150 research outputs found
Development of Hydrogen and Helium Proximity Zones around Quasars
Increasing evidence suggests that He II proximity profiles in the quasar
spectra at z ~ 3 - 4 are sensitive probes of quasar ages. But the development
of their H I counterparts is difficult to trace and remains poorly constrained.
We compare the UV spectra of 15 He II quasars with their high-resolution
optical counterparts and find a significant correlation between the sizes of He
II and H I proximity zones. The luminous quasar HE2347-4342 displays a null
proximity zone in both He II and H I, suggesting that it is extremely young
(age < 0.2 Myr). Three other quasars also display small proximity zones for He
II and H I. There is no evidence that a H I ionization zone expands
considerably faster than its He II counterpart. The results suggest that the
expansion of quasar ionizing fronts may be noticeably slower than the speed of
light, and raise the possibility of distinguishing young and old quasars from
the sizes of their H I proximity zones.Comment: To appear in The Astrophysical Journal, with 19 pages, 11 figures, 2
table
Edge Theories for Polarized Quantum Hall States
Starting from recently proposed bosonic mean field theories for fully and
partially polarized quantum Hall states, we construct corresponding effective
low energy theories for the edge modes. The requirements of gauge symmetry and
invariance under global O(3) spin rotations, broken only by a Zeeman coupling,
imply boundary conditions that allow for edge spin waves. In the generic case,
these modes are chiral, and the spin stiffness differs from that in the bulk.
For the case of a fully polarized state, our results agree with
previous Hartree-Fock calculations.Comment: 15 pages (number of pages has been reduced by typesetting in RevTeX);
2 references adde
The Properties of Two Low Redshift O VI Absorbers and Their Associated Galaxies Toward 3C 263
Ultraviolet observations of the QSO 3C 263 (zem = 0.652) with COS and FUSE
reveal O VI absorption systems at z = 0.06342 and 0.14072 . WIYN multi-object
spectrograph observations provide information about the galaxies associated
with the absorbers. The multi-phase system at z = 0.06342 traces cool
photoionized gas and warm collisionally ionized gas associated with a L ~
0.31L* compact spiral emission line galaxy with an impact parameter of 63 kpc.
The cool photoionized gas in the absorber is well modeled with log U ~ -2.6,
log N(H) ~17.8, log n(H) ~ -3.3 and [Si/H] = -0.14\pm0.23. The collisionally
ionized gas containing C IV and O VI probably arises in cooling shock heated
transition temperature gas with log T ~ 5.5. The absorber is likely tracing
circumgalactic gas enriched by gas ejected from the spiral emission line
galaxy. The simple system at z = 0.14072 only contains O VI and broad and
narrow H I. The O VI with b = 33.4\pm11.9 km s-1 is likely associated with the
broad H I {\lambda}1215 absorption with b = 86.7\pm15.4 km s-1. The difference
in Doppler parameters implies the detection of a very large column of warm gas
with log T = 5.61(+0.16, -0.25), log N(H) = 19.54(+0.26, -0.44) and [O/H] =
-1.48 (+0.46, -0.26). This absorber is possibly associated with a 1.6L*
absorption line galaxy with an impact parameter of 617 kpc although an origin
in warm filament gas or in the halo of a fainter galaxy is more likely.Comment: Accepted by the Astrophysical Journal. 24 pages and 9 figure
Parametrization of the Driven Betatron Oscillation
An AC dipole is a magnet which produces a sinusoidally oscillating dipole
field and excites coherent transverse beam motion in a synchrotron. By
observing this coherent motion, the optical parameters can be directly measured
at the beam position monitor locations. The driven oscillation induced by an AC
dipole will generate a phase space ellipse which differs from that of the free
oscillation. If not properly accounted for, this difference can lead to a
misinterpretation of the actual optical parameters, for instance, of 6% or more
in the cases of the Tevatron, RHIC, or LHC. The effect of an AC dipole on the
linear optics parameters is identical to that of a thin lens quadrupole. By
introducing a new amplitude function to describe this new phase space ellipse,
the motion produced by an AC dipole becomes easier to interpret. Beam position
data taken under the influence of an AC dipole, with this new interpretation in
mind, can lead to more precise measurements of the normal Courant-Snyder
parameters. This new parameterization of the driven motion is presented and is
used to interpret data taken in the FNAL Tevatron using an AC dipole.Comment: 8 pages, 8 figures, and 1 tabl
Experimental investigation of the edge states structure at fractional filling factors
We experimentally study electron transport between edge states in the
fractional quantum Hall effect regime. We find an anomalous increase of the
transport across the 2/3 incompressible fractional stripe in comparison with
theoretical predictions for the smooth edge potential profile. We interpret our
results as a first experimental demonstration of the intrinsic structure of the
incompressible stripes arising at the sample edge in the fractional quantum
Hall effect regime.Comment: 5 pages, 5 figures included. Submitted to JETP Letter
Blue Variable Stars from the MACHO database I: Photometry and Spectroscopy of the LMC sample
We present the photometric properties of 1279 blue variable stars within the
LMC. Photometry is derived from the MACHO database. The lightcurves of the
sample exhibit a variety of quasi-periodic and aperiodic outburst behavior. A
characteristic feature of the photometric variation is that the objects are
reddest when at maximum outburst. A subset of 102 objects were examined
spectroscopically. Within this subset, 91% exhibited Balmer emission in at
least one epoch, in some cases with spectacular spectral variability. The
variability observed in the sample is consistent with the establishment and
maintenance of the Be phenomenon.Comment: 19 pages, AJ accepte
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Transfer of a polarized proton beam from AGS to RHIC
As part of the RHIC project, the RHIC machine will also be able to accelerate polarized proton beam bunches. The bunches will be extracted from the AGS machine, with kinetic energy T = 25 GeV, and transferred into RHIC via the AtR transfer line. When the RHIC machine accelerates polarized protons, it will operate with two full snakes, which define the stable spin direction of a polarized proton beam circulating in each ring, along the vertical. Therefore a polarized proton beam should be injected into the RHIC machine with the stable spin direction along the vertical in order to match that of the RHIC machine. The layout of the dipole magnets of the AtR line creates a dependence, on the injection energy, of the stable spin direction of a polarized proton beam injected into the RHIC machine. In this paper, the study of the stable spin direction (at the RHIC injection point) of a polarized proton beam as a function of the injection energy is presented. A modification of the AtR transfer line, which eliminates this energy dependence (within the range of proton injection energies) of the stable spin direction is also presented
Hysteresis and Spikes in the Quantum Hall Effect
We observe sharp peaks and strong hysteresis in the electronic transport of a
two-dimensional electron gas (2DEG) in the region of the integral quantum Hall
effect. The peaks decay on time scales ranging from several minutes to more
than an hour. Momentary grounding of some of the contacts can vastly modify the
strength of the peaks. All these features disappear under application of a
negative bias voltage to the backside of the specimen. We conclude, that a
conduction channel parallel to the high mobility 2DEG is the origin for the
peaks and their hysteretic behavior.Comment: 7 pages, 3 eps figures. Submitted to Phys. Rev. Lett, minor typos
correcte
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