The presence of large amounts of dust in the habitable zones of nearby stars is a significant obstacle for future exo-Earth imaging missions. We executed the HOSTS (Hunt for Observable Signatures of Terrestrial Systems) survey to determine the typical amount of such exozodiacal dust around a sample of nearby main sequence stars. The majority of the data have been analyzed and we present here an update of our ongoing work. Nulling interferometry in N band was used to suppress the bright stellar light and to detect faint, extended circumstellar dust emission. We present an overview of the latest results from our ongoing work. We find seven new N band excesses in addition to the high confidence confirmation of three that were previously known. We find the first detections around Sun-like stars and around stars without previously known circumstellar dust. Our overall detection rate is 23%. The inferred occurrence rate is comparable for early type and Sun-like stars, but decreases from 71<sup>+11 -20</sup>% for stars with previously detected mid- to far-infrared excess to 11<sup>+9 -4</sup>% for stars without such excess, confirming earlier results at high confidence. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal luminosity function of the dust, we find upper limits on the median dust level around all stars without previously known mid to far infrared excess of 11.5 zodis at 95% confidence level. The corresponding upper limit for Sun-like stars is 16 zodis. An LBTI vetted target list of Sun-like stars for exo-Earth imaging would have a corresponding limit of 7.5 zodis. We provide important new insights into the occurrence rate and typical levels of habitable zone dust around main sequence stars. Exploiting the full range of capabilities of the LBTI provides a critical opportunity for the detailed characterization of a sample of exozodiacal dust disks to understand the origin, distribution, and properties of the dust.
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 <i>μ</i>m). PHASECam is LBTI's 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 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.
The Large Binocular Telescope Interferometer is a high contrast imager and interferometer that sits at the combined bent Gregorian focus of the LBT’s dual 8.4 m apertures. The interferometric science drivers dictate 0.1” resolution with 10<sup>3</sup> − 10<sup>4</sup> contrast at 10 μm, while the 4 μm imaging science drivers require even greater contrasts, but at scales <0.2”. In imaging mode, LBTI’s Adaptive Optics system is already delivering 4 μm contrast of 10<sup>4</sup> − 10<sup>5</sup> at 0.3" − 0.75" in good conditions. Even in poor seeing, it can deliver up to 90% Strehl Ratio at this wavelength. However, the performance could be further improved by mitigating Non-Common Path Aberrations. Any NCPA remedy must be feasible using only the current hardware: the science camera, the wavefront sensor, and the adaptive secondary mirror. In preliminary testing, we have implemented an “eye doctor” grid search approach for astigmatism and trefoil, achieving 5% improvement in Strehl Ratio at 4 μm, with future plans to test at shorter wavelengths and with more modes. We find evidence of NCPA variability on short timescales and discuss possible upgrades to ameliorate time-variable effects.
The Thermal Infrared imager for the GMT which provides Extreme contrast and Resolution (TIGER) is intended as a
small-scale, targeted instrument capable of detecting and characterizing exoplanets and circumstellar disks, around both
young systems in formation, and more mature systems in the solar neighborhood. TIGER can also provide general
purpose infrared imaging at wavelengths from 1.5-14 μm. The instrument will utilize the facility adaptive optics (AO)
system. With its operation at NIR to MIR wavelengths (where good image quality is easier to achieve), and much of the
high-impact science using modestly bright guide stars, the instrument can be used early in the operation of the GMT.
The TIGER concept is a dual channel imager and low resolution spectrometer, with high contrast modes of observations
to fulfill the above science goals. A long wavelength channel (LWC) will cover 7-14 μm wavelength, while a short
wavelength channel (SWC) will cover the 1.5-5 μm wavelength region. Both channels will have a 30° FOV. In addition
to imaging, low-resolution spectroscopy (R=300) is possible with TIGER for both the SWC and LWC, using insertable
The L/M-band (3−5 μm) InfraRed Camera (LMIRcam) sits at the combined focal plane of the Large Binocular
Telescope Interferometer (LBTI), ultimately imaging the coherently combined focus of the LBT’s two 8.4-meter
mirrors. LMIRcam achieved first light at the LBT in May 2011 using a single AO-enabled 8.4-meter aperture.
