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The Large Binocular Telescope (LBT) has two 8.4 m primary mirrors that produce beams that can be combined coherently in a “Fizeau” interferometric mode. In principle, the Fizeau point-spread function (PSF) enables the probing of structure at a resolution up to three times better than that of the adaptive-optics-corrected PSF of a single 8.4 m telescope. In this work, we examined the nearby star Altair (5.13 pc, type A7V, hundreds of Myr to ≈1.4 Gyr) in the Fizeau mode with the LBT at Brα(4.05μm) and carried out angular differential imaging to search for companions. This work presents the first filled-aperture LBT Fizeau science data set to benefit from a correcting mirror that provides active phase control. In the analysis of theλ/Dangular regime, the sensitivity of the data set is down to ≈0.5M_⊙at 1″ for a 1.0 Gyr system. This sensitivity remains limited by the small amount of integration time, which is in turn limited by the instability of the Fizeau PSF. However, in the Fizeau fringe regime we attain sensitivities of Δm≈ 5 at 0.″2 and put constraints on companions of 1.3M_⊙down to an inner angle of ≈0.″15, closer than any previously published direct imaging of Altair. This analysis is a pathfinder for future data sets of this type, and represents some of the first steps to unlocking the potential of the first Extremely Large Telescope. Fizeau observations will be able to reach dimmer targets with upgrades to the instrument, in particular the phase detector.

 

ABSTRACT Enabling efficient injection of light into single-mode fibres (SMFs) is a key requirement in realizing diffraction-limited astronomical spectroscopy on ground-based telescopes. SMF-fed spectrographs, facilitated by the use of adaptive optics (AO), offer distinct advantages over comparable seeing-limited designs, including higher spectral resolution within a compact and stable instrument volume, and a telescope independent spectrograph design. iLocater is an extremely precise radial velocity (EPRV) spectrograph being built for the Large Binocular Telescope (LBT). We have designed and built the front-end fibre injection system, or acquisition camera, for the SX (left) primary mirror of the LBT. The instrument was installed in 2019 and underwent on-sky commissioning and performance assessment. In this paper, we present the instrument requirements, acquisition camera design, as well as results from first-light measurements. Broad-band SMF coupling in excess of 35 per cent (absolute) in the near-infrared (0.97–1.31 ${\mu {\rm m}}$) was achieved across a range of target magnitudes, spectral types, and observing conditions. Successful demonstration of on-sky performance represents both a major milestone in the development of iLocater and in making efficient ground-based SMF-fed astronomical instruments a reality. 

Mount Cleveland is one of Alaska's most active volcanoes, yet little is known about the magmatic system driving persistent and dynamic volcanic activity. Volcanic gas and melt inclusion (MI) data from 2016 were combined to investigate shallow magmatic processes. SO₂emission rates were between 166 and 324 t/day and the H₂O/SO₂was 600 ± 53, whereas CO₂and H₂S were below detection. Olivine‐, clinopyroxene‐, and plagioclase‐hosted MIs have up to 3.8 wt.% H₂O, 514 ppm CO₂, and 2,320 ppm S. Equilibration depths, based on MI H₂O contents, suggest that a magmatic column extended from 0.5 to 3.0 km (~10–60 MPa). We used MI data to empirically model open‐system H‐C‐S degassing from 0 to 12 km and found that a column of magma between 0.5 and 3 km could produce the measured gas H₂O/SO₂ratio. However, additional magma deeper than 3 km is required to sustain emissions over periods greater than days to weeks, if the observed vent dimension is a valid proxy for the conduit. Assuming an initial S content of 2,320 ppm, the total magma supply needed to sustain the annual SO₂flux was 5 to 9.8 Mm³/yr, suggesting a maximum intrusive‐to‐extrusive ratio of 13:1. The model predicts degassing of <50 t/day CO₂for July 2016, which corresponds to a maximum predicted CO₂/SO₂of 0.2. Ultimately, frequent recharge from deeper, less degassed magma is required to drive the continuous activity observed over multiple years. During periods of recharge we would expect lower H₂O/SO₂and measurable volcanic CO₂.