1,598 research outputs found
MegaPipe: the MegaCam image stacking pipeline at the Canadian Astronomical Data Centre
This paper describes the MegaPipe image processing pipeline at the Canadian
Astronomical Data Centre. The pipeline combines multiple images from the
MegaCam mosaic camera on CFHT and combines them into a single output image.
MegaPipe takes as input detrended MegaCam images and does a careful astrometric
and photometric calibration on them. The calibrated images are then resampled
and combined into image stacks. The astrometric calibration of the output
images is accurate to within 0.15 arcseconds relative to external reference
frames and 0.04 arcseconds internally. The photometric calibration is good to
within 0.03 magnitudes. The stacked images and catalogues derived from these
images are available through the CADC website:Comment: Data available at
http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/megapipe/index.htm
Space-based tests of gravity with laser ranging
Existing capabilities in laser ranging, optical interferometry and metrology,
in combination with precision frequency standards, atom-based quantum sensors,
and drag-free technologies, are critical for the space-based tests of
fundamental physics; as a result, of the recent progress in these disciplines,
the entire area is poised for major advances. Thus, accurate ranging to the
Moon and Mars will provide significant improvements in several gravity tests,
namely the equivalence principle, geodetic precession, PPN parameters
and , and possible variation of the gravitational constant . Other
tests will become possible with development of an optical architecture that
would allow proceeding from meter to centimeter to millimeter range accuracies
on interplanetary distances. Motivated by anticipated accuracy gains, we
discuss the recent renaissance in lunar laser ranging and consider future
relativistic gravity experiments with precision laser ranging over
interplanetary distances.Comment: 14 pages, 2 figures, 1 table. To appear in the proceedings of the
International Workshop "From Quantum to Cosmos: Fundamental Physics Research
in Space", 21-24 May 2006, Warrenton, Virginia, USA
http://physics.jpl.nasa.gov/quantum-to-cosmos
The Orbit, Mass, and Albedo of Transneptunian Binary 1999 RZ253
We have observed 1999 RZ253 with the Hubble Space Telescope at seven separate
epochs and have fit an orbit to the observed relative positions of this binary.
Two orbital solutions have been identified that differ primarily in the
inclination of the orbit plane. The best fit corresponds to an orbital period,
P=46.263 +0.006/-0.074 days, semimajor axis a=4,660 +/-170 km and orbital
eccentricity e=0.460 +/-0.013 corresponding to a system mass m=3.7 +/-0.4
x10^18 kg. For a density of rho = 1000 kg m^-3 the albedo at 477 nm is p = 0.12
+/-0.01, significantly higher than has been commonly assumed for objects in the
Kuiper Belt. Multicolor, multiepoch photometry shows this pair to have colors
typical for the Kuiper belt with a spectral gradient of 0.35 per 100 nm in the
range between 475 and 775 nm. Photometric variations at the four epochs we
observed were as large as 12 +/-3% but the sampling is insufficient to confirm
the existence of a lightcurve
Kuiper Binary Object Formation
It has been observed that binary Kuiper Belt Objects (KBOs) exist contrary to
theoretical expectations. Their creation presents problems to most current
models. However, the inclusion of a third body (for example, one of the outer
planets) may provide the conditions necessary for the formation of these
objects. The presence of a third massive body not only helps to clear the
primordial Kuiper Belt but can also result in long lived binary Kuiper belt
objects. The gravitational interaction between the KBOs and the third body
causes one of four effects; scattering into the Oort cloud, collisions with the
growing protoplanets, formation of binary pairs, or creation of a single Kuiper
belt object. Additionally, the initial location of the progenitors of the
Kuiper belt objects also has a significant effect on binary formation
The Color Distribution in the Edgeworth-Kuiper Belt
We have started since 1997 the Meudon Multicolor Survey of Outer Solar System
Objects with the aim of collecting a large and homogeneous set of color data
for Trans-Neptunian and Centaurs objects [...] We have a combined sample of 52
B-R color measurements for 8 Centaurs, 22 Classicals, 13 Plutinos, 8 Scattered
objects and 1 object with unidentified dynamical class. This dataset is the
largest single and homogeneous published dataset to date [...]. A strong
(color) correlation with mean excitation velocity points toward a space
weathering/impact origin for the color diversity. However, thorough modeling of
the collisional/dynamical environment in the Edgeworth-Kuiper belt needs to be
done in order to confirm this scenario. We found also that the Classical TNOs
consist in the superposition of two distinct populations: the dynamically Cold
Classical TNOs (red colors, low i, small sizes) and the dynamically Hot
Classical TNOs (diverse colors, moderate and high i, larger sizes). [...] Our
specific observation strategy [...] permitted us to highlight a few objects
suspected to have true compositional and/or texture variation on their
surfaces. These are 1998 HK151, 1999 DF9, 1999 OY3, 2000 GP183, 2000 OK67, and
2001 KA77 and should be prime targets for further observations [...]. Our
