ARGOS is the laser guide star facility of the Large Binocular Telescope (LBT). It implements a Ra... more ARGOS is the laser guide star facility of the Large Binocular Telescope (LBT). It implements a Rayleigh Laser Guide Star system that provides Ground Layer Adaptive Optics (GLAO) correction for the LUCIs, the 2 wide- field near-infrared imagers and multi-object spectrographs installed on the 2 eyes of LBT. In this paper we describe how LBT’s adaptive optics operations have been tailored to ARGOS’s use cases based on the experience developed during over the ARGOS commissioning. We focus on all the aspects that are influenced by the use of the Laser Guide Stars, from collimation to acquisition and LGS guiding and we details the sequences to start, pause and resume the adaptive correction.
Proceedings of the Adaptive Optics for Extremely Large Telescopes 5, 2017
The majority of current Adaptive Optics (AO) systems do not properly compensate for vibrations wi... more The majority of current Adaptive Optics (AO) systems do not properly compensate for vibrations within the optical path. For this reason the mitigation of vibration effects in astronomical AO systems is extremely important. A key component of AO operations is the implementation of techniques to improve the mitigation of vibrations in the AO system. We are in the process of characterizing the LBT AO vibration environment through frequency-based analysis of the closed-loop data, i.e. residual tip-tilt, and accelerometers measurements on key optical components. In this work we describe the vibration environment of the LBT and possible strategies to minimize the effect of the vibrations in the AO performance.
Proceedings of the Adaptive Optics for Extremely Large Telescopes 5, 2017
A key aspect of LGS (Laser Guide Star) operations is the implementation of measures to prevent th... more A key aspect of LGS (Laser Guide Star) operations is the implementation of measures to prevent the illumination of aircraft flying overhead. In parallel to the use of aircraft spotters, we have an automatic aircraft detection system developed at UCSD known as TBAD (Transponder-Based Aircraft Detection). Our airspace is busier, if not the busiest, than for other telescope sites using LGS, and the constant interruptions, specially during the first half of the night, can have a big impact in the efficiency of the LGS operations. We describe the steps that we have taken to validate the operation of the automatic detection system, and show that the efficiency of our laser operation will improve by transitioning to a TBAD only-operation.
Image persistence can produce systematic errors, which remain significant in some applications ev... more Image persistence can produce systematic errors, which remain significant in some applications even when buried in noise. Ideally the image persistence amplitude, linearity and decay over time could be calibrated independently for each pixel to levels well below the noise floor, however averaging multiple measurements to characterize persistence to this accuracy is impractical due to the long time scales for the decay and the need to emulate the exposure and readout timing of the observations to be calibrated. We examine a compromise where the initial persistence response is characterized independently for each pixel but the latter parts of the decay are assumed to follow the mean decay curve. When averaged spatially, persistence increases monotonically with stimulus amplitude until the photodiodes approach forward bias. For several Teledyne 1.7 µm cutoff HgCdTe detectors tested, persistence is linear over most of the normal signal range. We characterize the temporal response, and examine the dependence of charge emission time constants on total stimulus duration. We describe the suppression of persistence by signal in the current frame and begin to examine the superposition of the decay curves from multiple stimuli.
Images with smooth and moderately flat illumination are commonly used to calibrate pixel to pixel... more Images with smooth and moderately flat illumination are commonly used to calibrate pixel to pixel sensitivity variation without consideration that some structure on short spatial scales may be due to reallocation of area between pixels. Errors in the position of pixel boundaries have the effect of repartitioning charge between pixels but do not affect the total charge collected. Since the resulting errors tend to cancel when combining signal from adjacent pixels, this effect has gone largely unnoticed. However proposed wide field astronomical surveys, which strive to achieve high photometric precision with coarse spatial sampling, must take this into account. We present simple analysis techniques to identify how much flat field structure is due to systematic and random variations in pixel area, rather than sensitivity, as a function of row/column direction and spatial frequency. Analysis of data from CCDs made with radically different technologies and pixel sizes by different manufacturers suggests that pixel size variation in the column direction probably dominates QE variations on short spatial scales for all CCDs. Refinements to flat field calibration methods and tests to confirm their efficacy are proposed.
