arXiv subjects

C. Loomis

Publications and source records attributed to C. Loomis.

8 recordsLinked to original sources

arXiv2017

Pioneering high contrast science instruments for planet characterization on giant segmented mirror telescopes

A suite of science instruments is critical to any high contrast imaging facility, as it defines the science capabilities and observing modes available. SCExAO uses a modular approach which allows for state-of-the-art visitor modules to be tested within an observatory environment on an 8-m class telescope. This allows for rapid prototyping of new and innovative imaging techniques that otherwise take much longer in traditional instrument design. With the aim of maturing science modules for an advanced high contrast imager on an giant segmented mirror telescopes (GSMTs) that will be capable of imaging terrestrial planets, we offer an overview and status update on the various science modules currently under test within the SCExAO instrument.

astro-ph.IM↗

arXiv2016

SUBARU prime focus spectrograph: integration, testing and performance for the first spectrograph

The Prime Focus Spectrograph (PFS) of the Subaru Measurement of Images and Redshifts (SuMIRe) project for Subaru telescope consists in four identical spectrographs fed by 600 fibers each. Each spectrograph is composed by an optical entrance unit that creates a collimated beam and distributes the light to three channels, two visibles and one near infrared. This paper presents the on-going effort for the tests & integration process for the first spectrograph channel: we have developed a detailed Assembly Integration and Test (AIT) plan, as well as the methods, detailed processes and I&T tools. We describe the tools we designed to assemble the parts and to test the performance of the spectrograph. We also report on the thermal acceptance tests we performed on the first visible camera unit. We also report on and discuss the technical difficulties that did appear during this integration phase. Finally, we detail the important logistic process that is require to transport the components from other country to Marseille.

astro-ph.IM↗

arXiv2009

Simple Behavior of Primary Cross Sections for Low Mass Particles in p-pbar Collisions at y=0 and sqrt(s)=1.8 TeV

A set of inclusive cross sections at zero rapidity is presented for p-pbar interactions at center of mass energy sqrt(s)=1.8 TeV. Six particle cross sections are corrected for secondary contributions from decays of higher mass resonances in order to produce a set of primary cross sections. The primary cross sections per spin state are well described by d(sigma^p)/dy|_(y=0)= 0.721*(pi*lambdabar_(pi)^2)*exp(-m/T), where m is the particle rest mass, T=hbar*c/r_h, and r_h=0.97 fm. The deuterium production cross section is also described if r_h is replaced by r_A=r_h*A^(1/3). The same exponential in m and T describes primary charm fractions in e+e- collisions at least up to the J/Psi mass. There is no significant evidence for strangeness or charm suppression if only primary production of light hadrons is considered. There is evidence that the primary cross section for each particle may have the same value for pp and pbar-p collisions and that it may have nearly constant values between sqrt(s)=63 GeV and sqrt(s)=1800 GeV. Fits to the final state transverse momenta of the particles using a gas model favor a temperature T=132 MeV, a chemical potential mu=129 MeV, and a transverse flow of the gas with beta_f=0.27.

hep-ex↗

arXiv2008

The Second-Generation Guide Star Catalog: Description and Properties

The GSC-II is an all-sky database of objects derived from the uncompressed DSS that the STScI has created from the Palomar and UK Schmidt survey plates and made available to the community. Like its predecessor (GSC-I), the GSC-II was primarily created to provide guide star information and observation planning support for HST. This version, however, is already employed at some of the ground-based new-technology telescopes such as GEMINI, VLT, and TNG, and will also be used to provide support for the JWST and Gaia space missions as well as LAMOST, one of the major ongoing scientific projects in China. Two catalogs have already been extracted from the GSC-II database and released to the astronomical community. A magnitude-limited (R=18.0) version, GSC2.2, was distributed soon after its production in 2001, while the GSC2.3 release has been available for general access since 2007. The GSC2.3 catalog described in this paper contains astrometry, photometry, and classification for 945,592,683 objects down to the magnitude limit of the plates. Positions are tied to the ICRS; for stellar sources, the all-sky average absolute error per coordinate ranges from 0.2" to 0.28" depending on magnitude. When dealing with extended objects, astrometric errors are 20% worse in the case of galaxies and approximately a factor of 2 worse for blended images. Stellar photometry is determined to 0.13-0.22 mag as a function of magnitude and photographic passbands (B,R,I). Outside of the galactic plane, stellar classification is reliable to at least 90% confidence for magnitudes brighter than R=19.5, and the catalog is complete to R=20.

