The Arizona Lenslets for Exoplanet Spectroscopy (ALES) is the world’s first AO-fed thermal infrared integral field spectrograph, mounted inside the Large Binocular Telescope Interferometer (LBTI) on the LBT. An initial mode of ALES allows 3-4 μm spectra at R 20 with 0.026” spaxels over a 1”x1” field-of-view. We are in the process of upgrading ALES with additional wavelength ranges, spectral resolutions, and plate scales allowing a broad suite of science that takes advantage of ALES’s unique ability to work at wavelengths >2 microns, and at the diffraction limit of the LBT’s full 23.8 meter aperture.
We present the data reduction pipeline, MEAD, for Arizona Lenslets for Exoplanet Spectroscopy (ALES), the first thermal infrared integral field spectrograph designed for high-contrast imaging. ALES is an upgrade of LMIRCam, the 1 - 5 μm imaging camera for the Large Binocular Telescope, capable of observing astronomical objects in the thermal infrared (3 - 5 μm) to produce simultaneous spatial and spectral data cubes. The pipeline is currently designed to perform L-band (2.8 - 4.2 μm) data cube reconstruction, relying on methods used extensively by current near-infrared integral field spectrographs. ALES data cube reconstruction on each spectra uses an optimal extraction method. The calibration unit comprises a thermal infrared source, a monochromator and an optical diffuser designed to inject specific wavelengths of light into LBTI to evenly illuminate the pupil plane and ALES lenslet array with monochromatic light. Not only does the calibration unit facilitate wavelength calibration for ALES and LBTI, but it also provides images of monochromatic point spread functions (PSFs). A linear combination of these monochromatic PSFs can be optimized to fit each spectrum in the least-square sense via x2 fitting.
The integral field spectrograph configuration of the LMIRCam science camera within the Large Binocular Telescope Interferometer (LBTI) facilitates 2 to 5 µm spectroscopy of directly imaged gas-giant exoplanets. The mode, dubbed ALES, comprises magnification optics, a lenslet array, and direct-vision prisms, all of which are included within filter wheels in LMIRCam. Our observing approach includes manual adjustments to filter wheel positions to optimize alignment, on/off nodding to track sky-background variations, and wavelength calibration using narrow band filters in series with ALES optics. For planets with separations outside our 1”x1” field of view, we use a three-point nod pattern to visit the primary, secondary and sky. To minimize overheads we select the longest exposure times and nod periods given observing conditions, especially sky brightness and variability. Using this strategy we collected several datasets of low-mass companions to nearby stars.
We are developing a stable and precise spectrograph for the Large Binocular Telescope (LBT) named “iLocater.” The instrument comprises three principal components: a cross-dispersed echelle spectrograph that operates in the YJ-bands (0.97-1.30 μm), a fiber-injection acquisition camera system, and a wavelength calibration unit. iLocater will deliver high spectral resolution (R~150,000-240,000) measurements that permit novel studies of stellar and substellar objects in the solar neighborhood including extrasolar planets. Unlike previous planet-finding instruments, which are seeing-limited, iLocater operates at the diffraction limit and uses single mode fibers to eliminate the effects of modal noise entirely. By receiving starlight from two 8.4m diameter telescopes that each use “extreme” adaptive optics (AO), iLocater shows promise to overcome the limitations that prevent existing instruments from generating sub-meter-per-second radial velocity (RV) precision. Although optimized for the characterization of low-mass planets using the Doppler technique, iLocater will also advance areas of research that involve crowded fields, line-blanketing, and weak absorption lines.
The demonstration of efficient single-mode fiber (SMF) coupling is a key requirement for the development of a compact, ultra-precise radial velocity (RV) spectrograph. iLocater is a next generation instrument for the Large Binocular Telescope (LBT) that uses adaptive optics (AO) to inject starlight into a SMF. In preparation for commissioning iLocater, a prototype SMF injection system was installed and tested at the LBT in the Y-band (0.970–1.065 μm). This system was designed to verify the capability of the LBT AO system as well as characterize on-sky SMF coupling efficiencies. SMF coupling was measured on stars with variable airmasses, apparent magnitudes, and seeing conditions for six half-nights using the Large Binocular Telescope Interferometer. We present the overall optical and mechanical performance of the SMF injection system, including details of the installation and alignment procedure. A particular emphasis is placed on analyzing the instrument's performance as a function of telescope elevation to inform the final design of the fiber injection system for iLocater.