With the delivery of LBT’s final adaptive secondary mirror in Fall of 2011, dual-aperture AO-corrected interferometric
fringes were realized in April 2012. We report on the performance of these configurations and characterize
the noise performance of LMIRcam’s HAWAII-2RG 5.3-μm cutoff array paired with Cornell FORCAST readout
electronics. In addition, we describe recent science highlights and discuss future improvements to the LMIRcam
The Giant Magellan Telescope is planning to provide adaptive wavefront correction of the low layers (<1 km) of
atmospheric turbulence in support of wide-field instrumentation. This ground-layer adaptive optics (GLAO) mode will
use the adaptive secondary mirrors to provide improved image quality over approximately 7 arcminutes FOV. We
present a comparison between the use of a sodium laser guide star asterism plus three tip-tilt natural guide stars versus
natural guide stars only on the average seeing width improvement. The layout and components of both (laser beacon
based and natural star only based) GLAO concepts are described and the impact and interaction with other GMT subsystems
The Giant Magellan Telescope adaptive optics system will be an integral part of the telescope, providing laser guide star
generation, wavefront sensing, and wavefront correction to most of the currently envisioned instruments. The system
will provide three observing modes: Natural Guidestar AO (NGSAO), Laser Tomography AO (LTAO), and Ground
Layer AO (GLAO).
Every AO observing mode will use the telescope’s segmented adaptive secondary mirror to deliver a corrected beam
directly to the instruments. High-order wavefront sensing for the NGSAO and LTAO modes is provided by a set of
wavefront sensors replicated for each instrument and fed by visible light reflected off the cryostat window. An infrared
natural guidestar wavefront sensor with open-loop AO correction is also required to sense tip-tilt, focus, segment piston,
and dynamic calibration errors in the LTAO mode. GLAO mode wavefront sensing is provided by laser guidestars over
a ~5 arcminute field of view, and natural guidestars over wider fields. A laser guidestar facility will project 120 W of
589 nm laser light in 6 beacons from the periphery of the primary mirror. An off-axis phasing camera and primary and
secondary mirror metrology systems will ensure that the telescope optics remain phased.
We describe the system requirements, overall architecture, and innovative solutions found to the challenges presented by high-order AO on a segmented extremely large telescope. Further details may be found in specific papers on each of the observing modes and major subsystems.
ARGOS the Advanced Rayleigh guided Ground layer adaptive Optics System for the LBT (Large Binocular Telescope)
is built by a German-Italian-American consortium. It will be a seeing reducer correcting the turbulence in the lower
atmosphere over a field of 2' radius. In such way we expect to improve the spatial resolution over the seeing of about a
factor of two and more and to increase the throughput for spectroscopy accordingly. In its initial implementation,
ARGOS will feed the two near-infrared spectrograph and imager - LUCI I and LUCI II.
The system consist of six Rayleigh lasers - three per eye of the LBT. The lasers are launched from the back of the
adaptive secondary mirror of the LBT. ARGOS has one wavefront sensor unit per primary mirror of the LBT, each of the
units with three Shack-Hartmann sensors, which are imaged on one detector.
