70 research outputs found
Wavefront sensing of atmospheric phase distortions at the Palomar 200-in. telescope and implications for adaptive optics
Major efforts in astronomical instrumentation are now being made to apply the techniques of adaptive optics to the correction of phase distortions induced by the turbulent atmosphere and by quasi-static aberrations in telescopes themselves. Despite decades of study, the problem of atmospheric turbulence is still only partially understood. We have obtained video-rate (30 Hz) imaging of stellar clusters and of single-star phase distortions over the pupil of the 200" Hale telescope on Palomar Mountain. These data show complex temporal and spatial behavior, with multiple components arising at a number of scale heights in the atmosphere; we hope to quantify this behavior to ensure the feasibility of adaptive optics at the Observatory. We have implemented different wavefront sensing techniques to measure aperture phase in wavefronts from single stars, including the classical Foucault test, which measures the local gradient of phase, and the recently-devised curvature sensing technique, which measures the second derivative of pupil phase and has formed the real-time wavefront sensor for some very productive astronomical adaptive optics. Our data, though not fast enough to capture all details of atmospheric phase fluctuations, provide important information regarding the capabilities that must be met by the adaptive optics system now being built for the 200" telescope by a team at the Jet Propulsion Lab. We describe our data acquisition techniques, initial results from efforts to characterize the properties of the turbulent atmosphere at Palomar Mountain, and future plans to extract additional quantitative parameters of use for adaptive optics performance predictions
Snow shoes and sandals? : genetic aspects of heat stress sensitivity and sow reproduction
Globally the average size of pig herds are increasing and amount of labour spent per sow / finisher pig is decreasing. These changes require sows which need less management interventions. In addition to easier manageable sows modern genotypes will also need to be more adaptable considering that global temperatures are expected to increase and pork production is partially moving to warmer climates. The end result is that commercial pigs nowadays will potentially face more heat stress challenges during their productive lives. In this thesis, a model was developed which was used to estimate upper critical temperatures for sows’ reproductive performance. Additionally the possibility to breed for reduced heat tolerance of sows was investigated. Therefore heritability for the random regression slope of farrowing rate against increasing temperature at day of insemination (= heat tolerance) and the genetic correlation between farrowing rate and heat tolerance was estimated.Commercial production pigs are crossbreds farmed all over the world. In contrast, selection is practiced mainly in temperate climates, in nucleus herds using purebred pigs. The success of genetic selection depends on how much genetic progress is realized in crossbred pigs. Within this thesis these genetic correlations for farrowing rate between purebreds and crossbreds were estimated. Sow productivity depends on a number of related traits, such as ovulation rate, the number of litters per sow per year, the number of weaned piglets per sow per year, and the length of productive live. Traditionally pig breeding programs have improved sow productivity by increasing number weaned piglets per sow per year. To improve herd-level litters per sow per year a new trait was proposed called problem free sow production by parity, which incorporates the traits interval weaning first insemination, non-return rate, farrowing rate, and selection for next parity. Heritability of problem free sow production and genetic correlations with other sow production traits were estimated. The main conclusion of this thesis was that it is possible to select for improved heat resistance in addition to improved commercial production levels in commercial pigs. However, genetic correlation between production in temperate and hot climates is high. This high correlation implies that, within-line, pigs with the best performance in a hot climate will be the best in temperate climate too. Most important for the success of a pig breeding program is to define appropriate breeding goals which are based on the environment(s) that market pigs are expected to perform in. The overall data collection for the genetic evaluation needs to be done in those specific environments and this will favour pigs which are able to produce over more than one specific environment.</p
High spectral and spatial resolution observations of the 12.28 micron emission from H2 in the Orion molecular cloud
The pure rotational S(2) line of molecular hydrogen at 12.28 microns was looked for in 44 positions in the Orion moleular cloud with 6 in. beams and 35 km/s spectral resolution; it was detected in 27 positions. Emission was observed over a velocity range of + or - 100 km/s. The lines are approximately symmetric, and have full widths at half maximum ranging from 100 km/s down to the resolution limit. The distribution of intensities and line shapes is largely consistent with that seen in the 2 micron hydrogen transitions. However, unexpectedly complex line profiles and point-to-point variations in linear shapes appear, particularly in the region near IRc9
On-sky observations with an achromatic hybrid phase knife coronagraph in the visible
CONTEXT: The four-quadrant phase mask stellar coronagraph, introduced by D.
Rouan et al., is capable of achieving very high dynamical range imaging and was
studied in the context of the direct detection of extra-solar planets.
