J band (infrared)

In infrared astronomy, the J band refers to an atmospheric transmission window (1.1 to 1.4 μm) centred on 1.25 micrometres (in the near-infrared).

Betelgeuse is the brightest near-IR source in the sky with a J band magnitude of −2.99.^[1] The next brightest stars in the J band are Antares (−2.7), R Doradus (−2.6), Arcturus (−2.2), and Aldebaran (−2.1).^[2] In the J band Sirius is the 9th brightest star.

The J band is a frequent source of ground based observations since the wavelengths it covers pass through clouds and other atmospheric gasses.^[3] The waveband does however suffer from contamination by water vapor lines and hydroxide emission lines leading to relatively high photometric error.^[4]

It can be used to scrutinize the photosphere of giant and supergiant stars while mostly avoiding opacities from molecular bands and also has access to the 1080 nm He I line which is useful in the study of circumstellar disk interactions around T-Tauri stars.^[5] J, H and K-band spectroscopy is also commonly used to observe and research brown dwarfs^[6] and directly imaged exoplanets.^[7]