Cosmic Origins Spectrograph Instrument Handbook for Cycle 17
 |
 |
 |
 |
 |
|
| Cosmic Origins Spectrograph Instrument Handbook for Cycle 17 | ||||
|
10.4 Extinction Correction
Extinction can dramatically alter the counts expected from your source, particularly in the ultraviolet. Figure 10.3 shows AV/E(B-V) values applicable to our Galaxy, taken from Seaton (1979, MNRAS, 187, 73P). This corresponds to the "Average Galactic" selection of the ETC.
Extinction curves, however, have a strong metallicity dependence, particularly at ultraviolet wavelengths. Sample extinction curves can be seen in Koornneef and Code [ApJ, 247, 860 1981 (LMC)], Bouchet et al. [A&A, 149, 330 1985 (SMC)], and Calzetti et al. [ApJ, 429, 582, 1994], and references therein. At lower metallicities, the 2200 Å bump which is so prominent in the Galactic extinction curve disappears, and AV/E(B-V) increases at shorter UV wavelengths.
The ETC allows the user to select among a variety of extinction curves and to apply the extinction correction either before or after the input spectrum is normalized.
Figure 10.3: Extinction in magnitude as a function of wavelength, using Seaton's 1979 Galactic model.
|
Space Telescope Science Institute http://www.stsci.edu Voice: (410) 338-1082 help@stsci.edu |
| |
|
|
|
|
