Antarctic Infrared Binocular Telescope: Early Data Release of Observations in the 1.4 μ m Water-vapor-absorption Band

Abstract Ground-based observations around 1.4 μ m are normally limited by strong absorption of telluric water-vapor. However, Dome A, Antarctica has exceptionally dry conditions that offer a unique opportunity for observations in this band. We designed a new filter covering 1.34–1.48 μ m, namely W ′ , and installed it on the Antarctic Infrared Binocular Telescope (AIRBT) at Dome A in 2025. AIRBT comprises two identical 15 cm optical tube assemblies and two InGaAs cameras equipped with J and W ′ filters, respectively. With this Early Data Release (EDR), we aim to evaluate the performance of the W ′ band at Dome A to observe objects with water-vapor features. This EDR covers ∼20 deg 2 in the Galactic plane using ∼20,000 images in three nights. For 2 s exposures, the 5 σ limiting magnitude histogram peaks at J ∼ 11.5 mag (Vega) and W ′ ∼ 9.9 mag, respectively. The J − W ′ versus J − H color–color diagram distinguishes ultracool candidates with water-vapor-absorption features from reddened early type stars. Furthermore, later-type stars tend to exhibit stronger water-vapor absorption. Some sources show larger Δ W ′ than Δ J across the three nights, which we attribute to variations of their water-vapor-absorption depth. We conclude that it will be efficient to search for ultracool stars and estimate their spectral subtypes using W ′ band imaging at Dome A, where the atmospheric transmission is high and stable.