Antarctic Infrared Binocular Telescope: Early Data Release of observations in the 1.4 {\mu}m water-vapor-absorption band

TL;DR

This paper reports on the early data release of the Antarctic Infrared Binocular Telescope (AIRBT) at Dome A, demonstrating its capability to observe water-vapor features in the 1.4 μm band with promising results for ultracool star detection.

Contribution

First implementation of a specialized 1.4 μm filter on AIRBT at Dome A, showcasing its potential for water-vapor-absorption studies and ultracool star identification.

Findings

Achieved limiting magnitudes of J~11.5 and W'~9.9 mag in 2s exposures.

Color-color diagrams effectively distinguish ultracool candidates.

Detected water-vapor absorption variations across observations.

Abstract

Ground-based observations around 1.4 $\mu$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 $\mu$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 $\thicksim 20 \ \mathrm{deg^2}$ in the Galactic plane using $\thicksim 20,000$ images in three nights. For 2 s exposures, the 5 $\sigma$ limiting magnitude histogram peaks at $J \thicksim 11.5$ mag (Vega) and $W' \thicksim 9.9$ mag, respectively. The $J-W'$ vs $J-H$ 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 $\Delta W'$ than $\Delta J$ 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.