Two interacting galaxies, M51 (Whirlpool Galaxy) and NGC 5195. Courtesy of Prof. Andrzej Pigulski, Wroclaw University, Poland
The high sensitivity, ultra-low noise performance of Andor Technology's vacuum Thermoelectric (TE) cooled CCD and Electron Multiplying CCD (EMCCD) cameras is well suited to a diversity of demanding astronomy applications.
The industry-leading TE vacuum cooling of the large area iKon CCD range, enable extensive field of view observation, coupled with long exposure times for deep space imaging. EMCCD technology (in the form of Andor's award-winning iXonEM+ range) has proven highly effective for Single Photon Counting, Lucky Astronomy and also Adaptive Optics.
Now, Andor have brought EMCCD single photon sensitivity to the mainstream astronomy community with the new low-cost LucaEM camera.
26 Sep 2006 Andor Cameras Help Astronomers Find Planets Around Distant Stars
The choice whether or not to opt for EMCCD for astronomy depends very much on your ability to employ longer exposure times to collect enough signal.
The rule of thumb is that if long exposures and slower pixel readout speeds can routinely be employed, such that enough photons can be collected to significantly overcome the read noise floor, then a low-noise, deep-cooled, back illuminated iKon slow-scan camera platform is recommended.
Finally, it should be remembered that EMCCDs can essentially be made single photon sensitive and can even be used to count individual photons!
iXonEM+ and LucaEM imaging EMCCD platforms, and the Newton spectroscopy EMCCD platform, all offer single photon sensitivity combined with high Quantum Efficiency (QE) at multi-MHz rapid readout speeds.
QE curves relevant to Astronomy
Spiral star cluster from SuperWASP project, courtesy of Dr Don Pollaco, Queen’s University of Belfast, UK
Andor's pioneering iXonEM+ is a revolutionary camera range that provides single photon detection sensitivity, highest QE and -100°C cooling at rapid frame rates, utilizing Andor's pioneering and award-winning EMCCD technology. The iXonEM+ is ideal for dynamic applications such as Lucky Astronomy and Adaptive Optics. The low-noise photon counting capabilities of the DU-897 can be harnessed to overcome multiplication noise. The DU-888 back illuminated, with 1024 x 1024 13μm pixels, offers an excellent combination of sensitivity and field of view. Andor-exclusive Real Gain™ sets the new standard in day-to-day EMCCD usage.
iXonEM+
Andor's LucaEM is the latest EMCCD innovation, a highly cost-effective option making EMCCD available to amateur astronomers. LucaEM DL-658 M provides single photon detection sensitivity and 52% QE at 30 full frames/sec, in a cooled USB 2.0 platform.
LucaEM
For photon counting we invariably recommend iXonEM+ DU-897 back illuminated EMCCD. The dark current and clock induced charge levels are the lowest available on the market.For imaging techniques that are fundamentally restricted by background photons the level of darkcurrent at shorter exposure times can be less critical, being masked by the photon background level. Consequently, either iXonEM or LucaEM cameras can be used to deliver enhanced EMCCD performance at high imaging rate, the choice depending on a number of factors such as:
In order to effectively harness EMCCD technology to levels where photon counting is possible, a number of key parameters must be addressed and optimised during camera design to deliver a truly high-end system. The pioneering iXonEM+ range was designed from first principles to maximize the potential that this new technology promised.
Photon counting screenshots: Left = -30°C (x1000 EM Gain), right =-80°C (x1000 EM gain)
An area that requires particular attention for optimising EMCCD performance is that of TE cooling.By housing the sensor into a hermetically sealed, permanent vacuum enclosure, designed also for absolute minimization of out-gassing (rather than the lower-end approach of an o-ring sealed, gas-filled housing), it is possible to achieve significantly lower temperatures in any ambient condition (down to –100°C). Enhanced cooling performance is desireable in EMCCD technology, since thermally generated electrons are amplified above the read noise floor, just as photoelectrons will be. It is thus crucial to minimize darkcurrent as far as possible, even under rapid frame rates, for true photon counting capability.
Dark images and corresponding line profiles taken with the iXonEM+ DU897 (containing the E2V CCD97-00 L3 sensor) at x1000 EM gain, 30 ms exposures, with three differentcooling temperatures. Black -30°C, Red -50° C & Blue -70°C.
Another parameter of EMCCD performance that requires considerable attention is the area of charge shifting. It is beneficial in a frame transfer device to offer the ability and flexibility to push vertical clock times as fast as possible, thus (a) minimizing smearing under short exposure times and (b) increasing frame rate. The challenge comes in doing this whilst retaining the essential sensitivity performance, since a form of spurious single electron noise called Clock Induced Charge (CIC) is particularly sensitive to clock conditions. It is through careful optimization of voltage clocking parameters, that the EMCCD can be operated successfully under these more challenging conditions.
