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Basden A.G.,Durham University | Chemla F.,University of Paris Descartes | Dipper N.,Durham University | Gendron E.,University of Paris Descartes | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The use of laser guide stars in astronomical adaptive optics results in elongated Shack-Hartmann wavefront sensor image patterns. Image correlation techniques can be used to determine local wavefront slope by correlating each sub-aperture image with its expected elongated shape, or reference image. Here, we present a technique which allows the correlation reference images to be updated while the adaptive optics loop is closed. We show that this can be done without affecting the resulting point spread functions. On-sky demonstration is reported. We compare different techniques for obtaining the reference images, and investigate performance over a wide range of adaptive optics system parameters. We find that image correlation techniques perform better than the standard centre-of-gravity algorithm and are highly suited for use with open-loop multiple object adaptive optics systems. © 2014 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society.


Gendron E.,University Paris Diderot | Vidal F.,University Paris Diderot | Brangier M.,University Paris Diderot | Morris T.,Durham University | And 18 more authors.
Astronomy and Astrophysics | Year: 2011

Context. A new challenging adaptive optics (AO) system, called multi-object adaptive optics (MOAO), has been successfully demonstrated on-sky for the first time at the 4.2 m William Herschel Telescope, Canary Islands, Spain, at the end of September 2010. Aims. This system, called CANARY, is aimed at demonstrating the feasibility of MOAO in preparation of a future multi-object near infra-red (IR) integral field unit spectrograph to equip extremely large telescopes for analysing the morphology and dynamics of high-z galaxies. Methods. CANARY compensates for the atmospheric turbulence with a deformable mirror driven in open-loop and controlled through a tomographic reconstruction by three widely separated off-axis natural guide star (NGS) wavefront sensors, which are in open loop too. We compared the performance of conventional closed-loop AO, MOAO, and ground-layer adaptive optics (GLAO) by analysing both IR images and simultaneous wave-front measurements. Results. In H-band, Strehl ratios of 0.20 are measured with MOAO while achieving 0.25 with closed-loop AO in fairly similar seeing conditions (r0 ≈ 15 cm at 0.5 μm). As expected, MOAO has performed at an intermediate level between GLAO and closed-loop AO. © 2011 ESO.


News Article | November 2, 2016
Site: www.eurekalert.org

The spires and pillars in the new images of the Carina Nebula are vast clouds of dust and gas within a hub of star formation about 7500 light-years away. The pillars in the nebula were observed by a team led by Anna McLeod, a PhD student at ESO, using the MUSE instrument on ESO's Very Large Telescope. The great power of MUSE is that it creates thousands of images of the nebula at the same time, each at a different wavelength of light. This allows astronomers to map out the chemical and physical properties of the material at different points in the nebula. Images of similar structures, the famous Pillars of Creation/ [1] in the Eagle Nebula and formations in NGC 3603, were combined with the ones displayed here. In total ten pillars have been observed, and in so doing a clear link was observed between the radiation emitted by nearby massive stars and the features of the pillars themselves. In an ironic twist, one of the first consequences of the formation of a massive star is that it starts to destroy the cloud from which it was born. The idea that massive stars will have a considerable effect on their surroundings is not new: such stars are known to blast out vast quantities of powerful, ionising radiation -- emission with enough energy to strip atoms of their orbiting electrons. However, it is very difficult to obtain observational evidence of the interplay between such stars and their surroundings. The team analysed the effect of this energetic radiation on the pillars: a process known as photoevaporation, when gas is ionised and then disperses away. By observing the results of photoevaporation -- which included the loss of mass from the pillars -- they were able to deduce the culprits. There was a clear correlation between the amount of ionising radiation being emitted by nearby stars, and the dissipation of the pillars. This might seem like a cosmic calamity, with massive stars turning on their own creators. However the complexities of the feedback mechanisms between the stars and the pillars are poorly understood. These pillars might look dense, but the clouds of dust and gas which make up nebulae are actually very diffuse. It is possible that the radiation and stellar winds from massive stars actually help create denser spots within the pillars, which can then form stars. These breathtaking celestial structures have more to tell us, and MUSE is an ideal instrument to probe them with. [1] The Pillars of Creation are an iconic [image] - https:/ , taken with the [NASA/ESA Hubble Space Telescope] - http://spacetelescope. , making them the most famous of these structures. Also known as [elephant trunks] - https:/ , they can be several light-years in length. This research was presented in a paper entitled "Connecting the dots: a correlation between ionising radiation and cloud mass-loss rate traced by optical integral field spectroscopy", by A. F. McLeod et al., published in the Monthly Notices of the Royal Astronomical Society. The team is composed of A. F. McLeod (ESO, Garching, Germany), M. Gritschneder (Universitäts-Sternwarte, Ludwig-Maximilians-Universität, Munich, Germany), J. E. Dale (Universitäts-Sternwarte, Ludwig-Maximilians-Universität, Munich, Germany), A. Ginsburg (ESO, Garching, Germany), P. D.Klaassen (UK Astronomy Technology Centre, Royal Observatory Edinburgh, UK), J. C. Mottram (Max Planck Institute for Astronomy, Heidelberg, Germany), T. Preibisch (Universitäts-Sternwarte, Ludwig-Maximilians-Universität, Munich, Germany), S. Ramsay (ESO, Garching, Germany), M. Reiter (University of Michigan Department of Astronomy, Ann Arbor, Michigan, USA) and L. Testi (ESO, Garching, Germany). ESO is the foremost intergovernmental astronomy organisation in Europe and the world's most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world's largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become "the world's biggest eye on the sky".


