T. McMahon

The Giant Magellan Telescope adaptive optics program

The Giant Magellan Telescope (GMT) adaptive optics (AO) system will be an integral part of the telescope, providing laser guidestar generation, wavefront sensing, and wavefront correction to every instrument currently planned on the 25.4 m diameter GMT. There will be three first generation AO observing modes: Natural Guidestar, Laser Tomography, and Ground Layer AO. All three will use a segmented adaptive secondary mirror to deliver a corrected beam directly to the instruments. The Natural Guidestar mode will provide extreme AO performance, with a total wavefront error less than 185 nm RMS using bright guidestars. The Laser Tomography mode uses 6 lasers and a single off-axis natural guidestar to deliver better than 290 nm RMS wavefront error at the science target, over 50% of the sky at the galactic pole. The Ground Layer mode uses 4 natural guidestars on the periphery of the science field to tomographically reconstruct and correct the ground layer AO turbulence, improving the image quality for wide-field instruments. A phasing system maintains the relative alignment of the primary and secondary segments using edge sensors and continuous feedback from an off-axis guidestar. We describe the AO system preliminary design, predicted performance, and the remaining technical challenges as we move towards the start of construction.

The Large Binocular Telescope mid-infrared camera (LMIRcam): final design and status

We report on the final design and the fabrication status of LMIRcam - a mid-infrared imager/spectrograph that will operate behind the Large Binocular Telescope Interferometer (LBTI) primarily at wavelengths between 3 and 5um (the astronomical L- and M-bands). Within LMIRcam a pair of diamond-turned biconic mirrors re-images a ten arcsecond square field onto a 1024x1024 HAWAII-1RG 5.1um cutoff array. The re-imaging optics provide two pupil planes for the placement of filters and grisms as well as an intermediate image plane. Flexible readout electronics enable operating modes ranging from high frame rate broadband imaging at the longest wavelengths to low background R=400 spectroscopy at shorter wavelengths. The LBTI will provide LMIRcam with a diffraction limited two-mirror PSF with first null dictated by the 14.4 meter separation of the two LBT mirror centers (22.8 meter baseline from edge to edge).

Nulling Data Reduction and On-sky Performance of the Large Binocular Telescope Interferometer

National Aeronautics and Space Administration, Exoplanet Exploration Program; National Aeronautics and Space Administration; European Union through ERC [279973]

Multiband imaging photometer for SIRTF

The Multiband Imaging Photometer for SIRTF (MIPS) provides the space IR telescope facility (SIRTF) with imaging, photometry, and total power measurement capability in broad spectral bands centered at 24, 70, and 160 micrometers , and with low resolution spectroscopy between 50 and 95 micrometers . The optical train directs the light from three zones in the telescope focal plane to three detector arrays: 128 by 128 Si:As BIB, 32 by 32 Ge:Ga, and 2 by 20 stressed Ge:Ga. A single axis scan mirror is placed at a pupil to allows rapid motion of the field of view as required to modulate above the 1/f noise in the germanium detectors. The scan mirror also directs the light into the different optical paths of the instrument and makes possible an efficient mapping mode in which the telescope line of sight is scanned continuously while the scan mirror freezes the image motion on the detector arrays. The instrument is designed with pixel sizes that oversample the telescope Airy pattern to operate at the diffraction limit and, through image processing, to allow superresolution beyond the traditional Rayleigh criterion. The instrument performance and interface requirements, the design concept, and the mechanical, optical, thermal, electrical, software, and radiometric aspects of MIPS are discussed in this paper. Solutions are shown to the challenge of operating the instrument below 3K, with focal plane cooling requirements done to 1.5K. The optical concept allows the versatile operations described above with only a single mechanism and includes extensive self-test and on- board calibration capabilities. In addition, we discuss the approach to cryogenic end-to-end testing and calibration prior to delivery of the instrument for integration into SIRTF.

Commissioning the LBTI for use as a nulling interferometer and coherent imager

The Large Binocular Telescope Interferometer (LBTI) is a strategically important instrument for exploiting the use of the LBT as a 22.7 m telescope. The LBTI has two science cameras (covering the 1.5-5 μm and 8-13 μm atmospheric windows), and a number of observing modes that allow it to carry out a wide range of high-spatial resolution observations. Some simple modes, such as AO imaging, are in routine use. We report here on testing and commissioning of the system for its more ambitious goals as a nulling interferometer and coherent imager. The LBTI will carry out key surveys to Hunt for Observable Signatures of Terrestrial planetary Systems (HOSTS) and an LBTI Exozodi-Exoplanet Common Hunt (LEECH). The current nulling and coherent imaging performance is described.

