276 research outputs found
Towards Precision LSST Weak-Lensing Measurement - I: Impacts of Atmospheric Turbulence and Optical Aberration
The weak-lensing science of the LSST project drives the need to carefully
model and separate the instrumental artifacts from the intrinsic lensing
signal. The dominant source of the systematics for all ground based telescopes
is the spatial correlation of the PSF modulated by both atmospheric turbulence
and optical aberrations. In this paper, we present a full FOV simulation of the
LSST images by modeling both the atmosphere and the telescope optics with the
most current data for the telescope specifications and the environment. To
simulate the effects of atmospheric turbulence, we generated six-layer phase
screens with the parameters estimated from the on-site measurements. For the
optics, we combined the ray-tracing tool ZEMAX and our simulated focal plane
data to introduce realistic aberrations and focal plane height fluctuations.
Although this expected flatness deviation for LSST is small compared with that
of other existing cameras, the fast f-ratio of the LSST optics makes this focal
plane flatness variation and the resulting PSF discontinuities across the CCD
boundaries significant challenges in our removal of the systematics. We resolve
this complication by performing PCA CCD-by-CCD, and interpolating the basis
functions using conventional polynomials. We demonstrate that this PSF
correction scheme reduces the residual PSF ellipticity correlation below 10^-7
over the cosmologically interesting scale. From a null test using HST/UDF
galaxy images without input shear, we verify that the amplitude of the galaxy
ellipticity correlation function, after the PSF correction, is consistent with
the shot noise set by the finite number of objects. Therefore, we conclude that
the current optical design and specification for the accuracy in the focal
plane assembly are sufficient to enable the control of the PSF systematics
required for weak-lensing science with the LSST.Comment: Accepted to PASP. High-resolution version is available at
http://dls.physics.ucdavis.edu/~mkjee/LSST_weak_lensing_simulation.pd
The path to excellence of the portuguese organizations recognized by the EFQM model
This paper presents research carried out in seven Portuguese organisations recognised
by the European Foundation for Quality Management (EFQM) Model between January
2009 and August 2011. Using a qualitative methodology, based on case studies, we
conducted semi-structured interviews to find out the motivations behind the adoption
of the EFQM Excellence Model of self-assessment, as well the companyâs current
state of maturity, their route to improvement for a greater maturity level, their
desirable future state of maturity, and finally, the definition of a methodology for
using self-assessment based on the EFQM Model with all the inputs achieved in
earlier stages. The main findings of this study are in accordance with other studies
carried out across Europe, namely the fact that the internal motivations are the key
factor for the implementation of the EFQM Excellence Model, the prevalence of
Public organisations due the investment of National Authorities, the key role of
CEOs and Top Managers and the ISO 9001 standard role in the successful
implementation of several criteria of the model. A new methodology has been
designed where the self-assessment team, Benchlearning and Benchmarking have a
remarkable mission in the implementation process of the EFQM Excellence Model
A Bound on the Light Emitted During the TP-AGB Phase
The integrated luminosity of the TP-AGB phase is a major uncertainty in
stellar population synthesis models. We use the white dwarf initial final mass
relation and stellar interiors models to demonstrate that a significant
fraction of the core mass growth for intermediate (1.5 < Msun < 6) mass stars
takes place during the TP-AGB phase. We find evidence that the peak fractional
core mass contribution for TP-AGB stars is ~20% and occurs for stars between 2
Msun and 3.5 Msun. Using a simple fuel consumption argument we couple this core
mass increase to a lower limit on the TP-AGB phase energy output. Roughly half
of the energy released in models of TP-AGB stars can be directly accounted for
by this core growth; while the remainder is predominantly the stellar yield of
He. A robust measurement of the emitted light in this phase will therefore set
strong constraints on helium enrichment from TP-AGB stars, and we estimate the
yields predicted by current models as a function of initial mass. Implications
for stellar population studies and prospects for improvements are discussed.Comment: Submitted to the Astrophysical Journal. 25 pages, 2 figures
Panoramic Views of the Cygnus Loop
We present a complete atlas of the Cygnus Loop supernova remnant in the light
of [O III] (5007), H alpha, and [S II] (6717, 6731). Despite its shell-like
appearance, the Cygnus Loop is not a current example of a Sedov-Taylor blast
wave. Rather, the optical emission traces interactions of the supernova blast