Cordiner M.A.,Goddard Center for Astrobiology | Cordiner M.A.,Queen's University of Belfast | Cordiner M.A.,Catholic University of America | Cox N.L.J.,Catholic University of Leuven | And 6 more authors.
Astrophysical Journal | Year: 2011

We present the largest sample to date of intermediate-resolution blue-to-red optical spectra of B-type supergiants in M31 and undertake the first survey of diffuse interstellar bands (DIBs) in this galaxy. Spectral classifications, radial velocities, and interstellar reddenings are presented for 34 stars in three regions of M31. Based on a subset of these stars with foreground-corrected reddening EB-VM31 ≥ 0.05, the strengths of the M31 DIBs are analyzed with respect to the amount of dust, ultraviolet radiation field strength, and polycyclic aromatic hydrocarbon emission flux. Radial velocities and equivalent widths are given for the λ5780 and λ6283 DIBs toward 11 stars. Equivalent widths are also presented for the following DIBs detected in three sightlines in M31: λλ4428, 5705, 5780, 5797, 6203, 6269, 6283, 6379, 6613, 6660, and 6993. All of these M31 DIB carriers reside in clouds at radial velocities matching those of interstellar Na i and/or H i. The relationships between DIB equivalent widths and reddening (EB-VM31) are consistent with those observed in the local interstellar medium (ISM) of the Milky Way (MW). Many of the observed sightlines show DIB strengths (per unit reddening) which lie at the upper end of the range of Galactic values. DIB strengths per unit reddening are found (with 68% confidence) to correlate with the interstellar UV radiation field strength. The strongest DIBs are observed where the interstellar UV flux is lowest. The mean Spitzer 8/24 μm emission ratio in our three fields is slightly lower than that measured in the MW, but we identify no correlation between this ratio and the DIB strengths in M31. Interstellar oxygen abundances derived from the spectra of three M31 H ii regions in one of the fields indicate that the average metallicity of the ISM in that region is 12 + log[O/H] = 8.54 ± 0.18, which is approximately equal to the value in the solar neighborhood. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.


News Article | November 2, 2016
Site: www.sciencedaily.com

Spectacular new observations of vast pillar-like structures within the Carina Nebula have been made using the MUSE instrument on ESO's Very Large Telescope. The different pillars analysed by an international team seem to be pillars of destruction -- in contrast to the name of the iconic Pillars of Creation in the Eagle Nebula, which are of similar nature.The spires and pillars in the new images of the Carina Nebula are vast clouds of dust and gas within a hub of star formation about 7500 light-years away. The pillars in the nebula were observed by a team led by Anna McLeod, a PhD student at ESO, using the MUSE instrument on ESO's Very Large Telescope. The great power of MUSE is that it creates thousands of images of the nebula at the same time, each at a different wavelength of light. This allows astronomers to map out the chemical and physical properties of the material at different points in the nebula. Images of similar structures, the famous Pillars of Creation* in the Eagle Nebula and formations in NGC 3603, were combined with the ones displayed here. In total ten pillars have been observed, and in so doing a clear link was observed between the radiation emitted by nearby massive stars and the features of the pillars themselves. In an ironic twist, one of the first consequences of the formation of a massive star is that it starts to destroy the cloud from which it was born. The idea that massive stars will have a considerable effect on their surroundings is not new: such stars are known to blast out vast quantities of powerful, ionising radiation -- emission with enough energy to strip atoms of their orbiting electrons. However, it is very difficult to obtain observational evidence of the interplay between such stars and their surroundings. The team analysed the effect of this energetic radiation on the pillars: a process known as photoevaporation, when gas is ionised and then disperses away. By observing the results of photoevaporation -- which included the loss of mass from the pillars -- they were able to deduce the culprits. There was a clear correlation between the amount of ionising radiation being emitted by nearby stars, and the dissipation of the pillars. This might seem like a cosmic calamity, with massive stars turning on their own creators. However the complexities of the feedback mechanisms between the stars and the pillars are poorly understood. These pillars might look dense, but the clouds of dust and gas which make up nebulae are actually very diffuse. It is possible that the radiation and stellar winds from massive stars actually help create denser spots within the pillars, which can then form stars. These breathtaking celestial structures have more to tell us, and MUSE is an ideal instrument to probe them with. * The Pillars of Creation are an iconic image, taken with the NASA/ESA Hubble Space Telescope, making them the most famous of these structures. Also known as elephant trunks, they can be several light-years in length. This research was presented in a paper entitled "Connecting the dots: a correlation between ionising radiation and cloud mass-loss rate traced by optical integral field spectroscopy," by A. F. McLeod et al., published in the Monthly Notices of the Royal Astronomical Society. The team is composed of A. F. McLeod (ESO, Garching, Germany), M. Gritschneder (Universitäts-Sternwarte, Ludwig-Maximilians-Universität, Munich, Germany), J. E. Dale (Universitäts-Sternwarte, Ludwig-Maximilians-Universität, Munich, Germany), A. Ginsburg (ESO, Garching, Germany), P. D.Klaassen (UK Astronomy Technology Centre, Royal Observatory Edinburgh, UK), J. C. Mottram (Max Planck Institute for Astronomy, Heidelberg, Germany), T. Preibisch (Universitäts-Sternwarte, Ludwig-Maximilians-Universität, Munich, Germany), S. Ramsay (ESO, Garching, Germany), M. Reiter (University of Michigan Department of Astronomy, Ann Arbor, Michigan, USA) and L. Testi (ESO, Garching, Germany).


