The Large Binocular Telescope Interferometer (LBTI) is a strategic instrument which combines the two 8.4m apertures of the LBT for sensitive, high-angular-resolution imaging and interferometric observations in the thermal infrared. Through its observing modes utilizing adaptive optics, Fizeau imaging, and nulling interferometry, the LBTI is in many respects the first ELT; it serves as a pioneer for upcoming ELTs in terms of both science and instrumentation. LBTI has completed a large survey for habitable-zone dust around main sequence stars, exploiting its angular resolution to obtain 100x better sensitivity than space-based photometric observations. Recently we have emphasized Fizeau imaging, supporting high-contrast and precision-astrometric observations. We obtained the first extragalactic and N band observations in this mode, demonstrating high-fidelity, high-sensitivity imaging on a 23m baseline. We are now pushing to image the first rocky planet in the habitable zone around a nearby Sun-like star. In this paper we present an overview of the LBTI’s design and capabilities as a 23 m telescope. In particular, we focus on open loop Fizeau imaging, presenting the state of the art. We measure the stability of the Fizeau PSF, test frame selection criteria, and demonstrate PSF deconvolution. Finally, we outline future developments and synergies with current and upcoming facilities.
NOTT (formerly Hi-5) is the L’-band (3.5-4.0μm) nulling interferometer of Asgard, an instrument suite in preparation for the VLTI visitor focus. The primary scientific objectives of NOTT include characterizing (i) young planetary systems near the snow line, a critical region for giant planet formation, and (ii) nearby mainsequence stars close to the habitable zone, with a focus on detecting exozodiacal dust that could obscure Earthlike planets. In 2023-2024, the final warm optics have been procured and assembled in a new laboratory at KU Leuven. First fringes and null measurements were obtained using a Gallium Lanthanum Sulfide (GLS) photonic chip that was also tested at cryogenic temperatures. In this paper, we present an overall update of the NOTT project with a particular focus on the cold mechanical design, the first results in the laboratory with the final NOTT warm optics, and the ongoing Asgard integration activities. We also report on other ongoing activities such as the characterization of the photonic chip (GLS, LiNbO3, SiO), the development of the exoplanet science case, the design of the dispersion control module, and the progress with the self-calibration data reduction software.
Hi-5 is the L’-band (3.5-4.0 μm) high-contrast imager of Asgard, an instrument suite in preparation for the visitor focus of the VLTI. The system is optimized for high-contrast and high-sensitivity imaging within the diffraction limit of a single UT/AT telescope. It is designed as a double-Bracewell nulling instrument producing spectrally-dispersed (R=20, 400, or 2000) complementary nulling outputs and simultaneous photometric outputs for self-calibration purposes. In this paper, we present an update of the project with a particular focus on the overall architecture, opto-mechanical design of the warm and cold optics, injection system, and development of the photonic beam combiner. The key science projects are to survey (i) nearby young planetary systems near the snow line, where most giant planets are expected to be formed, and (2) nearby main sequence stars near the habitable zone where exozodiacal dust that may hinder the detection of Earth-like planets. We present an update of the expected instrumental performance based on full end-to-end simulations using the new GRAVITY+ specifications of the VLTI and the latest planet formation models.
One of the main design considerations of the Large Binocular Telescope (LBT) was the goal to resolve the habitable zones (HZs) of the nearest stars at mid-infrared wavelengths around 10 μm. The LBT Interferometer (LBTI) makes use of the telescope’s two 8.4m mirrors on a common mount and their 22.7m edge-to-edge separation for sensitive, high-angular resolution observations at thermal-infrared wavelengths. In addition to adaptive optics imaging using the two mirrors separately, the instrument enables nulling and Fizeau imaging interferometry exploiting the full resolving power of the LBT. The LBTI team has successfully completed the Hunt for Observable Signatures of Terrestrial planetary Systems (HOSTS), for which we used nulling-interferometry to search for exozodiacal dust, and we are continuing the characterization of the detected systems. Here, we describe a new program to exploit the LBTI’s Fizeau imaging interferometric capabilities for a deep imaging search for low-mass, HZ planets around a small sample of particularly suitable, nearby stars. We also review the LBTI’s current status relevant to the proposed project to demonstrate the instrument is ready for such a large project.
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