1,091 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
Rotor Model Updating and Validation for an Active Magnetic Bearing Based High-Speed Machining Spindle
This paper presents an experimentally driven model updating approach to address the dynamic inaccuracy of the nominal finite element (FE) rotor model of a machining spindle supported on active magnetic bearings. Modeling error is minimized through the application of a numerical optimization algorithm to adjust appropriately selected FE model parameters. Minimizing the error of both resonance and antiresonance frequencies simultaneously accounts for rotor natural frequencies as well as for their mode shapes. Antiresonance frequencies, which are shown to heavily influence the model’s dynamic properties, are commonly disregarded in structural modeling. Evaluation of the updated rotor model is performed through comparison of transfer functions measured at the cutting tool plane, which are independent of the experimental transfer function data used in model updating procedures. Final model validation is carried out with successful implementation of robust controller, which substantiates the effectiveness of the model updating methodology for model correction
Determinación de órbitas preliminares mediante un computador IBM-360 : Aplicación a 20 pequeños planetas no identificados
Uno de los programas que se está realizando en la Estación Astronómica de Cerro El Roble, contempla la observación de pequeños planetas recomendados. Al observar el asteroide 919-ILSEBILL (recomendado) se encontró en su placa otros 12 planetoides, lo cual fue confirmado por series de placas tomadas en 9 fechas siguientes. En estas nuevas placas pudo identificarse, con la ayuda de las "Efemérides de Pequeños Planetas para 1968" (I.T,A,)(1), los planetoides 238 HYPATIA y 153 HILDA, no logró encontrarse el 198 AMPELIA siendo que por sus efemérides debía estar en varias de las placas tomadas. Además de estas identificaciones aumentó a 20 el numero de pequeños planetas no identificados al compararlos con las efemérides del I.T.A.Asociación Argentina de Astronomí
Transition from Baryon- to Meson-Dominated Freeze Out -- Early Decoupling around 30 A GeV?
The recently discovered sharp peak in the excitation function of the K+/pi+
ratio around 30 A GeV in relativistic heavy-ion collisions is discussed in the
framework of the Statistical Model. In this model, the freeze-out of an ideal
hadron gas changes from a situation where baryons dominate to one with mainly
mesons. This transition occurs at a temperature T = 140 MeV and baryon chemical
potential mu(B) = 410 MeV corresponding to an energy of sqrt(s) = 8.2 GeV. The
calculated maximum in the K+/pi+ ratio is, however, much less pronounced than
the one observed by the NA49 Collaboration. The smooth increase of the K-/pi-
ratio with incident energy and the shape of the excitation functions of the
Lambda/pi+, Xi-/pi+ and Omega/pi ratios all exhibiting maxima at different
incident energies, is consistent with the presently available experimental
data. The measured K+/pi+ ratio exceeds the calculated one just at the incident
energy when the freeze-out condition is changing.
We speculate that at this point freeze-out might occur in a modified way. We
discuss a scenario of an early freeze-out which indeed increases K+/pi+ ratio
while most other particle ratios remain essentially unchanged. Such an early
freeze-out is supported by results from HBT studies.Comment: 8 pages, 5 figures, SQM2006 conference, Los Angeles, March 200
Determinación de órbitas preliminares mediante un computador IBM-360 : Aplicación a 20 pequeños planetas no identificados
Uno de los programas que se está realizando en la Estación Astronómica de Cerro El Roble, contempla la observación de pequeños planetas recomendados. Al observar el asteroide 919-ILSEBILL (recomendado) se encontró en su placa otros 12 planetoides, lo cual fue confirmado por series de placas tomadas en 9 fechas siguientes. En estas nuevas placas pudo identificarse, con la ayuda de las "Efemérides de Pequeños Planetas para 1968" (I.T,A,)(1), los planetoides 238 HYPATIA y 153 HILDA, no logró encontrarse el 198 AMPELIA siendo que por sus efemérides debía estar en varias de las placas tomadas. Además de estas identificaciones aumentó a 20 el numero de pequeños planetas no identificados al compararlos con las efemérides del I.T.A.Asociación Argentina de Astronomí
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
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