Bogdanovic T.,University of Maryland University College | Reynolds C.S.,University of Maryland University College | Massey R.,Royal Observatory Edinburgh
Astrophysical Journal | Year: 2011

It has recently been suggested that conduction-driven magnetohydrodynamic (MHD) instabilities may operate at all radii within an intracluster medium (ICM) and profoundly affect the structure of a cluster's magnetic field. Where MHD instabilities dominate the dynamics of an ICM, they will re-orient magnetic field lines perpendicular to the temperature gradient inside a cooling core or parallel to the temperature gradient outside it. This characteristic structure of magnetic field could be probed by measurements of polarized radio emission from background sources. Motivated by this possibility we have constructed three-dimensional models of a magnetized cooling-core cluster and calculated Faraday rotation measure (RM) maps in the plane of the sky under realistic observing conditions. We compare a scenario in which magnetic field geometry is characterized by conduction-driven MHD instabilities to that where it is determined by isotropic turbulent motions. We find that future high-sensitivity spectropolarimetric measurements of RM, such as will be enabled by the Expanded Very Large Array and Square Kilometer Array, can distinguish between these two cases with plausible exposure times. Such observations will test the existence of conduction-driven MHD instabilities in dynamically relaxed cooling-core clusters. More generally, our findings imply that observations of Faraday RM should be able to discern physical mechanisms that result in qualitatively different magnetic field topologies, without a priori knowledge about the nature of the processes. © 2011. The American Astronomical Society. All rights reserved.


Rhodes J.,Jet Propulsion Laboratory | Rhodes J.,California Institute of Technology | Leauthaud A.,Lawrence Berkeley National Laboratory | Leauthaud A.,University of California at Berkeley | And 5 more authors.
Publications of the Astronomical Society of the Pacific | Year: 2010

We examine the effects of charge transfer inefficiency (CTI) during CCD readout on the demanding galaxy shape measurements required by studies of weak; gravitational lensing. We simulate a CCD readout with CTI such, as that caused by charged particle radiation damage in space-based detectors. We verify our simulations on real, data from fully depleted p-channel CCDs that have been deliberately irradiated in a laboratory. We show that only charge traps with time constants of the same order as the time between row transfers during readout, affect galaxy shape measurements. We simulate deep astronomical, images and the process of CCD readout, characterizing the effects of CTI on various galaxy populations. Our code and methods are general and can be applied to any CCDs, once the density and characteristic release times of their charge trap species are known. We baseline our study around p-channel CCDs that have been shown to have charge transfer efficiency up to an order of magnitude better than several models of n-channel CCDs designed for space applications. We predict that for galaxies furthest from the readout registers, bias in the measurement of galaxy shapes, Δe, will increase at a rate of (2.65 ± 0.02) × 10 -4 yr-1 at L2 for accumulated radiation exposure averaged over the solar cycle. If uncorrected, this will consume the entire shape measurement error budget of a dark, energy mission surveying the entire extragalactic sky within about 4 yr of accumulated radiation damage. However, software mitigation techniques demonstrated elsewhere can reduce this by a factor of ∼10, bringing the effect well below mission requirements. This conclusion is valid only for the p-channel CCDs we have modeled; CCDs with higher CTI will fare worse and may not meet the requirements of future dark energy missions. We also discuss additional ways in which hardware could be designed to further minimize the impact of CTI. © 2010. The Astronomical Society of the Pacific. All rights reserved.