High Energy, Optical, and Infrared Detectors for Astronomy II, 2006
We present the results of a detailed study of the noise performance of candidate NIR detectors fo... more We present the results of a detailed study of the noise performance of candidate NIR detectors for the proposed Super-Nova Acceleration Probe. Effects of Fowler sampling depth and frequency, temperature, exposure time, detector material, detector reverse-bias and multiplexer type are quantified. We discuss several tools for determining which sources of low frequency noise are primarily responsible for the sub-optimal noise improvement when multiple sampling, and the selection of optimum fowler sampling depth. The effectiveness of reference pixel subtraction to mitigate zero point drifts is demonstrated, and the circumstances under which reference pixel subtraction should or should not be applied are examined. Spatial and temporal noise measurements are compared, and a simple method for quantifying the effect of hot pixels and RTS noise on spatial noise is described.
Ground-based and Airborne Instrumentation for Astronomy III, 2010
The Palomar Transient Factory (PTF) is a new fully-automated, wide-field survey conducting a syst... more The Palomar Transient Factory (PTF) is a new fully-automated, wide-field survey conducting a systematic exploration of the optical transient sky. The transient survey is performed using a new 8.1 square degree, 101 megapixel camera installed on the 48-inch Samuel Oschin Telescope at Palomar Observatory. The PTF Camera achieved first light at the end of 2008, completed commissioning in July 2009, and is now in routine science operations. The camera is based on the CFH12K camera, and was extensively modified for use on the 48-inch telescope. A field-flattening curved window was installed, the cooling system was re-engineered and upgraded to closed-cycle, custom shutter and filter exchanger mechanisms were added, new custom control software was written, and many other modifications were made. We here describe the performance of these new systems during the first year of Palomar Transient Factory operations, including a detailed and long term on-sky performance characterization. We also describe lessons learned during the construction and commissioning of the upgraded camera, the photometric and astrometric precision currently achieved with the PTF camera, and briefly summarize the first supernova results from the PTF survey.
The red channel of the Palomar Double Spectrograph (DBSP) on the 200-inch Hale Telescope has been... more The red channel of the Palomar Double Spectrograph (DBSP) on the 200-inch Hale Telescope has been upgraded with a new deep-depletion CCD from LBNL. Its redder response produced a significant increase of the throughput above 550 nm, and its longer dimension more than doubled the spectral coverage. A special Dewar was designed to accommodate a detector mount which includes features to minimize CCD motion due to thermal cycling, in spite of the very simple "picture frame" packaging of the CCD. The new Dewar also includes some novel features to improve the liquid nitrogen hold time while staying within the size envelope allowed in the Cassegrain cage. We describe these changes along with the detector characterization.
Publications of the Astronomical Society of the Pacific, 2009
The Palomar Transient Factory (PTF) is a fully-automated, wide-field survey aimed at a systematic... more The Palomar Transient Factory (PTF) is a fully-automated, wide-field survey aimed at a systematic exploration of the optical transient sky. The transient survey is performed using a new 8.1 square degree camera installed on the 48-inch Samuel Oschin telescope at Palomar Observatory; colors and light curves for detected transients are obtained with the automated Palomar 60-inch telescope. PTF uses eighty percent of the 1.2-m and fifty percent of the 1.5-m telescope time. With an exposure of 60-s the survey reaches a depth of m g ′ ≈21.3 and m R ≈20.6 (5σ, median seeing). Four major experiments are planned for the five-year project: 1) a 5-day cadence supernova search; 2) a rapid transient search with cadences between 90 seconds and 1 day; 3) a search for eclipsing binaries and transiting planets in Orion; and 4) a 3π sr deep H-alpha survey. PTF provides automatic, realtime transient classification and followup, as well as a database including every source detected in each frame. This paper summarizes the PTF project, including several months of on-sky performance tests of the new survey camera, the observing plans and the data reduction strategy. We conclude by detailing the first 51 PTF optical transient detections, found in commissioning data.
