spectro-aras.com

David Boyd wrote:Robin,

That's an interesting question. I use an Astrodon V filter which has a significantly higher transmission at the [OIII] wavelength than the Bessel V which is used in ISIS for the V mag-based flux calculation. The Bessel filter transmission at the [OIII] wavelength is only 65% of the transmission of the Astrodon filter. When I convolve my recent spectra of V339 Del with the Astrodon filter profile, it reduces the intensity of the [OIII] line to 70% of it's original level but that wavelength is right on the edge of the filter profile where the gradient is large. A small change in the profile of the filter being used will potentially make a large change in the contribution of the [OIII] line to the overall magnitude being measured.

For this reason I am using the actual profile of my Astrodon filter, which I use to measure the V mag at the same time as taking the spectrum, to flux calibrate my spectra rather than the Bessel profile in ISIS.

David