The effect of EM-amplified darkcurrent is evident, even under conditions of short exposures. Deep cooling performance and minimization of CIC is critical for effective photon counting experiments with EMCCDs.
Andor's pioneering Newton is a revolutionary range of high-end spectroscopy EMCCD/CCD cameras that provide single photon detection sensitivity, back illuminated QE, and -90°C cooling at rapid frame rates. USB 2.0 connectivity provides plug and play operation.
Newton
The advent of EMCCD has pushed small size EMCCD sensors, such as the E2V CCD60, into the Adaptive Optics arena. However, in Adaptive Optics the data must be analysed in real time, and the standard PC is simply not good enough. Andor is working with several groups in this field and has designed different solutions to getting the data from the camera to the 3rd party DSP controllers with minimal delay. For those requiring the data to be transferred over short distances a small repeater/splitter has been developed. While for those requiring the data to be transferred over longer distances Andor has developed a solution using a fibre optic Serial FPDP design.
Andor's iKon-L is a revolutionary large area CCD platform, offering back illuminated (> 90% QE) full frame sensors up to 4MPixel(2k x 2k), 1 MHz readoutand unparalleled priority TE cooling down to –100°C.For astronomy we recommend the iKon-L DW-436 or iKon-L DZ-436. These back illuminated 2k x 2k cameras combine low noise readout of 2 to 3 electrons rms, > 90% QE with the exceptionally low darkcurrent enabled by Andor's exclusive 5- stage large area TE cooler.
iKon-L
Andor's iKon-M CCD range offers affordable, yet unmatched sensitivity for slow scan astronomy. The iKon-M platform houses a range of full frame and frame transfer sensors, in both front illuminated and back illuminated (> 90% QE) varieties.For astronomy we recommend the iKon-M DU-934N-BV. This back illuminated 1k x 1k camera, with 13μm2 pixels, offers low readout noise of 2 to 3 electrons rms, > 90% QE and –100°C TE cooling, sensitivity performance that remains unmatched in the market.
Lunar Picture taken with iKon. Image courtesy of Michel Boer from the Observatoire de Haute Provence.
Andor's iDus is a range of affordable yet high-end spectroscopy CCD cameras that house a range of sensor formats, both front and back illuminated, offering vacuum TE cooling to –90°C. USB 2.0 connectivity provides plug and play operation.
iDus
Courtesy of Niall Smith, Cork Institute of Technology.
Image of Blazar 0954+51
Quasars are the most luminous, continuously emitting, objects in the Universe. The standard quasar model invokes a super massive black hole at the centre of a galaxy, onto which matter flows from an accretion disk. In about 10% of cases, jet-like structures are seen to emanate from the core in radio observations.If the jet is beamed directly at the earth, the output may be dominated by emission from the jet, rather than the underlying accretion disk. Quasars that fit into this category are called blazars. Variability in blazars is known to occur on timescales ranging from hours to tens of years. The most rapid variations are likely to originate in shock fronts in the jet, where particles are accelerated via Fermi acceleration.
Rapid variability measurements, with time resolutions of the order of a minute, are important because they probe structures with angular diameters that cannot be imaged directly. Even planned space-borne mm-interferometry will fall short of this angular resolution by some three orders of magnitude. Blazars have been monitored intensively by many observers using conventional CCD technology, with typical integration times of 1 – 5 minutes. Whenever the sampling has been dense and temporally fast, there has been evidence for very fast variations. However, the observations have been hampered by the need to integrate for long enough to ensure the signal is well above the read-noise floor. The lack of sufficiently precise photometry at high time resolution has made it difficult to draw conclusions about the temporal shapes of fast flares and possible substructures contained within.Searching for fast variations almost inevitably results in low integrated fluxes per frame, hence optimum signal-to-noise (S/N) ratios must be achieved at very low photon fluxes.
Image plot of Blazar 0954+51. 0.2 sec exposure with EMCCD gain.
This prompted the group to make a series of observations of a small sample of blazars with the advanced iXonEM+ DU-897 EMCCD camera from Andor, featuring the CCD 97 back-illuminated L3 sensor from E2V, that offers unsurpassed sensitivity performance at high time resolution. Light curves of a number of blazars were recorded and clear evidence of variability was detected on timescales of 30 minutes and longer. No convincing evidence was found for variations on timescales of minutes. Significantly, the fast readout rates employed (by blazar monitoring standards) generated large numbers of datapoints. By binning these, they we were able to estimate the empirical errors for each datapoint and improve the reliability of the photometry. They have chosen the new Andor iXonEM+ with –100°C TE cooling and Linear Gain to advance future efforts in this field.
Couresty of Ian McWhirter, University College London.
