The J and K bands are bandwidths within the IR spectrum that correspond to around 1.1-1.4 and 2.0-2.4 microns in wavelength, respectively. The H band at 1.5-1.8 microns is also important as well. They're most commonly mentioned in solar astronomy as they denote the wavelengths at which lines of CaII (singly ionised Calcium) are found in the solar spectrum. You can also tell by the strength of these lines just where in the spectral classes of F, G and K, a star resides. The cooler the star, the stronger the lines...although they peak around G3-5. You can also get other molecules and elements appear in these bands as well, such as K, Fe, CO, Mn and others. What also appears in these IR bands is dependent on luminosity class as well, with supergiants, giants and main sequence stars all having somewhat different spectra for any given spectral class.
As for a good text, grab a hold of "Stellar Spectral Classification", By Rick Gray and Chris Corbally. You can pick it up at
Fishpond.com.
I'll fill you in on more tomorrow....it's getting late!!! (2am). Need some sleep
