49 research outputs found
The detection of M-dwarf UV flare events in the GALEX data archives
We present the preliminary results from implementing a new software tool that
enables inspection of time-tagged photon data for the astronomical sources
contained within individual GALEX ultraviolet images of the sky. We have
inspected the photon data contained within 1802 GALEX images to reveal rapid,
short-term (<500 sec) UV source variability in the form of stellar flares. The
mean associated change in NUV magnitude due to this flaring activity is
2.7+/-0.3 mag. A list of 49 new UV variable-star candidates is presented,
together with their associated Sloan Digital Sky Survey (SDSS) photometric
magnitudes. From these data we can associate the main source of these UV flare
events with magnetic activity on M-dwarf stars. Photometric parallaxes have
been determined for 32 of these sources, placing them at distances ranging from
approximately 25 to 1000pc. The average UV flare energy for these flare events
is 2.5E30 ergs, which is of a similar energy to that of U-band, X-ray and EUV
flares observed on many local M-dwarf stars. We have found that stars of
classes M0 to M5 flare with energies spanning a far larger range and with an
energy approximately 5 times greater than those of later (M6 to M8) spectral
type.Comment: Accepted for the Astrophysical Journal Supplement, GALEX Special
Issu
Triplet lifetime in gaseous argon
MiniCLEAN is a single-phase liquid argon dark matter experiment. During the
initial cooling phase, impurities within the cold gas (140 K) were monitored
by measuring the scintillation light triplet lifetime, and ultimately a triplet
lifetime of 3.480 0.001 (stat.) 0.064 (sys.) s was obtained,
indicating ultra-pure argon. This is the longest argon triplet time constant
ever reported. The effect of quenching of separate components of the
scintillation light is also investigated
The Galex Ultraviolet Variability (GUVV) Catalog
We present Version 1.0 of the NASA Galaxy Evolution Explorer (GALEX)
ultraviolet variability catalog (GUVV) that contains information on 84
time-variable and transient sources gained with simultaneous near and far
ultraviolet photometric observations. These time-variable sources were
serendipitously revealed in the various 1.2 degree star fields currently being
surveyed by the GALEX satellite in two ultraviolet bands (NUV 1750-2750A, FUV
1350-1750A) with limiting AB magnitudes of 23-25. The largest-amplitude
variable objects presently detected by GALEX are M-dwarf flare stars, which can
brighten by 5-10 mag in both the NUV and FUV bands during short duration (<
500s) outbursts. Other types of large-amplitude ultraviolet variable objects
include ab-type RR Lyrae stars, which can vary periodically by 2-5mag in the
GALEX FUV band. This first GUVV catalog lists galactic positions and possible
source identifications in order to provide the astronomical community with a
list of time-variable objects that can now be repeatedly observed at other
wavelengths. We expect the total number of time-variable source detections to
increase as the GALEX mission progresses, such that later version numbers of
the GUVV catalog will contain substantially more variable sources
The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe
The preponderance of matter over antimatter in the early Universe, the
dynamics of the supernova bursts that produced the heavy elements necessary for
life and whether protons eventually decay --- these mysteries at the forefront
of particle physics and astrophysics are key to understanding the early
evolution of our Universe, its current state and its eventual fate. The
Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed
plan for a world-class experiment dedicated to addressing these questions. LBNE
is conceived around three central components: (1) a new, high-intensity
neutrino source generated from a megawatt-class proton accelerator at Fermi
National Accelerator Laboratory, (2) a near neutrino detector just downstream
of the source, and (3) a massive liquid argon time-projection chamber deployed
as a far detector deep underground at the Sanford Underground Research
Facility. This facility, located at the site of the former Homestake Mine in
Lead, South Dakota, is approximately 1,300 km from the neutrino source at
Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino
charge-parity symmetry violation and mass ordering effects. This ambitious yet
cost-effective design incorporates scalability and flexibility and can
accommodate a variety of upgrades and contributions. With its exceptional
combination of experimental configuration, technical capabilities, and
potential for transformative discoveries, LBNE promises to be a vital facility
for the field of particle physics worldwide, providing physicists from around
the globe with opportunities to collaborate in a twenty to thirty year program
of exciting science. In this document we provide a comprehensive overview of
LBNE's scientific objectives, its place in the landscape of neutrino physics
worldwide, the technologies it will incorporate and the capabilities it will
possess.Comment: Major update of previous version. This is the reference document for
LBNE science program and current status. Chapters 1, 3, and 9 provide a
comprehensive overview of LBNE's scientific objectives, its place in the
landscape of neutrino physics worldwide, the technologies it will incorporate
and the capabilities it will possess. 288 pages, 116 figure
Phase transitions in quantum chromodynamics
The current understanding of finite temperature phase transitions in QCD is
reviewed. A critical discussion of refined phase transition criteria in
numerical lattice simulations and of analytical tools going beyond the
mean-field level in effective continuum models for QCD is presented.
Theoretical predictions about the order of the transitions are compared with
possible experimental manifestations in heavy-ion collisions. Various places in
phenomenological descriptions are pointed out, where more reliable data for
QCD's equation of state would help in selecting the most realistic scenario
among those proposed. Unanswered questions are raised about the relevance of
calculations which assume thermodynamic equilibrium. Promising new approaches
to implement nonequilibrium aspects in the thermodynamics of heavy-ion
collisions are described.Comment: 156 pages, RevTex. Tables II,VIII,IX and Fig.s 1-38 are not included
as postscript files. I would like to ask the requestors to copy the missing
tables and figures from the corresponding journal-referenc
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A low energy measurement of the ⁸B solar neutrino spectrum at the Sudbury Neutrino Observatory
textThe Sudbury Neutrino Observatory has previously shown that ⁸B solar neutrinos undergo flavor transformation between the Sun and the Earth. This work presents a joint analysis of one-third of the pure D₂O and salt phase data sets with an electron energy threshold of 3.5 MeV. A measurement of the neutral current interaction rate, sensitive to all neutrino flavors, gives a total ⁸B flux of 4.79 ± 0.22 (stat) ± 0.13(syst) × 10⁶ cm⁻²s⁻¹. This is in agreement with the prediction of the Standard Solar Model. For the first time we obtain the v[sunscript e] survival probability separately for downward-going (day) and upward-going (night) solar neutrinos. No significant distortion is observed day or night for ⁸B neutrinos with energies greater than 6 MeV. The lack of distortion, but overall suppression of electron neutrinos relative to the total flux, is consistent with matter-induced neutrino transformation in the Sun and the large mixing angle solution.Physic