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+11 -20% for stars with previously detected mid- to far-infrared excess to 11+9 -4% 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 Richard F. Caris Mirror Lab at the University of Arizona continues the production of 8.4 m lightweight honeycomb segments for the primary mirror of the Giant Magellan Telescope. GMT will have a center segment surrounded by six identical off-axis segments, plus an additional off-axis segment to allow continuous operation as segments are removed for coating. Production highlights of the last two years include the spin-casting of Segment 5, preliminary polishing of Segment 2, and completion of the rear surface processing for Segments 3 and 4. We completed a preliminary design of the significant modifications of the test systems required for Segment 4, the center segment. We finished an upgrade of the 8.4 m polishing machine; both the upgrade and experience gained with Segment 1 have contributed to much faster polishing convergence for Segment 2. Prior to polishing Segment 2, we verified the stability and accuracy of the measurement systems by re-measuring Segment 1, achieving good agreement among multiple independent tests as well as good agreement with the original acceptance tests of Segment 1.
Vertical profiles of the atmospheric optical turbulence strength and velocity is of critical importance for simulating, designing, and operating the next generation of instruments for the European Extremely Large Telescope. Many of these instruments are already well into the design phase meaning these profies are required immediately to ensure they are optimised for the unique conditions likely to be observed. Stereo-SCIDAR is a generalised SCIDAR instrument which is used to characterise the profile of the atmospheric optical turbulence strength and wind velocity using triangulation between two optical binary stars. Stereo-SCIDAR has demonstrated the capability to resolve turbulent layers with the required vertical resolution to support wide-field ELT instrument designs. These high resolution atmospheric parameters are critical for design studies and statistical evaluation of on-sky performance under real conditions. Here we report on the new Stereo-SCIDAR instrument installed on one of the Auxillary Telescope ports of the Very Large Telescope array at Cerro Paranal. Paranal is located approximately 20 km from Cerro Armazones, the site of the E-ELT. Although the surface layer of the turbulence will be different for the two sites due to local geography, the high-altitude resolution profiles of the free atmosphere from this instrument will be the most accurate available for the E-ELT site. In addition, these unbiased and independent profiles are also used to further characterise the site of the VLT. This enables instrument performance calibration, optimisation and data analysis of, for example, the ESO Adaptive Optics facility and the Next Generation Transit Survey. It will also be used to validate atmospheric models for turbulence forecasting. We show early results from the commissioning and address future implications of the results.
The Large Binocular Telescope Interferometer (LBTI) is a strategic instrument of the LBT designed for highsensitivity, high-contrast, and high-resolution infrared (1.5-13 μm) imaging of nearby planetary systems. To carry out a wide range of high-spatial resolution observations, it can combine the two AO-corrected 8.4-m apertures of the LBT in various ways including direct (non-interferometric) imaging, coronagraphy (APP and AGPM), Fizeau imaging, non-redundant aperture masking, and nulling interferometry. It also has broadband, narrowband, and spectrally dispersed capabilities. In this paper, we review the performance of these modes in terms of exoplanet science capabilities and describe recent instrumental milestones such as first-light Fizeau images (with the angular resolution of an equivalent 22.8-m telescope) and deep interferometric nulling observations.
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 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 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 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 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.
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
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
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 Observatory's 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.
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).
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.
Presented is the design of a nulling interferometer testbed which is capable of maintaining the suppression of a
broadband, infrared source in the presence of external perturbations. Pathlength stability is accomplished by
introducing a dispersive phase shift which allows light at a SWIR band to be used as a wavefront sensor to stabilize the
nulled output of a broadband MWIR channel. Since both channels are common path, fluctuations in OPD observed
with the wavefront sensor directly correlate to fluctuations of the nulling passband. Results obtained from the testbed
will be useful to future nulling interferometers such as the Large Binocular Telescope Interferometer and the Terrestrial
Planet Finder Interferometer which are currently being designed to aid in the search for earth-like planets outside our
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.
We describe the test approaches and results for the Multiband Imaging Photometer for SIRTF. To verify the performance within a `faster, better, cheaper' budget required innovations in the test plan, such as heavy reliance on measurements with optical photons to determine instrument alignment, and use of an integrating sphere rather than a telescope to feed the completed instrument at its operating temperature. The tests of the completed instrument were conducted in a cryostat of unique design that allowed us to achieve the ultra-low background levels the instrument will encounter in space. We controlled the instrument through simulators of the mission operations control system and the SIRTF spacecraft electronics, and used cabling virtually identical to that which will be used in SIRTF. This realistic environment led to confidence in the ultimate operability of the instrument. The test philosophy allowed complete verification of the instrument performance and showed it to be similar to pre-integration predictions and to meet the instrument requirements.
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.
The Mid-Infrared Spectrometer (MIRS) is one of four instruments that will fly aboard the orbiting Infrared Telescope in Space (IRTS). This telescope is a joint NASA/Japanese Space Agency (ISAS) project that is scheduled for a Spring, 1995, launch aboard a Japanese expendable launch vehicle and subsequent retrieval by the space shuttle. The telescope itself is liquid helium-cooled with a 15 cm aperture and will survey approximately 10% of the sky before its cryogen runs out and it begins to warm up. The MIRS was developed jointly by NASA, the University of Tokyo, and ISAS and operates over a wavelength range of 4.5 to 11.7 microns with a resolution of 0.23 and 0.36 microns. The MIRS has a conventional entrance aperture, so that spectral studies can be made of extended as well as point-sources. A cold shutter and an internal calibrator allow accurate absolute flux determinations. Calibration and sensitivity tests in the laboratory have shown that the instrument sensitivity will be limited by the fluctuations due to the zodiacal dust emission over the wavelength range of the spectrometer. The large A-omega of the spectrometer, the cryogenic optics, and the survey nature of the telescope will allow very sensitive studies of the spectral characteristics of diffuse extended emission. These observations will help in determining the composition of the galactic dust responsible for the warm component of the infrared cirrus. In secondary observing programs, the MIRS will also take spectra of the zodiacal dust emission as well as measure the infrared spectra of an estimated 9,800 point-source objects.