The Palomar Double Spectrograph (DBSP) was installed on the Hale 200-inch telescope in 1982, and ... more The Palomar Double Spectrograph (DBSP) was installed on the Hale 200-inch telescope in 1982, and its red channel was last refurbished in 1995. In order to modernize the instrument and provide new capabilities, we replaced the red channel’s detector with a deep-depletion CCD manufactured by Lawrence Berkeley National Laboratories. This change increased the spectrograph’s throughput by a factor of 1.5 between 5500 Å and 8000 Å, and well over a factor of 2 at redder wavelengths. The throughput peaks at 37%, remains above 20% through 9500 Å, and remains above 5% through 10200 Å. Because the chip is longer, the spectral range in a single exposure was increased by a factor of 2.5. The new red channel entered into service on 2011 October 27. Subject headings: instrumentation: detectors — instrumentation: spectrographs
Software and Cyberinfrastructure for Astronomy III, 2014
Commissioning time for an instrument at an observatory is precious, especially the night time. Wh... more Commissioning time for an instrument at an observatory is precious, especially the night time. Whenever astronomers come up with a software feature request or point out a software defect, the software engineers have the task to find a solution and implement it as fast as possible. In this project phase, the software engineers work under time pressure and stress to deliver a functional instrument control software (ICS). The shortness of development time during commissioning is a constraint for software engineering teams and applies to the ARGOS project as well. The goal of the ARGOS (Advanced Rayleigh guided Ground layer adaptive Optics System) project is the upgrade of the Large Binocular Telescope (LBT) with an adaptive optics (AO) system consisting of six Rayleigh laser guide stars and wavefront sensors. For developing the ICS, we used the technique Test- Driven Development (TDD) whose main rule demands that the programmer writes test code before production code. Thereby, TDD can yield a software system, that grows without defects and eases maintenance. Having applied TDD in a calm and relaxed environment like office and laboratory, the ARGOS team has profited from the benefits of TDD. Before the commissioning, we were worried that the time pressure in that tough project phase would force us to drop TDD because we would spend more time writing test code than it would be worth. Despite this concern at the beginning, we could keep TDD most of the time also in this project phase This report describes the practical application and performance of TDD including its benefits, limitations and problems during the ARGOS commissioning. Furthermore, it covers our experience with pair programming and continuous integration at the telescope.
ARGOS is the laser guide star facility of the Large Binocular Telescope (LBT). It implements a Ra... more ARGOS is the laser guide star facility of the Large Binocular Telescope (LBT). It implements a Rayleigh Laser Guide Star system that provides Ground Layer Adaptive Optics (GLAO) correction for the LUCIs, the 2 wide- field near-infrared imagers and multi-object spectrographs installed on the 2 eyes of LBT. In this paper we describe how LBT’s adaptive optics operations have been tailored to ARGOS’s use cases based on the experience developed during over the ARGOS commissioning. We focus on all the aspects that are influenced by the use of the Laser Guide Stars, from collimation to acquisition and LGS guiding and we details the sequences to start, pause and resume the adaptive correction.
Proceedings of the Adaptive Optics for Extremely Large Telescopes 5, 2017
The majority of current Adaptive Optics (AO) systems do not properly compensate for vibrations wi... more The majority of current Adaptive Optics (AO) systems do not properly compensate for vibrations within the optical path. For this reason the mitigation of vibration effects in astronomical AO systems is extremely important. A key component of AO operations is the implementation of techniques to improve the mitigation of vibrations in the AO system. We are in the process of characterizing the LBT AO vibration environment through frequency-based analysis of the closed-loop data, i.e. residual tip-tilt, and accelerometers measurements on key optical components. In this work we describe the vibration environment of the LBT and possible strategies to minimize the effect of the vibrations in the AO performance.
Proceedings of the Adaptive Optics for Extremely Large Telescopes 5, 2017
A key aspect of LGS (Laser Guide Star) operations is the implementation of measures to prevent th... more A key aspect of LGS (Laser Guide Star) operations is the implementation of measures to prevent the illumination of aircraft flying overhead. In parallel to the use of aircraft spotters, we have an automatic aircraft detection system developed at UCSD known as TBAD (Transponder-Based Aircraft Detection). Our airspace is busier, if not the busiest, than for other telescope sites using LGS, and the constant interruptions, specially during the first half of the night, can have a big impact in the efficiency of the LGS operations. We describe the steps that we have taken to validate the operation of the automatic detection system, and show that the efficiency of our laser operation will improve by transitioning to a TBAD only-operation.
