Space Telescope Science Institute   9.4.2 Sky Background  9.6 Exposure-Time Examples

9.5 Extinction Correction


Extinction can dramatically reduce the counts expected from your source, particularly in the ultraviolet. Figure 9.3 shows the average
Av /E(B-V) values for our galaxy, taken from (Seaton, MNRAS, 187, 73P, 1979). Large variations about the average are observed (Witt, Bohlin, Stecher, ApJ, 279, 698, 1984).

Extinction curves have a strong metallicity dependence, particularly in the UV 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, Kinney and Storchi-Bergmann, 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) may increase monotonically at UV wavelengths.

Figure 9.3: Extinction versus wavelength.

 

 9.4.2 Sky Background  9.6 Exposure-Time Examples
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