1,183 research outputs found
The Solar Neighborhood XV: Discovery of New High Proper Motion Stars with mu >= 0.4"/yr between Declinations -47 degrees and 00 degrees
We report the discovery of 152 new high proper motion systems (mu >= 0.4"/yr)
in the southern sky (Declination = -47 degrees to 00 degrees) brighter than
UKST plate R_{59F} =16.5 via our SuperCOSMOS-RECONS (SCR) search. This paper
complements Paper XII in The Solar Neighborhood series, which covered the
region from Declination = -90 degrees to -47 degrees and discussed all 147 new
systems from the southernmost phase of the search. Among the total of 299
systems from both papers, there are 148 (71 in Paper XII, 77 in this paper) new
systems moving faster than 0.5"/yr that are additions to the classic ``LHS''
(Luyten Half Second) sample. These constitute an 8% increase in the sample of
all stellar systems with mu >= 0.5"/yr in the southern sky.
As in Paper XII, distance estimates are provided for the systems reported
here based upon a combination of photographic plate magnitudes and 2MASS
photometry, assuming all stars are on the main sequence. Two SCR systems from
the portion of the sky included in this paper are anticipated to be within 10
pc, and an additional 23 are within 25 pc. In total, the results presented in
Paper XII and here for this SCR sweep of the entire southern sky include five
new systems within 10 pc and 38 more between 10 and 25 pc. The largest number
of nearby systems have been found in the slowest proper motion bin, 0.6"/yr >
mu >= 0.4"/yr, indicating that there may be a large population of low proper
motion systems very near the Sun.Comment: 36 pages, 5 figures, accepted for publication in Astronomical Journa
The Solar Neighborhood XII: Discovery of New High Proper Motion Stars with 1.0"/yr > mu >= 0.4"/yr between Declinations -90 degrees and -47 degrees
We report the discovery of 141 new high proper motion systems (1.0"/yr > mu
>= 0.4"/yr) in the southern sky (Declination = -90 degrees to -47 degrees)
brighter than UKST plate R_{59F} = 16.5 via our SuperCOSMOS-RECONS (SCR)
search. When combined with the nine systems having mu >= 1.0"/yr and/or late
spectral type from the initial phases of this effort (Hambly et al. 2004, Henry
et al. 2004), we find that 73 of the 150 total systems are moving faster than
0.5"/yr, and are therefore new members of the classic "LHS" (Luyten Half
Second) sample. These constitute a 21% increase in the sample of stars with mu
>= 0.5"/yr in the declination region searched, thereby comprising an important
addition to this long-neglected region of the sky.
Distance estimates are provided for the entire sample, based upon a
combination of photographic plate magnitudes and 2MASS photometry, using the
relations presented in Hambly et al. (2004) for the presumed main sequence
stars. Three systems are anticipated to be within 10 pc, and an additional 15
are within 25 pc. Eight of these 18 nearby systems have proper motions falling
between 0.4"/yr and 0.6"/yr, hinting at a large population of nearby stars with
fast, but not extremely high, proper motions that have not been thoroughly
investigated.Comment: 45 pages, 6 figures, accepted for publication in Astronomical Journal
(January 2005
Application of Stereo PIV on a Supersonic Parachute Model
The Mars Science Laboratory (MSL) is the next step in NASA's Mars Exploration Program, currently scheduled for 2011. The spacecraft's descent into the Martian atmosphere will be slowed from Mach 2 to subsonic speeds via a large parachute system with final landing under propulsive control. A Disk-Band-Gap (DBG) parachute will be used on MSL similar to the designs that have been used on previous missions, however; the DBG parachute used by MSL will be larger (21.5 m) than in any of the previous missions due to the weight of the payload and landing site requirements. The MSL parachute will also deploy at higher Mach number (M 2) than previous parachutes, which can lead to instabilities in canopy performance. Both the increased size of the DBG above previous demonstrated configurations and deployment at higher Mach numbers add uncertainty to the deployment, structural integrity and performance of the parachute. In order to verify the performance of the DBG on MSL, experimental testing, including acquisition of Stereo Particle Imaging Velocimetry (PIV) measurements were required for validating CFD predictions of the parachute performance. A rigid model of the DBG parachute was tested in the 10x10 foot wind tunnel at GRC. Prior to the MSL tests, a PIV system had never been used in the 10x10 wind tunnel. In this paper we discuss some of the technical challenges overcome in implementing a Stereo PIV system with a 750x400 mm field-of-view in the 10x10 wind tunnel facility and results from the MSL hardshell canopy tests
Factors Associated with the Diversification of the Gut Microbial Communities within Chimpanzees from Gombe National Park.