Solar winds buffet and distort the earth's magnetic field
The Atmospheric Physics Laboratory of University College London is one of the foremost groups engaged in studies of the upper atmosphere by optical methods. They have developed a network of Fabry-Perot Interferometers (FPIs) installed at dark observing sites in the Scandinavian Arctic. They measure atmospheric winds and temperatures in the thermosphere and upper mesosphere by observing the 630.0nm and 557.7nm oxygen emissions. These instruments run continuously during hours of darkness and are controlled and monitored at UCL via the Internet. Current work focuses on the study of small-scale structure in the Aurora. It is, therefore, necessary to increase the temporal and spatial resolution of measurements as much as possible.
Low light-level imaging devices are essential for the instruments and research into state-of-the-art detectors has always been a major part of their engineering programme. The detectors have progressed over the years from microchannel plate electron multipliers with position-sensing anodes, to intensified CCDs, bare CCDs and, most recently, EMCCDs by Andor. The time resolution of one of the FPIs at Kiruna in Sweden has been much improved by the installation of one of the first Andor EMCCDs.
The Aurora: Atoms and molecules in the upper atmosphere are excited by incoming electrons and protons, emitting light. Image taken at the Spectrographic Imaging Facility located at Adventdalen on the island of Svalbard.
They have also built a Spectrographic Imaging Facility located on the island of Svalbard, 800 miles from the North Pole. It consists of a high resolution imaging spectrograph, four high speed photometers and an auroral video camera. This is a joint project with Southampton University, and has so far been used mainly for studies of Proton aurora. This year it will be improved by the addition of an iXonEM+ EMCCD.
Svalbard laser image
They are now beginning the design and construction of a new Scanning Doppler Imaging System (SCANDI). This will make simultaneous measurements over an all-sky field of view at high resolution. The iXonEM+, with its fast imaging capabilities, will be an important part of this instrument. Its high sensitivity and excellent signal-to-noise ratio will also enable the FPIs to record the dimmer emission lines emitted from other species, such as the OH radical.
Courtesy of Don Pollaco, Queen's University of Belfast.
Andor camera array at SuperWASP observatory
SuperWASP (Wide Angle Search for Planets) is the UK's leading extra-solar planet detection program comprising of a consortium of eight academic institutions which include Cambridge University, the Instituto de Astrofisica de Canarias, the Isaac Newton Group of telescopes, Keele University, Leicester University, the Open University, Queen's University Belfast and St. Andrew's University. It is expected that SuperWASP will revolutionise our understanding of planet formation paving the way for future space missions searching for "earth" like worlds that might hold life.
SuperWASP-North is an observatory on the island of La Palma and is located amongst the Isaac Newton Group of telescopes. It consists of 8 wide-angle cameras that simultaneously monitor the sky for planetary transit events.
SuperWASP display graph
A transit occurs when a planet passes in front of its parent star temporarily blocking some of the light from it. By continuously imaging the sky, SuperWASP can detect these changes in brightness and infer the presence of a planet. There are an estimated 10 billion planetary systems in our galaxy alone, yet to-date, only 133 (as of Nov 2004) have been discovered. SuperWASP detects planets by looking for "transits". These occur when a planet passes in front of its parent star, temporarily obscuring some of its light. This can be detected from the earth as a slight dimming of the star's luminosity. The dimming can be as little as 1% so extremely accurate measurements are needed. The image below is a transit diagram demonstrating the process. As the planet passes in front of the star it produces a characteristic "light-curve" whose shape is affected by the size and orbital distance (and hence orbital period) of the planet. SuperWASP constantly monitors the brightness of the stars in its field of view and alerts us of any variations that may be due to the presence of a planet.
The SuperWASP observatories consist of an array of 8 Andor iKon-L large-area CCD cameras, each housing a vacuum sealed, TE cooled E2V 42-20 sensor with 2k x 2k pixels. These systems are extremely wide field - 2000x greater than a conventional astronomical telescope. The cameras continuously photograph the night sky, each camera capturing up to 50,000 stars per image (this many are needed to stand any chance of detecting transiting planets). This amounts to over 40 gigabytes of observational data per night, which is automatically processed by a custom built computer "Pipeline".
The "Pipeline" first reduces the images by removing errors such as variations in pixel sensitivity, dirt/scratches on the lenses, noise etc. The "pipeline" then examines the images and matches each star with an astronomical catalog of stars to identify them. Finally a complex photometric analysis is performed where the brightness of every star is measured and the results sent to the SuperWASP archive in Leicester.When sufficient observations have been made (over several months) searches for changes in brightness can be made which might indicate the presence of a planet. The 'light-curves' of all the candidate variable stars are plotted and then examined to determine if the changes in brightness are caused by a planet or another astronomical phenomenon. Unfortunately there are a large number of phenomenon, other than planets, that can cause changes in stellar brightness. The most common include:
Very careful analysis is needed to verify the presence of a planet that can include follow-up observations using large telescopes to measure properties such as "Radial velocity" or color variations.
