VV Cep: Fe absorptions increase around Ca II doublet

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Moderator for this forum: Ernst Pollmann
Ernst Pollmann
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Re: VV Cep: Fe absorptions increase around Ca II doublet

Post by Ernst Pollmann »

Hi James, Robin, Peter, Andrew,
could you be so friendly to write here some words regarding to the aims of observation within that wavelength area?
To read your experimental effort is one thing, but what is the background?
Thanks in advance !

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

Post by Peter Somogyi »

Hello Ernst,

> ... what is the background?

My reasons for this (2400/mm highest resolution + 35 micron):
- unique possibility at this brightness (won't come back soon); I did read Robin's effort on AZ Cas on this forum (locked) and VV Cep looks very similar, but magnitudes brighter
- blue/UV end changes the most
- want to see if there's any weak effects before/after eclipse (eclipse itself may be too hard)
- measure CaII velocities, EW
- EWs of other absorptions (Fe, Ti)
- compare H-alpha with its blue variants
- any correlation of the above with Bmag/Umag, and H-alpha variation (shooting that one, too)
- already have compareable material from 2015, don't loose the serie

Of course, I'm only a speculative amateur here, not requesting any follower, and not having any confirmed professional contact for this.

Cheers,
Peter
Robin Leadbeater
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Re: VV Cep: Fe absorptions increase around Ca II doublet

Post by Robin Leadbeater »

Hi Ernst,

The eclipse can be followed in this region independent of the circumstellar material. This will provide eclipse timings for other measurements, eg of the circumstellar material at H alpha. (Which already appears to be well covered by other observers)

Cheers
Robin
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Ernst Pollmann
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Re: VV Cep: Fe absorptions increase around Ca II doublet

Post by Ernst Pollmann »

Hi Peter and Robin,
thanks a lot for your explanations. That makes the intention of your observations more transparent.
@ Robin:
I can´t wait to see that how it works out!

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

Post by Ernst Pollmann »

... let me add the following description of Phil Bennet some month ago:

In order to observe step by step the disappearance also of the higher lines of the Balmer series until the accretion disk is totaly disappeared, one should take the wavelength section below 4000 A until 3800 A, as it was done by James Foster. The advantage of this spectral section would be that one 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 Balmer lines of the disk until approx. to H10 and the important CaII lines H & K!! While the entire disk eclipse one would have the rare opportunity, starting with the disappearance of the disk line Hα until to H10 and the corresponding time marks, to analyse the disk extension.
But the first indicator of the beginning of the disk eclipse will be the decreasing of the Hα EW (first contact), because this emission line represents the outer diameter of the accretion disk.

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

Post by Peter Somogyi »

Dear Ernst,

Do we have the calculated time interval in days to observe this contact with the accretion disk?
Asking it for planning, we might be a bit few for this (call for other observers?) - maybe I could do a 2nd observe below 3850A when time is critical, for example - question if it's worth in my setup.
Imagine we typically observe every 1-2 weeks on average (some weeks can be out due to weather etc..., I am also weekend oriented), and there may be priority conflicts with other stars.

I'm planning to further use the 2400/mm grating, as I read earlier docs + links the CaII 3933A is a classical diagostics and requires highest resolution, metallic lines need also good resolution to get their EW without contamination, and I am speculating about seeing absorptions earlier than the H-alpha contact (question whether the actual H-alpha EW variation allows to detect the chromosphere or other gases early enough).

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

Post by James Foster »

To: Ernst,

RE:"In order to observe step by step the disappearance also of the higher lines of the Balmer series until the accretion disk is totaly disappeared, one should take the wavelength section below 4000 A until 3800 A, as it was done by James Foster."

I'll remember to send you my Cak observation from this last 10 days to you......will be on a small hiatus pending the acquisition of a LiHiresIII i just ordered with the 1800 l/mm grating.

James
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Ernst Pollmann
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Re: VV Cep: Fe absorptions increase around Ca II doublet

Post by Ernst Pollmann »

Dear Peter,
relating to the higher Balmer lines until H10 and the Ca II H&K there are information in the publikation of M. Hack et al. at Astron. Astrophys. Suppl. Ser. 95, 589-601 (1992). They describing the profiles of that lines versus phase measured at the observatorium OHP during the 1977 eclipse.
With the time of phases in Fig. 7 of that paper there is a chance, along with the period of 7430 d (Wright 1977) to calculate the contact times until the accretion disk is totaly disappeared.
Hope that helps...

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

Post by Peter Somogyi »

Ernst, thank you it was a good reading, however I don't think Figure 7. had enough time resolution.
Based on asxiv: 1102.5198 ("...AZ Cas and VV Cep") Fig. 1 U-curve, the 2 transitions between high and low U-mag I can read by eye should be like a 0.01-0.02 phase.
0.02 * 7430 = 148 day = like a 4.5 month, or maybe half of it (if want strong effect), very roughly.
So then we should take like 2 spectra per month, ideally. That fits well.

Meanwhile I've found a drastic increase of Ti II 3900, 3913 absorptions, easy to see via division of my spectra.
This change is consistent and stable, but not sudden: decreasing from month to month slowly started this year.
Will come up with an EW measure soon, once established a continuum rectification in this region.

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

Post by Peter Somogyi »

Finally, managed to reduce Alp Ori (taken last year), by norming to 1, then subtract 1 (0 average), then multiply by 1/6 (0.1666), added +1, then used this spectrum (shifting by correlated velocities) to divide all the normal spectra. Tried to use a larger ratio than 1/6, but met with less straight continuum (all used ref.star 7 cep, even Alp Ori itself corrected).

Having Alp Ori reduced, generated now this graph (contninuum rectified to 1 with a lengthy selection of tiny regions) using iRAF/specplot:
serie_all_reduced_alpori_cmpr.png
Again, all spectra are normed to 1, having step 1 in between.

EWs of TiII 3900, 3913 increased from 0.1 to 0.5 with a very high variance (0.15), unable to determine the gradient. Better to look at the above graph how the lines widening.
Also made +2 weekly shots in the meantime (and, I won't be able observe for 2-3 weeks from now).
At least, some trends can be read, by theory - inserting shorter periods are helpful to see variations, I believe CaII doublet + H5, H6 are varying on a very short timescale (few days).

Of course, there are lots of details that could be done differently, and have measurements of M component radial shifts (40 km/s common difference - with a +/- 7 km/s variance) to do the reduction at the lowest error. Only the fixed chosen constant of 0.1666 that is a very rough guess (based on material from 2015) and would be very tricky to measure per-spectra.

Enjoy!
Peter
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