VV Cep: Fe absorptions increase around Ca II doublet

VV Cep 2017-2019 Campaign
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Re: VV Cep: Fe absorptions increase around Ca II doublet

Postby Phil Bennett » Mon Aug 14, 2017 5:14 pm

Hi Robin, Peter, Ernst,

These UV spectra of VV Cep are very useful, especially the record of growth of Fe I and Ti II lines into eclipse -- these lines are formed in the outer atmosphere of the M supergiant and are prominent during the eclipse ingress and egress phases. At these times, the line of sight to the hot B star passes through the outer atmosphere of the M star -- this is chromospheric eclipse.

The higher Balmer lines require hotter, denser gas for their excitation, and are believed to form deep in the accretion disk around B star. In contrast, although these regions also emit H-alpha, that line also is formed throughout the extensive H II region (where H is nearly all ionized to H+) present around the B star. This H II region extends far beyond the actual accretion disk region (which is small in spatial extent), and is somewhat larger in size than the M star itself. That is why the H-alpha emission decreases in strength during total eclipse, but does not entirely disappear. The H II region is too large to be totally eclipsed. In contrast, the higher Balmer lines, formed in the accretion disk, disappear during totality as the disk is completely eclipsed.

Please continue with these UV spectroscopic observations through the eclipse period. They will be extremely useful in helping construct a model of the M supergiant's outer atmosphere.

Phil
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Re: VV Cep: Fe absorptions increase around Ca II doublet

Postby Robin Leadbeater » Thu Aug 17, 2017 4:51 pm

My latest spectrum shows clear broadening of the CaK (and CaH/H epsilon) lines.

vvcep_CaHK_20170804_20170815_Leadbeater.png
vvcep_CaHK_20170804_20170815_Leadbeater.png (40.21 KiB) Viewed 2669 times


This was also seen during ingress of the AZCas eclipse.
http://www.threehillsobservatory.co.uk/ ... tra_43.htm
(spectra 15,14)

The eclipse may have started. Confirming spectra needed

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Re: VV Cep: Fe absorptions increase around Ca II doublet

Postby Robin Leadbeater » Thu Aug 17, 2017 5:35 pm

There has also been an increase the depth of the absorption lines at 4030/4033A (Ti??)

Robin
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vvcep_20170804-20170815_Leadbeater_4030-4033.png
vvcep_20170804-20170815_Leadbeater_4030-4033.png (52.68 KiB) Viewed 2664 times
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Re: VV Cep: Fe absorptions increase around Ca II doublet

Postby Ernst Pollmann » Thu Aug 17, 2017 8:19 pm

Hi Robin,
in context with your spectra a very early investigation of V. Geodecke "A Study of the Spectrum of VV Cep" (Publications of the Observatory of the University of Michigan, 1943) is helpful to read. That paper shows in Fig. 9 an instructive drawing of the location of the elements forming, within the outer atmosphere of the M super giant (depending of inclination and computed by the Gaposchkin-Method). Corresponding to that drawing (so far I understand), absorption lines of Titan seem to react first during the eclipse (Knowledge 1943).
goedecke.png
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Re: VV Cep: Fe absorptions increase around Ca II doublet

Postby Peter Somogyi » Thu Aug 17, 2017 9:00 pm

Hi Robin,

I confirm these days the CaII 3933A blue wing show larger depth:
pso_serie_20170527_0813.gif

However, I did see a similar state on 2017-JUN-04 although not this deep.
The Ca II has always been changing heavily (so as the Balmer lines).

Interestingly, the Ti II 3900, 3913 hasn't changed for a few weeks (Ti II 3900 is contaminated with Fe I 3899.707 from the left side) whilst Fe I and the right side absorptions on my spectra (looks Ti ? - not that obvious) increasing like 5-10% every week.

- Peter
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Re: VV Cep: Fe absorptions increase around Ca II doublet

Postby Olivier Thizy » Fri Aug 18, 2017 11:45 am

Hello,


I also seem to see a decrease in Halpha but I am careful as variations occured outside eclipse too. For exemple spectra taken also ten days apart with last year/this year for comparison:
graphasdb_vvcep_20170818_070_Ha.png


and it is even less obvious on Hbeta:
graphasdb_vvcep_20170818_070_Hb.png


I guess the event will take a very long time, with a "noise" level fairly high from the hot emission source...


