Hi Hugh,
not to be misunderstood: I really want to encourage you, to have a closer look onto your data and existing calibration! Probably, you should present an amplified plot of what is going on with your spectra in details in the blue part of your spectra. Just to gain impression what might be worth for all of us to observe and think about the difficulties and pitfalls. I think it will be worth for us all to learn during this critical path of the ongoing occultation to adjust our ongoing measurements.
Hi Robin,
Robin Leadbeater wrote:I am not yet convinced from these plots that there is necessarily an extinction (or other instrument response) problem here as the effect should be seen more severely at the blue end with little difference at the red end, though I agree it is difficult to see from these differently scaled plots.
Yes, I agree. That's why I said it was my "first impulse". At least, the observations, Hugh presented to all of us, are not too long distance over months and I assume observations were taken at similar air mass (I saw, the observations have been taken not too far away from each other in terms of season). So it could be real. For clarification of these effects, we should consider to carefully calibrate flux. All we know, the binary companion shall be present in the blue end. Therefore, low dispersion profiles, S/N in the blue, a very well known (I don't said good, but well-known) flux reference in the blue might be important.
I'm trying to do this in a way to try to observe alpha Lyr and VV Cep at similar air masses. This is not possible in the final end, but alpha Lyr is one of our best known flux standards. The idea behind this is to take spectra of alpha Lyr, then wait and observe VV Cep later. In the meanwhile taking spectra of "something". Just to get an impression, of what my feeling is.
Just my few cents and not really knowing what will be the output of my spectra of VV Cep.
And, Ernst, I'm speaking about low dispersion behaviour in the blue end, not taking into account H-alpha. Both effects could be very anti-correlated, while the star, accretion disk (if any) and other facts must not be correlated in any way. But, this is also fascinating. This will tell more about the nature of the binary, accretion disk, transfer of material. More, than just observe H-alpha alone.
Thilo