en.wikipedia.org/wiki/Tau_Ceti
1 correction found
Ca II emissions around the H and K infrared bands show a possible 11-year cycle
The Ca II H and K lines are not infrared. They are at about 393.4 and 396.9 nm, in the violet/near-ultraviolet part of the spectrum.
Full reasoning
This sentence misidentifies the spectral region of the Ca II H and K lines.
NASA lists the laboratory wavelengths of the calcium K and H lines as 3934 Å and 3969 Å respectively. Those are 393.4 nm and 396.9 nm. NASA also explains that ultraviolet radiation spans 290–400 nm, while near-infrared is just beyond the visible spectrum and is commonly discussed at wavelengths such as 0.81 µm (810 nm).
So the Ca II H and K lines are not infrared; they lie at the violet edge / near-ultraviolet part of the spectrum. Calling them “infrared bands” is a factual error, likely a confusion with the separate Ca II infrared triplet.
3 sources
- Imagine the Universe! — Observing the Spectrum of M31
The laboratory wavelengths for them are given below... Calcium K laboratory wavelength, λ0, Ca K = 3934 angstrom; Calcium H laboratory wavelength, λ0, Ca H = 3969 angstrom.
- Ultraviolet Radiation: How It Affects Life on Earth - NASA Science
Ultraviolet (UV) radiation that reaches the Earth's surface is in wavelengths between 290 and 400 nm... This is shorter than wavelengths of visible light, which are 400 to 700 nm.
- Reflected Near-Infrared Waves - NASA Science
A portion of radiation that is just beyond the visible spectrum is referred to as near-infrared... Data from ASTER's visible and near-infrared bands at 0.81 µm, 0.56 µm, and .66 µm are composited...