1,567 research outputs found
New halo stars of the Galactic globular clusters M3 and M13 in the LAMOST DR1 Catalog
M3 and M13 are Galactic globular clusters with previous reports of
surrounding stellar halos. We present the results of a search for members and
extratidal cluster halo stars within and outside of the tidal radius of these
clusters in the LAMOST Data Release 1. We find seven candidate cluster members
(inside the tidal radius) of both M3 and M13 respectively. In M3 we also
identify eight candidate extratidal cluster halo stars at distances up to ~9.8
times the tidal radius, and in M13 we identify 12 candidate extratidal cluster
halo stars at distances up to ~13.8 times the tidal radius. These results
support previous indications that both M3 and M13 are surrounded by extended
stellar halos, and we find that the GC destruction rates corresponding to the
observed mass loss are generally significantly higher than theoretical studies
predict.Comment: 21 pages, 10 figures. Accepted for publication in Ap
New cluster members and halo stars of the Galactic globular cluster NGC 1851
NGC 1851 is an intriguing Galactic globular cluster, with multiple stellar
evolutionary sequences, light and heavy element abundance variations and
indications of a surrounding stellar halo. We present the first results of a
spectroscopic study of red giant stars within and outside of the tidal radius
of this cluster. Our results identify nine probable new cluster members (inside
the tidal radius) with heliocentric radial velocities consistent with that of
NGC 1851. We also identify, based on their radial velocities, four probable
extratidal cluster halo stars at distances up to ~3.1 times the tidal radius,
which are supportive of previous findings that NGC 1851 is surrounded by an
extended stellar halo. Proper motions were available for 12 of these 13 stars
and all are consistent with that of NGC 1851. Apart from the cluster members
and cluster halo stars, our observed radial velocity distribution agrees with
the expected distribution from a Besancon disk/N-body stellar halo Milky Way
model generated by the Galaxia code, suggesting that no other structures at
different radial velocities are present in our field. The metallicities of
these stars are estimated using equivalent width measurements of the near
infrared calcium triplet absorption lines and are found, within the limitations
of this method, to be consistent with that of NGC 1851. In addition we recover
110 red giant cluster members from previous studies based on their radial
velocities and identify three stars with unusually high radial velocities.Comment: 10 pages, 8 figures. Accepted for publication in MNRA
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Simulations of Turbulence over Superhydrophobic Surfaces
Significant effort has been placed on the development of surfaces which reduce the amount of drag experienced by a fluid as it passes over the surface. Alterations to the fluid itself, as well as the chemical and physical composition of the surface have been investigated with varying success. Investigations into turbulent drag reduction have been mostly limited to those involving bubbles and riblets. Superhydrophobic surfaces, which combine hydrophobic surface chemistry with a regular array of microfeatures, have been shown to provide significant drag reduction in the laminar regime, with the possibility of extending these results into turbulent flows. Direct numerical simulations are used to investigate the drag reducing performance of superhydrophobic surfaces in turbulent channel flow. Slip velocities, wall shear stresses, and Reynolds stresses are considered for a variety of superhydrophobic surface microfeature geometry configurations at friction Reynolds numbers of Re = 180, Re = 395, and Re = 590. This work provides evidence that superhydrophobic surfaces are capable of reducing drag in turbulent flow situations by manipulating the laminar sublayer and turbulent energy cascade. For the largest micro-feature spacing of 90 microns an average slip velocity over 80% of the bulk velocity is obtained, and the wall shear stress reduction is found to be greater than 50%. The simulation results suggest that the mean velocity profile near the superhydrophobic wall continues to scale with the wall shear stress, but is offset by a slip velocity that increases with increasing micro-feature spacing
ESO452-SC11: The lowest mass globular cluster with a potential chemical inhomogeneity
We present the largest spectroscopic investigation of one of the faintest and
least studied stellar clusters of the Milky Way, ESO452-SC11. Using the
Anglo-Australian Telescope AAOmega and Keck HIRES spectrographs we have
identified 11 members of the cluster and found indications of star-to-star
light element abundance variation, primarily using the blue cyanogen (CN)
absorption features. From a stellar density profile, we estimate a total
cluster mass of solar masses. This would make
ESO452-SC11 the lowest mass cluster with evidence for multiple populations.
These data were also used to measure the radial velocity of the cluster
( km s) and confirm that ESO452-SC11 is relatively
metal-rich for a globular cluster ([Fe/H]). All known massive
clusters studied in detail show multiple populations of stars each with a
different chemical composition, but many low-mass globular clusters appear to
be chemically homogeneous. ESO452-SC11 sets a lower mass limit for the multiple
stellar population phenomenon.Comment: 13 pages, 11 figures. Accepted for publication in MNRA
Comprehensive study of Leon-Queretaro area
There are no author-identified significant results in this report
CN Bimodality at Low Metallicity: The Globular Cluster M53
We present low resolution UV-blue spectroscopic observations of red giant
stars in the globular cluster M53 ([Fe/H]=-1.84), obtained to study primordial
abundance variations and deep mixing via the CN and CH absorption bands. The
metallicity of M53 makes it an attractive target: a bimodal distribution of
3883 angstrom CN bandstrength is common in moderate- and high-metallicity
globular clusters ([Fe/H] > -1.6) but unusual in those of lower metallicity
([Fe/H] < -2.0). We find that M53 is an intermediate case, and has a broad but
not strongly bimodal distribution of CN bandstrength, with CN and CH
bandstrengths anticorrelated in the less-evolved stars. Like many other
globular clusters, M53 also exhibits a general decline in CH bandstrength and
[C/Fe] abundance with rising luminosity on the red giant branch.Comment: 8 pages including 11 figures and 1 table, accepted by PAS
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Brief behavioural activation for adolescent depression: working with complexity and risk
Given the long-term negative outcomes associated with depression in adolescence, there is a pressing need to develop brief, evidence based treatments that are accessible to more young people experiencing low mood. Behavioural Activation (BA) is an effective treatment for adult depression, however little research has focused on the use of BA with depressed adolescents, particularly with briefer forms of BA. In this article we outline an adaptation of brief Behavioral Activation Treatment of Depression (BATD) designed for adolescents and delivered in eight sessions (Brief BA). This case example illustrates how a structured, brief intervention was useful for a depressed young person with a number of complicating and risk factors
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