In 2010 and 2011, we already mounted parts of the instrument at the telescope to provide an environment for the main
sub-systems. The commissioning of the instrument will start in 2012 in a staged approach. We will give an overview of
ARGOS and its goals and report about the status and new challenges we encountered during the building phase. Finally
we will give an outlook of the upcoming work, how we will operate it and further possibilities the system enables by
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
ARGOS, the laser-guided adaptive optics system for the Large Binocular Telescope (LBT), is now under construction at
the telescope. By correcting atmospheric turbulence close to the telescope, the system is designed to deliver high
resolution near infrared images over a field of 4 arc minute diameter. Each side of the LBT is being equipped with three
Rayleigh laser guide stars derived from six 18 W pulsed green lasers and projected into two triangular constellations
matching the size of the corrected field. The returning light is to be detected by wavefront sensors that are range gated
within the seeing-limited depth of focus of the telescope. Wavefront correction will be introduced by the telescope's
deformable secondary mirrors driven on the basis of the average wavefront errors computed from the respective guide
star constellation. Measured atmospheric turbulence profiles from the site lead us to expect that by compensating the
ground-layer turbulence, ARGOS will deliver median image quality of about 0.2 arc sec across the JHK bands. This will
be exploited by a pair of multi-object near-IR spectrographs, LUCIFER1 and LUCIFER2, with 4 arc minute field already
operating on the telescope. In future, ARGOS will also feed two interferometric imaging instruments, the LBT
Interferometer operating in the thermal infrared, and LINC-NIRVANA, operating at visible and near infrared
wavelengths. Together, these instruments will offer very broad spectral coverage at the diffraction limit of the LBT's
combined aperture, 23 m in size.
Laser tomography capability using a multi laser guide star (LGS) system is being implemented at the 6.5 m MMT
telescope on Mt. Hopkins, AZ. The system uses five range-gated and dynamically refocused Rayleigh laser beacons to
sense the atmospheric wavefront aberration. Corrections are then applied to the wavefront using the 336-actuator
adaptive secondary mirror of the telescope. So far, the system has demonstrated successful control of ground-layer
aberration over a field of view substantially wider than is delivered by conventional adaptive optics. In this paper, we
report the latest results from this mode of operation, using for the first time a plate scale on our IR science camera that
samples the diffraction scale at the Nyquist limit. We also discuss findings for a reduction in the width of the on-axis
point-spread function from 1.07" to <0.2" in H band and present the progress achieved toward the implementation of
laser tomography. This will be attempted by means of a least squares reconstructor, which is obtained using
simultaneous measurements of the wavefronts from the LGS and an additional natural guide star.
We present progress and results for the pyramid wavefront sensor unit on the Large Binocular Telescope's
Interferometer (LBTI). The system is a clone of the pyramid sensor unit developed at Arcetri Observatory for
the LUCIFER instrument. We discuss the performance of simulated reconstructors during preliminary on-sky
testing at the MMT. These reconstructors were generated with the code AOSim2, a customizable end-to-end
simulator of a telescope and its AO system. We used the 3-5μm imager Clio to take fast exposures at 3.8μm, from
which we calculated Strehl Ratios (SR) for each pyramid configuration and for the Shack-Hartmann (SH) system
currently installed. We obtained instantaneous SR as high as 60% for the pyramid as compared to 65% mean for
the SH.We identify improvements which will increase the SR in future implementations. These tests demonstrate
the feasibility of commissioning a pyramid wavefront sensor on LBTI using a synthetic reconstructor.
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).
We outline the design considerations and principles for developing a graphical user interface for configuring and
operating Large Binocular Telescope Interferometer (LBTI) on sky, and examine the "weblication" methodology to
deliver this astronomical software over the web. LBTI is an instrument to be installed at the Large Binocular Telescope
to search for exo-planets. The instrument consists of a universal beam combiner to combine the light from both arms of
the LBT, an L and M band science camera, a K band nulling channel along with wave front sensor units for adaptive
optics correction. Additionally, the application will have an interface to the telescope control system and XML based
telescope telemetry data flow.
The Laser Adaptive Optics system of the 6.5 m MMT telescope has now been commissioned with Ground Layer
Adaptive Optics operations as a tool for astronomical science. In this mode the wavefronts sampled by each of five laser
beacons are averaged, leading to an estimate of the aberration in the ground layer. The ground layer is then compensated
by the deformable secondary mirror at 400 Hz. Image quality of
0.2-0.3 arc sec is delivered in the near infrared bands
from 1.2-2.5 μm over a field of view of 2 arc minutes. Tomographic wavefront sensing tests in May 2010 produced open
loop data necessary to streamline the software to generate a Laser Tomography Adaptive Optics (LTAO) reconstructor.
