines can provide very reliable results. We foresee no major difficulty in applying the technique to other similar stars, and obtaining similar accuracies, using spectra with a resolving power about 50,000 and a signal-to-noise ratio as low as 30.Comment: 65 pages, figures included; uses aastex; to appear in The Astrophysical Journa

Learning to Think Iconically in the Human and Social Sciences: Iconic Standards of Understanding as a Pivotal Challenge for Method Development

Theoretically as well as alongside an empirical research idea, this paper outlines conditions for the development of social scientific empirical methods able to further exploit the iconic potential of the image. Reconstructing the role of formal pictorial elements for the standards of understanding within the medium “image” is considered pivotal in this endeavor. Within the context of language, standards of communication have already been extensively researched. The linguistic format of the narrative, for instance, is well studied. Up to now, though, comparable formal vehicles of iconic semantics have only been examined in aesthetics and art history. Nevertheless, standards of iconic understanding are part of our implicit knowledge, are incessantly in use in everyday practice and, thus, the basis of everyday identity formation. With the help of empirical methods based on an iconic logos we can deepen our understanding of orientations, longings, and anxieties of our time that are often silently conveyed by images. Fashion will be outlined as a prototypical field, in which an empirically based development of such methods might start off

Abundances of 30 elements in 23 metal-poor stars

We report the abundances of 30 elements in 23 metal-poor ([Fe/H] <-1.7) giants. These are based on 7774 equivalent widths and spectral synthesis of 229 additional lines. Hyperfine splitting is taken into account when appropriate. Our choice of model atmospheres has the most influence on the accuracy of our abundances. We consider the effect of different model atmospheres on our results. In addition to the random errors in Teff, log g, and microturbulent velocity, there are several sources of systematic error. These include using Teff determined from FeI lines rather than colors, ignoring NLTE effects on the FeI/FeII ionization balance, using models with solar [alpha/Fe] ratios and using Kurucz models with overshooting. Of these, only the use of models with solar [alpha/Fe] ratios had a negligible effect. However, while the absolute abundances can change by > 0.10 dex, the relative abundances, especially between closely allied atoms such as the rare earth group, often show only small (<0.03 dex) changes. We found that some strong lines of FeI, MnI and CrI consistently gave lower abundances by ~0.2 dex, a number larger than the quoted errors in the gf values. After considering a model with depth-dependent microturbulent velocity and a model with hotter temperatures in the upper layers, we conclude that the latter did a better job of resolving the problem and agreeing with observational evidence for the structure of stars. The error analysis includes the effects of correlation of Teff, log g, and microturbulent velocity errors, which is crucial for certain element ratios, such as [Mg/Fe]. The abundances presented here are being analyzed and discussed in a separate series of papers.Comment: 27 pages, 9 figures, Table 2 included separately, to published in ApJ

Remarks on the Concept of Critique in Habermasian Thought

The main purpose of this paper is to examine the concept of critique in Habermasian thought. Given that the concept of critique is a central theoretical category in the work of the Frankfurt School, it comes as a surprise that little in the way of a systematic account which sheds light on the multifaceted meanings of the concept of critique in Habermas’s oeuvre can be found in the literature. This paper aims to fill this gap by exploring the various meanings that Habermas attributes to the concept of critique in 10 key thematic areas of his writings: (1) the public sphere, (2) knowledge, (3) language, (4) morality, (5) ethics, (6) evolution, (7) legitimation, (8) democracy, (9) religion, and (10) modernity. On the basis of a detailed analysis of Habermas’s multifaceted concerns with the nature and function of critique, the study seeks to demonstrate that the concept of critique can be considered not only as a constitutive element but also as a normative cornerstone of Habermasian thought. The paper draws to a close by reflecting on some of the limitations of Habermas’s conception of critique, arguing that in order to be truly critical in the Habermasian sense we need to turn the subject of critique into an object of critique