wave with clumps of gas. The surrounding interstellar medium forms the walls of
a cavity through which the blast wave now propagates, including a nearly
complete shell in which non-radiative filaments are detected. The Cygnus Loop
blast wave is not breaking out of a dense cloud, but is instead running into
confining walls. The interstellar medium dominates not only the appearance of
the Cygnus Loop but also the continued evolution of the blast wave. If this is
a typical example of a supernova remnant, then global models of the
interstellar medium must account for such significant blast wave deceleration.Comment: 28 pages AAS Latex, 28 black+white figures, 6 color figures. To be
published in The Astrophysical Journal Supplement Serie
DDO Photometry of M71: Carbon and Nitrogen Patterns Among Evolving Giants
We present V, B-V, and DDO C(41-42) and C(42-45) photometry for a sample of
75 red giants down to M_V = +2 in the relatively metal-rich Galactic globular
cluster M71. The C(41-42) colors reveal a bimodal distribution of CN band
strengths generally anticorrelated with CH band strength as measured by the
C(42-45) color. Both DDO colors agree well with those found in 47 Tucanae -- a
nearby globular cluster of similar metallicity -- and suggest nearly identical
C and N abundance patterns among the giants of both clusters. A comparison with
synthetic DDO colors demonstrates that little change in surface C or N
abundance is required to match the colors of the M71 giants over the entire
luminosity range observed. Apparently like 47 Tuc (a cluster of much greater
mass and central concentration), M71 exhibits an abundance pattern which cannot
be solely the result of internal mixing.Comment: To appear in the Astronomical Journal, November 2001. 17 Pages, 5
Figure
Parametrization and Classification of 20 Billion LSST Objects: Lessons from SDSS
The Large Synoptic Survey Telescope (LSST) will be a large, wide-field
ground-based system designed to obtain, starting in 2015, multiple images of
the sky that is visible from Cerro Pachon in Northern Chile. About 90% of the
observing time will be devoted to a deep-wide-fast survey mode which will
observe a 20,000 deg region about 1000 times during the anticipated 10
years of operations (distributed over six bands, ). Each 30-second long
visit will deliver 5 depth for point sources of on average.
The co-added map will be about 3 magnitudes deeper, and will include 10 billion
galaxies and a similar number of stars. We discuss various measurements that
will be automatically performed for these 20 billion sources, and how they can
be used for classification and determination of source physical and other
properties. We provide a few classification examples based on SDSS data, such
as color classification of stars, color-spatial proximity search for wide-angle
binary stars, orbital-color classification of asteroid families, and the
recognition of main Galaxy components based on the distribution of stars in the
position-metallicity-kinematics space. Guided by these examples, we anticipate
that two grand classification challenges for LSST will be 1) rapid and robust
classification of sources detected in difference images, and 2) {\it
simultaneous} treatment of diverse astrometric and photometric time series
measurements for an unprecedentedly large number of objects.Comment: Presented at the "Classification and Discovery in Large Astronomical
Surveys" meeting, Ringberg Castle, 14-17 October, 200
Properties of Ellipticity Correlation with Atmospheric Structure from Gemini South
Cosmic shear holds great promise for a precision independent measurement of
, the mass density of the universe relative to the critical
density. The signal is expected to be weak, so a thorough understanding of
systematic effects is crucial. An important systematic effect is the
atmosphere: shear power introduced by the atmosphere is larger than the
expected signal. Algorithms exist to extract the cosmic shear from the
atmospheric component, though a measure of their success applied to a range of
seeing conditions is lacking.
To gain insight into atmospheric shear, Gemini South imaging in conjunction
with ground condition and satellite wind data were obtained. We find that under
good seeing conditions Point-Spread-Function (PSF) correlations persist well
beyond the separation typical of high-latitude stars. Under these conditions,
ellipticity residuals based on a simple PSF interpolation can be reduced to
within a factor of a few of the shot-noise induced ellipticity floor. We also
find that the ellipticity residuals are highly correlated with wind direction.
Finally, we correct stellar shapes using a more sophisticated procedure and
generate shear statistics from stars. Under all seeing conditions in our data
set the residual correlations lie everywhere below the target signal level. For
good seeing we find that the systematic error attributable to atmospheric
turbulence is comparable in magnitude to the statistical error (shape noise)
over angular scales relevant to present lensing surveys.Comment: To appear in ApJ April 10, 2007, 659
- âŠ