In addition, we present the work being done to achieve optimal control PID wavefront control and thus increase the
disturbance rejection frequency response for the system. Finally, we briefly describe plans to mount the ARIES near
infrared imager and echelle spectrograph, which will support the 2 arc min ground-layer corrected field and will exploit
the diffraction limit anticipated with LTAO.
The MMT observatory has recently implemented and tested an optimal wavefront controller for the NGS
adaptive optics system. Open loop atmospheric data collected at the telescope is used as the input to a
MATLAB based analytical model. The model uses nonlinear constrained minimization to determine controller
gains and optimize the system performance. The real-time controller performing the adaptive optics close loop
operation is implemented on a dedicated high performance PC based quad core server. The controller algorithm
is written in C and uses the GNU scientific library for linear algebra. Tests at the MMT confirmed the optimal
controller significantly reduced the residual RMS wavefront compared with the previous controller. Significant
reductions in image FWHM and increased peak intensities were obtained in J, H and K-bands. The optimal PID
controller is now operating as the baseline wavefront controller for the MMT NGS-AO system.
The Large Binocular Telescope Interferometer, a thermal infrared imager and nulling interferometer for the LBT, is
currently being integrated and tested at Steward Observatory. The system consists of a general purpose or universal
beamcombiner (UBC) and three camera ports, one of which is populated currently by the Nulling and Imaging Camera
(NIC). Wavefront sensing is carried out using pyramid-based "W" units developed at Arcetri Observatory. The system
is designed for high spatial resolution, high dynamic range imaging in the thermal infrared. A key project for the
program is to survey nearby stars for debris disks down to levels which may obscure detection of Earth-like planets.
During 2007-2008 the UBC portion of the LBTI was assembled and tested at Steward Observatory. Initial integration of
the system with the LBT is currently in progress as the W units and NIC are being completed in parallel.
LBTI is a thermal imager and a nulling interferometer to be installed on the Large Binocular Telescope (LBT). Here,
we present the distributed component architecture model and its simple yet powerful software structure designed to
complement the LBTI hardware model that comprises pyramid wave front sensors with its control electronic universal
beam combiner, phase sensor, science imager, and all housekeeping duties to run the cryogenics, compressors, vibration
monitors and the interface to the telescope control systems.
PC Reconstructor (PCR) is the control software for the natural guide star and the laser guide star systems at the 6.5m Multiple Mirror Telescope (MMT) operating with the adaptive secondary mirror on Mt. Hopkins south of Tucson, AZ.
The PCR computes and corrects atmospheric turbulence featuring a common interface between the wave front sensor
camera control link and the deformable mirror, diagnostic data management, vibration control, closed-loop data
distribution and saving routines, and housekeeping modules. We report here on the development, use and the on-sky
performance of the PCR.
Over the past several years, experiments in adaptive optics involving multiple natural and Rayleigh laser guide stars
have been carried out by our group at the 1.5 m Kuiper telescope and the 6.5 m MMT telescope. From open-loop data
we have calculated the performance gains anticipated from ground-layer adaptive optics (GLAO) and laser tomography
adaptive optics corrections. In July 2007, the GLAO control loop was closed around the focus signal from all five laser
guide stars at the MMT, leading to a reduction in the measured focus mode on the laser wavefront sensor by 60%. For
the first time, we expect to close the full high order GLAO control loop around the five laser beacons and a tilt star at the
MMT in October 2007, where we predict image quality of < 0.2 arc seconds FWHM in K band (λ = 2.2 μm) over a 2 arc
minute field. We intend to explore the image quality, stability and sensitivity of GLAO correction as a function of
waveband with the science instrument PISCES. PISCES is a 1-2.5 µm imager with a field of view of 110 arc seconds, at
a scale of 0.11 arc seconds per pixel. This is well matched to the expected FWHM performance of the GLAO corrected
field and will be able to examine PSF non-uniformity and temporal stability across a wide field. FGD.