The gastrointestinal tract harbors large and diverse populations of bacteria that vary among individuals and within individuals over time. Numerous internal and external factors can influence the contents of these microbial communities, including diet, geography, physiology, and the extent of contact among hosts. To investigate the contributions of such factors to the variation and changes in gut microbial communities, we analyzed the distal gut microbiota of individual chimpanzees from two communities in Gombe National Park, Tanzania. These samples, which were derived from 35 chimpanzees, many of whom have been monitored for multiple years, provide an unusually comprehensive longitudinal depth for individuals of known genetic relationships. Although the composition of the great-ape microbiota has been shown to codiversify with host species, indicating that host genetics and phylogeny have played a major role in its differentiation over evolutionary timescales, the geneaological relationships of individual chimpanzees did not coincide with the similarity in their gut microbial communities. However, the inhabitants from adjacent chimpanzee communities could be distinguished based on the contents of their gut microbiota. Despite the broad similarity of community members, as would be expected from shared diet or interactions, long-term immigrants to a community often harbored the most distinctive gut microbiota, suggesting that individuals retain hallmarks of their previous gut microbial communities for extended periods. This pattern was reinforced in several chimpanzees sampled over long temporal scales, in which the major constituents of the gut microbiota were maintained for nearly a decade
Meeting the Cool Neighbors X: Ultracool dwarfs from the 2MASS All-Sky Data Release
Using data from the 2MASS All-Sky Point Source Catalogue, we have extended
our census of nearby ultracool dwarfs to cover the full celestial sphere above
Galactic latitute 15 degrees. Starting with an initial catalogue of 2,139,484
sources, we have winnowed the sample to 467 candidate late-type M or L dwarfs
within 20 parsecs of the Sun. Fifty-four of those sources already have
spectroscopic observations confirming them as late-type dwarfs. We present
optical spectroscopy of 376 of the remaining 413 sources, and identify 44 as
ultracool dwarfs with spectroscopic distances less than 20 parsecs. Twenty-five
of the 37 sources that lack optical data have near-infrared spectroscopy.
Combining the present sample with our previous results and data from the
literature, we catalogue 94 L dwarf systems within 20 parsecs. We discuss the
distribution of activity, as measured by H-alpha emission, in this
volume-limited sample. We have coupled the present ultracool catalogue with
data for stars in the northern 8-parsec sample and recent (incomplete)
statistics for T dwarfs to provide a snapshot of the current 20-parsec census
as a function of spectral type.Comment: Accepted for publication by the Astronomical Journa
Strange Particle Production from SIS to LHC
>1A review of meson emission in heavy ion collisions at incident energies
from SIS up to collider energies is presented. A statistical model assuming
chemical equilibrium and local strangeness conservation (i.e. strangeness
conservation per collision) explains most of the observed features.
Emphasis is put onto the study of and emission at low incident
energies. In the framework of this statistical model it is shown that the
experimentally observed equality of and rates at
``threshold-corrected'' energies is due to a
crossing of two excitation functions. Furthermore, the independence of the
to ratio on the number of participating nucleons observed between
SIS and RHIC is consistent with this model.
It is demonstrated that the production at SIS energies occurs
predominantly via strangeness exchange and this channel is approaching chemical
equilibrium. The observed maximum in the excitation function is
also seen in the ratio of strange to non-strange particle production. The
appearance of this maximum around 30 GeV is due to the energy
dependence of the chemical freeze-out parameters and .Comment: Presented at the International Workshop "On the Physics of the
Quark-Gluon Plasma", Palaiseau, France, September 2001. 10 pages, 8 figure
Status of Chemical Equilibrium in Relativistic Heavy Ion Collisions
Recent work on chemical equilibrium in heavy ion collisions is reviewed. The
energy dependence of thermal parameters is discussed. The centrality dependence
of thermal parameters at SPS energies is presented.Comment: 7 pages, 7 Postscript figure
Strangeness Production at RHIC in the Perturbative Regim
We investigate strange quark production in Au-Au collisions at RHIC in the
framework of the Parton Cascade Model(PCM). The yields of (anti-) strange
quarks for three production scenarios -- primary-primary scattering, full
scattering, and full production -- are compared to a proton-proton baseline.
Enhancement of strange quark yields in central Au-Au collisions compared to
scaled p-p collisions increases with the number of secondary interactions. The
centrality dependence of strangeness production for the three production
scenarios is studied as well. For all production mechanisms, the strangeness
yield increases with . The perturbative QCD regime
described by the PCM is able to account for up to 50% of the observed
strangeness at RHIC.Comment: 10 pages, 4 figures, IOP forma
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