... Pierre and Alain sent me their spectra for EW evaluation.
Here the results:
Pierre (observation at 22:38:02): EW (average EXCEL/MK32) = -91.8 A Alain (observation at 00:30:90): EW (average EXCEL/MK32) = -99.4 A
These results confirms, what we could assume meanwhile during the last weeks:
there is a shortterm variability in EW and hence in V too. It's really a large incidental occurence, that both observer just during this jerky phase did take such important spectra. And fortunately with a certain difference (approx. 2 hr) in time. Within the project consortium we discussed already somewhat about the phenomenology behind this behaviour of the star.
Observation facts:
A clear anti-correlation between Halpha EW (fig.1) and the continuum brightness (fig.2). Latter represented as photometric V measurements of the AAVSO-observer. We have to expect such a connection between Halpha EW and the underlaying continuum brightness (Vphot), because of the continuum normalisation for EW calculation. Since the beginning of the campaign (November 2008) we haven't been able, to find with this large clarity this connection, how it is observable during the last weeks. Currently we can demonstrate, what's among others behind the huge variability in EW: variations of the continuum brightness (Vphot) and the Halpha line flux itself (see below).
Questions:
The question is, what causes the variability in Vphot. Variable mass-loss in the outer photosphere of the central star ? Variability of the ionisation structure in the wind ?
To get somewhat more clarity here, we monitor within the project campaign the intrinsic Halpha line flux (fig.3; for definition of the flux see description of the Y-axis). To find out if and how the flux obtained from the spectral line profiles varies, the EW measurements is corrected for the effect of continuum variation. In practise, we correct EW with a simple division by 10(0.4*Vphot). Then the derived quantity is not the line flux in physical units, but a quantity proportional to the physical line flux, corrected for continuum variations.
The observation of the intrinsic line flux is significant, because the included intrinsic variations are due to variable mass-loss rate as variations of wind density and to changes in the ionisation structure. The Halpha line flux does show us in fig.3, there is a fairly variability during the last weeks.
A variability in mass-loss rate should be also observable in the helium forming zones, near the central star (approx. 12-13 stellar radii). That's why I monitor contemporaneously to Halpha the emission and absorption component in He6678. That's why it would be great, to get spectra of the ARAS-group, which includes this spectral region.
In order to avoid too long text, I will come back for a discussion about the He6678 line later.
Ernst Pollmann
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Active Spectroscopy in Astronomy
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