First AO-corrected interferometry with LBTI: Steps towards routine coherent imaging observations

We report the first phased images using adaptive optics correction from the Large Binocular Telescope Interferometer. LBTI achieved first fringes in late 2010, with seeing-limited operation. Initial tests verified the feasibility of the setup and allowed us to characterize the phase variations from both the atmosphere and mechanical vibrations. Integration of the secondary-base AO systems was carried out in spring 2011 and spring 2012 for the right and left side respectively. Single aperture, diffraction-limited, operation has been commissioned and is used as a productive mode of the LBTI with the LMIRCam subsystem. We describe the initial observation for dual aperture observations and coherent imaging results.

OVMS - the optical path difference and vibration monitoring system for the LBT and its interferometers

Characterisation, mitigation and correction of telescope vibrations have proven to be crucial for the performance of astronomical infrared interferometers. The project teams of the interferometers for the LBT, LINC-NIRVANA and LBTI, and LBT Observatory (LBTO) have embarked on a joint effort to implement an accelerometer-based vibration measurement system distributed over the optical elements of the LBT. OVMS, the Optical Path Difference and Vibration Monitoring System will serve to (i) ensure conditions suitable for adaptive optics (AO) and interferometric (IF) observations and (ii) utilize vibration information, converted into tip-tilt and optical path difference data, in the control strategies of the LBT adaptive secondary mirrors and the beam combining interferometers. The system hardware is mainly developed by Steward Observatorys LBTI team and its installation at the LBT is underway. The OVMS software development and associated computer infrastructure is the responsibility of the LINC-NIRVANA team at MPIA Heidelberg. Initially, the OVMS will fill a data archive provided by LBTO that will be used to study vibration data and correlate them with telescope movements and environmental parameters thereby identifiying sources of vibrations and to eliminate or mitigate them. Data display tools will help LBTO staff to keep vibrations within predefined thresholds for quiet conditions for AO and IF observations. Later-on real-time data from the OVMS will be fed into the control loops of the AO systems and IF instruments in order to permit the correction of vibration signals with frequencies up to 450 Hz.

Co-phasing the Large Binocular Telescope: status and performance of LBTI/PHASECam

The Large Binocular Telescope Interferometer is a NASA-funded nulling and imaging instrument designed to coherently combine the two 8.4-m primary mirrors of the LBT for high-sensitivity, high-contrast, and highresolution infrared imaging (1.5-13 μm). PHASECam is LBTIs near-infrared camera used to measure tip-tilt and phase variations between the two AO-corrected apertures and provide high-angular resolution observations. We report on the status of the system and describe its on-sky performance measured during the first semester of 2014. With a spatial resolution equivalent to that of a 22.8-meter telescope and the light-gathering power of single 11.8-meter mirror, the co-phased LBT can be considered to be a forerunner of the next-generation extremely large telescopes (ELT).

The HOSTS Survey—Exozodiacal Dust Measurements for 30 Stars

The HOSTS (Hunt for Observable Signatures of Terrestrial Systems) survey searches for dust near the habitable zones (HZs) around nearby, bright main sequence stars. We use nulling interferometry in N band to suppress the bright stellar light and to probe for low levels of HZ dust around the 30 stars observed so far. Our overall detection rate is 18%, including four new detections, among which are the first three around Sun-like stars and the first two around stars without any previously known circumstellar dust. The inferred occurrence rates are comparable for early type and Sun-like stars, but decrease from 60 (+16/-21)% for stars with previously detected cold dust to 8 (+10/-3)% for stars without such excess, confirming earlier results at higher sensitivity. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal excess luminosity function, we put upper limits on the median HZ dust level of 13 zodis (95% confidence) for a sample of stars without cold dust and of 26 zodis when focussing on Sun-like stars without cold dust. However, our data suggest that a more complex luminosity function may be more appropriate. For stars without detectable LBTI excess, our upper limits are almost reduced by a factor of two, demonstrating the strength of LBTI target vetting for future exo-Earth imaging missions. Our statistics are so far limited and extending the survey is critical to inform the design of future exo-Earth imaging surveys.

Large Binocular Telescope Interferometer: the universal beam combiner

The Large Binocular Telescope with its single mount design and adaptive optics integrated into the secondary mirrors, provides a unique platform for mid-infrared interferometry. The Large Binocular Telescope Interferometer is designed to take advantage of this platform, specifically for extrasolar planet detection in preparation for the Terrestrial Planet Finder mission. The instrument consists of three components: a general purpose or Universal Beam Combiner (UBC) which preserves the sine condition of the array, a nulling interferometer for the LBT (NIL) to overlap the two beams and sense phase variations, and a nulling-optimized mid-infrared camera (NOMIC) for detection of the final images. Here we focus on the design and tolerancing of the UBC. The components of the system are currently being fabricated and the instrument is planned to be integrated with the LBT in 2006.