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Barium star with SA-100

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#1 mwr

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Posted 21 November 2019 - 05:16 PM

The Barium stars have attracted recently my attention because they had remained somewhat of an astrophysical enigma for several decades: They are Population I G-K giants that have enhanced abundances of carbon (G band of CH molecules) and s-process elements (notably lines of Ba II and Sr II) as prominent anomalous features. Today it is clear that the origin of these anomalous abundances in barium stars can be explained by the discovery that they are likely all members of binary systems. A mass exchange has taken place and is responsible for the detected anomalous abundances.

 

I have tried to record a spectrum of the Barium star HD 223617 using the SA 100. Ba and Sr lines could not be detected due to the low resolution. However, a weak CH band at 4380 A and the weak G band at 4300 A could tentatively be detected. As positive control for these CH bands I have recored the carbon CH star HD 5223, as negative control the carbon star Z Psc (showing mainly C2 bands).

 

Folie2.JPG

 

Folie3.JPG

 

Reference spectra of these stars are shown below:

 

Folie1.JPG

 

I haven't found so far low resolution spectra of Barium stars in this forum or in the BAA-spectroscopy database and it would be interesting to see some ALPY or SA-200 spectra for comparison. 

 

 


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#2 mwr

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Posted 23 November 2019 - 11:32 AM

 

I haven't found so far low resolution spectra of Barium stars in this forum or in the BAA-spectroscopy database and it would be interesting to see some ALPY or SA-200 spectra for comparison. 

After some literature search I have finally found a publication by Charles Gow (1976) (http://articles.adsa...000993.000.html) which contains some low resolution spectra of barium and CH carbon stars. The reported 30-A resolution in this publication is quite similar to the resolution of my SA-100 setup and a comparison of the spectra shows a good match for the C2- and CH-bands (the spectrum of the Barium star with the SA-100 was rectified using VSpec):

 

Ba_star_vs_lit.jpg

 

Anyway, other low resolution spectra of Barium stars for comparison are highly appreciated.



#3 Organic Astrochemist

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Posted 24 November 2019 - 01:11 AM

Thanks for mentioning Barium stars. I read a little bit by McClure He said that the carbon features aren't directly correlated in strength with the s-process element lines and as you say it's hard to see that Ba II line at 455.4 nm. But it is cool to think that these are Population I stars.

 

I decided to check out 22 Piscium because it is relatively bright and should have good Ba abundance (classified as Ba1) 

 

I had a really bad night with lots of high clouds. I did this quick check of nearby 18 Psc, which looked all right.

18 Psc with A7V.png

 

I could see the G and CH bands you talked about in 22 Psc, but it wasn't a great spectrum. A little noisy. Maybe focus wasn't great. All in all I think barium stars are a difficult target and I'll stick with easier things.

22 Psc with K4III.png

 


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#4 mwr

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Posted 24 November 2019 - 07:09 AM

 

I could see the G and CH bands you talked about in 22 Psc, but it wasn't a great spectrum. A little noisy. Maybe focus wasn't great. All in all I think barium stars are a difficult target and I'll stick with easier things.

attachicon.gif 22 Psc with K4III.png

Thanks for giving it a try and posting it ! Although the characteristic Ba II-line at 455 nm is quite weak, I think you have picked up the Ba II-line at 650 nm close to H alpha:

 

Ba_OrgA.jpg

 

In my Ba star spectrum it is also visible, but I wasn't sure about its identity. 

 

Ba is an "s-process" element with an atomic number of 56 and far beyond Fe ( atomic number 26)  in the periodic system. For me, it is remarkable to detect it with the SA-100 and it prompted me to dive a little bit deeper into the slow neutron capture process  in stars - beautiful observational astrophysics!



#5 Organic Astrochemist

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Posted 24 November 2019 - 03:13 PM

The line at 649.7 nm is a blend of not only Ba II but also Ti, Fe and Ca. It is supposed to show anomalous values for barium stars, but not with my system: the ratio between H-alpha and this line were the same in this spectrum of 22 Psc and the K4III reference.

Even the area around the 455.4 nm Ba II line looks pretty crowded.

My personal experience has been that it’s not always easy to tell what will make a good target for the SA 100, that is, one that is both interesting and that will afford sufficient details and precision in the data.

#6 mwr

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Posted 25 November 2019 - 07:08 AM

My personal experience has been that it’s not always easy to tell what will make a good target for the SA 100, that is, one that is both interesting and that will afford sufficient details and precision in the data.

That's why I appreciate the "Observational Astrophysics" section so much: A lot of interesting posts that give valuable hints for good SA-100 targets. Sometimes the results, that I could achieve,  are surprisingly good, sometimes rather disapointing. And it's always interesting to discuss the results with critical peers ;-)


Edited by mwr, 25 November 2019 - 10:46 AM.



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