Image persistence can produce systematic errors, which remain significant in some applications ev... more Image persistence can produce systematic errors, which remain significant in some applications even when buried in noise. Ideally the image persistence amplitude, linearity and decay over time could be calibrated independently for each pixel to levels well below the noise floor, however averaging multiple measurements to characterize persistence to this accuracy is impractical due to the long time scales for the decay and the need to emulate the exposure and readout timing of the observations to be calibrated. We examine a compromise where the initial persistence response is characterized independently for each pixel but the latter parts of the decay are assumed to follow the mean decay curve. When averaged spatially, persistence increases monotonically with stimulus amplitude until the photodiodes approach forward bias. For several Teledyne 1.7 µm cutoff HgCdTe detectors tested, persistence is linear over most of the normal signal range. We characterize the temporal response, and examine the dependence of charge emission time constants on total stimulus duration. We describe the suppression of persistence by signal in the current frame and begin to examine the superposition of the decay curves from multiple stimuli.
Images with smooth and moderately flat illumination are commonly used to calibrate pixel to pixel... more Images with smooth and moderately flat illumination are commonly used to calibrate pixel to pixel sensitivity variation without consideration that some structure on short spatial scales may be due to reallocation of area between pixels. Errors in the position of pixel boundaries have the effect of repartitioning charge between pixels but do not affect the total charge collected. Since the resulting errors tend to cancel when combining signal from adjacent pixels, this effect has gone largely unnoticed. However proposed wide field astronomical surveys, which strive to achieve high photometric precision with coarse spatial sampling, must take this into account. We present simple analysis techniques to identify how much flat field structure is due to systematic and random variations in pixel area, rather than sensitivity, as a function of row/column direction and spatial frequency. Analysis of data from CCDs made with radically different technologies and pixel sizes by different manufacturers suggests that pixel size variation in the column direction probably dominates QE variations on short spatial scales for all CCDs. Refinements to flat field calibration methods and tests to confirm their efficacy are proposed.
High Energy, Optical, and Infrared Detectors for Astronomy II, 2006
We present the results of a detailed study of the noise performance of candidate NIR detectors fo... more We present the results of a detailed study of the noise performance of candidate NIR detectors for the proposed Super-Nova Acceleration Probe. Effects of Fowler sampling depth and frequency, temperature, exposure time, detector material, detector reverse-bias and multiplexer type are quantified. We discuss several tools for determining which sources of low frequency noise are primarily responsible for the sub-optimal noise improvement when multiple sampling, and the selection of optimum fowler sampling depth. The effectiveness of reference pixel subtraction to mitigate zero point drifts is demonstrated, and the circumstances under which reference pixel subtraction should or should not be applied are examined. Spatial and temporal noise measurements are compared, and a simple method for quantifying the effect of hot pixels and RTS noise on spatial noise is described.
Ground-based and Airborne Instrumentation for Astronomy III, 2010
The Palomar Transient Factory (PTF) is a new fully-automated, wide-field survey conducting a syst... more The Palomar Transient Factory (PTF) is a new fully-automated, wide-field survey conducting a systematic exploration of the optical transient sky. The transient survey is performed using a new 8.1 square degree, 101 megapixel camera installed on the 48-inch Samuel Oschin Telescope at Palomar Observatory. The PTF Camera achieved first light at the end of 2008, completed commissioning in July 2009, and is now in routine science operations. The camera is based on the CFH12K camera, and was extensively modified for use on the 48-inch telescope. A field-flattening curved window was installed, the cooling system was re-engineered and upgraded to closed-cycle, custom shutter and filter exchanger mechanisms were added, new custom control software was written, and many other modifications were made. We here describe the performance of these new systems during the first year of Palomar Transient Factory operations, including a detailed and long term on-sky performance characterization. We also describe lessons learned during the construction and commissioning of the upgraded camera, the photometric and astrometric precision currently achieved with the PTF camera, and briefly summarize the first supernova results from the PTF survey.
