54675242
Impacts of Dark Stars on Reionization and Signatures in the Cosmic Microwave Background
We perform a detailed and systematic investigation of the possible impacts of dark stars on the reionization history of the universe, and its signatures in the cosmic microwave background (CMB). We compute hydrogen reionization histories, CMB optical depths, and anisotropy power spectra for a range of stellar populations including dark stars. If dark stars capture large amounts of dark matter (DM) via nuclear scattering, reionization can be substantially delayed, leading to decreases in the integrated optical depth to last scattering and large-scale power in the EE polarization power spectrum. Using the integrated optical depth observed by the Wilkinson Microwave Anistropy Probe seven-year mission, in our canonical reionization model we rule out the section of parameter space where dark stars with high scattering-induced capture rates tie up 90% of all the first star-forming baryons, and live for 250 Myr. When nuclear scattering delivers only moderate amounts of DM, reionization can instead be sped up slightly, modestly increasing the CMB optical depth. If dark stars do not obtain any DM via nuclear scattering, effectsonreionizationandtheCMBarenegligible.TheeffectsofdarkstarsonreionizationanditsCMBmarkerscan be largely mimicked or compensated for by changes in the existing parameters of reionization models, making dark stars difficult to disentangle from astrophysical uncertainties, but also widening the range of standard parameters in reionization models that can be made consistent with observations.
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.
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.
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.
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.
4277613
Observation of a Rapidly Pulsating Radio Source
Unusual signals from pulsating radio sources have been recorded at the Mullard Radio Astronomy Observatory. The radiation seems to come from local objects within the galaxy, and may be associated with oscillations of white dwarf or neutron stars.
20064658
AMI radio continuum observations of young stellar objects with known outflows
We present 16 GHz (1.9 cm) deep radio continuum observations made with the Arcminute Microkelvin Imager (AMI) of a sample of low-mass young stars driving jets. We combine these new data with archival information from an extensive literature search to examine spectral energy distributions (SEDs) for each source and calculate both the radio and sub-mm spectral indices in two different scenarios: (1) fixing the dust temperature (T_d) according to evolutionary class; and (2) allowing T_d to vary. We use the results of this analysis to place constraints on the physical mechanisms responsible for the radio emission. From AMI data alone, as well as from model fitting to the full SED in both scenarios, we find that 80 per cent of the objects in this sample have spectral indices consistent with free–free emission. We find an average spectral index in both T_d scenarios, consistent with free–free emission. We examine correlations of the radio luminosity with bolometric luminosity, envelope mass and outflow force, and find that these data are consistent with the strong correlation with envelope mass seen in lower luminosity samples. We examine the errors associated with determining the radio luminosity and find that the dominant source of error is the uncertainty on the opacity index, β. We examine the SEDs for variability in these young objects, and find evidence for possible radio flare events in the histories of L1551 IRS 5 and Serpens SMM 1.
10867413
Detection of cosmic microwave background structure in a second field with the Cosmic Anisotropy Telescope
We describe observations at frequencies near 15 GHz of the second 2×2 deg2 field imaged with the Cambridge Cosmic Anisotropy Telescope (CAT). After the removal of discrete radio sources, structure is detected in the images on characteristic scales of about half a degree, corresponding to spherical harmonic multipoles in the range l≈330–680. A Bayesian analysis confirms that the signal arises predominantly from the cosmic microwave background (CMB) radiation for multipoles in the lower half of this range; the average broad-band power in a bin with centroid =422 (θ≈51 arcmin) is estimated to be . For multipoles centred on l=615 (θ≈35 arcmin), we find contamination from Galactic emission is significant, and constrain the CMB contribution to the measured power in this bin to be ΔTT<2.0×10−5 (1σ upper limit). These new results are consistent with the first detection made by CAT in a completely different area of sky. Together with data from other experiments, this new CAT detection adds weight to earlier evidence from CAT for a downturn in the CMB power spectrum on scales smaller than 1 deg. Improved limits on the values of H0 and Ω are determined using the new CAT data.
18192370
First results from the Very Small Array – IV. Cosmological parameter estimation
We investigate the constraints on basic cosmological parameters set by the first compact-configuration observations of the Very Small Array (VSA), and other cosmological data sets, in the standard inflationary ΛCDM model. Using the weak priors 40 < H0 < 90 km s−1 Mpc−1 and 0 < τ < 0.5, we find that the VSA and COBE-DMR data alone produce the constraints Ωtot= 1.03+0.12−0.12, Ωbh2= 0.029+0.009−0.009, Ωcdmh2= 0.13+0.08−0.05 and ns= 1.04+0.11−0.08 at the 68 per cent confidence level. Adding in the Type Ia supernova constraints, we additionally find Ωm= 0.32+0.09−0.06 and ΩΛ= 0.71+0.07−0.07. These constraints are consistent with those found by the BOOMERanG, DASI and MAXIMA experiments. We also find that, by combining all these cosmic microwave background experiments and assuming the Hubble Space Telescope Key Project limits for H0 (for which the X-ray plus Sunyaev–Zel'dovich route gives a similar result), we obtain the tight constraints Ωm= 0.28+0.14−0.07 and ΩΛ= 0.72+0.07−0.13, which are consistent with, but independent of, those obtained using the supernova data.
56432272
Future Science Prospects for AMI
The Arcminute Microkelvin Imager (AMI) is a telescope specifically designed for high sensitivity measurements of low-surface-brightness features at cm-wavelength and has unique, important capabilities. It consists of two interferometer arrays operating over 13.5-18 GHz that image structures on scales of 0.5-10 arcmin with very low systematics. The Small Array (AMI-SA; ten 3.7-m antennas) couples very well to Sunyaev-Zel'dovich features from galaxy clusters and to many Galactic features. The Large Array (AMI-LA; eight 13-m antennas) has a collecting area ten times that of the AMI-SA and longer baselines, crucially allowing the removal of the effects of confusing radio point sources from regions of low surface-brightness, extended emission. Moreover AMI provides fast, deep object surveying and allows monitoring of large numbers of objects. In this White Paper we review the new science - both Galactic and extragalactic - already achieved with AMI and outline the prospects for much more.