2,496 research outputs found
Optical Design of the SuMIRe PFS Spectrograph
The SuMIRe Prime Focus Spectrograph (PFS), developed for the 8-m class SUBARU
telescope, will consist of four identical spectrographs, each receiving 600
fibers from a 2394 fiber robotic positioner at the telescope prime focus. Each
spectrograph includes three spectral channels to cover the wavelength range
0.38-1.26 um with a resolving power ranging between 2000 and 4000. A medium
resolution mode is also implemented to reach a resolving power of 5000 at 0.8
um. Each spectrograph is made of 4 optical units: the entrance unit which
produces three corrected collimated beams and three camera units (one per
spectral channel). The beam is split by using two large dichroics; and in each
arm, the light is dispersed by large VPH gratings. The proposed optical design
was optimized to achieve the requested image quality while simplifying the
manufacturing of the whole optical system. The camera design consists in an
innovative Schmidt camera observing a large field-of-view (10 degrees) with a
very fast beam. To achieve such a performance, the classical spherical mirror
is replaced by a catadioptric mirror (i.e meniscus lens with a reflective
surface on the rear side of the glass, like a Mangin mirror). This article
focuses on the optical architecture of the PFS spectrograph and the perfornance
achieved. We will first described the global optical design of the
spectrograph. Then, we will focus on the Mangin-Schmidt camera design. The
analysis of the optical performance and the results obtained are presented in
the last section.Comment: 8 pages - submitted at SPIE Astronomical Telescopes - Instrumentation
2014 - Montrea
Experiments on transformation thermodynamics: Molding the flow of heat
It has recently been shown theoretically that the time-dependent heat
conduction equation is form-invariant under curvilinear coordinate
transformations. Thus, in analogy to transformation optics, fictitious
transformed space can be mapped onto (meta-)materials with spatially
inhomogeneous and anisotropic heat-conductivity tensors in the laboratory
space. On this basis, we design, fabricate, and characterize a micro-structured
thermal cloak that molds the flow of heat around an object in a metal plate.
This allows for transient protection of the object from heating, while
maintaining the same downstream heat flow as without object and cloak.Comment: 10 pages, 4 figure
Tracking the effects of interactions on spinons in gapless Heisenberg chains
We consider the effects of interactions on spinon excitations in Heisenberg spin-1/2 chains. We compute the exact two-spinon part of the longitudinal structure factor of the infinite chain in zero field for all values of anisotropy in the gapless antiferromagnetic regime, via an exact algebraic approach. Our results allow us to quantitatively describe the behavior of these fundamental excitations throughout the observable continuum, for cases ranging from free to fully coupled chains, thereby explicitly mapping the effects of "turning on the interactions" in a strongly correlated system
Measurement of the Radius of Neutron Stars with High S/N Quiescent Low-mass X-ray Binaries in Globular Clusters
This paper presents the measurement of the neutron star (NS) radius using the
thermal spectra from quiescent low-mass X-ray binaries (qLMXBs) inside globular
clusters (GCs). Recent observations of NSs have presented evidence that cold
ultra dense matter -- present in the core of NSs -- is best described by
"normal matter" equations of state (EoSs). Such EoSs predict that the radii of
NSs, Rns, are quasi-constant (within measurement errors, of ~10%) for
astrophysically relevant masses (Mns > 0.5 Msun). The present work adopts this
theoretical prediction as an assumption, and uses it to constrain a single Rns
value from five qLMXB targets with available high signal-to-noise X-ray
spectroscopic data. Employing a Markov-Chain Monte-Carlo approach, we produce
the marginalized posterior distribution for Rns, constrained to be the same
value for all five NSs in the sample. An effort was made to include all
quantifiable sources of uncertainty into the uncertainty of the quoted radius
measurement. These include the uncertainties in the distances to the GCs, the
uncertainties due to the Galactic absorption in the direction of the GCs, and
the possibility of a hard power-law spectral component for count excesses at
high photon energy, which are observed in some qLMXBs in the Galactic plane.
Using conservative assumptions,we found that the radius, common to the five
qLMXBs and constant for a wide range of masses, lies in the low range of
possible NS radii, Rns=9.1(+1.3)(-1.5) km (90%-confidence). Such a value is
consistent with low-res equations of state. We compare this result with
previous radius measurements of NSs from various analyses of different types of
systems. In addition, we compare the spectral analyses of individual qLMXBs to
previous works.Comment: Accepted to Apj. 31 pages, 17 figures, 8 table
- …