The red channel of the Palomar Double Spectrograph (DBSP) on the 200-inch Hale Telescope has been... more The red channel of the Palomar Double Spectrograph (DBSP) on the 200-inch Hale Telescope has been upgraded with a new deep-depletion CCD from LBNL. Its redder response produced a significant increase of the throughput above 550 nm, and its longer dimension more than doubled the spectral coverage. A special Dewar was designed to accommodate a detector mount which includes features to minimize CCD motion due to thermal cycling, in spite of the very simple "picture frame" packaging of the CCD. The new Dewar also includes some novel features to improve the liquid nitrogen hold time while staying within the size envelope allowed in the Cassegrain cage. We describe these changes along with the detector characterization.
Publications of the Astronomical Society of the Pacific, 2009
The Palomar Transient Factory (PTF) is a fully-automated, wide-field survey aimed at a systematic... more The Palomar Transient Factory (PTF) is a fully-automated, wide-field survey aimed at a systematic exploration of the optical transient sky. The transient survey is performed using a new 8.1 square degree camera installed on the 48-inch Samuel Oschin telescope at Palomar Observatory; colors and light curves for detected transients are obtained with the automated Palomar 60-inch telescope. PTF uses eighty percent of the 1.2-m and fifty percent of the 1.5-m telescope time. With an exposure of 60-s the survey reaches a depth of m g ′ ≈21.3 and m R ≈20.6 (5σ, median seeing). Four major experiments are planned for the five-year project: 1) a 5-day cadence supernova search; 2) a rapid transient search with cadences between 90 seconds and 1 day; 3) a search for eclipsing binaries and transiting planets in Orion; and 4) a 3π sr deep H-alpha survey. PTF provides automatic, realtime transient classification and followup, as well as a database including every source detected in each frame. This paper summarizes the PTF project, including several months of on-sky performance tests of the new survey camera, the observing plans and the data reduction strategy. We conclude by detailing the first 51 PTF optical transient detections, found in commissioning data.
The Palomar Double Spectrograph (DBSP) was installed on the Hale 200-inch telescope in 1982, and ... more The Palomar Double Spectrograph (DBSP) was installed on the Hale 200-inch telescope in 1982, and its red channel was last refurbished in 1995. In order to modernize the instrument and provide new capabilities, we replaced the red channel’s detector with a deep-depletion CCD manufactured by Lawrence Berkeley National Laboratories. This change increased the spectrograph’s throughput by a factor of 1.5 between 5500 Å and 8000 Å, and well over a factor of 2 at redder wavelengths. The throughput peaks at 37%, remains above 20% through 9500 Å, and remains above 5% through 10200 Å. Because the chip is longer, the spectral range in a single exposure was increased by a factor of 2.5. The new red channel entered into service on 2011 October 27. Subject headings: instrumentation: detectors — instrumentation: spectrographs
Software and Cyberinfrastructure for Astronomy III, 2014
Commissioning time for an instrument at an observatory is precious, especially the night time. Wh... more Commissioning time for an instrument at an observatory is precious, especially the night time. Whenever astronomers come up with a software feature request or point out a software defect, the software engineers have the task to find a solution and implement it as fast as possible. In this project phase, the software engineers work under time pressure and stress to deliver a functional instrument control software (ICS). The shortness of development time during commissioning is a constraint for software engineering teams and applies to the ARGOS project as well. The goal of the ARGOS (Advanced Rayleigh guided Ground layer adaptive Optics System) project is the upgrade of the Large Binocular Telescope (LBT) with an adaptive optics (AO) system consisting of six Rayleigh laser guide stars and wavefront sensors. For developing the ICS, we used the technique Test- Driven Development (TDD) whose main rule demands that the programmer writes test code before production code. Thereby, TDD can yield a software system, that grows without defects and eases maintenance. Having applied TDD in a calm and relaxed environment like office and laboratory, the ARGOS team has profited from the benefits of TDD. Before the commissioning, we were worried that the time pressure in that tough project phase would force us to drop TDD because we would spend more time writing test code than it would be worth. Despite this concern at the beginning, we could keep TDD most of the time also in this project phase This report describes the practical application and performance of TDD including its benefits, limitations and problems during the ARGOS commissioning. Furthermore, it covers our experience with pair programming and continuous integration at the telescope.
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Papers by Gustavo Rahmer