Attempting an SA100 spectrum on 2Lyr and 4Lyr/5Lyr

[SteveBz]

So this is the second, dimmer star, 7 Lyr using the same response calibration as before. I've tried to show it on the same chart as the previous star (6 Lyr).  I've scaled as per Merlin66's suggestion for 370-750, but I think I'll go with nm - in case I want to get published 😄:

The stars themselves don't look so different, but the spectrum for 7 Lyr is very much dimmer than 6 Lyr as you can see.

I think the spectra are probably not high enough quality to make any determination about how similar the stars were or were not.

Do you think I should have (or could have) taken a second longer exposer to make 7 Lyr more readable and let 6 Lyr saturate? Maybe I'll try next clear night.

What do you think?

Kind regards

Steve.

 

[robin_astro]

I suggest scaling them so that the intensity is 1 at the same wavelength which makes them easier to compare independent of their brightness. (550nm is commonly chosen). 

 

Edited September 10, 2021 by robin_astro

[robin_astro]

7 Lyr is straightforward. It is an F0v star, a main sequence star hotter than the sun (G2v) but cooler than Vega (A0v) for example.  Its spectrum is dominated by strong Hydrogen Balmer lines. You could try overlaying the F0v spectrum from the Pickles library

6 Lyr is much more complex, it is a binary so a mix of spectral types and at least one of the components has an unusual  metal composition which further confuses the classification (ie the spectral classification is different depending on which lines you look at)  so is classified for example as kA5hF0VmF3

To see these features though you would need a much higher resolution spectrograph than the Star Analyser and  overall, Hydrogen Balmer lines again dominate your spectrum.

To see the published classifications for a particular star I can suggest Brian Skiff's huge Catalogue of Stellar Spectral Classifications"

http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/mk

Note though that it is only possible to make an approximate spectra classification at the resolution of these spectra. To do this accurately needs higher resolution and some specialist knowledge

Cheers

Robin

Edited September 10, 2021 by robin_astro
clarification of definition Am type classification

[robin_astro]

Note  that while zeta Lyr is visually a double star it is not necessarily a binary pair. To be a binary the two have to be gravitationally bound ie in orbit round each other

Robin 

Edited September 10, 2021 by robin_astro

[SteveBz]

10 hours ago, robin_astro said:

To see the published classifications for a particular star I can suggest Brian Skiff's huge Catalogue of Stellar Spectral Classifications"

http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/mk

Note though that it is only possible to make an approximate spectra classification at the resolution of these spectra. To do this accurately needs higher resolution and some specialist knowledge

Cheers

Hi Robin,

This is very nice. It seems to have the classification.  Does Vizier also have the actual spectra?

Kind regards

Steve.

[robin_astro]

1 hour ago, SteveBz said:

Does Vizier also have the actual spectra?

If you follow the references in Skiff's catalogue you will find how the classification was made. In some cases you might find a spectrum but in general the classification just follows from the features seen in the spectrum. Also you can do general research on a particular star by following up the references found by looking it up directly in SIMBAD eg

https://simbad.u-strasbg.fr/simbad/sim-id?Ident=6+Lyr

Gray and Corbally "Stellar Spectral Classification" is the "bible" on how to do spectral classification but more accessible for amateurs is perhaps Richard Walker's excellent "Spectral Atlas for Amateur Astronomers"  

A set of spectra of "normal" stars though can be found in the Pickles library found in the various software, which is why I suggested overlaying some on your spectra to see if you can find the  best match

7 Lyr should be a good match to F0v 

6 Lyr is odd though. This is because it is an Am star. 

https://en.wikipedia.org/wiki/Am_star

The classification kA5hF0VmF3 means it looks like an A5 star based on the strength of  the Ca II K line but F0V based on the strength of the Balmer lines and F3 based on the strength of other metal lines.  At your resolution I expect it will look like an F0v so similar to 7Lyr with similar strength  Balmer lines.

Spectroscopic classification is not a big area of interest for amateurs though as it has mostly already been done. Most amateur research work in spectroscopy is on stars that are unusual in some way or vary in interesting ways. 

