Thanks François, ChristianFrancois Teyssier wrote:Good work Rob in !Robin Leadbeater wrote:An update of my calculations of H alpha line strength (absolute flux, arbitrary units, click on the attachment to see the trend graphs)
The spectra are low resolution (LISA and ALPY) from the database and scaled to the continuum at H alpha
The H alpha EW is then converted to absolute flux (arbitrary units) using the AAVSO Vmag values (Flux = EW/10^0.4Vmag)
These values are then individually corrected for the ratio of the weighted mean flux in the Vmag passband to that in the continuum at the H alpha line.
(The weighted mean in the Vmag passband is calculated by multiplying the spectra by the normalised Bessel V response and calculating the mean of the result)
Cheers
Robin
Could you compute the absolute flux ?
François
Using the same technique to calculate the absolute flux was my next step and was very simple. I used Christian's relative and absolute flux calibrated ALPY/LISA spectra as a test. The results are in the attached table
I used the AAVSO Vmag data and the formula that Christian uses in method 1 step 2 here
http://www.astrosurf.com/buil/calibrati ... ration.htm
to calculate the flux at 5556A and compared it with the calculated weighted mean relative flux in the Vmag passband from the relative flux calibrated spectra
The relative flux spectrum is then just multiplied by Flux5556A / (weighted mean relative flux) to give the spectrum in absolute flux.
The two methods (Christian's and mine) give very similar answers within a few percent. (probably dependent on the accuracy of the AAVSO Vmag data)
Cheers
Robin