Defining the Infrared Region in Astronomy
| Spectral region | Wavelength range
(μm) | Temperature range
(oK) | What can be observed |
|---|
| Near IR | (0.7-1.0) -- 5.0 | 740 -- (3000-5200) | Cool red stars; red giants; high-redshift explosions; galaxies; early universe. Dust is transparent. |
| Mid IR | 5.0 -- (25-40) | (92.5-140) -- 740 | Planets; comets; small planets; protoplanetary disks; dust warmed by starlight |
| Far IR | (25-40) -- (200-350) | (10.6-18.5) -- (92.5-140) | Central regions of galaxies; very cold molecular clouds; emission from the cold dust |
Definition of Infrared Based on the Detector Response
| Near IR | 0.7 - 1.0 μm | from the response of the eye to silicon |
| Short-wave IR | 1.0 - 3.0 μm | from silicon to mid-wave-IR atmospheric window
Indium gallium arsenide (InGaAs) covers up to 1.8 μm;
less sensitive lead salts cover this region |
| Mid-wave IR | 3.0 - 5.0 μm | defined by the atmospheric window
covered by InSb, HgCdTe, and partially by PbSe |
| Long-wave IR | 8.0 - 12.0 μm
7.0-14.0 μm | atmospheric window
covered by HgCdTe and microbolometers |
| Very-long-wave IR | 12.0 - 30.0 μm | covered by doped silicon |
Infrared Reflectance of Metal Coatings
Atmospheric Transmittance and Reflectivity
Photon Flux in the Known Bands
| Band | λc (μm) | Flux @m=0 (Jy) | Reference | Transmissivity |
|---|
| U | 0.36 | 1810 | (1) | |
| B | 0.44 | 4260 | (1) | |
| g | 0.52 | 3730 | (2) | |
| V | 0.55 | 3640 | (1) | |
| R | 0.64 | 3080 | (1) | |
| r | 0.67 | 4490 | (2) | |
| I | 0.79 | 2550 | (1) | |
| i | 0.79 | 4760 | (2) | |
| z | 0.91 | 4810 | (2) | |
| Infrared Bands | | | |
|---|
| J | 1.1-1.4 | 1600 | (3) | High |
| H | 1.5-1.8 | 1080 | (3) | High |
| K | 2.0-2.4 | 670 | (3) | High |
| L | 3.0-4.0 | | | 3.0-3.5: Normal
3.5-4.0: High |
| M | 4.6-5.0 | | | Low |
| N | 7.5-14.5 | | | 8.0-9.0: Normal
10.0-12.0: Normal
Rest: Low |
| Q | 17-25 | | | Very low |
| Z | 28-40 | | | Very low |
(1) Bessel (1979)
(2) Schneider, Gunn, & Hoessel (1983)
(3) Campins, Reike, & Lebovsky (1985)
