197 research outputs found
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
VASAO: visible all sky adaptive optics: a new adaptive optics concept for CFHT
International audienceVASAO is an ambitious project that explores new conceptual direction in the field of astronomical adaptive optics. In the era of 8 meter and larger telescopes, and their instrument costs and telescope time pressure, there is a natural niche for such ground-breaking conceptual development in the 4 meter class telescope. The aim of VASAO is to provide diffraction limited imaging in the visible with 100% sky coverage; the challenge (but potential rewards) arises from the simultaneity of these requirements. To this end, CFHT is conducting a feasibility study based on the polychromatic guide star concept (Foy et al., 1995 [4]) coupled with a high order curvature AO system, presented in this paper. A number of experiments have been started (or carried out) to study the challenges and limits of the techniques involved in an operational setting; these include the FlyEyes detector, and a polychromatic tip-tilt test on natural stars. Because such a project straddles such a fine line between facility instrument and experimental facility, careful thought has to be given to the balance between modes of operations and potential astrophysical targets
Combined Extraction Processes of Lipid from Chlorella vulgaris Microalgae: Microwave Prior to Supercritical Carbon Dioxide Extraction
Extraction yields and fatty acid profiles from freeze-dried Chlorella vulgaris by microwave pretreatment followed by supercritical carbon dioxide (MW-SCCO2) extraction were compared with those obtained by supercritical carbon dioxide extraction alone (SCCO2). Work performed with pressure range of 20–28 Mpa and temperature interval of 40–70 °C, gave the highest extraction yield (w/w dry weight) at 28 MPa/40 °C. MW-SCCO2 allowed to obtain the highest extraction yield (4.73%) compared to SCCO2 extraction alone (1.81%). Qualitative and quantitative analyses of microalgae oil showed that palmitic, oleic, linoleic and α-linolenic acid were the most abundant identified fatty acids. Oils obtained by MW-SCCO2 extraction had the highest concentrations of fatty acids compared to SCCO2 extraction without pretreatment. Native form, and microwave pretreated and untreated microalgae were observed by scanning electronic microscopy (SEM). SEM micrographs of pretreated microalgae present tearing wall agglomerates. After SCCO2, microwave pretreated microalgae presented several micro cracks; while native form microalgae wall was slightly damaged
Astro2020 Science White Paper: Triggered High-Priority Observations of Dynamic Solar System Phenomena
Unexpected dynamic phenomena have surprised solar system observers in the
past and have led to important discoveries about solar system workings.
Observations at the initial stages of these events provide crucial information
on the physical processes at work. We advocate for long-term/permanent programs
on ground-based and space-based telescopes of all sizes - including Extremely
Large Telescopes (ELTs) - to conduct observations of high-priority dynamic
phenomena, based on a predefined set of triggering conditions. These programs
will ensure that the best initial dataset of the triggering event are taken;
separate additional observing programs will be required to study the temporal
evolution of these phenomena. While not a comprehensive list, the following are
notional examples of phenomena that are rare, that cannot be anticipated, and
that provide high-impact advances to our understandings of planetary processes.
Examples include: new cryovolcanic eruptions or plumes on ocean worlds; impacts
on Jupiter, Saturn, Uranus, or Neptune; extreme eruptions on Io; convective
superstorms on Saturn, Uranus, or Neptune; collisions within the asteroid belt
or other small-body populations; discovery of an interstellar object passing
through our solar system (e.g. 'Oumuamua); and responses of planetary
atmospheres to major solar flares or coronal mass ejections.Comment: Astro2020 white pape
LBTO's long march to full operation: step 2
Step 1 (Veillet et al.1), after a review of the development of the Large Binocular Telescope Observatory (LBTO from the early concepts of the early 80s to mid-2014, outlined a six-year plan (LBT2020) aimed at optimizing LBTO's scientific production while mitigating the consequences of the inevitable setbacks brought on by the considerable complexity of the telescope and the very diverse nature of the LBTO partnership. Step 2 is now focusing on the first two years of implementation of this plan, presenting the encountered obstacles, technical, cultural and political, and how they were overcome. Weather and another incident with one of the Adaptive Secondaries slowed down commissioning activities. All the facility instruments should have been commissioned and offered in binocular mode in early or mid-2016. It will happen instead by the end of 2016. On a brighter side, the first scientific publications using the LBT as a 23-m telescope through interferometry were published in 2015 and the overall number of publications has been raising at a good pace. Three second generation instruments were selected, scheduled to come on the telescope in the next three to five years. They will all use the excellent performance of the LBT Adaptive Optics (AO), which will be even better thanks to an upgrade of the AO to be completed in 2018. Less progress than hoped was made to move the current observing mode of the telescope to a whole LBT-wide queue. In two years from now, we should have a fully operational telescope, including a laser-based Ground Layer AO (GLAO) system, hopefully fully running in queue, with new instruments in development, new services offered to the users, and a stronger scientific production
Performance of the CMS Cathode Strip Chambers with Cosmic Rays
The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device
in the CMS endcaps. Their performance has been evaluated using data taken
during a cosmic ray run in fall 2008. Measured noise levels are low, with the
number of noisy channels well below 1%. Coordinate resolution was measured for
all types of chambers, and fall in the range 47 microns to 243 microns. The
efficiencies for local charged track triggers, for hit and for segments
reconstruction were measured, and are above 99%. The timing resolution per
layer is approximately 5 ns
Performance and Operation of the CMS Electromagnetic Calorimeter
The operation and general performance of the CMS electromagnetic calorimeter
using cosmic-ray muons are described. These muons were recorded after the
closure of the CMS detector in late 2008. The calorimeter is made of lead
tungstate crystals and the overall status of the 75848 channels corresponding
to the barrel and endcap detectors is reported. The stability of crucial
operational parameters, such as high voltage, temperature and electronic noise,
is summarised and the performance of the light monitoring system is presented
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