8,607 research outputs found
Xenon in Mercury-Manganese Stars
Previous studies of elemental abundances in Mercury-Manganese (HgMn) stars
have occasionally reported the presence of lines of the ionized rare noble gas
Xe II, especially in a few of the hottest stars with Teff ~ 13000--15000 K. A
new study of this element has been undertaken using observations from Lick
Observatory's Hamilton Echelle Spectrograph. In this work, the spectrum
synthesis program UCLSYN has been used to undertake abundance analysis assuming
LTE. We find that in the Smith & Dworetsky sample of HgMn stars, Xe is vastly
over-abundant in 21 of 22 HgMn stars studied, by factors of 3.1--4.8 dex. There
does not appear to be a significant correlation of Xe abundance with Teff. A
comparison sample of normal late B stars shows no sign of Xe II lines that
could be detected, consistent with the expected weakness of lines at normal
abundance. The main reason for the previous lack of widespread detection in
HgMn stars is probably due to the strongest lines being at longer wavelengths
than the photographic blue. The lines used in this work were 4603.03A, 4844.33A
and 5292.22A.Comment: 8 pages, 4 figures. Accepted by Monthly Notices of the Royal
Astronomical Society, 8 January 200
Inclination-Independent Galaxy Classification
We present a new method to classify galaxies from large surveys like the
Sloan Digital Sky Survey using inclination-corrected concentration,
inclination-corrected location on the color-magnitude diagram, and apparent
axis ratio. Explicitly accounting for inclination tightens the distribution of
each of these parameters and enables simple boundaries to be drawn that
delineate three different galaxy populations: Early-type galaxies, which are
red, highly concentrated, and round; Late-type galaxies, which are blue, have
low concentrations, and are disk dominated; and Intermediate-type galaxies,
which are red, have intermediate concentrations, and have disks. We have
validated our method by comparing to visual classifications of high-quality
imaging data from the Millennium Galaxy Catalogue. The inclination correction
is crucial to unveiling the previously unrecognized Intermediate class.
Intermediate-type galaxies, roughly corresponding to lenticulars and early
spirals, lie on the red sequence. The red sequence is therefore composed of two
distinct morphological types, suggesting that there are two distinct mechanisms
for transiting to the red sequence. We propose that Intermediate-type galaxies
are those that have lost their cold gas via strangulation, while Early-type
galaxies are those that have experienced a major merger that either consumed
their cold gas, or whose merger progenitors were already devoid of cold gas
(the ``dry merger'' scenario).Comment: Accepted for publication in ApJ. 7 pages in emulateap
Globalization and Equestrian Cultures: The case of Equitation in the French Tradition
In 2011, Equitation in the French Tradition was included on the UNESCO list of the Intangible Cultural Heritage of Humanity. This listing brings not only notions of heritage and culture, but also the complex balance between global and local scales to the forefront. France, like many other countries, has an age-old equestrian culture which is still alive and well, nourished by various international and local influences and sometimes by conflicting ideas.  In second half of the 20th century, both the nation and its equestrian culture were brought within the sphere of Western societies of leisure and consumption under the hegemony of the American model, upsetting the ancestral utilitarian functions of horses and riding and urging their redefinition within the prism of pleasure-oriented, sporting and emotional relationships. This in turn raised issues about what constitutes the French equestrian culture which is protected today, within the more general landscape of globalization. This chapter examines its construction and definition within a progressive society, combining both resistance to and assimilation of new national and international trends. The methodology employed conjoins diachronic and synchronic approaches, associating quantitative and qualitative data in a study based on historical bibliography, current French Equestrian Federation and the French Institute for Horse and Horse Riding (IFCE) statistics, in-depth interviews with key actors of French equestrian and cultural institutions and observations and interviews undertaken during introductory ‘baucheriste’ horse-riding training
Investigating Heating and Cooling in the BCS & B55 Cluster Samples
We study clusters in the BCS cluster sample which are observed by Chandra and
are more distant than redshift, z>0.1. We select from this subsample the
clusters which have both a short central cooling time and a central temperature
drop, and also those with a central radio source. Six of the clusters have
clear bubbles near the centre. We calculate the heating by these bubbles and
express it as the ratio r_heat/r_cool=1.34+/-0.20. This result is used to
calculate the average size of bubbles expected in all clusters with central
radio sources. In three cases the predicted bubble sizes approximately match
the observed radio lobe dimensions.
