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Advanced Camera for Surveys Instrument Handbook for Cycle 20 > Chapter 9: Exposure-Time Calculations > 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(BV) 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  bump which is so prominent in the Galactic extinction curve disappears; and Av/E(BV) may increase monotonically at UV wavelengths.
Figure 9.3: Extinction versus wavelength.

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