Near-UV observation

VV Cep 2017-2019 Campaign
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Near-UV observation

Postby Paolo Berardi » Mon Aug 31, 2015 10:06 pm

An attempt to capture the near-UV spectral region around Calcium H and K lines with R~4000 on 27.863 aug 2015. In this region the spectrum should be dominated by the hot companion. I don't understand if what appears to be emission lines is actually the continuum between absorption lines... This appears to be the case of space between Ca II H (3968.5A) and H-epsilon (3970.1A).

Image

I also show the entire captured spectral range. It should be noted that, due to chromatic aberration of collimator, both ends of spectrum are moderately unfocused and the resolution decreases:

Image

The same spectral interval for Vega:

Image

Paolo
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Re: Near-UV observation

Postby Ernst Pollmann » Tue Sep 01, 2015 7:12 am

Dear Paolo,
following the investigation of Hack et al., with our modern spectrograph nowadays we should be able too, to try on the way of spectra differences, like SP(M+B) - SP(M), to find out a more clear spectroscopic signature of the B component, particularly in the near UV area. The pure SP(M) is easy to receive during the eclipse.
What's your opinion ?

Ernst

By the way:
by using the reference star µ Cep, it might be possibly already now.
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Re: Near-UV observation

Postby Robin Leadbeater » Tue Sep 01, 2015 3:07 pm

Very Interesting Paolo,

Here is the same region for the similar system AZ Cas which I followed through eclipse.
http://www.threehillsobservatory.co.uk/ ... tra_43.htm
My resolution was not as high (R~1500) as AZ Cas is much fainter but outside eclipse the spectrum looked much more like a pure hot star with only faint M star features and no obvious emission. I think emission lines are quite common in the spectra of red giants though.

Robin
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Re: Near-UV observation

Postby Paolo Berardi » Tue Sep 01, 2015 9:31 pm

Ernst, Robin, thank you for your comments. Removing the M spectrum from M+B is very interesting (we should see the hot star spectrum). Following the Ernst advice I'm trying to observe mu Cep with the same setup. No sign of emission (or "false emission" between absorptions) is visible in the first frames:

Image

I hope to complete a valid spectrum, many clouds in the sky here...

Paolo
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Re: Near-UV observation

Postby Thilo Bauer » Wed Sep 02, 2015 6:13 pm

Paolo,

this is very interesting to see the UV part in more detail. Having the plots "normalized" to equal width of the uploaded images probably would it make easier to compare spectral portions and wavelength identification of lines of alpha Lyr and VV Cep.

Ginestet and Carquillat (2002) so far noted the following about spectral classification in this wavelength range (3800-4800 A):

"Nevertheless, the various spectral classifications published for a given star are often very different, for both the hot and the cool components, and, for the latter, the determination of the luminosity class was a further difficulty. Moreover, in the conventional spectral domain of the MK classification (3800–4800 A ̊ ), the spectra of the two com- ponents appear inextricably tangled. Consequently, the spectral classifications of these binaries carried out in this spectral domain will inevitably be erroneous: the hot components will be classified as too late and the cool com- ponents as too early." - Ginestet and Carquillat, 2002. The Astrophysical Journal Supplement Series, 143:513–537

I think "different" spectral classification found for the VV Cep system is due to its variability during orbital phases and probably the stars and the shell (disk?) themselves.

The published work so far tends to recommend to observe both, the near UV (~3800-4800 A) and IR (~8000–8900 A) part of the composite spectrum.

Finally the authors noted for VV Cep:

"HD 208816.—VV Cep. No appropriate standard for subtraction."

Ernst, what do you think? Seems not that easy.

BTW: The UV part for me is included with Alpy, while the IR (~8000–8900 A) will be excluded due to geometry of optics and mean wavelength of the grism. Maybe the IR part is better for observers using Lisa with IR pack.

Thilo
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Re: Near-UV observation

Postby Ernst Pollmann » Wed Sep 02, 2015 8:22 pm

Hi Thilo,
in order to avoid to talk nonsens, I would like to see at first the result of spectra subtraction by Paolo.
In the meantime I tried also in that way with ELODIE (OHP) spectra of VV Cep and µ Cep, to isolate the spectrum of the B component. But without any success, because these spectra began too late at 400 nm.

Ernst
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Re: Near-UV observation

Postby Paolo Berardi » Wed Sep 02, 2015 9:15 pm

Hi Thilo, thank you for the answer. This is the first time I observe VV Cep. Surely it's not easy for me to decipher the spectrum...

I just try to rescale the mu Cep spectrum (the star I observed yesterday as advised by Ernst) to approximately matching the VV Cep cold star spectral features (in the 4000-4100A interval):

Image

then I subtract it from VV Cep spectrum:

Image

The result shows some emission lines and reverse P-cygni for Balmer lines with a complex profile on H-epsilon and Ca II H lines (around 3970A). I don't know how much of this is real and what might be artifacts.

Please note that the spectrum is properly focused only in the central part (for chromatic aberration of spectrograph doublet).

The comparisons between two-dimensional spectra of VV Cep and mu Cep (central part of spectrum):

Image

Paolo
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Re: Near-UV observation

Postby Robin Leadbeater » Thu Sep 03, 2015 10:21 am

I did something similar with my AZ Cas data but at H alpha which was quite successful at removing the cool star component
viewtopic.php?f=25&t=416
I used a UVES library spectrum of a similar star, filtered to match the FWHM of the lines in the AZ Caz spectrum.
(Note this was done during ingress when the light from the hot star was being filtered by the cool star atmosphere so not a direct sum of the two components)

I will dig out the UV end spectra outside and during eclipse and try subtracting them from each other. Curiously the post eclipse AZ Cas spectra seemed to show a larger cool star contribution compared with pre eclipse. Perhaps there is some remnant of the cool star outer atmosphere extending further in that direction which was still filtering the hot star spectrum?

Robin
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Re: Near-UV observation

Postby Ernst Pollmann » Thu Sep 03, 2015 2:03 pm

Dear Paolo,
thanks for sending me your subtraction spectrum.
After a rough line identification, I re-calibrated the spectrum with the labeled lines and its wavelengths. The calibration accuracy (RMS) has been (+/-) 0.35 Angstr./pix.
It seems, that you has been able to "isolate" several members of the higher Balmer sequence. But the quetion is, whether these lines are coming from the B component, or still from the accretion disk.
Nevertheless, with this sort of subtraction spectra it will be possible along with Hbeta and Halpha, to observe the temporal sequence of the eclipse.

Ernst
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Re: Near-UV observation

Postby Ernst Pollmann » Thu Sep 03, 2015 4:01 pm

Dear Paolo,
as addition here in instructive plot of Möllenhoff & Schaifers (A&A, 94, 333-337) of the 1976-78 eclipse.

Ernst
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