1,078 research outputs found
Alien Registration- Hawthorn, Wilmot E. (Blaine, Aroostook County)
https://digitalmaine.com/alien_docs/27345/thumbnail.jp
Astrophotonic micro-spectrographs in the era of ELTs
The next generation of Extremely Large Telescopes (ELT), with diameters up to
39 meters, will start opera- tion in the next decade and promises new
challenges in the development of instruments. The growing field of
astrophotonics (the use of photonic technologies in astronomy) can partly solve
this problem by allowing mass production of fully integrated and robust
instruments combining various optical functions, with the potential to reduce
the size, complexity and cost of instruments. In this paper, we focus on
developments in integrated micro-spectrographs and their potential for ELTs. We
take an inventory of the identified technologies currently in development, and
compare the performance of the different concepts. We show that in the current
context of single-mode instruments, integrated spectrographs making use of,
e.g., a photonic lantern can be a solution to reach the desired performance.
However, in the longer term, there is a clear need to develop multimode devices
to improve overall the throughput and sensitivity, while decreasing the
instrument complexity.Comment: 9 pages. 2 figures. Proceeding of SPIE 9147 "Ground-based and
Airborne Instrumentation for Astronomy V
A Tunable Echelle Imager
We describe and evaluate a new instrument design called a Tunable Echelle
Imager (TEI). In this instrument, the output from an imaging Fabry-Perot
interferometer is cross-dispersed by a grism in one direction and dispersed by
an echelle grating in the perpendicular direction. This forms a mosaic of
different narrow-band images of the same field on a detector. It offers a
distinct wavelength multiplex advantage over a traditional imaging Fabry-Perot
device.
Potential applications of the TEI include spectrophotometric imaging and
OH-suppressed imaging by rejection.Comment: 11 pages, 12 figures, accepted by PAS
The Escape of Ionizing Photons from the Galaxy
The Magellanic Stream and several high velocity clouds have now been detected
in optical line emission. The observed emission measures and kinematics are
most plausibly explained by photoionization due to hot, young stars in the
Galactic disk. The highly favorable orientation of the Stream allows an
unambiguous determination of the fraction of ionizing photons, F_esc, which
escape the disk. We have modelled the production and transport of ionizing
photons through an opaque interstellar medium. Normalization to the Stream
detections requires F_esc = 6%, in reasonable agreement with the flux required
to ionize the Reynolds layer. Neither shock heating nor emission within a hot
Galactic corona can be important in producing the observed H-alpha emission. If
such a large escape fraction is typical of L_* galaxies, star-forming systems
dominate the extragalactic ionizing background. Within the context of this
model, both the three-dimensional orientation of the Stream and the distances
to high-velocity clouds can be determined by sensitive H-alpha observations.Comment: 4 pages; LaTeX2e, emulateapj.sty, apjfonts.sty; 4 encapsulated PS
figures. For correct labels, may need to print Fig. 3 separately due to psfig
limitation. Astrophysical Journal (Letters), accepte
Spin and Charge Transport on the Surface of a Topological Insulator
We derive diffusion equations, which describe spin-charge coupled transport
on the helical metal surface of a three-dimensional topological insulator. The
main feature of these equations is a large magnitude of the spin-charge
coupling, which leads to interesting and observable effects. In particular, we
predict a new magnetoresistance effect, which manifests in a nonohmic
correction to a voltage drop between a ferromagnetic spin-polarized electrode
and a nonmagnetic electrode, placed on top of the helical metal. This
correction is proportional to the cross-product of the spin polarization of the
ferromagnetic electrode and the charge current between the two electrodes. We
also demonstrate tunability of this effect by applying a gate voltage, which
makes it possible to operate the proposed device as a transistor.Comment: 4 pages, 1 figure; published versio
Anharmonic mixing in a magnetic trap
We have experimentally observed re-equilibration of a magnetically trapped
cloud of metastable neon atoms after it was put in a non-equilibrium state.
Using numerical simulations we show that anharmonic mixing, equilibration due
to the collisionless dynamics of atoms in a magnetic trap, is the dominant
process in this equilibration. We determine the dependence of its time on trap
parameters and atom temperature. Furthermore we observe in the simulations a
resonant energy exchange between the radial and axial trap dimensions at a
ratio of trap frequencies \omega_r / \omega_z = 3/2. This resonance is
explained by a simple oscillator model.Comment: 9 pages, 6 figure
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