3,664 research outputs found
Magellanic Cloud Periphery Carbon Stars IV: The SMC
The kinematics of 150 carbon stars observed at moderate dispersion on the
periphery of the Small Magellanic Cloud are compared with the motions of
neutral hydrogen and early type stars in the Inter-Cloud region. The
distribution of radial velocities implies a configuration of these stars as a
sheet inclined at 73+/-4 degrees to the plane of the sky. The near side, to the
South, is dominated by a stellar component; to the North, the far side contains
fewer carbon stars, and is dominated by the neutral gas. The upper velocity
envelope of the stars is closely the same as that of the gas. This
configuration is shown to be consistent with the known extension of the SMC
along the line of sight, and is attributed to a tidally induced disruption of
the SMC that originated in a close encounter with the LMC some 0.3 to 0.4 Gyr
ago. The dearth of gas on the near side of the sheet is attributed to ablation
processes akin to those inferred by Weiner & Williams (1996) to collisional
excitation of the leading edges of Magellanic Stream clouds. Comparison with
pre LMC/SMC encounter kinematic data of Hardy, Suntzeff, & Azzopardi (1989) of
carbon stars, with data of stars formed after the encounter, of Maurice et al.
(1989), and Mathewson et al. (a986, 1988) leaves little doubt that forces other
than gravity play a role in the dynamics of the H I.Comment: 30 pages; 7 figures, latex compiled, 1 table; to appear in AJ (June
2000
The Extended Shapes of Galactic Satellites
We are exploring the extended stellar distributions of Galactic satellite
galaxies and globular clusters. For seven objects studied thus far, the
observed profile departs from a King function at large r, revealing a ``break
population'' of stars. In our sample, the relative density of the ``break''
correlates to the inferred M/L of these objects. We discuss opposing hypotheses
for this trend: (1) Higher M/L objects harbor more extended dark matter halos
that support secondary, bound, stellar ``halos''. (2) The extended populations
around dwarf spheroidals (and some clusters) consist of unbound, extratidal
debris from their parent objects, which are undergoing various degrees of tidal
disruption. In this scenario, higher M/L ratios reflect higher degrees of
virial non-equilibrium in the parent objects, thus invalidating a precept
underlying the use of core radial velocities to obtain masses.Comment: 8 pages, including 2 figures Yale Cosmology Workshop: The Shapes of
Galaxies and Their Halo
Determination of step--edge barriers to interlayer transport from surface morphology during the initial stages of homoepitaxial growth
We use analytic formulae obtained from a simple model of crystal growth by
molecular--beam epitaxy to determine step--edge barriers to interlayer
transport. The method is based on information about the surface morphology at
the onset of nucleation on top of first--layer islands in the submonolayer
coverage regime of homoepitaxial growth. The formulae are tested using kinetic
Monte Carlo simulations of a solid--on--solid model and applied to estimate
step--edge barriers from scanning--tunneling microscopy data on initial stages
of Fe(001), Pt(111), and Ag(111) homoepitaxy.Comment: 4 pages, a Postscript file, uuencoded and compressed. Physical Review
B, Rapid Communications, in press
Phylogenetic inferences of Atelinae (Platyrrhini) based on multi-directional chromosome painting in Brachyteles arachnoides, Ateles paniscus paniscus and Ateles b. marginatus
We performed multi-directional chromosome painting in a comparative cytogenetic study of the three Atelinae species Brachyteles arachnoides, Ateles paniscus paniscus and Ateles belzebuth marginatus, in order to reconstruct phylogenetic relationships within this Platyrrhini subfamily. Comparative chromosome maps between these species were established by multi-color fluorescence in situ hybridization ( FISH) employing human, Saguinus oedipus and Lagothrix lagothricha chromosome-specific probes. The three species included in this study and four previously analyzed species from all four Atelinae genera were subjected to a phylogenetic analysis on the basis of a data matrix comprised of 82 discrete chromosome characters. The results confirmed that Atelinae represent a monophyletic clade with a putative ancestral karyotype of 2n = 62 chromosomes. Phylogenetic analysis revealed an evolutionary branching sequence \{Alouatta \{Brachyteles \{Lagothrix and Ateles\}\}\} in Atelinae and \{Ateles belzebuth marginatus \{Ateles paniscus paniscus \{Ateles belzebuth hybridus and Ateles geoffroyi\}\}\} in genus Ateles. The chromosomal data support a re-evaluation of the taxonomic status of Ateles b. hybridus. Copyright (C) 2005 S. Karger AG, Basel
