484 research outputs found
Ca II Triplet Spectroscopy of Small Magellanic Cloud Red Giants. I. Abundances and Velocities for a Sample of Clusters
We have obtained near-infrared spectra covering the Ca II triplet lines for a
number of stars associated with 16 SMC clusters using the VLT + FORS2. These
data compose the largest available sample of SMC clusters with
spectroscopically derived abundances and velocities. Our clusters span a wide
range of ages and provide good areal coverage of the galaxy. Cluster members
are selected using a combination of their positions relative to the cluster
center as well as their abundances and radial velocities. We determine mean
cluster velocities to typically 2.7 km/s and metallicities to 0.05 dex (random
errors), from an average of 6.4 members per cluster. (continued in paper)Comment: 68 pages, 15 figures, Accepted to AJ Reason for the replacement:
section 7 and fig. 9 have been modified according referee suggestion
Magnetosphere-ionosphere coupling at Jupiter-like exoplanets with internal plasma sources: implications for detectability of auroral radio emissions
In this paper we provide the first consideration of magnetosphere-ionosphere
coupling at Jupiter-like exoplanets with internal plasma sources such as
volcanic moons. We estimate the radio power emitted by such systems under the
condition of near-rigid corotation throughout the closed magnetosphere, in
order to examine the behaviour of the best candidates for detection with next
generation radio telescopes. We thus estimate for different stellar X-ray-UV
(XUV) luminosity cases the orbital distances within which the ionospheric
Pedersen conductance would be high enough to maintain near-rigid corotation,
and we then consider the magnitudes of the large-scale magnetosphere-ionosphere
currents flowing within the systems, and the resulting radio powers, at such
distances. We also examine the effects of two key system parameters, i.e. the
planetary angular velocity and the plasma mass outflow rate from sources
internal to the magnetosphere. In all XUV luminosity cases studied, a
significant number of parameter combinations within an order of magnitude of
the jovian values are capable of producing emissions observable beyond 1 pc, in
most cases requiring exoplanets orbiting at distances between ~1 and 50 AU, and
for the higher XUV luminosity cases these observable distances can reach beyond
~50 pc for massive, rapidly rotating planets. The implication of these results
is that the best candidates for detection of such internally-generated radio
emissions are rapidly rotating Jupiter-like exoplanets orbiting stars with high
XUV luminosity at orbital distances beyond ~1 AU, and searching for such
emissions may offer a new method of detection of more distant-orbiting
exoplanets.Comment: 15 pages, 9 figures. In press at Mon. Not. R. Astron. So
White Dwarfs in Globular Clusters: HST Observations of M4
Using WFPC2 on the Hubble Space Telescope, we have isolated a sample of 258
white dwarfs (WDs) in the Galactic globular cluster M4. Fields at three radial
distances from the cluster center were observed and sizeable WD populations
were found in all three. The location of these WDs in the color-magnitude
diagram, their mean mass of 0.51()M, and their luminosity
function confirm basic tenets of stellar evolution theory and support the
results from current WD cooling theory. The WDs are used to extend the cluster
main-sequence mass function upward to stars that have already completed their
nuclear evolution. The WD/red dwarf binary frequency in M4 is investigated and
found to be at most a few percent of all the main-sequence stars. The most
ancient WDs found are about 9 Gyr old, a level which is set solely by the
photometric limits of our data. Even though this is less than the age of M4, we
discuss how these cooling WDs can eventually be used to check the turnoff ages
of globular clusters and hence constrain the age of the Universe.Comment: 46 pages, latex, no figures included, figures available at
ftp://ftp.astro.ubc.ca/pub/richer/wdfig.uu size 2.7Mb. To be published in the
Astrophysical Journa
Incongruence between nurses\u27 and patients\u27 understandings and expectations of rehabilitation