Courtesy of Richard Wilson, Durham University.
Example WFS EM-CCD frame for a binary target with component magnitudes V=5.1 and V=6.0 (1ms exposure).
The ultra fast iXon DV860-BV EMCCD camera has been applied as the wavefront sensor in a new optical system for profiling of atmospheric turbulence strength with altitude, based on low-light level stellar wavefront sensing. The detector has a peak quantum efficiency of 92 percent at 550nm, and a maximum EM gain of 1000 times which yields an effective RMS read noise of <0.1 electron. Frame rates of up to 500Hz (full frame 128 x 128 pixels with no binning) are possible. Typically frame rates of approx. 200Hz are used for SLODAR, with exposure times of 1-2 ms.
The applications of the system are in optimization of adaptive optical correction on large astronomical telescopes, and in site testing for the next generation of extremely large telescopes ("ELTs"). The system was commissioned by the European Southern Observatory (ESO) and constructed by the Center for Advanced Instrumentation (CfAI) at the University of Durham, UK. It is currently installed at the ESO observatory at Cerro Paranal in Chile. The camera, operated through Linux, performs optimally in relation to low light level wavefront sensing in astronomy.
ELT of the ESO observatory at Cerro Paranal in Chile
The system comprises a Shack-Hartmann wave-front sensor mounted on a Meade 40cm Schmidt-Cassegrain telescope. The WFS is made up of a collimating lens, a lenslet array, and a short pass filter (550nm cut-off), in a compact tube mounting attached directly to the EMCCD head. Two separate and interchangeable WFS optics sets are used with the system, each of which divides the telescope pupil into an array of 8 x 8 sub-apertures. The first is optimized for low-altitude profiling using widely separated binary targets (~60 arcsec). In this mode the spot patterns are fully separated on the detector. The second mode is used for more generalized profiling to high altitudes, employing narrow binaries (~6 arcsec), with the spot patterns interleaved. The camera head and optics are mounted on a powered rotating stage at the Cassegrain focus of the telescope, to permit alignment of the binary position angle relative to the CCD and WFS, and to track the side real field rotation.
SPECIAL DELIVERY: by Hercules on skis!
In late 1999, an Andor CCD was sent to Antarctica to be an integral part of the Antarctic Fibre-Optic Spectrometer (AFOS). AFOS is part of a battery of instruments at the un-manned Automated Astrophysical Site-Testing Observatory (AASTO) at latitude 89° 59' 39'', a self-contained observatory that needs no human intervention to run for a year at ambient temperatures down to -80°C. Comprising a 30-inch aperture telescope linked by optical fibers to a spectroscope and the Andor CCD, AFOS' purpose is to determine the transmission of the Earth's atmosphere from UV wavelengths to the visible red, contributing to a comprehensive range of observations that will help identify a suitable site for a future large telescope in Antarctica. The AFOS points a 30-inch aperture telescope at bright stars, sends the light down two bundles of optical fibres into a spectrometer and the Andor CCD.
Researcher with Andor camera at the Antarctic
Why Antarctica? The fact that the Antarctic plateau is cold, high and dry makes it an ideal candidate for an observatory site. Low temperatures make for darker skies in the infrared,high altitude means there is less atmosphere to look through and low moisture levels mean less ultraviolet radiation is absorbed - all in all an ideal combination for observing, provided the systems involved can withstand the extreme cold.
Mounted on top of a tower at the South Pole, the telescope has to cope directly with the rigors of the Antarctic climate. Made from Invar (a special steel that, practically speaking, neither expands nor contracts with temperature changes) the telescope can be aligned at room temperature back at the lab in Sydney, and then operated without further adjustment at ambient temperatures of -80°C on the Antarctic plateau.
Images were taken by:Prof. S.S. Hasan, Prof. Jagdev Singh, Prof. R. Srinivasan and Prof. S. Bagare, Mr. F. Gabriel
Therewas a total solar eclipse of 4 minute duration, visible from South Africa, Egypt, Turkey and some other middle eastern countries. The weather was very good during the eclipse in Turkey. IIA scientists planned an Indian expedition comprising of teams from IIA, Bangalore toTurkey and to conduct experiments during the total solar eclipse. They performed high spatial resolution narrow band photometry of coronal structures (images shown on the right) to investigate the waves and the nature of waves from the study of intensity oscillations in the coronal green line and red emission lines. 14 inch Meade telescopes, 0.5 nm pass-band filters and the Andor iKon with read out speed at 1 MHz were used.Image of the coronal structures (visible only during eclipses): taken with red filter, 100ms exposure, full resolution.
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