13,917 research outputs found
Variables in Globular Cluster NGC 5024
We present the results of a commissioning campaign to observe Galactic
globular clusters for the search of microlensing events. The central 10' X 10'
region of the globular cluster NGC 5024 was monitored using the 2-m Himalayan
Chandra Telescope in R-band for a period of about 8 hours on 24 March 2010.
Light curves were obtained for nearly 10,000 stars, using a modified Difference
Image Analysis (DIA) technique. We identified all known variables within our
field of view and revised periods and status of some previously reported
short-period variables. We report about eighty new variable sources and present
their equatorial coordinates, periods, light curves and possible types. Out of
these, 16 are SX Phe stars, 10 are W UMa-type stars, 14 are probable RR Lyrae
stars and 2 are detached eclipsing binaries. Nine of the newly discovered SX
Phe stars and two eclipsing binaries belong to the Blue Straggler Star (BSS)
population.Comment: 29 pages, 22 figures, replaced with rewritten data reduction par
Radiative and Collisional Jet Energy Loss in a Quark-Gluon Plasma
We calculate radiative and collisional energy loss of hard partons traversing
the quark-gluon plasma created at RHIC and compare the respective size of these
contributions. We employ the AMY formalism for radiative energy loss and
include additionally energy loss by elastic collisions. Our treatment of both
processes is complete at leading order in the coupling, and accounts for the
probabilistic nature of jet energy loss. We find that a solution of the
Fokker-Planck equation for the probability density distributions of partons is
necessary for a complete calculation of the nuclear modification factor
for pion production in heavy ion collisions. It is found that the
magnitude of is sensitive to the inclusion of both collisional and
radiative energy loss, while the average energy is less affected by the
addition of collisional contributions. We present a calculation of for
at RHIC, combining our energy loss formalism with a relativistic
(3+1)-dimensional hydrodynamic description of the thermalized medium.Comment: 4 pages, 4 figures, contributed to Quark Matter 2008, Jaipur, Indi
Beam-Energy and System-Size Dependence of Dynamical Net Charge Fluctuations
We present measurements of net charge fluctuations in collisions at
19.6, 62.4, 130, and 200 GeV, collisions at
62.4, 200 GeV, and collisions at 200
GeV using the net charge dynamical fluctuations measure . The
dynamical fluctuations are non-zero at all energies and exhibit a rather modest
dependence on beam energy. We find that at a given energy and collision system,
net charge dynamical fluctuations violate scaling, but display
approximate scaling. We observe strong dependence of dynamical
fluctuations on the azimuthal angular range and pseudorapidity widths.Comment: 4 pages, 4 figures, presented at the 19th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur,
India, February 4-10, 200
Electrochemical Behavior of SWCNT-TPLF Electrode Compared to SWCNT-coated GCE and GE Electrodes
Redox reaction [Fe(CN)6]3– / [Fe(CN)6]4– has been studied with a Single-Walled Carbon Nanotube
(SWCNT)-coated Glassy Carbon Electrode (GCE), SWCNT-coated Gold Electrode (GE)
and a lab-made SWCNT-TPLF (SWCNT-Thin-Paper-Like-Film) Electrode. The SWCNT-modified
electrode has shown a well-defined redox peak compared to bare electrodes. Cyclic voltammetry
was used in 50.0 × 10–3 M aqueous solution of KCl containing K4[Fe(CN)6] to obtain
information on both the capacitive background and electron transfer from the faradaic reaction
of the redox species. The capacitance gives insight into the effective surface area (including
both the exterior and interior surfaces within the coated and TPLF electrodes) as well as the
pseudocapacitance due to faradaic reactions of surface bonded oxides. Among the three types
of electrodes, the SWCNT-TPLF electrode showed the largest volume specific capacitance,
consistent with its highest carbon nanotube packing density and largest effective surface area.
This indicates that the carbon nanotube working electrode (whether coated or film electrode)
behaves as a three-dimensional electrode. The redox reaction of [Fe(CN)6]3– / [Fe(CN)6]4– was
found to occur not only at the outer surface of the carbon nanotube but also at the interior
surface of the thin paper like nanotube electrode
Photon Production from a Quark-Gluon-Plasma at Finite Baryon Chemical Potential
We compute the photon production of a QCD plasma at leading order in the
strong coupling with a finite baryon chemical potential. Our approach starts
from the real time formalism of finite temperature field theory. We identify
the class of diagrams contributing at leading order when a finite chemical
potential is added and resum them to perform a full treatment of the LPM effect
similar to the one performed by Arnold, Moore, and Yaffe at zero chemical
potential. Our results show that the contribution of and processes grows as the chemical potential grows.Comment: 28 pages, 14 figure
Black Hole Feedback On The First Galaxies
We study how the first galaxies were assembled under feedback from the accretion onto a central black hole (BH) that is left behind by the first generation of metal-free stars through self-consistent, cosmological simulations. X-ray radiation from the accretion of gas onto BH remnants of Population III (Pop III) stars, or from high-mass X-ray binaries (HMXBs), again involving Pop III stars, influences the mode of second generation star formation. We track the evolution of the black hole accretion rate and the associated X-ray feedback starting with the death of the Pop III progenitor star inside a minihalo and following the subsequent evolution of the black hole as the minihalo grows to become an atomically cooling galaxy. We find that X-ray photoionization heating from a stellar-mass BH is able to quench further star formation in the host halo at all times before the halo enters the atomic cooling phase. X-ray radiation from a HMXB, assuming a luminosity close to the Eddington value, exerts an even stronger, and more diverse, feedback on star formation. It photoheats the gas inside the host halo, but also promotes the formation of molecular hydrogen and cooling of gas in the intergalactic medium and in nearby minihalos, leading to a net increase in the number of stars formed at early times. Our simulations further show that the radiative feedback from the first BHs may strongly suppress early BH growth, thus constraining models for the formation of supermassive BHs.Astronom
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