astro-ph↗

arXiv2007

An Improved Photometric Calibration of the Sloan Digital Sky Survey Imaging Data

We present an algorithm to photometrically calibrate wide field optical imaging surveys, that simultaneously solves for the calibration parameters and relative stellar fluxes using overlapping observations. The algorithm decouples the problem of "relative" calibrations, from that of "absolute" calibrations; the absolute calibration is reduced to determining a few numbers for the entire survey. We pay special attention to the spatial structure of the calibration errors, allowing one to isolate particular error modes in downstream analyses. Applying this to the Sloan Digital Sky Survey imaging data, we achieve ~1% relative calibration errors across 8500 sq.deg. in griz; the errors are ~2% for the u band. These errors are dominated by unmodelled atmospheric variations at Apache Point Observatory. These calibrations, dubbed "ubercalibration", are now public with SDSS Data Release 6, and will be a part of subsequent SDSS data releases.

astro-ph↗

arXiv2004

Structure Function Analysis of Long Term Quasar Variability

In our second paper on long-term quasar variability, we employ a much larger database of quasars than in de Vries, Becker & White. This expanded sample, containing 35165 quasars from the Sloan Digital Sky Survey Data Release 2, and 6413 additional quasars in the same area of the sky taken from the 2dF QSO Redshift Survey, allows us to significantly improve on our earlier conclusions. As before, all the historic quasar photometry has been calibrated onto the SDSS scale by using large numbers of calibration stars around each quasar position. We find the following: (1) the outbursts have an asymmetric light-curve profile, with a fast-rise, slow-decline shape; this argues against a scenario in which micro-lensing events along the line-of-sight to the quasars are dominating the long-term variations in quasars; (2) there is no turnover in the Structure Function of the quasars up to time-scales of ~40 years, and the increase in variability with increasing time-lags is monotonic and constant; and consequently, (3) there is not a single preferred characteristic outburst time-scale for the quasars, but most likely a continuum of outburst time-scales, (4) the magnitude of the quasar variability is a function of wavelength: variability increases toward the blue part of the spectrum, (5) high-luminosity quasars vary less than low-luminosity quasars, consistent with a scenario in which variations have limited absolute magnitude. Based on this, we conclude that quasar variability is intrinsic to the Active Galactic Nucleus, is caused by chromatic outbursts / flares with a limited luminosity range and varying time-scales, and which have an overall asymmetric light-curve shape. Currently the model that has the most promise of fitting the observations is based on accretion disk instabilities.

astro-ph↗

arXiv2003

Running CMS software on GRID Testbeds

Starting in the middle of November 2002, the CMS experiment undertook an evaluation of the European DataGrid Project (EDG) middleware using its event simulation programs. A joint CMS-EDG task force performed a "stress test" by submitting a large number of jobs to many distributed sites. The EDG testbed was complemented with additional CMS-dedicated resources. A total of ~ 10000 jobs consisting of two different computational types were submitted from four different locations in Europe over a period of about one month. Nine sites were active, providing integrated resources of more than 500 CPUs and about 5 TB of disk space (with the additional use of two Mass Storage Systems). Descriptions of the adopted procedures, the problems encountered and the corresponding solutions are reported. Results and evaluations of the test, both from the CMS and the EDG perspectives, are described.

physics.comp-ph↗

arXiv1996

Searching for Doubly-Charged Higgs Bosons at Future Colliders

Doubly-charged Higgs bosons ($Δ^{--}/Δ^{++}$) appear in several extensions to the Standard Model and can be relatively light. We review the theoretical motivation for these states and present a study of the discovery reach in future runs of the Fermilab Tevatron for pair-produced doubly-charged Higgs bosons decaying to like-sign lepton pairs. We also comment on the discovery potential at other future colliders.

hep-ph↗