Achromatic four-quadrant phase mask is currently being developed for broadband
IR applications. AIMS: We report on laboratory and on-sky tests of a prototype
coronagraph in the visible. This prototype, the achromatic hybrid phase knife
coronagraph, was derived from the four-quadrant phase mask principle. METHODS:
The instrumental setup implementing the coronagraph itself was designed to
record the pre- and post-coronagraphic images simultaneously so that an
efficient real-time image selection procedure can be performed. We describe the
coronagraph and the associated tools that enable robust and repeatable
observations. We present an algorithm of image selection that has been tested
against the real on-sky data of the binary star HD80081 (* 38 Lyn). RESULTS
Although the observing conditions were poor, the efficiency of the proposed
method is proven. From this experiment, we derive procedures that can apply to
future focal instruments associating adaptive optics and coronagraphy,
targeting high dynamic range imaging in astronomy, such as detecting
extra-solar planets
The Magnetised Bellows of Betelgeuse
We present calculations for a magnetised hybrid wind model for Betelegeuse
(Orionis). The model is a direct application of our previously
derived theory, combining a canonical Weber-Davis (WD) stellar wind with dust
grains in the envelope of an AGB star \citep[see][]{Thirumalai2010}. The
resulting hybrid picture provides a mechanism for solving the problem of
lifting stellar material up from the photosphere \citep[e.g.][]
{Harper2009,Guandalini2006,Jura1984} and into the circumstellar envelope. It
also predicts wind velocities in agreement with current estimates. Our approach
reveals that magnetic fields in supergiant stars like Betelgeuse
\citep[see][]{Auriere2010}, may play a vital role in determining the nature of
the stellar outflow and consequently, opens a new avenue of investigation in
the field of hybrid stellar winds.Comment: 13 pages, 4 figure
Opening a new window to other worlds with spectropolarimetry
A high level of diversity has already been observed among the planets of our
own Solar System. As such, one expects extrasolar planets to present a wide
range of distinctive features, therefore the characterisation of Earth- and
super Earth-like planets is becoming of key importance in scientific research.
The SEARCH (Spectropolarimetric Exoplanet AtmospheRe CHaracerisation) mission
proposal of this paper represents one possible approach to realising these
objectives. The mission goals of SEARCH include the detailed characterisation
of a wide variety of exoplanets, ranging from terrestrial planets to gas
giants. More specifically, SEARCH will determine atmospheric properties such as
cloud coverage, surface pressure and atmospheric composition, and may also be
capable of identifying basic surface features. To resolve a planet with a semi
major axis of down to 1.4AU and 30pc distant SEARCH will have a mirror system
consisting of two segments, with elliptical rim, cut out of a parabolic mirror.
This will yield an effective diameter of 9 meters along one axis. A phase mask
coronagraph along with an integral spectrograph will be used to overcome the
contrast ratio of star to planet light. Such a mission would provide invaluable
data on the diversity present in extrasolar planetary systems and much more
could be learned from the similarities and differences compared to our own
Solar System. This would allow our theories of planetary formation, atmospheric
accretion and evolution to be tested, and our understanding of regions such as
the outer limit of the Habitable Zone to be further improved.Comment: 23 pages, accepted for publication in Experimental Astronom
Flares and Proper Motions of Ground-State OH Masers in W75N
The star-forming region W75N hosts bright OH masers that are observed to be
variable. We present observations taken in 2008 of the ground-state OH maser
transitions with the Very Long Baseline Array (VLBA) and the Multi-Element
Radio-Linked Interferometer Network (MERLIN) and with the Nancay Radio
Telescope in 2011. Several of the masers in W75N were observed to be flaring,
with the brightest 1720-MHz maser in excess of 400 Jy. The 1720-MHz masers
appear to be associated with the continuum source VLA 1, unlike the bright
flaring 1665- and 1667-MHz masers, which are associated with VLA 2. The
1720-MHz masers are located in an outflow traced by water masers and are
indicative of very dense molecular material near the H II region. The magnetic
field strengths are larger in the 1720-MHz maser region than in most regions
hosting only main-line OH masers. The density falls off along the outflow, and
the order of appearance of different transitions of OH masers is consistent
with theoretical models. The 1665- and 1667-MHz VLBA data are compared against
previous epochs over a time baseline of over 7 years. The median maser motion
is 3.5 km/s, with a scatter that is comparable to thermal turbulence. The
general pattern of maser proper motions observed in the 1665- and 1667-MHz
transitions is consistent with previous observations.Comment: 14 pages, accepted for publication in MNRA
SOWS AND PIGLETS THERMAL COMFORT: A COMPARATIVE STUDY OF THE TILES USED IN THE FARROWING HOUSING
Factors for improving reproductive performance of sows and herd productivity in commercial breeding herds
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