1,715 research outputs found
The Most Metal-Poor Stars. II. Chemical Abundances of 190 Metal-Poor Stars Including 10 New Stars With [Fe/H] < -3.5
We present a homogeneous chemical abundance analysis of 16 elements in 190
metal-poor Galactic halo stars (38 program and 152 literature objects). The
sample includes 171 stars with [Fe/H] < -2.5, of which 86 are extremely metal
poor, [Fe/H] < -3.0. Our program stars include ten new objects with [Fe/H] <
-3.5. We identify a sample of "normal" metal-poor stars and measure the trends
between [X/Fe] and [Fe/H], as well as the dispersion about the mean trend for
this sample. Using this mean trend, we identify objects that are chemically
peculiar relative to "normal" stars at the same metallicity. These chemically
unusual stars include CEMP-no objects, one star with high [Si/Fe], another with
high [Ba/Sr], and one with unusually low [X/Fe] for all elements heavier than
Na. The Sr and Ba abundances indicate that there may be two nucleosynthetic
processes at lowest metallicity that are distinct from the main r-process.
Finally, for many elements, we find a significant trend between [X/Fe] versus
Teff which likely reflects non-LTE and/or 3D effects. Such trends demonstrate
that care must be exercised when using abundance measurements in metal-poor
stars to constrain chemical evolution and/or nucleosynthesis predictions.Comment: Accepted for publication in Ap
Child-stripping in the Victorian City
During the nineteenth century, police, magistrates, reformers and the press noticed a rising tide of juvenile crime. Child-stripping, the crime of stealing young children's clothes by force or deception, was an activity of this type which caused alarm among contemporaries. As the century progressed, improved policing, urbanization and Irish migration, allied to growing social concern, caused more cases of child-stripping to be noticed. Accounts by Dickens, Mayhew and others characterized child-stripping as an activity indulged in by old women who were able to make money by victimizing the weakest strata of society. However, research in the British Library's digitized newspaper collections as well as in parliamentary papers conclusively demonstrates that child-stripping, far from being the domain of Dickensian crones, was actually perpetrated by older children, notably girls, against children even younger than themselves. Despite widespread revulsion, which at times approached a ‘moral panic’ prompted by the nature of the crime, progressive attitudes largely prevailed with most child-stripping children being sent to reformatories or industrial schools in the hope of reforming their behaviour. This article thus conforms with Foucauldian notions of the switch from physical to mental punishments and aligns with the Victorians’ invention of children as a category of humanity that could be saved
Herschel/PACS far-infrared photometry of two z>4 quasars
We present Herschel far-infrared (FIR) observations of two sub-mm bright
quasars at high redshift: SDSS J1148+5251 (z=6.42) and BR 1202-0725 (z=4.69)
obtained with the PACS instrument. Both objects are detected in the PACS
photometric bands. The Herschel measurements provide additional data points
that constrain the FIR spectral energy distributions (SEDs) of both sources,
and they emphasise a broad range of dust temperatures in these objects. For
lambda_rest ~< 20mu, the two SEDs are very similar to the average SEDs of
quasars at low redshift. In the FIR, however, both quasars show excess emission
compared to low-z QSO templates, most likely from cold dust powered by vigorous
star formation in the QSO host galaxies. For SDSS J1148+5251 we detect another
object at 160mu with a distance of ~10 arcseconds from the QSO. Although no
physical connection between the quasar and this object can be shown with the
available data, it could potentially confuse low-resolution measurements, thus
resulting in an overestimate of the FIR luminosity of the z=6.42 quasar.Comment: 4 pages, 3 figures, accepted for publication in the A&A special issue
on Hersche
A multi-wavelength census of star formation activity in the young embedded cluster around Serpens/G3-G6
Aims. The aim of this paper is to characterise the star formation activity in
the poorly studied embedded cluster Serpens/G3-G6, located ~ 45' (3 pc) to the
south of the Serpens Cloud Core, and to determine the luminosity and mass
functions of its population of Young Stellar Objects (YSOs).
Methods. Multi-wavelength broadband photometry was obtained to sample the
near and mid-IR spectral energy distributions to separate YSOs from field stars
and classify the YSO evolutionary stage. ISOCAM mapping in the two filters LW2
(5-8.5 um) and LW3 (12-18 um) of a 19' x 16' field was combined with JHKs data
from 2MASS, Ks data from Arnica/NOT, and L' data from SIRCA/NOT. Continuum
emission at 1.3 mm (IRAM) and 3.6 cm (VLA) was mapped to study the cloud
structure and the coldest/youngest sources. Deep narrow band imaging at the
2.12 um S(1) line of H2 from NOTCam/NOT was obtained to search for signs of
bipolar outflows.
Results. We have strong evidence for a stellar population of 31 Class II
sources, 5 flat-spectrum sources, 5 Class I sources, and two Class 0 sources.
Our method does not sample the Class III sources. The cloud is composed of two
main dense clumps aligned along a ridge over ~ 0.5 pc plus a starless core
coinciding with absorption features seen in the ISOCAM maps. We find two
S-shaped bipolar collimated flows embedded in the NE clump, and propose the two
driving sources to be a Class 0 candidate (MMS3) and a double Class I (MMS2).