As a reminder, spectra sent to to me (thizy@free.fr) for the ARAS database, are included and visible on:
http://www.astrosurf.com/aras/Aras_DataBase/VVCepStars/VVCep.htm


Cordialement,
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Re: VV Cep: Fe absorptions increase around Ca II doublet

Postby Peter Somogyi » Fri Aug 18, 2017 12:47 pm

Hi Olivier,

For H-alpha variability discussions, I'd recommend these key readings:
viewtopic.php?f=19&t=1797&start=10
viewtopic.php?f=19&t=1813
From the latter forum, has V/R started to closing (1-2 weeks ago), which means the "contact" reached the main H-alpha emission core (is it in L1, or disk? yet unclean).
I am speculating also that this is a real core M contact, not just the outer cloud (what I already see in my UV exposures since restarted it in 2017-May).

Though Ernst is the specialist of H-alpha area, let me add a thought for an experiment: since H-alpha generated in the overall region (mostly outer), we might assume most of its region being unchanged on short term.
What needs to be done, is removing a similar M continuum matching perfectly from the H-alpha spectra (to have continuum fully zeroed everywhere - including the H-alpha region, assume already telluric removed!), and then play further with the H-alpha part only and get them to a common mean for that area.
Then you should be able to generate difference spectra and see their velocities.
The reason is, the M star's continuum observed to be changing heavily, so all emission-type EWs in the absolute sense are "invalid". What is not invalid, to get the ratio of these EWs (like V/R).

What you could also do Olivier, to gather all eShels and do a similar metrics on the H-beta.

BTW seeing that H-alpha started to contact in the past 2 weeks, having CaII doublet affected this early is a surprise to me, seeking answers for this (outer disk also CaII ?) and need further spectra to confirm this fading due to its variability.

- Peter
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Re: VV Cep: Fe absorptions increase around Ca II doublet

Postby Ernst Pollmann » Fri Aug 18, 2017 3:19 pm

Hi Peter,
you wote:
… since H-alpha generated in the overall region (mostly outer), we might assume most of its region being unchanged on short term. What needs to be done, is removing a similar M continuum matching perfectly from the H-alpha spectra (to have continuum fully zeroed everywhere - including the H-alpha region, assume already telluric removed …
Then you should be able to generate difference spectra and see their velocities. The reason is, the M star's continuum observed to be changing heavily, so all emission-type EWs in the absolute sense are "invalid".


Olivier Thizy and I have had a similar discussion with Phil Bennet about that topic. He wrote:
There is some apparently random variation in Halpha emission on short time scales, but it going to take more work to get a result out of this.
In principle, you could subtract off the M supergiant component in VV Cep to recover the B star and its accretion disk (and Halpha, Hbeta…). But this is tricky because the spectrum won't exactly match. You would need to match fluxes at the red end (where you're comparing the supergiant flux in VV Cep to that of the mu Cep supergiant). But because of spectrum mismatch, the blue end will not exactly subtract and the residual left will probably by errors resulting from this mismatch.
And: don´t forget the stellar continuum part of the B star (my comment).
A better way would be use to coadded spectra from near mid-eclipse, but you'll have to wait to get these!

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Re: VV Cep: Fe absorptions increase around Ca II doublet

Postby Ernst Pollmann » Fri Aug 18, 2017 3:42 pm

Dear colleagues,
... the eclipse may have started... ??

With view on the variability of EW & PH in the attached monitoring we have to consider the following comment of Phil:
About the changing amplitude of the V component with time, I think this due to the effect of orbital motion. As eclipse approaches, the orbital motion becomes more and more tangential to our line of sight, and so the H-alpha emission peak moves more towards the systemic velocity (the radial velocity of the centre of mass of the binary system). This is because purely tangential orbital motion will have a radial velocity component close to that of the systemic velocity. Since the absorption feature (always) has a radial velocity close to systemic, what is happening is that more of the emission peak is moving into the window where the velocity is absorbed by the local circumstellar medium. That means there is less apparent change in the peak flux of the H-alpha feature: the peak flux ratio to the M star's continuum is presumably still varying as before, but the region of the peak is being absorbed by low velocity circumstellar gas.
vvcep_EW&PH.png
vvcep_EW&PH.png (110.32 KiB) Viewed 2597 times

Has the eclipse really started...??
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Re: VV Cep: Fe absorptions increase around Ca II doublet

Postby Robin Leadbeater » Fri Aug 18, 2017 5:49 pm

Changes in the spectrum could be very fast at the start of the eclipse. As a comparison, during the AZ Cas eclipse, most of the change in the spectrum in this region at egress took place in less than 6 days (unfortunately I was clouded out at the start of ingress).

azcas_20130305_20130311_Leadbeater.png


(The total ingress and egress time was much longer photometrically.)



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