Relationship between Tibial conformation, cage size and advancement achieved in TTA procedure
Previous studies have suggested that there is a theoretical discrepancy between the cage size and the resultant tibial tuberosity advancement, with the cage size consistently providing less tibial tuberosity advancement than predicted. The purpose of this study was to test and quantify this in clinical cases. The hypothesis was that the advancement of the tibial tuberosity as measured by the widening of the proximal tibia at the tibial tuberosity level after a standard TTA, will be less than the cage sized used, with no particular cage size providing a relative smaller or higher under-advancement, and that the conformation of the proximal tibia will have an influence on the amount of advancement achieved
Attenuation of leukocyte sequestration by selective blockade of PECAM-1 or VCAM-1 in murine endotoxemia
Background: Molecular mechanisms regulating leukocyte sequestration into the tissue during endotoxemia and/or sepsis are still poorly understood. This in vivo study investigates the biological role of murine PECAM-1 and VCAM-1 for leukocyte sequestration into the lung, liver and striated skin muscle. Methods: Male BALB/c mice were injected intravenously with murine PECAM-1 IgG chimera or monoclonal antibody (mAb) to VCAM-1 ( 3 mg/kg body weight); controls received equivalent doses of IgG2a ( n = 6 per group). Fifteen minutes thereafter, 2 mg/kg body weight of Salmonella abortus equi endotoxin was injected intravenously. At 24 h after the endotoxin challenge, lungs, livers and striated muscle of skin were analyzed for their myeloperoxidase activity. To monitor intravital leukocyte-endothelial cell interactions, fluorescence videomicroscopy was performed in the skin fold chamber model of the BALB/c mouse at 3, 8 and 24 h after injection of endotoxin. Results: Myeloperoxidase activity at 24 h after the endotoxin challenge in lungs (12,171 +/- 2,357 mU/g tissue), livers ( 2,204 +/- 238 mU/g) and striated muscle of the skin ( 1,161 +/- 110 mU/g) was significantly reduced in both treatment groups as compared to controls, with strongest attenuation in the PECAM-1 IgG treatment group. Arteriolar leukocyte sticking at 3 h after endotoxin (230 +/- 46 cells x mm(-2)) was significantly reduced in both treatment groups. Leukocyte sticking in postcapillary venules at 8 h after endotoxin ( 343 +/- 69 cells/mm(2)) was found reduced only in the VCAM-1-mAb-treated animals ( 215 +/- 53 cells/mm(2)), while it was enhanced in animals treated with PECAM-1 IgG ( 572 +/- 126 cells/mm(2)). Conclusion: These data show that both PECAM-1 and VCAM-1 are involved in endotoxin-induced leukocyte sequestration in the lung, liver and muscle, presumably through interference with arteriolar and/or venular leukocyte sticking. Copyright (C) 2004 S. Karger AG, Basel
Exploring Halo Substructure with Giant Stars. VI. Extended Distributions of Giant Stars Around the Carina Dwarf Spheroidal Galaxy -- How Reliable Are They?
The question of the existence of active tidal disruption around various dSph
galaxies remains controversial. That debate often centers on the nature (bound
vs. unbound) of extended populations of stars. However, the more fundamental
issue of the very existence of the extended populations is still contentious.
We present an evaluation of the debate centering on one particular dSph,
Carina, for which claims both for and against the existence of stars beyond the
King radius have been made. Our review includes an examination of all previous
studies bearing on the Carina radial profile and shows that the survey method
which achieves the highest detected dSph signal-to-background in the outer
parts of the galaxy is the Washington M, T2 + DDO51 (MTD) filter approach from
Paper II in this series. We then address statistical methods used to evaluate
the reliability of MTD surveys in the presence of photometric errors and for
which a new, a posteriori statistical analysis methodology is provided.
Finally, these statistical methods are tested by new spectroscopy of stars in
the MTD-selected Carina candidate sample. Of 74 candidate giants with follow-up
spectroscopy, the MTD technique identified 61 new Carina members, including 8
stars outside the King radius. From a sample of 29 stars not initially
identified as candidate Carina giants but that lie just outside of our
selection criteria, 12 have radial velocities consistent with membership,
including 5 extratidal stars. Carina is shown to have an extended population of
giant stars extending to a major axis radius of 40' (1.44x the nominal King
radius).Comment: 56 pages, 10 figures. Submitted to the Astronomical Journal, 2004 Sep
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