HMI and AIA Channels

SDO carries some of the most advanced examples of spectroheliographs, instruments designed to produce images of the Sun in a narrow band of wavelengths of light, ever produced. Similar instruments were developed over 100 years ago to take advantage of the closeness of the Sun and its brightness. The wavelength band is usually chosen to include a spectral line of an element in the solar atmosphere.

HMI scans a narrow (75 mÅ) filter across the Fe I 6173 spectral line to produce images of the photosphere at several wavelengths. The images are combined to produce four main observables: continuum images of the solar photosphere near the Fe I 6173 absorption line, maps of the line-of-sight velocity (Dopplergrams), and both line-of-sight and vector maps of the magnetic field (magnetograms).

AIA images the Sun in seven EUV and three UV/visible channels. Temperature maps of the solar corona from below 1 MK to above 20 MK can be created from the six EUV channels in different states of ionized iron. The presence of emissions from these iron ions shows that the corona is very hot and what parts get hotter during flares.

EVE measures the EUV output of the whole Sun (the EUV spectral irradiance), showing how the complicated solar spectrum changes because of solar activity and flares.

HMI and AIA Spectral Bands

Band	FWHM (Δλ, Å)	Primary role, ion(s)	Region of the Sun's atmosphere	Typical Temperature (as log T[K])
6173 Å	75 mÅ	HMI scans Fe i 6173	Intensity, velocity, and magnetic field of photosphere	3.7
4500 Å	500	Continuum	Photosphere	3.7
1700 Å	200	Continumm	Temperature minimum, photosphere	3.7
304 Å	12.7	He ii	Chromosphere, transition region	4.7
1600 Å	200	C iv, continumm	Transition region, upper photosphere	5.0
171 Å	4.7	Fe ix	Quiet corona, upper transition region	5.8
193 Å	6.0	Fe xii, xxiv	Corona and hot flare plasma	6.1, 7.3
211 Å	7.0	Fe xiv	Active region corona	6.3
335 Å	16.5	Fe xvi	Active region corona	6.4
94 Å	0.9	Fe xviii	Flaring regions	6.8
131 Å	4.4	Fe xx, xxiii	Flaring regions	7.0, 7.2