Please enter the magnitude or flux value below along with a wavelength, and this form will return the conversions between these quantities. (Note that even if you choose a filter, you still need something > zero for the wavelength, although the value itself will otherwise be ignored.) To use the "monochromatic" option the wavelength must be in the range covered by the spectral template--1.0 to 35.0 microns.
For the infrared continuum and the Michelle/T-ReCS filters these values are based upon the Cohen et al. Spectral Irradiance Calibration in the Infrared series of papers. The "system" is described in the paper Cohen, Walker, Barlow, and Deacon, 1992, Astronomical Journal, vol. 104, 1650-1657. Zero magnitude flux values have been derived from the Cohen spectral template for alpha CMa and the listed magnitude values from this paper. The formal uncertainties in the values are about 2%.
I have also included absolute flux conversions for a variety of other filters, in the optical and near-infrared mostly; the references for these are given below. This is a intrinsically tricky business. For the wider filters "color corrections" are an issue when converting from magnitude to flux. Even for the narrow-band filters there are other issues in transformation and standardization. The paper M. S. Bessel (2005; Annual Reviews of Astronomy and Astrophysics, volume 43, page 293) discusses standard photometric systems and the transformation between them at some length...but it gives no information about conversion from magnitudes to fluxes.
A magnitude value may be obtained for one of various Gemini mid-IR filters, which has to be chosen above. The alternative is use the "monochromatic" value which is found directly from the alpha CMa spectral energy distribution template given by Martin Cohen. In that case the zero magnitude value is interpolated to the specified wavelength.
Where one of the Gemini mid-infrared filters is specified, the zero magnitude flux density value is found by integrating the Cohen spectral template over the assumed filter profile, weighted by photon number since the normal mid-infrared detectors are photon-counting devices. There is some uncertainty in this process because the filter response curves were measured at liquid N temperature, 77 K, but they are used at liquid He temperatures, around 8 K. This is a potentially serious problem. Where possible the effects of the instrument window and any blocking elements have been included. Any wavelength dependent reflectivity in the telescope mirrors or other wavelength dependent effects in the system, including the atmospheric transmission, have not been taken into account in these calculations.
If you specify a T-ReCS or Michelle filter the effective wavelength (for a hot star as in the case of alpha CMa) will be returned, but there still has to be some value in the "wavelength" field above even though it will not be used.