14228406
Line formation in solar granulation VII. CO lines and the solar C and O isotopic abundances
CO spectral line formation in the Sun has long been a source of consternation for solar physicists, as have the elemental a bundances it seems to imply. We modelled solar CO line formation using a realistic, ab initio, time-dependent 3D radiative-hydrodynamic model atmosphere. Results were compared with space-based observations from the ATMOSspace shuttle experiment. We employed weak 12 C 16 O, 13 C 16 O and 12 C 18 O lines from the fundamental (�v = 1) and first overtone ( �v = 2) bands to determine the solar carbon abundance, as well as the 12 C/ 13 C and 16 O/ 18 O isotopic ratios. A weighted solar carbon abundance of logǫC = 8.39± 0.05 was found. We note with satisfaction that the derived abundance is identical to our recent 3D determination based on Ci, [Ci], C2 and CH lines, increasing our confidence in the accuracy of bot h results. Identical calculations were carried out using 1D models, but only the 3D model was able to produce abundance agreement between different CO lines and the other atomic and molecular diagnostics. Solar 12 C/ 13 C and 16 O/ 18 O ratios were measured as 86.8 +3.9 −3.7 (δ 13 C = 30 +46 −44) and 479 +29 −28 (δ 18 O = 41 +67 −59), respectively. These values may require current theories of solar system formation, such as the CO self-shielding hypothesis, to be revised. Excellent agreement was seen between observed and predicted weak CO line shapes, without invoking micro- or macroturbulence. Agreement breaks down for the strongest CO lines however, which are formed in very high atmospheric layers. Whilst the line asymmetries (bisectors) were reasonably well reproduced, line strengt hs predicted on the basis of C and O abundances from other diagnostics were weaker than observed. The simplest explanation is that temperatures are overestimated in the highest layers of the 3D simulation. Thus, our analysis supports the presence of a COmosphere above the traditional photospheric temperature minimum, with an average temperature of less than 4000K. The shortcoming of the model atmosphere is not surprising, given that it was never intended to properly describe such high layers.
119289890
The elemental composition of the Sun I. The intermediate mass elements Na to Ca
The chemical composition of the Sun is an essential piece of reference data for astronomy, cosmology, astroparticle, space and geophysics: elemental abundances of essentially all astronomical objects are referenced to the solar composition, and basically every process involving the Sun depends on its composition. This article, dealing with the intermediate-mass elements Na to Ca, is the first in a series describing the comprehensive re-determination of the solar composition. In this series we severely scrutinise all ingredients of the analysis across all elements, to obtain the most accurate, homogeneous and reliable results possible. We employ a highly realistic 3D hydrodynamic model of the solar photosphere, which has successfully passed an arsenal of observational diagnostics. For comparison, and to quantify remaining systematic errors, we repeat the analysis using three different 1D hydrostatic model atmospheres (marcs, miss and Holweger & Muller 1974, Sol. Phys., 39, 19) and a horizontally and temporally-averaged version of the 3D model (〈3D〉). We account for departures from local thermodynamic equilibrium (LTE) wherever possible. We have scoured the literature for the best possible input data, carefully assessing transition probabilities, hyperfine splitting, partition functions and other data for inclusion in the analysis. We have put the lines we use through a very stringent quality check in terms of their observed profiles and atomic data, and discarded all that we suspect to be blended. Our final recommended 3D+NLTE abundances are: log e = 6:21 ± 0:04, log e = 7:59 ± 0:04, log e = 6:43 ± 0:04, log e = 7:51 ± 0:03, log e = 5:41 ± 0:03, log e = 7:13 ± 0:03, log e = 5:04 ± 0:05 and log e = 6:32 ± 0:03. The uncertainties include both statistical and systematic errors. Our results are systematically smaller than most previous ones with the 1D semi-empirical Holweger & Muller model, whereas the 〈3D〉 model returns abundances very similar to the full 3D calculations. This analysis provides a complete description and a slight update of the results presented in Asplund et al. (2009, ARA&A, 47, 481) for Na to Ca, and includes full details of all lines and input data used.
17921922
The Chemical Composition of the Sun
The solar chemical composition is an important ingredient in our understanding of the formation, structure, and evolution of both the Sun and our Solar System. Furthermore, it is an essential refer ...
118475756
The elemental composition of the Sun - II. The iron group elements Sc to Ni
We redetermine the abundances of all iron group nuclei in the Sun, based on neutral and singly-ionised lines of Sc, Ti, V, Mn, Fe, Co and Ni in the solar spectrum. We employ a realistic 3D hydrodynamic model solar atmosphere, corrections for departures from local thermodynamic equilibrium (NLTE), stringent line selection procedures and high quality observational data. We have scoured the literature for the best quality oscillator strengths, hyperfine constants and isotopic separations available for our chosen lines. We find log ∈ = 3.16 ± 0.04, log ∈ = 4.93 ± 0.04, log ∈ = 3.89 ± 0.08, log ∈ = 5.62 ± 0.04, log ∈ = 5.42 ± 0.04, log ∈ = 7.47 ± 0.04, log ∈ = 4.93 ± 0.05 and log ∈ = 6.20 ± 0.04. Our uncertainties factor in both statistical and systematic errors (the latter estimated for possible errors in the model atmospheres and NLTE line formation). The new abundances are generally in good agreement with the CI meteoritic abundances but with some notable exceptions. This analysis constitutes both a full exposition and a slight update of the preliminary results we presented in Asplund et al. (2009, ARA&A, 47, 481), including full line lists and details of all input data we employed.
3586757
Fundamental statistical limitations of future dark matter direct detection experiments
We discuss irreducible statistical limitations of future ton-scale dark matter direct detection experiments. We focus in particular on the coverage of confidence intervals, which quantifies the reliability of the statistical method used to reconstruct the dark matter parameters and the bias of the reconstructed parameters. We study 36 benchmark dark matter models within the reach of upcoming ton-scale experiments. We find that approximate confidence intervals from a profile-likelihood analysis exactly cover or overcover the true values of the weakly interacting massive particle (WIMP) parameters, and hence are conservative. We evaluate the probability that unavoidable statistical fluctuations in the data might lead to a biased reconstruction of the dark matter parameters, or large uncertainties on the reconstructed parameter values. We show that this probability can be surprisingly large, even for benchmark models leading to a large event rate of order a hundred counts. We find that combining data sets from two different targets leads to improved coverage properties, as well as a substantial reduction of statistical bias and uncertainty on the dark matter parameters.
