168 research outputs found
The Beam Screen for the LHC Injection Kicker Magnets
The two LHC injection kicker magnet systems must each produce a kick of 1.2 T.m with a flattop duration variable up to 7.86 ìs, and rise and fall times of less than 0.9 ìs and 3 ìs, respectively. Each system is composed of four 5 Ù transmission line kicker magnets with matched terminating resistors and pulse forming networks (PFN). The LHC beam has a high intensity, hence a beam screen is required in the aperture of the magnets This screen consists of a ceramic tube with conducting ?stripes? on the inner wall. The stripes provide a path for the image current of the beam and screen the magnet ferrites against Wake fields. The stripes initially used gave adequately low beam impedance however stripe discharges occured during pulsing of the magnet: hence further development of the beam screen was undertaken. This paper presents options considered to meet the often conflicting needs for low beam impedance, shielding of the ferrite, fast field rise time and good electrical and vacuum behaviour
Discovery of the lensed quasar eRASS1 J050129.5-073309 with eROSITA and
We report the discovery and spectroscopic identification of the bright doubly
lensed quasar eRASS1 J050129.5-073309 at redshift , selected from the
first all-sky survey of the eROSITA
telescope and the EDR3 catalog. We systematically search for
extragalactic sources with eROSITA X-ray positions having multiple
counterparts and have started spectroscopic follow-up of the most promising
candidates using long-slit spectroscopy with NTT/EFOSC2 to confirm the lens
nature. The two images are separated by and their average
-band magnitudes are 16.95 and 17.33. Legacy Survey DR10 imaging and
image modeling reveal both the lensing galaxy and tentatively the lensed image
of the quasar host galaxy. Archival optical light curves show evidence of a
variability time delay with the fainter component lagging the brighter by about
100 days. The fainter image has also decreased its brightness by about 1
magnitude since 2019. This dimming was still obvious at the time of the
spectroscopic observations and is probably caused by microlensing. The optical
spectroscopic follow-up obtained from NTT/EFOSC2 and the evidence provided by
the imaging and timing analysis allow us to confirm the lensed nature of eRASS1
J050129.5-073309.Comment: Accepted for publication in A&
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
Investigating the spectroscopic, magnetic and circumstellar variability of the O9 subgiant star HD 57682
XXL-HSC: An updated catalogue of high-redshift (z3.5) X-ray AGN in the XMM-XXL northern field: Constraints on the bright end of the soft log N -log S
X-rays offer a reliable method to identify active galactic nuclei (AGNs). However, in the high-redshift Universe, X-ray AGNs are poorly sampled due to their relatively low space density and the small areas covered by X-ray surveys. In addition to wide-area X-ray surveys, it is important to have deep optical data in order to locate the optical counterparts and determine their redshifts. In this work, we built a high-redshift (z3.5) X-ray-selected AGN sample in the XMM-XXL northern field using the most updated [0.5-2 keV] catalogue along with a plethora of new spectroscopic and multi-wavelength catalogues, including the deep optical Subaru Hyper Suprime-Cam (HSC) data, reaching magnitude limits i 26 mag. We selected all the spectroscopically confirmed AGN and complement this sample with high-redshift candidates that are HSC g- and r-band dropouts. To confirm the dropouts, we derived their photometric redshifts using spectral energy distribution techniques. We obtained a sample of 54 high-z sources (28 with spec-z), the largest in this field so far (almost three times larger than in previous studies), and we estimated the possible contamination and completeness. We calculated the number counts (log N-log S) in different redshift bins and compared our results with previous studies and models. We provide the strongest high-redshift AGN constraints yet at bright fluxes (f0.52 keV>10 15 ergs 1 cm2). The samples of z 3.5, z4, and z5 are in agreement with an exponential decline model similar to that witnessed at optical wavelengths. Our work emphasises the importance of using wide-area X-ray surveys with deep optical data to uncover high-redshift AGNs
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