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Questions to the campaign

PostPosted: Fri Aug 04, 2017 9:13 pm
by Ernst Pollmann
Dear colleagues,
there are obviously complaints in other websites concerning the question "What should amateurs measure, in order to contribute to the VV Cep campaign".
Well, these people might have a look into the huge and comprehensive information and activity pool, for example at this ARAS forum or at the following sites:

They would find helpful professional and amateur contributions as a guideline to answer their question above. If there are further questions concerning the campaign, please use this forum. Here is the focus of the campaign.

Ernst Pollmann

Re: Questions to the campaign

PostPosted: Sun Aug 27, 2017 10:07 am
by Ernst Pollmann
Hi Phil,
our current state of observation results raises some questions (please see the attached Fig. and the ARAS subforum We believe that the eclipse has started at least in May this year (approx. since JD 2457900).
VV Cep.png
VV Cep.png (122.76 KiB) Viewed 2779 times

1) Our monitoring of the Halpha EW and peakheights of the V&R component shows a simultaneously decrease, althougth one should expect a time delay between V and R because of the large diameter of the accretion disk.
Question is, why?

2) Our Halpha V/R monitoring shows during the current atmospheric eclipse cyclic variability, even in a small range, but clearly to detect. Also here the question, what could be the reason.

It would be great if you could give some help to understand these phenomena!
Best wishes,

Re: Questions to the campaign

PostPosted: Thu Aug 31, 2017 6:23 pm
by Ernst Pollmann
Dear colleagues,
Phil Bennett wrote:
Hi Ernst,
With regard to your questions, I can make some educated guesses as to what is going on:

1. The peak V & R fluxes form quite close in to the hot star (these peaks are actually a single peak with a central dip due to absorption in H-alpha along the line of sight). So the size of the peak-line-forming region in H-alpha probably isn't all that much larger than the B star, perhaps just a few times the size of the B star itself in extent. That probably is too small to be give rise to a noticeable effect in V/R (either in peak height or EW).

2. The effect (decrease in V H-alpha flux over the R wing flux due to progressive occultation by the M star) should be present. But you'll have to look at the *wings* of the H-alpha profile to see this, and this takes more work since there is less flux here.
You will probably need to subtract the continuum first. To do this, I suggest averaging several recent nights spectra and smoothly joining this to a spectrum of mu Cep (or alpha Ori) in the region of the emission line (to estimate the intrinsic M star continuum in this region). Once you have a template M star continuum spectrum constructed, just scale this to optimize the removal of the continuum for each spectrum. That should leave spectrum with (mostly) on the H-alpha emission present. Now estimate the Vx EW, where Vx is the flux blueward of, say, 0.3*V_peak, and the Rx EW, where Rx is the flux redward of 0.3*V_peak. The factor of 0.3 of the peak height is arbitrary -- you simply want some consistent measure of the flux coming form the outermost parts of the accretion region. I expect you should see the effect of the eclipse in Vx and Rx.

3. The cyclic variation is interesting since it looks to be close to the M star photometric period.
Do you have an V photometry for this period? Since we are now in atmospheric eclipse, any variation in the M star size due to pulsation would be expected to modulate the transmitted H-alpha flux (from the vicinity of the B star) correspondingly.

That would be my guess as to what is happening.


Re: Questions to the campaign

PostPosted: Thu Aug 31, 2017 6:31 pm
by Ernst Pollmann
Hi Phil,
first, many thanks for your "open ear" relating to our questions.
To 1)
Yes, this sounds plausible. I forgot to take into account the size ratios of the M to the B star respectively the disk.

To 2)
In order to review the evaluation in that sense it would be a lot of additional work at the moment. I suggest to think about that complex later.

