146 research outputs found
The Subaru Coronagraphic Extreme Adaptive Optics system: enabling high-contrast imaging on solar-system scales
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a
multipurpose high-contrast imaging platform designed for the discovery and
detailed characterization of exoplanetary systems and serves as a testbed for
high-contrast imaging technologies for ELTs. It is a multi-band instrument
which makes use of light from 600 to 2500nm allowing for coronagraphic direct
exoplanet imaging of the inner 3 lambda/D from the stellar host. Wavefront
sensing and control are key to the operation of SCExAO. A partial correction of
low-order modes is provided by Subaru's facility adaptive optics system with
the final correction, including high-order modes, implemented downstream by a
combination of a visible pyramid wavefront sensor and a 2000-element deformable
mirror. The well corrected NIR (y-K bands) wavefronts can then be injected into
any of the available coronagraphs, including but not limited to the phase
induced amplitude apodization and the vector vortex coronagraphs, both of which
offer an inner working angle as low as 1 lambda/D. Non-common path, low-order
aberrations are sensed with a coronagraphic low-order wavefront sensor in the
infrared (IR). Low noise, high frame rate, NIR detectors allow for active
speckle nulling and coherent differential imaging, while the HAWAII 2RG
detector in the HiCIAO imager and/or the CHARIS integral field spectrograph
(from mid 2016) can take deeper exposures and/or perform angular, spectral and
polarimetric differential imaging. Science in the visible is provided by two
interferometric modules: VAMPIRES and FIRST, which enable sub-diffraction
limited imaging in the visible region with polarimetric and spectroscopic
capabilities respectively. We describe the instrument in detail and present
preliminary results both on-sky and in the laboratory.Comment: Accepted for publication, 20 pages, 10 figure
Low-lying quadrupole collective states of the light and medium Xenon isotopes
Collective low lying levels of light and medium Xenon isotopes are deduced
from the Generalized Bohr Hamiltonian (GBH). The microscopic seven functions
entering into the GBH are built from a deformed mean field of the Woods-Saxon
type. Theoretical spectra are found to be close to the ones of the experimental
data taking into account that the calculations are completely microscopic, that
is to say, without any fitting of parameters.Comment: 8 pages, 4 figures, 1 tabl
Gemini multi-conjugate adaptive optics system review II: Commissioning, operation and overall performance
The Gemini Multi-conjugate Adaptive Optics System - GeMS, a facility
instrument mounted on the Gemini South telescope, delivers a uniform, near
diffraction limited images at near infrared wavelengths (0.95 microns- 2.5
microns) over a field of view of 120 arc seconds. GeMS is the first sodium
layer based multi laser guide star adaptive optics system used in astronomy. It
uses five laser guide stars distributed on a 60 arc seconds square
constellation to measure for atmospheric distortions and two deformable mirrors
to compensate for it. In this paper, the second devoted to describe the GeMS
project, we present the commissioning, overall performance and operational
scheme of GeMS. Performance of each sub-system is derived from the
commissioning results. The typical image quality, expressed in full with half
maximum, Strehl ratios and variations over the field delivered by the system
are then described. A discussion of the main contributor to performance
limitation is carried-out. Finally, overheads and future system upgrades are
described.Comment: 20 pages, 11 figures, accepted for publication in MNRA
High intensity proton beams in a multi-cycled SPS
The SPS ran for 247 days during 1994; 64% of this was with high intensity proton beam for physics data taking in the Fixed Target mode of operation, 12% was for a lead run at the end of the year, with the remaining 24% spent in setting up and machine development. The SPS supplied LEP with 8 bunches of electrons and 8 bunches of positrons either in the 14.4 or 19.2 seconds interleaved cycling mode during the operation with protons or lead ions respectively. The new record peak intensity during the year was 3.9x1013 protons per pulse at 450GeV. A total of 11x1018 proton were delivered to all targets, with an overall average during physics of 2.5x1013 protons per pulse at 450GeV. Some 6x1018 protons were delivered to both neutrino experiments
Investigating the spectroscopic, magnetic and circumstellar variability of the O9 subgiant star HD 57682
The O9IV star HD 57682, discovered to be magnetic within the context of the
MiMeS survey in 2009, is one of only eight convincingly detected magnetic
O-type stars. Among this select group, it stands out due to its sharp-lined
photospheric spectrum. Since its discovery, the MiMeS Collaboration has
continued to obtain spectroscopic and magnetic observations in order to refine
our knowledge of its magnetic field strength and geometry, rotational period,
and spectral properties and variability. In this paper we report new ESPaDOnS
spectropolarimetric observations of HD 57682, which are combined with
previously published ESPaDOnS data and archival H{\alpha} spectroscopy. This
dataset is used to determine the rotational period (63.5708 \pm 0.0057 d),
refine the longitudinal magnetic field variation and magnetic geometry (dipole
surface field strength of 880\pm50 G and magnetic obliquity of 79\pm4\circ as
measured from the magnetic longitudinal field variations, assuming an
inclination of 60\circ), and examine the phase variation of various lines. In
particular, we demonstrate that the H{\alpha} equivalent width undergoes a
double-wave variation during a single rotation of the star, consistent with the
derived magnetic geometry. We group the variable lines into two classes: those
that, like H{\alpha}, exhibit non-sinusoidal variability, often with multiple
maxima during the rotation cycle, and those that vary essentially sinusoidally.
Based on our modelling of the H{\alpha} emission, we show that the variability
is consistent with emission being generated from an optically thick, flattened
distribution of magnetically-confined plasma that is roughly distributed about
the magnetic equator. Finally, we discuss our findings in the magnetospheric
framework proposed in our earlier study.Comment: 21 pages, 19 figures, Accepted for publication in MNRA
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