118516213
Sunyaev-Zel'dovich observations of LoCuSS clusters with the Arcminute Microkelvin Imager: high X-ray luminosity sample
We present observations from the Small Array of the Arcminut e Microkelvin Imager (AMI) of eight high X-ray luminosity galaxy cluster systems selec ted from the Local Cluster Substructure Survey (LoCuSS) sample. We detect the Sunyaev-Ze l’dovich (SZ) effect in seven of these clusters. With the assumptions that galaxy clusters a r i othermal, have a density profile described by a spherical β -model and obey the theoretical M-T relation, we are able to d erive cluster parameters at r200 from our SZ data. With the additional assumption of hydrosta tic equilibrium we are able to derive parameters at r500. We present posterior probability distributions for cluster parameters such as mass, radius and temp erature ( TSZ,MT ). Combining our sample with that of AMI Consortium: Rodrı́guez-Gonzálvez et al. (2011) and using largeradius X-ray temperature estimates ( TX ) from Chandra andSuzaku observations, we find that there is reasonable correspondence between TX andTSZ,MT values at lowTX , but that for clusters withTX above around 6keV the correspondence breaks down with TX exceedingTSZ,MT ; we stress that this finding is based on just ten clusters.
118451498
AMI Large Array radio continuum observations of Spitzer c2d small clouds and cores
We perform deep 1.8 cm radio continuum imaging towards thirteen protostellar regions selected from the Spitzer c2d small clouds and cores programme at high resolution (25 00 ) in order to detect and quantify the cm‐wave emission from deeply embedded young protostars. Within these regions we detect fifteen compact radio sources which we identify as radio protostars including two probable new detections. The sample is in general of low bolometric luminosity and contains several of the newly detected VeLLO sources. We determine the 1.8 cm radio luminosity to bolometric luminosity correlation, Lrad − Lbol, for the sample and discuss the nature of the radio emission in terms of the available sources of ionized gas. We also investigate the Lrad− LIR correlation and suggest that radio flux density may be used as a proxy for the internal luminosity of low luminosity protostars.
1866023
AMI Galactic Plane Survey at 16 GHz – I. Observing, mapping and source extraction
The Arcminute Microkelvin Imager (AMI) Galactic Plane Survey is a large-area survey of the outer Galactic plane to provide arcminute resolution images at milli-Jansky sensitivity in the centimetre-wave band. Here we present the first data release of the survey, consisting of 868 deg^2 of the Galactic plane, covering the area 76° ⪅ l ⪅ 170° between latitudes of |b| ⪅ 5°, at a central frequency of 15.75 GHz (1.9 cm). We describe in detail the drift-scan observations which have been used to construct the maps, including the techniques used for observing, mapping and source extraction, and summarize the properties of the finalized data sets. These observations constitute the most sensitive Galactic plane survey of large extent at centimetre-wave frequencies greater than 1.4 GHz.
18950684
The Very Small Array - status report
We are contructing an interferometric telescope, the Very Small Array, to study the cosmic microwave background on angular scales 0.2--4.5 degrees. The physical layout and electronic design of the telescope are optimised to give maximum protection from systematic effects, while still providing sufficient sensitivity to make high signal-to-noise images. A prototype single baseline is currently being tested, with scientific results expected during 2000.
17100244
Multifrequency spectral analysis of extragalactic radio sources in the 33‐GHz VSA catalogue: sources with flattening and upturn spectrum
We present an analysis of the spectral properties of the extragalactic radio sources in the nearly complete Very Small Array (VSA) sample at 33 GHz. Data from different surveys are used to study source spectra between 1.4 and 33 GHz. We find that, in general, spectra cannot be well described by a single power law in the range of frequencies considered. In particular, most of the VSA sources that are steep between 1.4 and 5 GHz, show a spectral flattening at ν > 5 GHz. We identify 20 objects (19 per cent of the sample) clearly characterized by an upturn spectrum, i.e. a spectrum falling at low frequencies (ν less than or similar to 5 GHz) and inverted at higher frequencies. Spectra with high-frequency flattening or upturn shape are supposed to occur when the emission from the active galactic nucleus (AGN) compact core begins to dominate over the component from extended lobes. This picture fits well with the AGN unified scheme, for objects observed at intermediate viewing angles of the AGN jet. Finally, we discuss implications that this class of sources can have on future cosmic microwave background observations at high resolution.
7064706
The CMB power spectrum out to l=1400 measured by the VSA
We have observed the cosmic microwave background (CMB) in three regions of sky using the Very Small Array (VSA) in an extended configuration with antennas of beamwidth 2 degrees at 34 GHz. Combined with data from previous VSA observations using a more compact array with larger beamwidth, we measure the power spectrum of the primordial CMB anisotropies between angular multipoles l = 160 - 1400. Such measurements at high l are vital for breaking degeneracies in parameter estimation from the CMB power spectrum and other cosmological data. The power spectrum clearly resolves the first three acoustic peaks, shows the expected fall off in power at high l and starts to constrain the position and height of a fourth peak.
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.
118656895
The elemental composition of the Sun - III. The heavy elements Cu to Th
We re-evaluate the abundances of the elements in the Sun from copper (Z = 29) to thorium (Z = 90). Our results are mostly based on neutral and singly-ionised lines in the solar spectrum. We use the latest 3D hydrodynamic solar model atmosphere, and in a few cases also correct for departures from local thermodynamic equilibrium (LTE) using non-LTE (NLTE) calculations performed in 1D. In order to minimise statistical and systematic uncertainties, we make stringent line selections, employ the highest-quality observational data and carefully assess oscillator strengths, hyperfine constants and isotopic separations available in the literature, for every line included in our analysis. Our results are typically in good agreement with the abundances in the most pristine meteorites, but there are some interesting exceptions. This analysis constitutes both a full exposition and a slight update of the relevant parts 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 that we have employed.
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.
5675666
Observational constraints on supermassive dark stars
Some of the first stars could be cooler and more massive than standard stellar models would suggest, due to the effects of dark matter annihilation in their cores. It has recently been argued that ...
122558225
Gamma-Rays from Ultracompact Primordial Dark Matter Minihalos
Ultracompact minihalos have been proposed as a new class of dark matter structure. They would be produced by phase transitions in the early Universe or features in the inflaton potential, and constitute nonbaryonic massive compact halo objects today. We examine the prospects of detecting these minihalos in gamma rays if dark matter can self-annihilate. We compute present-day fluxes from minihalos produced in the e(+)e(-) annihilation epoch and the QCD and electroweak phase transitions. Even at a distance of 4 kpc, minihalos from the e(+)e(-) epoch would be eminently detectable today by the Fermi satellite or air Ccerenkov telescopes, or even in archival EGRET data. Within 2 kpc, they would appear as extended sources to Fermi. At 4 kpc, minihalos from the QCD transition have similar predicted fluxes to dwarf spheroidal galaxies, so might also be detectable by present or upcoming experiments.