Aims and objectives. To explore nurses\u27 understandings and expectations of rehabilitation and nurses\u27 perceptions of patients\u27 understandings and expectations of rehabilitation.Background. Within the context of a broadening appreciation of the benefits of rehabilitation, interest in the nature of rehabilitation is growing. Some believe that rehabilitation services do not adequately meet the needs of patients. Others are interested in the readiness of patients to participate in rehabilitation.Design. Qualitative.Method. Grounded theory using data collected during interviews with nurses in five inpatient rehabilitation units and during observation of the nurses\u27 everyday practice.Findings. According to nurses working in inpatient rehabilitation units, there is a marked incongruence between nurses\u27 understandings and expectations of rehabilitation and what they perceive patients to understand and expect.Conclusion. Given these different understandings, an important nursing role is the education of patients about the nature of rehabilitation and how to optimise their rehabilitation.Relevance to clinical practice. Before patients are transferred to rehabilitation, the purpose and nature of rehabilitation, in particular the roles of patients and nurses, needs to be explained to them. The understandings of rehabilitation that nurses in this study possessed provide a framework for the design of education materials and orientation programmes that inform patients (and their families) about rehabilitation. In addition, reinforcement of the differences between acute care and rehabilitation will assist patients new to rehabilitation to understand the central role that they themselves can play in their recovery.<br /
3D kinematics through the X-shaped Milky Way bulge
Context. It has recently been discovered that the Galactic bulge is X-shaped, with the two southern arms of the X both crossing the lines of sight at l = 0 and | b| > 4, hence producing a double red clump in the bulge color magnitude diagram. Dynamical models predict the formation of X-shaped bulges as extreme cases of boxy-peanut bulges. However, since X-shaped bulges were known to be present only in external galaxies, models have never been compared to 3D kinematical data for individual stars.
Aims. We study the orbital motion of Galactic bulge stars in the two arms (overdensities) of the X in the southern hemisphere. The goal is to provide observational constraints to bulge formation models that predict the formation of X-shapes through bar dynamical instabilities.
Methods. Radial velocities have been obtained for a sample of 454 bulge giants, roughly equally distributed between the bright and the faint red clump, in a field at (l,b) = (0, â6). Proper motions were derived for all red clump stars in the same field by combining images from two epochs, which were obtained 11 years apart, with WFI at the 2.2âm at La Silla. The observed field contains the globular cluster NGC 6558, whose member stars were used to assess the accuracy of the proper motion measurement. At the same time, as a by-product, we provide the first proper motion measurement of NGC 6558. The proper motions for the spectroscopic subsample are analyzed for a subsample of 352 stars, taking into account the radial velocities and metallicities measured from near-infrared calcium triplet lines.
Results. The radial velocity distribution of stars in the bright red clump, which traces the closer overdensity of bulge stars, shows an excess of stars moving towards the Sun. Similarly, an excess of stars receding from the Sun is seen in the far overdensity, which is traced by faint red clump stars. This is explained by the presence of stars on elongated orbits, which are most likely streaming along the arms of the X-shaped bulge. Proper motions for these stars are consistent with qualitative predictions of dynamical models of peanut-shaped bulges. Surprisingly, stars on elongated orbits have preferentially metal-poor (subsolar) metallicities, while the metal rich ones, in both overdensities, are preferentially found in more axisymmetric orbits. The observed proper motion of NGC 6558 has been measured as (ÎŒlcos â (b),ÎŒb) = (0.30 â ± â 0.14, â0.43 ± 0.13), with a velocity dispersion of (Ïlcos(b),Ïb) = (1.8,1.7) mas/yr. This is the first proper motion measurement for this cluster
Study of the Sextans dwarf spheroidal galaxy from the DART CaII triplet survey
We use VLT/FLAMES intermediate resolution (R~6500) spectra of individual red
giant branch stars in the near-infrared CaII triplet (CaT) region to
investigate the wide-area metallicity properties and internal kinematics of the
Sextans dwarf spheroidal galaxy (dSph). Our final sample consists of 174
probable members of Sextans with accurate line-of-sight velocities (+- 2 km/s)
and CaT [Fe/H] measurements (+- 0.2 dex). We use the MgI line at 8806.8 \AA\,
as an empirical discriminator for distinguishing between probable members of
the dSph (giant stars) and probable Galactic contaminants (dwarf stars).