survey has also highlighted 1998 SN165 whose colors and dynamical properties
puts it in a new dynamical class distinct from the Classicals, its previously
assigned dynamical class.Comment: Accepted for publication in Astronomical Journal (38 pages, inc. 11
figures
Hunting for planets in the HL Tau disk
Recent ALMA images of HL Tau show gaps in the dusty disk that may be caused
by planetary bodies. Given the young age of this system, if confirmed, this
finding would imply very short timescales for planet formation, probably in a
gravitationally unstable disk. To test this scenario, we searched for young
planets by means of direct imaging in the L'-band using the Large Binocular
Telescope Interferometer mid-infrared camera. At the location of two prominent
dips in the dust distribution at ~70AU (~0.5") from the central star we reach a
contrast level of ~7.5mag. We did not detect any point source at the location
of the rings. Using evolutionary models we derive upper limits of ~10-15MJup at
<=0.5-1Ma for the possible planets. With these sensitivity limits we should
have been able to detect companions sufficiently massive to open full gaps in
the disk. The structures detected at mm-wavelengths could be gaps in the
distributions of large grains on the disk midplane, caused by planets not
massive enough to fully open gaps. Future ALMA observations of the molecular
gas density profile and kinematics as well as higher contrast infrared
observations may be able to provide a definitive answer.Comment: Accepted for publication on ApJ Letter
A Cryogenic Test Set-Up for the Qualification of Pre-Series Test Cells for the LHC Cryogenic Distribution Line
Three pre-series Test Cells of the LHC Cryogenic Distribution Line (QRL) [1], manufactured by three European industrial companies, will be tested in the year 2000 to qualify the design chosen and verify the thermal and mechanical performances. A dedicated test stand (170 m x 13 m) has been built for extensive testing and performance assessment of the pre-series units in parallel. They will be fed with saturated liquid helium at 4.2 K supplied by a mobile helium dewar. In addition, LN2 cooled helium will be used for cool-down and thermal shielding. For each of the three pre-series units, a set of end boxes has been designed and manufactured at CERN. This paper presents the layout of the cryogenic system for the pre-series units, the calorimetric methods as well as the results of the thermal calculation of the end box test
Evidence for a colour dependence in the size distribution of main belt asteroids
We present the results of a project to detect small (~1 km) main-belt
asteroids with the 3.6 meter Canada-France-Hawaii Telescope (CFHT). We observed
in 2 filters (MegaPrime g' and r') in order to compare the results in each
band. Owing to the observational cadence we did not observe the same asteroids
through each filter and thus do not have true colour information. However
strong differences in the size distributions as seen in the two filters point
to a colour-dependence at these sizes, perhaps to be expected in this regime
where asteroid cohesiveness begins to be dominated by physical strength and
composition rather than by gravity. The best fit slopes of the cumulative size
distributions (CSDs) in both filters tend towards lower values for smaller
asteroids, consistent with the results of previous studies. In addition to this
trend, the size distributions seen in the two filters are distinctly different,
with steeper slopes in r' than in g'. Breaking our sample up according to
semimajor axis, the difference between the filters in the inner belt is found
to be somewhat less pronounced than in the middle and outer belt, but the CSD
of those asteroids seen in the r' filter is consistently and significantly
steeper than in g' throughout. The CSD slopes also show variations with
semimajor axis within a given filter, particularly in r'. We conclude that the
size distribution of main belt asteroids is likely to be colour dependent at
kilometer sizes and that this dependence may vary across the belt.Comment: 28 pages, 5 figures, submitted to the Astronomical Journa
Constraining the rate of GRB visible afterglows with the CFHTLS Very Wide Survey
We analyze images of the CFHTLS Very Wide Survey to search for visible orphan
afterglows from gamma-ray bursts (GRBs). We have searched 490 square degrees
down to magnitude r'=22.5 for visible transients similar to GRB afterglows. We
translate our observations into constraints on the number of GRB visible
afterglows in the sky, by measuring the detection efficiency of our search with
a simulation reproducing the characteristics of our observational strategy and
the properties of on-axis GRB afterglows. We have found only three potential
candidates, of which two are most probably variable stars, and one presents
similarities to an orphan afterglow. We constrain the number of visible
afterglows to be less than 220 down to r'=22.5 in the whole sky at any time.
Our observations are marginally consistent with the most optimistic model,
which predicts orphan afterglows to be about 10 times more frequent than GRBs.
This search has led to the detection of one possible GRB afterglow, and
provides the strongest constraints on the rate of GRB visible afterglows as
well as an estimation of the observing time required to detect a significant
number of GRB afterglows.Comment: 4 pages, 3 figures, 2 tables. Accepted by A&A Lette
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