We combine this cluster sample with the B55 sample studied in earlier work to
increase the total sample size and redshift range. This extended sample
contains 71 clusters in the redshift range 0<z<0.4. The average distance out to
which the bubbles offset the X-ray cooling in the combined sample is at least
r_heat/r_cool=0.92+/-0.11. The distribution of central cooling times for the
combined sample shows no clusters with clear bubbles and t_cool>1.2Gyr. An
investigation of the evolution of cluster parameters within the redshift range
of the combined samples does not show any clear variation with redshift.Comment: 12 pages, 9 figures, accepted for publication in MNRA
Cool White Dwarfs Identified in the Second Data Release of the UKIRT Infrared Deep Sky Survey
We have paired the Second Data Release of the Large Area Survey of the UKIRT
Infrared Deep Sky Survey with the Fifth Data Release of the Sloan Digital Sky
Survey to identify ten cool white dwarf candidates, from their photometry and
astrometry. Of these ten, one was previously known to be a very cool white
dwarf. We have obtained optical spectroscopy for seven of the candidates using
the GMOS-N spectrograph on Gemini North, and have confirmed all seven as white
dwarfs. Our photometry and astrometry indicates that the remaining two objects
are also white dwarfs. Model analysis of the photometry and available
spectroscopy shows that the seven confirmed new white dwarfs, and the two new
likely white dwarfs, have effective temperatures in the range Teff = 5400-6600
K. Our analysis of the previously known white dwarf confirms that it is cool,
with Teff = 3800 K. The cooling age for this dwarf is 8.7 Gyr, while that of
the nine ~6000 K white dwarfs is 1.8-3.6 Gyr. We are unable to determine the
masses of the white dwarfs from the existing data, and therefore we cannot
constrain the total ages of the white dwarfs. The large cooling age for the
coolest white dwarf in the sample, combined with its low estimated tangential
velocity, suggests that it is an old member of the thin disk, or a member of
the thick disk of the Galaxy, with an age 10-11 Gyr. The warmer white dwarfs
appear to have velocities typical of the thick disk or even halo; these may be
very old remnants of low-mass stars, or they may be relatively young thin disk
objects with unusually high space motion.Comment: 37 pages (referee format), 4 tables, 7 figures, accepted to Ap
Extremely metal-poor stars from the SDSS
We give a progress report about the activities within the CIFIST Team related
to the search for extremely metal-poor stars in the Sloan Digital Sky Survey's
spectroscopic catalog. So far the search has provided 25 candidates with
metallicities around or smaller -3. For 15 candidates high resolution
spectroscopy with UVES at the VLT has confirmed their extremely metal-poor
status. Work is under way to extend the search to the SDSS's photometric
catalog by augmenting the SDSS photometry, and by gauging the capabilities of
X-shooter when going to significantly fainter targets.Comment: 6 pages, 6 figures, Proceedings paper of the conference "A stellar
journey: A symposium in celebration of Bengt Gustafsson's 65th birthday
Outliers from the Mass--Metallicity Relation II: A Sample of Massive Metal-Poor Galaxies from SDSS
We present a sample of 42 high-mass low-metallicity outliers from the
mass--metallicity relation of star-forming galaxies. These galaxies have
stellar masses that span log(M_*/M_sun) ~9.4 to 11.1 and are offset from the
mass--metallicity relation by -0.3 to -0.85 dex in 12+log(O/H). In general,
they are extremely blue, have high star formation rates for their masses, and
are morphologically disturbed. Tidal interactions are expected to induce
large-scale gas inflow to the galaxies' central regions, and we find that these
galaxies' gas-phase oxygen abundances are consistent with large quantities of
low-metallicity gas from large galactocentric radii diluting the central
metal-rich gas. We conclude with implications for deducing gas-phase
metallicities of individual galaxies based solely on their luminosities,
specifically in the case of long gamma-ray burst host galaxies.Comment: Accepted for publication in ApJ; 11 pages, 11 figure
Theoretical determination of lifetimes of metastable states in Sc III and Y III
Lifetimes of the first two metastable states in Sc^{2+} and Y^{2+} are
determined using the relativistic coupled-cluster theory. There is a
considerable interest in studying the electron correlation effects in these
ions as though their electronic configurations are similar to the neutral
alkali atoms, their structures are very different from the latter. We have made
a comparative study of the correlation trends between the above doubly ionized
systems with their corresponding neutral and singly ionized iso-electronic
systems. The lifetimes of the excited states of these ions are very important
in the field of astrophysics, especially for the study of post-main sequence
evolution of the cool giant stars.Comment: 13 pages, 1 figure and 5 table
Pathways to mental health services for young people: a systematic review
Purpose: While early access to appropriate care can minimise the sequelae of mental illnesses, little is known about how youths come to access mental healthcare. We therefore conducted a systematic review to synthesise literature on the pathways to care of youths across a range of mental health problems. Methods: Studies were identified through searches of electronic databases (MEDLINE, PsycINFO, Embase, HealthSTAR and CINAHL), supplemented by backward and forward mapping and hand searching. We included studies on the pathways to mental healthcare of individuals aged 11–30 years. Two reviewers independently screened articles and extracted data. Results: Forty-five studies from 26 countries met eligibility criteria. The majority of these studies were from settings that offered services for the early stages of psychosis, and others included inpatient and outpatient settings targeting wide-ranging mental health problems. Generally, youths’ pathways to mental healthcare were complex, involved diverse contacts, and, sometimes, undue treatment delays. Across contexts, family/carers, general practitioners and emergency rooms featured prominently in care pathways. There was little standardization in the measurement of pathways. Conclusions: Except in psychosis, youths’ pathways to mental healthcare remain understudied. Pathways to care research may need to be reconceptualised to account for the often transient and overlapping nature of youth mental health presentations, and the possibility that what constitutes optimal care may vary. Despite these complexities, additional research, using standardized methodology, can yield a greater understanding of the help-seeking behaviours of youths and those acting on their behalf; service responses to help-seeking; and the determinants of pathways. This understanding is critical to inform ongoing initatives to transform youth mental healthcare
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