Sextans shows a similar chemo-dynamical behaviour to other Milky Way dSphs,
with its central regions being more metal rich than the outer parts and with
the more metal-rich stars displaying colder kinematics than the more metal-poor
stars. Hints of a velocity gradient are found along the projected major axis
and along an axis at P.A.=191 deg, however a larger and more spatially extended
sample may be necessary to pin down the amplitude and direction of this
gradient. We detect a cold kinematic substructure at the centre of Sextans,
consistent with being the remnant of a disrupted very metal poor stellar
cluster. We derive the most extended line-of-sight velocity dispersion profile
for Sextans, out to a projected radius of 1.6 deg. From Jeans modelling of the
observed line-of-sight velocity dispersion profile we find that this is
consistent with both a cored dark matter halo with large core radius and cuspy
halo with low concentration. The mass within the last measured point is in the
range 2-4 x 10^8 M_sun, giving very large mass-to-light ratios, from 460 to 920
(M/L)_(V,sun).Comment: 30 pages, 17 figures; 4 tables. Accepted for publication in MNRAS.
Table 4 will appear as online material in the published version of the
manuscript. Typo correcte
Variation of Jupiter's aurora observed by Hisaki/EXCEED: 1. Observed characteristics of the auroral electron energies compared with observations performed using HST/STIS
Temporal variation of Jupiter's northern aurora is detected using the Extreme Ultraviolet Spectroscope for Exospheric Dynamics (EXCEED) on board JAXA's Earth-orbiting planetary space telescope Hisaki. The wavelength coverage of EXCEED includes the H2 Lyman and Werner bands at 80â148ânm from the entire northern polar region. The prominent periodic modulation of the observed emission corresponds to the rotation of Jupiter's main auroral oval through the aperture, with additional superposed â50%â100% temporal variations. The hydrocarbon color ratio (CR) adopted for the wavelength range of EXCEED is defined as the ratio of the emission intensity in the long wavelength range of 138.5â144.8ânm to that in the short wavelength range of 126.3â130ânm. This CR varies with the planetary rotation phase. Short- (within one planetary rotation) and long-term (> one planetary rotation) enhancements of the auroral power are observed in both wavelength ranges and result in a small CR variation. The occurrence timing of the auroral power enhancement does not clearly depend on the central meridian longitude. Despite the limitations of the wavelength coverage and the large field of view of the observation, the auroral spectra and CR-brightness distribution measured using EXCEED are consistent with other observations
The institutional shaping of management: in the tracks of English individualism
Globalisation raises important questions about the shaping of economic action by cultural factors. This article explores the formation of what is seen by some as a prime influence on the formation of British management: individualism. Drawing on a range of historical sources, it argues for a comparative approach. In this case, the primary comparison drawn is between England and Scotland. The contention is that there is a systemic approach to authority in Scotland that can be contrasted to a personal approach in England. An examination of the careers of a number of Scottish pioneers of management suggests the roots of this systemic approach in practices of church governance. Ultimately this systemic approach was to take a secondary role to the personal approach engendered by institutions like the universities of Oxford and Cambridge, but it found more success in the different institutional context of the USA. The complexities of dealing with historical evidence are stressed, as is the value of taking a comparative approach. In this case this indicates a need to take religious practice as seriously as religious belief as a source of transferable practice. The article suggests that management should not be seen as a simple response to economic imperatives, but as shaped by the social and cultural context from which it emerges
Characterizing the limitations to the coupling between Saturn's ionosphere and middle magnetosphere
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