To 3)
The attached Fig. shows the comparison of contemporaneous Vmag to Halpha V/R. Whilest the V/R ratio shows a very pronounced cyclic behavior, the Vmag doesn´t show this. It is striking that the amplitude of the V/R variability seem to becomes more and more smaller, the closer total eclipse comes. Comes this effect really from the M star pulsation?
VtoR versus Vmag.png
VtoR versus Vmag.png (103.08 KiB) Viewed 2727 times


Re: Questions to the campaign

PostPosted: Thu Aug 31, 2017 6:34 pm
by Ernst Pollmann
Dear colleageus,
Phil Bennett wrote:
As for the cyclic variation in H-alpha V/R, if the V mag data doesn't show this, then it might be due to some variation in the disk or accretion region instead. Short-period variability has also been noted in U-band data over the years (I think Wright mentioned a 30-day periodicity seen at certain times in the UV, i.e., U-band photometry).
He attributed this to possible precession of an accretion disk, so that at times the disk is more fully "open" to our viewing angle, and at other times is seen more edge-on, so the effective area (and thus flux) varies in a periodic manner. Think of the appearance of the rings of Saturn as the viewing angle changes.


Re: Questions to the campaign

PostPosted: Thu Aug 31, 2017 9:44 pm
by marcoastro+
Very interesting considerations, Ernst.

To the short cyclic variation:

My proposal of a possible mechanism of apsidal motion, which results in precession could be a good train of thought here.
The remark of Phil on "atmospheric eclipse " stage occurring now, makes me think also on influences of tidal oscillations, which can cause similar precession like effects.
Of course with spectroscopy we are limited to an interpretation of " in line of sight" observations.

So we can conclude here: the real eclipse has yet to come.....

Kind regards,

Re: Questions to the campaign

PostPosted: Fri Sep 01, 2017 8:14 am
by Ernst Pollmann
Hi Marc,
if we see the cyclic variations as indicator of precession effects (like disk nodding for example), then it should mean that we see the disk in every case not pole-on, but more or less edge-on.
And on the other hand the very small "precession period" (?) of approx. 40 days would mean that the mass of the B star disk has to be corresponding "small", what ever small does mean.
In every case it is amazing that this small Halpha V/R variability reflects such a mechanical effects within the B star disk of VV Cep (!).
Also seems to be clear that such a small effects, seen in the observers line of sight, are hardly to find in photometrical Vmag measurements.

Best wishes,

Re: Questions to the campaign

PostPosted: Wed Mar 21, 2018 2:16 pm
by Christof Wiedemair
Dear fellow astronomers,
we have been collecting several spectra of VVCep in the range from 4700 to 6800 Angstrom during the last months. We used a DADOS spectrograph with a 1200l/mm grating and now we are working in BASS. Now we have some questions about how to evaluate the data
The struggle begins with the continuum removal: Is there a best or recommended way to do it? Should we use the same points for every graph?
We set the points for it on every peak on the graph, except on those of Halpha and Hbeta.
Here you can see some screenshots of how we set the points for the continuum removal.

The two images are very similar, the major difference is, that the second one does not have a point set in between the Na D lines. Which one of the two do you think is better?

Here you can see the final result after we removed the pseudocontinuum.

After this step, we would like to calculate the equivalent width. Which approach do you suggest?

Any further hints concerning the best VVCep workflow would be appreciated.
Here you can look at one of our Bass projects:

We are newcomers in spectroscopy. It would be awesome if an experienced forum member would be willing to talk to us personally over video-chat.
I am looking forward to hear back from you.

I am a high school student and I am attending my Senior year. I would like to bring this project to my final exam this July. I hope I can count on your help.

Kind regards,
Patrick Franzinelli

Re: Questions to the campaign

PostPosted: Thu Mar 22, 2018 8:59 am
by Ernst Pollmann
Hi Patrick,
I would like to help you with your question of continuum normalization. Please send me your 1D fits file for doing that to show, how you should perform this procedure. The way you choosed here, is not to recommend.


Re: Questions to the campaign

PostPosted: Fri Mar 23, 2018 11:27 pm
by James Foster
To Patrick,

I agree with Ernst's comments.
I love using BaSS for charting my spectra, but Isis is the preferred software to process 2d spectra data into 1d highly accurate spectral data. Of course you'll need your raw, dark, bias, & flat images as well as the Ne line calibrations files, but after gathering these, Isis can process most visual-band spectra effortlessly; especially if it contains the Ha band. Here is a link:

I know its learning curve is steeper than Bass, but you'll be rewarded with superbly processed data that's easy to share here or with the professional community.

Sincerely Yours,

James Foster
Los Angeles, CA