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TV Aurigae S star: Molecular ZrO bands with SA-100

beginner dslr
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#1 mwr

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Posted 01 December 2019 - 09:36 AM

In S star spectra ZrO almost entirely replaces the TiO absorption. The chemistry behind this phenomenon is quite interesting and well explained in Richard Walker's excellent chapter on "Spectral Class S on the AGB" in his "Spectroscopic Atlas" Version 3.0 (2012). In this chapter he gives some valuable hints for the observation of S-class stars but he states at the same time that "the dissapointment is great for beginners, when in low resolution spectra, if at all, only weak signs of zirconium can be seen". I have chosen TV Aur (Class S 7.5 Zr 5) to test wether signs of Zr can be detected with my low resolution SA-100 setup (20 frames at  200 sec. each were stacked).

 

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Several band heads of ZrO were indeed detectable. To distinguish these ZrO bands from TiO bands, I have compared this spectrum with a spectrum of Mira (o cet; M-class), which shows intense TiO bands:

 

Folie2.JPG

 

Some ZrO bands of TV Aur are separated from the TiO bands of Mira and do not overlap. M- and S-class can thus clearly be distinguished.

 

To check for artefacts, I have compared my spectrum with a ProAm spectrum of TV Aur (ALPY 600) from J Foster https://britastro.or...ment=&plot=Plot

 

Folie3.JPG

 

 

Finally, I have determined the magnitude (v-T) of TV Aur and compared it with recently available  AAVSO data:

 

Folie5.JPG

 

Folie4.JPG

 

So my spectrum has apparently been recorded around the minimum of TV Aur.

 

Again, it would be interesting to see other SA-100 spectra of S-class stars (perhaps of the SX(e) class; the showcase object R Cyg is obstructed by the roof of my neighbour's house).

 

I have just ordered the SA-200, so this is probably the last post of my beginner SA-100 era.

 

Folie6.JPG


Edited by mwr, 01 December 2019 - 11:43 AM.

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#2 Organic Astrochemist

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Posted 01 December 2019 - 11:07 AM

Great job! It looks like zirconium is a much easier s-process element to detect than barium.

At some level I guess I don’t understand why sodium and calcium produce such deep wide lines compared to other atomic metals. Why are the Ca II H and K lines so much bigger than Ca I lines, for example? I don’t think it can only be a question of abundances.

With molecules, the peaks are wide due to molecular motions and the strength of the peaks corresponds more closely with the abundances. That’s why we see more TiO in M stars, ZrO in S stars and more CN in carbon stars and lines are strong and wide enough that the Star Analyzer can distinguish these. So these probably are excellent targets for the Star Analyzer.

Edited by Organic Astrochemist, 01 December 2019 - 11:12 AM.


#3 mwr

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Posted 01 December 2019 - 11:58 AM

Great job! It looks like zirconium is a much easier s-process element to detect than barium.

 

Thanks! Barium was a real flop with the SA-100 and Zirconium is definitely better to detect.

 

 

That’s why we see more TiO in M stars, ZrO in S stars and more CN in carbon stars and lines are strong and wide enough that the Star Analyzer can distinguish these. So these probably are excellent targets for the Star Analyzer.

I've come to the same conclusion: Rotational und vibrational line broadening are a SA-100 user's best friends.


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