First Daytime Near-infrared Photometric Observations at Antarctic Dome A

Abstract Located at the highest point on the Antarctic Plateau’s ice sheet, Dome A is generally believed to be one of the best places on Earth for nighttime astronomy in the optical and near-infrared (NIR) bands. Daytime optical/NIR site characteristics are yet to be quantified, however. Here we report the first daytime observations of bright stars at the J band during the austral summer of 2023/2024. The experiments were conducted using a 150 mm telescope with a field of view of 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 87 × 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 69 and a pixel size of 2 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>″</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 5. The sky brightness at zenith was measured to be ∼5.2 mag arcsec −2 at noon when the solar elevation was ∼27°, and it slightly darkened to ∼5.8 mag arcsec −2 at midnight with a solar elevation angle of ∼10°. Stars as faint as J = 10.06 mag were significantly detected at 5 σ levels with an effective exposure time of 175 s around midnight. The pathfinding experiments indicate that a sensitivity ∼2 mag deeper can be reached by the planned 1 m class telescopes, taking advantage of the small free atmosphere seeing. Considering the high latitude and the extremely high fraction of clear days at this site, valuable bright transients with J ≲ 12 mag, such as (super)novae in the local universe and space debris at low orbits, within ∼1/4 of the whole sky around the south celestial pole can be timely discovered and continuously monitored throughout the year.