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

Ground-based observations around 1.4 μm 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 μm, 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 deg2 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 ΔW′ than ΔJ 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.