Cheers

Robin

[SteveBz]

12 hours ago, robin_astro said:

Note  that while zeta Lyr is visually a double star it is not necessarily a binary pair. To be a binary the two have to be gravitationally bound ie in orbit round each other

Robin 

This is also a good point.  However, it seems likely to me that they are indeed a bound pair.  On the positive side they are at about the same distance with a parallax of about 20 mas or about 50 pc.  They also have similar proper motions in the place of the sky of about 32 mas/yr.  Sadly the Gaia DR3 radial velocities have not yet been published and they don't have a DR2 radial velocity (actually, I think they're both on Hipparcos at about -25 km/s).  Here are the details:

Lyr 7: magnitude 5.6, Px 20.66, PM 33.5
Lyr 6: magnitude 4.3, Px 20.64, PM 32.2

As I'm sure you've seen, you can find these details easily on the Aladin website at:

Aladin Lite (u-strasbg.fr)

12 hours ago, robin_astro said:

6 Lyr is much more complex, it is a binary so a mix of spectral types and at least one of the components has an unusual  metal composition

Where did you get this from? As I don't imagine it was my spectrum 😢 

I'm going to run longer exposures next time to see if I can get the companion star's spectrum more clearly.

[robin_astro]

If you are interested generally in  the sort of research work amateurs are doing in spectroscopy then I can recommend browsing the ARAS forum. This is mostly with equipment more sophisticated than the Star Analyser though

https://www.spectro-aras.com/forum/

For a wide ranging overview of everything spectroscopic from an amateur perspective explore Christian Buil's website

http://www.astrosurf.com/buil/index.html

A good source of amateur spectra is the BAA database

https://britastro.org/specdb/

and there are a number of other spectroscopy related resources on the BAA website here

https://britastro.org/node/19378

A good overview of an interesting range of targets for low resolution spectroscopy, many accessible with the Star Analyser is Francois Teyssier's "Low resolution spectroscopy observer's guide" from this page

http://www.astronomie-amateur.fr/

 

Cheers

Robin

[robin_astro]

4 minutes ago, SteveBz said:

This is also a good point.  However, it seems likely to me that they are indeed a bound pair.

They may well be but I stand by my original statement, unless you have proof of orbital motion. SIMBAD describes zet Lyr  as  a double or multiple star

[robin_astro]

9 minutes ago, SteveBz said:

Where did you get this from? As I don't imagine it was my spectrum 😢 

I'm going to run longer exposures next time to see if I can get the companion star's spectrum more clearly.

From the classification in SIMBAD. I see it even has its own wikipedia page https://en.wikipedia.org/wiki/Zeta1_Lyrae

Your signal/noise is already very high so longer exposures will not give you any more detail. You can already see the characteristics  of a hot star eg F0 in your spectrum but you need a higher resolution spectrograph to do detailed spectroscopic classification. Your Star Analyser setup is not suitable for this sort of work.

Robin

 

[robin_astro]

8 minutes ago, robin_astro said:

I'm going to run longer exposures next time to see if I can get the companion star's spectrum more clearly.

I am not sure the 6 Lyr binary companion is even visible in the spectrum. According to the wikipedia page it is a single line spectroscopic binary, ie it was discovered to be a binary from the periodic doppler shift in the lines in the  primary star spectrum. A literature search though might throw more recent light on this. It is very unlikely you will be able to untangle the components in a  low resolution star Analyser spectrum though

Edited September 11, 2021 by robin_astro

[robin_astro]

There is an extremely high resolution professional spectrum of 6 Lyr in the ELODIE archive

http://atlas.obs-hp.fr/elodie/fE.cgi?ob=objname,dataset,imanum&c=o&o=6 lyr

Cheers

Robin

[SteveBz]

1 hour ago, robin_astro said:

At your resolution I expect it will look like an F0v so similar to 7Lyr with similar strength  Balmer lines.

Yes, that's what I though it was.

[SteveBz]

52 minutes ago, robin_astro said:

Your Star Analyser setup is not suitable for this sort of work.

That's sad to hear.

In fact I'm doing a project with a researcher from a Mexican university on the orbits of binary stars.  As an amateur astronomer, I wanted to see if I could follow up any of it with my scope.  Actually, I find the shots of the binary stars through an amateur scope are every bit as aesthetically attractive as the professional ones in Aladin etc, although distant stars are more visible and more point-like in the professional ones.

I don't think I can hold a torch to the professional spectra though.  I do have a 3d printer, which I'm about to dust off, but it maybe easier to go down the Alpy route.  I'm just having difficulty justifying the extra costs involved 😅

Thanks for your comments.

Kind regards

Steve.

