2,887 research outputs found
Every Touchpoint Matters: Developing a Systematic Tool to Measure the Impact of Hospice Services upon Patients, their Families and Carers
Spitzer Space Telescope spectral observations of AGB stars in the Fornax dwarf spheroidal galaxy
We have observed five carbon-rich AGB stars in the Fornax dwarf spheroidal
(dSph) galaxy, using the Infrared Spectrometer on board the Spitzer Space
Telescope. The stars were selected from a near-infrared survey of Fornax and
include the three reddest stars, with presumably the highest mass-loss rates,
in that galaxy. Such carbon stars probably belong to the intermediate-age
population (2-8 Gyr old and metallicity of [Fe/H] -1) of Fornax. The primary
aim of this paper is to investigate mass-loss rate, as a function of luminosity
and metallicity, by comparing AGB stars in several galaxies with different
metallicities. The spectra of three stars are fitted with a radiative transfer
model. We find that mass-loss rates of these three stars are 4-7x10^-6 Msun
yr-1. The other two stars have mass-loss rates below 1.3x10^-6 Msun yr-1. We
find no evidence that these rates depend on metallicity, although we do suggest
that the gas-to-dust ratio could be higher than at solar metallicity, in the
range 240 to 800. The C2H2 bands are stronger at lower metallicity because of
the higher C/O ratio. In contrast, the SiC fraction is reduced at low
metallicity, due to low silicon abundance. The total mass-loss rate from all
known carbon-rich AGB stars into the interstellar medium of this galaxy is of
the order of 2x10^-5 Msun yr-1. This is much lower than that of the dwarf
irregular galaxy WLM, which has a similar visual luminosity and metallicity.
The difference is attributed to the younger stellar population of WLM. The
suppressed gas-return rate to the ISM accentuates the difference between the
relatively gas-rich dwarf irregular and the gas-poor dwarf spheroidal galaxies.
Our study will be useful to constrain gas and dust recycling processes in low
metallicity galaxies.Comment: MNRAS accepte
Long-term impact of land management in soil biological processes can be assessed by fingerprint of dissolved organic carbon and peroxidase activity in topsoil and subsoil
A near-infrared study of AGB and red giant stars in the Leo I dSph galaxy
A near-infrared imaging study of the evolved stellar populations in the dwarf
spheroidal galaxy Leo I is presented. Based on JHK observations obtained with
the WFCAM wide-field array at the UKIRT telescope, we build a near-infrared
photometric catalogue of red giant branch (RGB) and asymptotic giant branch
(AGB) stars in Leo I over a 13.5 arcmin square area. The V-K colours of RGB
stars, obtained by combining the new data with existing optical observations,
allow us to derive a distribution of global metallicity [M/H] with average
[M/H] = -1.51 (uncorrected) or [M/H] = -1.24 +/- 0.05 (int) +/- 0.15 (syst)
after correction for the mean age of Leo I stars. This is consistent with the
results from spectroscopy once stellar ages are taken into account. Using a
near-infrared two-colour diagram, we discriminate between carbon- and
oxygen-rich AGB stars and obtain a clean separation from Milky Way foreground
stars. We reveal a concentration of C-type AGB stars relative to the red giant
stars in the inner region of the galaxy, which implies a radial gradient in the
intermediate-age (1-3 Gyr) stellar populations. The numbers and luminosities of
the observed carbon- and oxygen-rich AGB stars are compared with those
predicted by evolutionary models including the thermally-pulsing AGB phase, to
provide new constraints to the models for low-metallicity stars. We find an
excess in the predicted number of C stars fainter than the RGB tip, associated
to a paucity of brighter ones. The number of O-rich AGB stars is roughly
consistent with the models, yet their predicted luminosity function is extended
to brighter luminosity. It appears likely that the adopted evolutionary models
overestimate the C star lifetime and underestimate their K-band luminosity.Comment: MNRAS, accepte
Seasonal and dietary influences on adipose tissue and systemic gene expression in control and previously laminitic ponies
The aims of the study were to determine whether adipose tissue global gene expression (i) differs between never laminitic (NL) and previously laminitic (PL) ponies; (ii) is influenced by season and/or a diet designed to simulate spring grass and (iii) differences seen also occur systemically in peripheral blood mononuclear cells (PBMCs). Subcutaneous adipose tissue and PBMCs were obtained from six NL and six PL ponies on three occasions; summer, winter (season study) and in winter after consuming a diet simulating spring grass for seven days (diet study). Adipose tissue global gene expression was determined using a 44K equine specific microarray, validated using multiplex quantitative real time PCR (qRT-PCR) and analysed using GeneSpring software and Ingenuity Pathway Analysis. PBMC gene expression was quantified using qRT-PCR. The total number of genes whose expression differed (=2-fold change, p=0.01) between PL and NL ponies was greater in summer (192 genes) compared to winter (58 genes); 40/192 genes influenced by disease in the summer were also seasonally regulated and were predominantly associated with inflammation. The genes modified by dietary intervention and PBMC gene expression did not follow the same pattern as the season study. Thus, adipose tissue global gene expression differed between NL and PL ponies most in summer compared to winter, and these differentially expressed genes predominantly related to inflammation
Geochemical and isotopic insights into the assembly, evolution and disruption of a magmatic plumbing system before and after a cataclysmic caldera-collapse eruption at Ischia volcano (Italy)
New geochemical and isotopic data on volcanic rocks spanning the period ~75–50 ka BP on Ischia volcano, Italy, shed light on the evolution of the magmatic system before and after the catastrophic, caldera-forming Monte Epomeo Green Tuff (MEGT) eruption. Volcanic activity during this period was influenced by a large, composite and differentiating magmatic system, replenished several times with isotopically distinct magmas of deep provenance. Chemical and isotopic variations highlight that the pre-MEGT eruptions were fed by trachytic/phonolitic magmas from an isotopically zoned reservoir that were poorly enriched in radiogenic Sr and became progressively less radiogenic with time. Just prior to the MEGT eruption, the magmatic system was recharged by an isotopically distinct magma, relatively more enriched in radiogenic Sr with respect to the previously erupted magmas. This second magma initially fed several SubPlinian explosive eruptions and later supplied the climactic, phonolitic-to-trachytic MEGT eruption(s). Isotopic data, together with erupted volume estimations obtained for MEGT eruption(s), indicate that >5–10 km3 of this relatively enriched magma had accumulated in the Ischia plumbing system. Geochemical modelling indicates that it accumulated at shallow depths (4–6 km), over a period of ca. 20 ka. After the MEGT eruption, volcanic activity was fed by a new batch of less differentiated (trachyte-latite) magma that was slightly less enriched in radiogenic Sr. The geochemical and Sr–Nd-isotopic variations through time reflect the upward flux of isotopically distinct magma batches, variably contaminated by Hercynian crust at 8–12 km depth. The deep-sourced latitic to trachytic magmas stalled at shallow depths (4–6 km depth), differentiated to phonolite through crystal fractionation and assimilation of a feldspar-rich mush, or ascended directly to the surface and erupted
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