E(B-V) and the Interstellar Extinction Curve
The ETC supports six different extinction relations:
- Average Galactic: An average Galactic extinction curve taken from Seaton (MNRAS, 187, 75, 1979).
- gal3: A Galactic extinction curve taken from Cardelli, Clayton & Mathis (ApJ, 345, 245, 1989).
- LMC Extinction: An LMC extinction curve taken from Koorneef & Code (ApJ, 247, 860, 1981).
- SMC Extinction: An SMC extinction curve taken from Prevot, et al. (A&A, 132, 389, 1984).
- Starburst: A general extra-Galactic extinction curve taken from Calzetti, Kinney, & Storchi-Bergmann (ApJ, 429, 582, 1994).
Normally, the extinction factor is applied by default before the flux is normalized to the specified value in Sec.4. That is, in this case the normalized flux will correspond to the actual observed flux.
One can, however, specifiy an alternate computation order, in which the extinction is applied after the normalization takes place. This is useful when planning observations of targets where the "observed magnitude" is being calculated from the absolute magnitude and distance in a region of space where there is a known, measured extinction.
Important Note
The extinction laws used by the ETC are dated and will be replaced with more recent determinations soon. Most importantly, the LMC extinction law (Koorneef & Code, ApJ, 247, 860, 1981) applies essentially only to 30 Doradus, where the UV extinction is higher than in most of the LMC. Therefore, for the moment it is preferable to use the Galactic extinction law for the LMC outside of the 30 Doradus region.