Wade G.A.,Royal Military College of Canada | Grunhut J.,Royal Military College of Canada | Grunhut J.,Queen's University | Grafener G.,Armagh Observatory | And 10 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We report magnetic and spectroscopic observations and modelling of the Of?p star HD 148937 within the context of the Magnetism in Massive Stars (MiMeS) Large Program at the Canada-France-Hawaii Telescope. 32 high signal-to-noise ratio circularly polarized (Stokes V) spectra and 13 unpolarized (Stokes I) spectra of HD 148937 were acquired in 2009 and 2010. A definite detection of a Stokes V Zeeman signature is obtained in the grand mean of all observations [in both least-squares deconvolved (LSD) mean profiles and individual spectral lines]. The longitudinal magnetic field inferred from the Stokes V LSD profiles is consistently negative, in contrast to the essentially zero field strength measured from the diagnostic null profiles. A period search of new and archival equivalent width measurements confirms the previously reported 7.03 d variability period. The variation of equivalent widths is not strictly periodic: we present evidence for evolution of the amount or distribution of circumstellar plasma. Interpreting the 7.03 d period as the stellar rotational period within the context of the oblique rotator paradigm, we have phased the equivalent widths and longitudinal field measurements. The longitudinal field measurements show a weak sinusoidal variation of constant sign, with extrema out of phase with the Hα variation by about 0.25 cycles. From our constraint on v sini≤ 45 kms -1, we infer that the rotational axis inclination i≤ 30°. Modelling the longitudinal field phase variation directly, we obtain the magnetic obliquity β= 38 +17 -28° and dipole polar intensity B d= 1020 -380 +310 G. Simple modelling of the Hα equivalent width variation supports the derived geometry. The inferred magnetic configuration confirms the suggestion of Nazé et al., who proposed that the weaker variability of HD 148937 as compared to other members of this class is a consequence of the stellar geometry. Based on the derived magnetic properties and published wind characteristics, we find a wind magnetic confinement parameter η *≃ 20 and rotation parameter W= 0.12, supporting a picture in which the Hα emission and other line variability have their origin in an oblique, rigidly rotating magnetospheric structure resulting from a magnetically channelled wind. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.


Coles B.C.,Rutherford Appleton Laboratory | Webb S.E.D.,Rutherford Appleton Laboratory | Schwartz N.,Royal Observatory Edinburgh | Rolfe D.J.,Rutherford Appleton Laboratory | And 2 more authors.
Biomedical Optics Express | Year: 2016

Optical aberrations degrade image quality in fluorescence microscopy, including for single-molecule based techniques. These depend on post-processing to localize individual molecules in an image series. Using simulated data, we show the impact of optical aberrations on localization success, accuracy and precision. The peak intensity and the proportion of successful localizations strongly reduces when the aberration strength is greater than 1.0 rad RMS, while the precision of each of those localisations is halved. The number of false-positive localisations exceeded 10% of the number of true-positive localisations at an aberration strength of only ~0.6 rad RMS when using the ThunderSTORM package, but at greater than 1.0 rad RMS with the Radial Symmetry package. In the presence of coma, the localization error reaches 100 nm at ~0.6 rad RMS of aberration strength. The impact of noise and of astigmatism for axial resolution are also considered. Understanding the effect of aberrations is crucial when deciding whether the addition of adaptive optics to a single-molecule microscope could significantly increase the information obtainable from an image series. © 2016 Optical Society of America.


PubMed | Royal Observatory Edinburgh and Rutherford Appleton Laboratory
Type: Journal Article | Journal: Biomedical optics express | Year: 2016

Optical aberrations degrade image quality in fluorescence microscopy, including for single-molecule based techniques. These depend on post-processing to localize individual molecules in an image series. Using simulated data, we show the impact of optical aberrations on localization success, accuracy and precision. The peak intensity and the proportion of successful localizations strongly reduces when the aberration strength is greater than 1.0 rad RMS, while the precision of each of those localisations is halved. The number of false-positive localisations exceeded 10% of the number of true-positive localisations at an aberration strength of only ~0.6 rad RMS when using the ThunderSTORM package, but at greater than 1.0 rad RMS with the Radial Symmetry package. In the presence of coma, the localization error reaches 100 nm at ~0.6 rad RMS of aberration strength. The impact of noise and of astigmatism for axial resolution are also considered. Understanding the effect of aberrations is crucial when deciding whether the addition of adaptive optics to a single-molecule microscope could significantly increase the information obtainable from an image series.

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