Integral field spectrographs are an important technology for exoplanet imaging, due to their ability to take spectra in a high-contrast environment, and improve planet detection sensitivity through spectral differential imaging. ALES is the first integral field spectrograph capable of imaging exoplanets from 3-5 μm, and will extend our ability to characterize self-luminous exoplanets into a wavelength range where they peak in brightness. ALES is installed inside LBTI/LMIRcam on the Large Binocular Telescope, taking advantage of existing AO systems, camera optics, and a HAWAII-2RG detector. The new optics that comprise ALES are a Keplerian magnifier, a silicon lenslet array with diffraction suppressing pinholes, a direct vision prism, and calibration optics. All of these components are installed in filter wheels making ALES a completely modular design. ALES saw first light at the LBT in June 2015.
The Large Binocular Telescope (LBT) houses two 8.4-meter mirrors separated by 14.4 meters on a common mount. Coherent combination of these two AO-corrected apertures via the LBT Interferometer (LBTI) produces Fizeau interferometric images with a spatial resolution equivalent to that of a 22.8-meter telescope and the light- gathering power of single 11.8-meter mirror. Capitalizing on these unique capabilities, we used LBTI/LMIRcam to image thermal radiation from volcanic activity on the surface of Io at M-Band (4.8 μm) over a range of parallactic angles. At the distance of Io, the M-Band resolution of the interferometric baseline corresponds to a physical distance of ~135 km, enabling high-resolution monitoring of Io volcanism such as ares and outbursts inaccessible from other ground-based telescopes operating in this wavelength regime. Two deconvolution routines are used to recover the full spatial resolution of the combined images, resolving at least sixteen known volcanic hot spots. Coupling these observations with advanced image reconstruction algorithms demonstrates the versatility of Fizeau interferometry and realizes the LBT as the first in a series of extremely large telescopes.
In Spring 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began its ~130-night campaign from the Large Binocular Telescope (LBT) atop Mt Graham, Arizona. This survey benefits from the many technological achievements of the LBT, including two 8.4-meter mirrors on a single fixed mount, dual adaptive secondary mirrors for high Strehl performance, and a cold beam combiner to dramatically reduce the telescope’s overall background emissivity. LEECH neatly complements other high-contrast planet imaging efforts by observing stars at L’ (3.8 μm), as opposed to the shorter wavelength near-infrared bands (1-2.4 μm) of other surveys. This portion of the spectrum offers deep mass sensitivity, especially around nearby adolescent (~0.1-1 Gyr) stars. LEECH’s contrast is competitive with other extreme adaptive optics systems, while providing an alternative survey strategy. Additionally, LEECH is characterizing known exoplanetary systems with observations from 3-5μm in preparation for JWST.
The L/M-band mid-InfraRed Camera (LMIRcam) will use a mid-wave (5.1 μm cut-off) Teledyne Imaging Systems
HgCdTe HAWAII 1-RG array to image the coherently combined (Fizeau) focus of the Large Binocular Telescope's
twin 8.4-meter primary mirrors generated by the University of Arizona's beam combiner - the Large Binocular
Telescope Interferometer (LBTI). The 1024x1024 array will have a pixel scale of 10.9 milliarcsec (mas) per
pixel and a field of view of 10"x10". The highest achievable angular resolution will be 26mas (34mas) for
3.6 μm (4.8 μm). LMIRcam will operate in parallel with the Nulling Infrared Camera (NIC), sharing the same
Dewar. In addition to a suite of broad and narrow-band filters, LMIRcam will contain grisms for low-resolution
spectroscopy, and serve as a test-bed for novel pupil masks to enable high-contrast imaging. The opto-mechanical
design, anticipated performance, and a sample of potential science applications are presented. LMIRcam is funded
by the National Science Foundation and the University of Virginia.