55777556
Pippi — Painless parsing, post-processing and plotting of posterior and likelihood samples
Abstract.Interpreting samples from likelihood or posterior probability density functions is rarely as straightforward as it seems it should be. Producing publication-quality graphics of these distributions is often similarly painful. In this short note I describe pippi, a simple, publicly available package for parsing and post-processing such samples, as well as generating high-quality PDF graphics of the results. Pippi is easily and extensively configurable and customisable, both in its options for parsing and post-processing samples, and in the visual aspects of the figures it produces. I illustrate some of these using an existing supersymmetric global fit, performed in the context of a gamma-ray search for dark matter. Pippi can be downloaded and followed at http://github.com/patscott/pippi.
119201232
Sunyaev–Zel’dovich observation of the Bullet-like cluster Abell 2146 with the Arcminute Microkelvin Imager
We present 13.9―18.2 GHz observations of the Sunyaev-Zel'dovich (SZ) effect towards Abell 2146 using the Arcminute Microkelvin Imager (AMI). The cluster is detected with a peak signal-to-noise ratio of 13ϭ in the radio source subtracted map from 9 h of data. Comparison of the SZ image with the X-ray image from Russell et al. suggests that both have extended regions which lie approximately perpendicular to one another, with their emission peaks significantly displaced. These features indicate non-uniformities in the distributions of the gas temperature and pressure, and suggest complex dynamics indicative of a cluster merger. We use a fast, Bayesian cluster analysis to explore the high-dimensional parameter space of the cluster-plus-sources model to obtain robust cluster parameter estimates in the presence of radio point sources, receiver noise and primordial cosmic microwave background (CMB) anisotropy; despite the substantial radio emission from the direction of Abell 2146, the probability of SZ + CMB primordial structure + radio sources + receiver noise to CMB + radio sources + receiver noise is 3 x 10 6 : 1. We compare the results from three different cluster models. Our preferred model exploits the observation that the gas fractions do not appear to vary greatly between clusters. Given the relative masses of the two merging systems in Abell 2146, the mean gas temperature can be deduced from the virial theorem (assuming all of the kinetic energy is in the form of internal gas energy) without being affected significantly by the merger event, provided the primary cluster was virialized before the merger. In this model we fit a simple spherical isothermal β-model to our data, despite the inadequacy of this model for a merging system like Abell 2146, and assume the cluster follows the mass-temperature relation of a virialized, singular, isothermal sphere. We note that this model avoids inferring large-scale cluster parameters internal to r 200 under the widely used assumption of hydrostatic equilibrium. We find that at r 200 the average total mass M T = (4.1 ± 0.5) x 10 14 h ―1 M⊙ and the mean gas temperature T = 4.5 ± 0.5 keV.
59386633
Bayesian analysis of weak gravitational lensing and Sunyaev-Zel'dovich data for six galaxy clusters
We present an analysis of observations made with the Arcminute Microkelvin Imager (AMI) and the Canada–France–Hawaii Telescope (CFHT) of six galaxy clusters in a redshift range of 0.16–0.41. The cluster gas is modelled using the Sunyaev–Zel’dovich (SZ) data provided by AMI, while the total mass is modelled using the lensing data from the CFHT. In this paper, we (i) find very good agreement between SZ measurements (assuming large-scale virialization and a gas-fraction prior) and lensing measurements of the total cluster masses out to r200; (ii) perform the first multiple-component weak-lensing analysis of A115; (iii) confirm the unusual separation between the gas and mass components in A1914 and (iv) jointly analyse the SZ and lensing data for the relaxed cluster A611, confirming our use of a simulation-derived mass–temperature relation for parametrizing measurements of the SZ effect.
118474158
Parameterization Effects in the analysis of Sunyaev-Zel'dovich Observations
Current studies of the Sunyaev-Zel'dovich (SZ) effect are based on parameterized models of galaxy clusters. Investigating the effects of different parameterizations and the assumptions made within any parameterized model are,therefore, crucial in extracting cluster physical properties in a robust way. In this paper, we study three different parameterizations of the well-studied isothermal beta-model applied to a simulated Arcminute Microkelvin Imager observation of a galaxy cluster through its SZ effect. We propose a method for generating simulated SZ data that leads to consistent values of cluster physical properties upon employing different parameterization methods. The results of our study clearly reveal different biases and constraints induced by each parameterization. We also find that the way in which conventional assumptions on the dynamical state of the gas and dark matter are applied to a parameterized cluster model play a significant role in both determining degeneracies and deriving apparent constraints. By comparing different parameterizations, we confirm the model parameters that cannot be constrained by SZ data alone. We also find that the assumption of isothermality when the cluster hot gas is in hydrostatic equilibrium with its total gravitational potential introduces clear biases in the posterior probability distributions of the cluster parameters, as the temperature gradient is eliminated from the analysis. However, our results show that by employing a scaling relation to link cluster total mass internal to the virial radius with mean temperature, we are able to obtain reliable results for extracting physical cluster parametes compared to the corresponding true input values in the simulation .
17275325
Follow-up observations at 16 and 33 GHz of extragalactic sources from WMAP 3-yr data: II – Flux density variability
Using the Arcminute Microkelvin Imager (AMI) at 16 GHz and the Very Small Array (VSA) at 33 GHz to make follow-up observations of sources in the New Extragalactic WMAP Point Source catalogue, we have investigated the flux density variability in a complete sample of 97 sources over time-scales of a few months to ≈1.5 yr. 
 
