
	User's Guide Contents
	Return to ETC Welcome SYNPHOT SNR and Exposure Time SNR Time Optimal SNR Spectroscopy Target Acquisition Basic Use Page Heirarchy Reference Extraction Regions Spectral Distribution User Spectra Other Spectra Extinction Normalization Background CCD Parameters ID Number Calculations SYNPHOT Calls Call Descriptions Call Parameters NICMOS Spectroscopic Extraction Regions Tables Spectral Elements NICMOS Filters NICMOS Dispersers ACS Filters and Dispersers COS Dispersers WFC3 Filters and Dispersers STIS Filters and Dispersers NICMOS Tables COS Tables STIS Tables and Topical Help

E(B-V) and the Interstellar Extinction Curve

The ETC supports six different extinction relations:

An average Galactic extinction curve taken from Seaton (MNRAS, 187, 75, 1979).
A Galactic extinction curve taken from Savage & Mathis (ARA&A, 17, 73, 1979).
A Galactic extinction curve taken from Cardelli, Clayton & Mathis (ApJ, 345, 245, 1989).
An LMC extinction curve taken from Koorneef & Code (ApJ, 247, 860, 1981).
An SMC extinction curve taken from Prevot, et al. (A&A, 132, 389, 1984).
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.