Little Extinction Curve Utility
Joachim Köppen Kiel/Strasbourg/Illkirch Oct.97
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.
- 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
- works in the same way as the Band fields, but the field
always shows the central wavelength of the photometric band
- --- 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
- --- clicking the button itself allows to switch between
magnitudes, the attenuations exp(-tau), and the optical depths
for all the wavelengths
- here one may enter the extinction measure c commonly
used for gaseous nebulae. Hitting the Enter key causes
recalculation of the other extinctions
- enter the ratio of total extinction to reddening. The
applet's default value is 3.09
- 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
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