 
 
We find that 53 per cent of the 93 sources, for which we have multiple observations, are variable, at the 99 per cent confidence level, above the flux density calibration uncertainties of ≈4 per cent at 16 GHz; the fraction of sources having varied by more than 20 per cent is 15 per cent at 16 GHz and 20 per cent at 33 GHz. Not only is this common occurrence of variability at high frequency of interest for source physics, but also strategies for coping with source contamination in cosmic microwave background work must take this variability into account. 
 
 
 
There is no strong evidence of a correlation between variability and flux density for the sample as a whole. For those sources classified as variable, the mean fractional rms variation in flux density increases significantly with the length of time separating observation pairs. Using a maximum likelihood method, we calculate the correlation in the variability at the two frequencies in a subset of sources classified as variable from both the AMI and VSA data and find the Pearson product–moment correlation coefficient to be very high (0.955 ± 0.034). We also find the degree of variability at 16 GHz (0.202 ± 0.028) to be very similar to that at 33 GHz (0.224 ± 0.039). 
 
 
 
Finally, we have investigated the relationship between variability and spectral index, α33.7513.9 (where S∝ν−α), and find a significant difference in the spectral indices of the variable sources (−0.06 ± 0.05) and non-variable sources (0.13 ± 0.04).
10370174
Source subtraction for the extended Very Small Array and 33-GHz source count estimates
We describe the source subtraction strategy and observations for the extended Very Small Array (VSA), a cosmic microwave background interferometer operating at 33 GHz. A total of 453 sources were monitored at 33 GHz using a dedicated source subtraction baseline. 131 sources brighter than 20 mJy were directly subtracted from the VSA visibility data. Some characteristics of the subtracted sources, such as spectra and variability, are discussed. The 33-GHz source counts are estimated from a sample selected at 15 GHz. The selection of VSA fields in order to avoid bright sources introduces a bias into the observed counts. This bias is corrected and the resulting source count is estimated to be complete in the flux-density range 20‐114 mJy. The 33-GHz source counts are used to calculate a correction to the VSA power spectrum for sources below the subtraction limit. Ke yw ords: surveys ‐ cosmic microwave background ‐ radio continuum: galaxies.