spectro-aras.com

Olivier Thizy sent me spectra of µ Cep and VV Cep, in order to see, what result a division (VV through µ) would produce.
But as a first step I compared both (instr. resp. corr.) spectra with Planck temperature curves. As we can see, the µ Cep continuum slope fits at the best between 2500 to 3000 K, and for VV Cep between 3000 to 3500 K. If we consider the temperature uncertainties in literature, these results do fit very well. The next consideration was, whether a division of VV Cep by µ Cep for this spectral section is really meaningful.
I think, not really. The question is, what could we expect by that?
My opinion is that the result of this division delivers more or less the spectral features of the accretion disk (Halpha, Hbeta & Hgamma), but very strongly overlaid by the continuum flux of the super giant. In order to observe step by step the process of the eclipse, until the accretion disk is totaly disappeared, we should take the wavelength section below 4000 A until 3800 A, as it was done by James Foster (Los Angeles). The advantage of this spectral section would be that we would (by division of VV Cep to µ Cep) measure hardly flux portions of the M super giant, but more or less strongly dominant the higher Balmer lines until to H10!!!! of the disk.
While the entire disk eclipse we would have the rare opportunity, starting with the disappearance of the disk line Halpha until to Balmerline H10 and the corresponding time marks, to analyse the disk extension.
The first indicator of the beginning of the disk eclipse will be the decreasing of the Halpha EW (first contact), because this emission line represents the outer diameter of the accretion disk.

Comments are welcome!!

Ernst Pollmann

Ernst,


Do you have by any chance a link to litterature regarding the continuum spectrum of the super giant atmosphere?

One thought still: maybe we should rescale the mu Cep spectrum to match the level (ie: magnitude) or VV Cep and substract that spectrum from VV Cep spectrum - this would makes more sense as the spectrum we observe is the *sum* of both stars/disk spectra...

And I still have the question how we should be able to detect the beginning of the eclipse in our spectra - any thoughts on this?


Cordialement,
Olivier Thizy

Olivier,
Kawabata et al. had published a very instructive observation which shows, how the blue component of Halpha is suitable to determine the different contacts of ingress and egress of the disk eclipse (see the enclosed Fig.) Ernst

I have forgotten to demonstrate here the other good example how to observe the beginning of the eclipse (published by the same authors). The Fig. shows the equivalent width of the violet (filled circles) and red (open circles) components of the Hα emission as functions of the Julian Date during the 1976-78 eclipse (from Kawabata et al. Pub. Astr. Soc. Japan 33, 1981), but it can be transferred to the eclipse 2017-18.

Next eclipse time (based on 1998 eclipse):
04 August 2017 (JD 2457970) = first contact
27 October 2017 (JD 2458054) = second contact
01 June 2018 (JD 2458288) = mid-eclipse
06 February 2019 (JD 2458620) = third contact
16 May 2019 (JD 2458620) = forth contact

The values decrease drastically in the eclipse. In the ingress the violet component first begins to decrease its intensity and the red component does. The dashed (violet) and dotted (red) lines connected average values, where each average value is that of the values, where each average value is that of the values obtained on three successive days. The arrows indicate the phases corresponding to abrupt variations in intensity.

Ernst