This little Extinction Utility allows to compute the extinction due to interstellar dust for any wavelength from the ultraviolet to the infrared, and to convert magnitudes into optical depths and attenuation factors. The standard interstellar extinction curve is used: for the optical (Scheffler 1982, in Landoldt-Börnstein, Vol. 2c, p.45), ultraviolet (Seaton 1979, MNRAS 93, 73P), and infrared (Rieke & Lebofsky 1985, ApJ 288, 618, extrapolated linearly beyond 20 microns).

Note added in Dec. 2007: Various other extinction laws have been added: Cardelli, Clayton, & Mathis (1989 ApJ 345, 245) - which also allows to change the value of R - Whitford (1958, AJ 63, 201), Schild (1977, AJ 82, 337), Savage & Mathis (1979, ARAA 17, 73), Nandy et al. (1975, A&A 44, 195) and Seaton (1979, MNRAS 187, 785). They are chosen by an additional button in the lower right corner.

Note added in May 2011: The reddening curve from Fitzpatrick (1999 PASP 111, 63) has been added, which also provides a family of curves, depending on R. As the original formulae yield a slightly smaller ratio of A_V/E(B-V) than the inputted value of R, the anchor point near to the V band was slightly modified.

The controls:

Band

in any of the fields below one may enter either the name of the photometric filter (U, B, V, ... Q, u, b, y, ....) or the wavelength in Å or in micro metres (by adding the letter "u" after the number. Hitting the Enter key causes the calculation and display of the extinction value. The field will display the name of the band

Wavelength

works in the same way as the Band fields, but the field always shows the central wavelength of the photometric band

A[mag]

--- the fields below show the extinctions. But also, one may enter the extinction value at the appropriate wavelength, hitting the Enter key (or clicking the radio button to the right of the field) recomputes the extinctions for all the other wavelengths

--- clicking the button itself allows to switch between magnitudes, the attenuations exp(-tau), and the optical depths for all the wavelengths

c(Hbeta)=

here one may enter the extinction measure c commonly used for gaseous nebulae. Hitting the Enter key causes recalculation of the other extinctions

R

enter the ratio of total extinction to reddening. The applet's default value is 3.09

E(B-V)=

enter the colour excess

Johnson UBV ....

these buttons allow to put certain standard photometric systems into the rows, each of which may be changed to other wavelengths