For the Class II population we find a best age of ~ 2 Myr and compatibility
with recent Initial Mass Functions (IMFs) by comparing the observed Class II
luminosity function (LF), which is complete to 0.08 L_sun, to various model LFs
with different star formation scenarios and input IMFs.Comment: 18 pages, 16 figures, 3 online tables, accepted by A&
Dressed Bose-Einstein Condensates in High-Q Cavities
We propose and analyze a way in which effective multicomponent condensates
can be created inside high-Q multimode cavities. In contrast to the situation
involving several atomic species or levels, the coupling between the various
components of the dressed condensates is linear. We predict analytically and
numerically confirm the onset of instabilities in the quasiparticle excitation
spectrum.Comment: plain tex, 20 pages, 4 figure
The World Hip Trauma Evaluation Study 3 HEMIARTHROPLASTY EVALUATION BY MULTICENTRE INVESTIGATION - WHiTE 3: HEMI - AN ABRIDGED PROTOCOL
Approximately half of all hip fractures are displaced intracapsular fractures. The standard treatment for these fractures is either hemiarthroplasty or total hip arthroplasty. The recent National Institute for Health and Care Excellence (NICE) guidance on hip fracture management recommends the use of 'proven' cemented stem arthroplasty with an Orthopaedic Device Evaluation Panel (ODEP) rating of at least 3B (97% survival at three years). The Thompsons prosthesis is currently lacking an ODEP rating despite over 50 years of clinical use, likely due to the paucity of implant survival data. Nationally, adherence to these guidelines is varied as there is debate as to which prosthesis optimises patient outcomes.This study design is a multi-centre, multi-surgeon, parallel, two arm, standard-of-care pragmatic randomised controlled trial. It will be embedded within the WHiTE Comprehensive Cohort Study (ISRCTN63982700). The main analysis is a two-way equivalence comparison between Hemi-Thompson and Hemi-Exeter polished taper with Unitrax head. Secondary outcomes will include radiological leg length discrepancy measured as per Bidwai and Willett, mortality, re-operation rate and indication for re-operation, length of index hospital stay and revision at four months. This study will be supplemented by the NHFD (National Hip Fracture Database) dataset.Evidence on the optimum choice of prosthesis for hemiarthroplasty of the hip is lacking. National guidance is currently based on expert opinion rather than empirical evidence. The incidence of hip fracture is likely to continue to increase and providing high quality evidence on the optimumCite this article: A. L. Sims. The World Hip Trauma Evaluation Study 3: Hemiarthroplasty Evaluation by Multicentre Investigation - WHITE 3: HEMI - An Abridged Protocol. Bone Joint Res 2016;5:18-25. doi: 10.1302/2046-3758.51.2000473
Collective coherence in planar semiconductor microcavities
Semiconductor microcavities, in which strong coupling of excitons to confined
photon modes leads to the formation of exciton-polariton modes, have
increasingly become a focus for the study of spontaneous coherence, lasing, and
condensation in solid state systems. This review discusses the significant
experimental progress to date, the phenomena associated with coherence which
have been observed, and also discusses in some detail the different theoretical
models that have been used to study such systems. We consider both the case of
non-resonant pumping, in which coherence may spontaneously arise, and the
related topics of resonant pumping, and the optical parametric oscillator.Comment: 46 pages, 12 figure
Bayesian fitting of Taurus brown dwarf spectral energy distributions
We present derived stellar and disc parameters for a sample of Taurus brown
dwarfs both with and without evidence of an associated disc. These parameters
have been derived using an online fitting tool
(http://bd-server.astro.ex.ac.uk/), which includes a statistically robust
derivation of uncertainties, an indication of pa- rameter degeneracies, and a
complete treatment of the input photometric and spectroscopic observations. The
observations of the Taurus members with indications of disc presence have been
fitted using a grid of theoretical models including detailed treatments of
physical processes accepted for higher mass stars, such as dust sublimation,
and a simple treatment of the accretion flux. This grid of models has been
designed to test the validity of the adopted physical mechanisms, but we have
also constructed models using parameterisation, for example semi-empirical dust
sublimation radii, for users solely interested in parameter derivation and the
quality of the fit. The parameters derived for the naked and disc brown dwarf
systems are largely consistent with literature observations. However, our inner
disc edge locations are consistently closer to the star than previous results
and we also derive elevated accretion rates over non-SED based accretion rate
derivations. For inner edge locations we attribute these differences to the
detailed modelling we have performed of the disc structure, particularly at the
crucial inner edge where departures in geometry from the often adopted vertical
wall due to dust sublimation (and therefore accretion flux) can compensate for
temperature (and therefore distance) changes to the inner edge of the dust
disc. In the case of the elevated derived accretion rates, in some cases, this
may be caused by the intrinsic stellar luminosities of the targets exceeding
that predicted by the isochrones we have adopted.Comment: The paper contains 35 pages with 15 figures and 17 tables. Accepted
for publication in MNRA
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