577 research outputs found
Technologies for Astronomical Wide-Field Adaptive Optics
Adaptive Optics (AO) can greatly enhance the resolution of astronomical images, achieving close to diffraction-limited performance in the near infrared; however there are a number of areas where significant improvements can be made, one of them being the very limited field of view that current AO systems can achieve. ‘Wide-field AO’ encompasses those techniques devised to widen the corrected field of view, from a few tens of arcseconds in ‘classical AO’ systems to several arcminutes in Multi-Object AO (MOAO).
This thesis researches some topics within ‘wide-field AO’ for astronomy, concentrating its experimental work in some of the key technologies required to implement MOAO: open-loop models to run deformable mirrors (DM) in a MOAO system and a ‘Figure Sensor’ to measure the shape of a DM with required accuracy and at high-speed, in order to incorporate it into the AO control system
Cryogenic VPH gratings for the CELT/TMT
Characterization of Volume Phase Holographic gratings at cryogenic temperatures have been conducted using a new test facility at Caltech. The new test bench includes a cryostat that allows large angles for incident and diffracted light. Gratings under tests are shielded from thermal background, and precisely and uniformly temperature controlled. Preliminary results are presented and show little temperature dependence of the efficiency function
Cryogenic VPH gratings for the CELT/TMT
Characterization of Volume Phase Holographic gratings at cryogenic temperatures have been conducted using a new test facility at Caltech. The new test bench includes a cryostat that allows large angles for incident and diffracted light. Gratings under tests are shielded from thermal background, and precisely and uniformly temperature controlled. Preliminary results are presented and show little temperature dependence of the efficiency function
The Automated Palomar 60-Inch Telescope
We have converted the Palomar 60-inch telescope (P60) from a classical night
assistant-operated telescope to a fully robotic facility. The automated system,
which has been operational since September 2004, is designed for moderately
fast (t <~ 3 minutes) and sustained (R <~ 23 mag) observations of gamma-ray
burst afterglows and other transient events. Routine queue-scheduled
observations can be interrupted in response to electronic notification of
transient events. An automated pipeline reduces data in real-time, which is
then stored on a searchable web-based archive for ease of distribution. We
describe here the design requirements, hardware and software upgrades, and
lessons learned from roboticization. We present an overview of the current
system performance as well as plans for future upgrades.Comment: Accepted in PASP; 26 pages, 7 figures; high resolution version at
http://www.srl.caltech.edu/~cenko/public/papers/p60.p
Cluster Lensing And Supernova survey with Hubble (CLASH): An Overview
The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit
multi-cycle treasury program to use the gravitational lensing properties of 25
galaxy clusters to accurately constrain their mass distributions. The survey,
described in detail in this paper, will definitively establish the degree of
concentration of dark matter in the cluster cores, a key prediction of CDM. The
CLASH cluster sample is larger and less biased than current samples of
space-based imaging studies of clusters to similar depth, as we have minimized
lensing-based selection that favors systems with overly dense cores.
Specifically, twenty CLASH clusters are solely X-ray selected. The X-ray
selected clusters are massive (kT > 5 keV; 5 - 30 x 10^14 M_solar) and, in most
cases, dynamically relaxed. Five additional clusters are included for their
lensing strength (Einstein radii > 35 arcsec at z_source = 2) to further
quantify the lensing bias on concentration, to yield high resolution dark
matter maps, and to optimize the likelihood of finding highly magnified
high-redshift (z > 7) galaxies. The high magnification, in some cases, provides
angular resolutions unobtainable with any current UVOIR facility and can yield
z > 7 candidates bright enough for spectroscopic follow-up. A total of 16
broadband filters, spanning the near-UV to near-IR, are employed for each
20-orbit campaign on each cluster. These data are used to measure precise
(sigma_phz < 0.02(1+z)) photometric redshifts for dozens of newly discovered
multiply-lensed images per cluster. Observations of each cluster are spread
over 8 epochs to enable a search, primarily in the parallel fields, for Type Ia
supernovae at z > 1 to improve constraints on the time dependence of the dark
energy equation of state and the evolution of such supernovae in an epoch when
the universe is matter dominated.Comment: Accepted for publication in the Astrophysical Journal Supplements, 22
pages, 16 figures. Updated Tables 3,4,8 and figures 6 and 8 to reflect
replacement of Abell 963 with Abell 1423 in CLASH survey. A963 cannot be
observed with WFC3 due to the lack of usable guide star
Inclusive J/ψ production at forward and backward rapidity in p-Pb collisions at √sNN=8.16 TeV
Inclusive J/psi production is studied in p-Pb interactions at a centre-of-mass
energy per nucleon-nucleon collision sqrt(s_NN) = 8.16TeV, using the ALICE detector at the
CERN LHC. The J/psi meson is reconstructed, via its decay to a muon pair, in the centre-of-mass
rapidity intervals 2.03 < ycms < 3.53 and -4.46 < ycms < -2.96, where positive
and negative ycms refer to the p-going and Pb-going direction, respectively. The transverse
momentum coverage is pT < 20 GeV/c. In this paper, ycms- and pT-differential cross
sections for inclusive J/psi production are presented, and the corresponding nuclear modification
factors RpPb are shown. Forward results show a suppression of the J/psi yield with
respect to pp collisions, concentrated in the region pT < 5 GeV/c. At backward rapidity
no significant suppression is observed. The results are compared to previous measurements
by ALICE in p-Pb collisions at sqrt(s_NN) = 5.02TeV and to theoretical calculations. Finally,
the ratios RFB between forward- and backward-ycms RpPb values are shown and discussed
First measurement of the |t|-dependence of coherent J/ψ photonuclear production
The first measurement of the cross section for coherent J/ψ photoproduction as a function of |t|, the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb–Pb collisions at a centre-of-mass energy per nucleon pair sNN=5.02TeV with the J/ψ produced in the central rapidity region |y|<0.8, which corresponds to the small Bjorken-x range (0.3−1.4)×10−3.
The measured |t|-dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky–Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken-x.publishedVersio
Spin alignment measurements using vector mesons with ALICE detector at the LHC
We present new measurements related to spin alignment of K*(0) vector
mesons at mid-rapidity for Pb-Pb collisions at root s(NN) = 2.76 and
5.02 TeV. The spin alignment measurements are carried out with respect
to production plane and 2nd order event plane. At low p(T) the spin
density matrix element rho(00) for K*(0) is found to have values
slightly below 1/3, while it is consistent with 1/3, i.e. no spin
alignment, at high p(T). Similar values of rho(00) are observed with
respect to both production plane and event plane. Within statistical and
systematic uncertainties, rho(00) values are also found to be
independent of root s(NN). rho(00) also shows centrality dependence with
maximum deviation from 1/3 for mid-central collisions with respect to
both the kinematic planes. The measurements for K*(0) in pp collisions
at root s = 13 TeV and for K-s(0) (a spin 0 hadron) in 20-40\% central
Pb-Pb collisions at root s(NN) = 2.76 TeV are consistent with no spin
alignment
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