[SteveBz]

55 minutes ago, robin_astro said:

I am not sure the 6 Lyr binary companion is even visible in the spectrum. According to the wikipedia page it is a single line spectroscopic binary, ie it was discovered to be a binary from the periodic doppler shift in the lines in the  primary star spectrum. A literature search though might throw more recent light on this. It is very unlikely you will be able to untangle the components in a  low resolution star Analyser spectrum though

It may well be a hierarchical binary with one or both of the stars having a dimmer or closer companion.  Just to be clear, 6 & 7 Lyr are the stars that I'm speculating are close enough to be a binary pair.  It may be that 6 Lyr also has a further close companion a few AU from it that don't appear in Gaia and that is what is showing in the 6Lyr spectrum.  Gaia DR2 policy at the time was anyway not to provide radial velocities for spectroscopic binaries because the velocities would be unreliable, ie +/- the orbital velocity around the other star. So this may be why I can't find one for it.  

Regarding the spectrum you directed me to:

Is that not just noise?  Or is that some sort of complex metalicity?

Kind regards

Steve.

[SteveBz]

1 hour ago, robin_astro said:

There is an extremely high resolution professional spectrum of 6 Lyr in the ELODIE archive

http://atlas.obs-hp.fr/elodie/fE.cgi?ob=objname,dataset,imanum&c=o&o=6 lyr

Cheers

Robin

Actually, that's a fantastic resource. I shall look into it more.

[robin_astro]

1 hour ago, SteveBz said:

s that not just noise?  Or is that some sort of complex metalicity?

No not noise (The SNR is given as 320 which is very high.) If you zoom in you can see the details of the lines. The spectrum is not particularly complex. Even a normal F0v star will show lots of metal lines though they become stronger at lower temperatures eg in G an K spectral types. Here is an F0iv star from UVES POP, another source of very high resolution spectra 

https://www.eso.org/sci/php/tools/uvespop/bin/readspectra.cgi?wave_LO=3060&wave_HI=10000&out_FORMAT=gif&star_ID=19319&sa=Plot

Amateurs are capable of high resolution spectra on bright objects like this though. For example take a look at recent spectra by Joan Guarro Flo in the BAA database using an echelle spectrograph built by him from a design by Tim Lester, another amateur. eg here is symbiotic star CQ Dra

https://britastro.org/specdb/data_graph.php?obs_id=10258

again, zoom in to see the detail

Cheers

Robin

Edited September 11, 2021 by robin_astro

[robin_astro]

7 hours ago, SteveBz said:

It may be that 6 Lyr also has a further close companion a few AU from it that don't appear in Gaia and that is what is showing in the 6Lyr spectrum.

Yes 6Lyr definitely  is a known binary with a close secondary (The orbital period is just 4.3 days) but the secondary is not seen in the spectrum, most likely because it is much fainter. We know it is a binary because the lines in the spectrum from the primary move back and forth on a 4.3 day period. This is known as  a single line spectroscopic binary. See the wikipedia page  for the reference to the 1910 paper

Cheers

Robin

[robin_astro]

6 Lyr is also one of the stars in  the MILES catalogue of stars (referenced on my web page on flux calibration.) Here it is in the database included with ISIS software. 

[SteveBz]

20 hours ago, robin_astro said:

Yes 6Lyr definitely  is a known binary with a close secondary (The orbital period is just 4.3 days) but the secondary is not seen in the spectrum, most likely because it is much fainter. We know it is a binary because the lines in the spectrum from the primary move back and forth on a 4.3 day period. This is known as  a single line spectroscopic binary. See the wikipedia page  for the reference to the 1910 paper

Cheers

Robin

So it's a hierarchical system. 6 Lyr is the brighter one and it has a close invisible companion only detectable because of it's variable effect on the spectrum.  7 Lyr is fainter and may be a wide companion for 6 Lyr.  So the nice strong spectrum I have is for the brighter star (ie 6 Lyr), but I don't have the resolution to show the detail you showed earlier.  Do you think I could improve the spectrum I got, or is that pretty much as good as it gets with the SA?  I was pretty sure you had some better resolved ones.

Kind regards

Steve.

[robin_astro]

18 hours ago, SteveBz said:

Do you think I could improve the spectrum I got, or is that pretty much as good as it gets with the SA?  I was pretty sure you had some better resolved ones.

Careful focusing on the specific region of interest and choosing targets at high elevation and nights with better seeing can help but I think that is pretty typical for the Star Analyser used in the conventional way. I use other spectrographs for high resolution work. There are examples using the Star Analyser with combinations of wedge prisms at very high dispersions to get high resolution but these are either objective grating setups (ie mounted in front of the telescope/camera lens) or are high focal ratio setups which reduce the aberrations that the converging beam produces. but these are tricky to use and calibrate compared with the standard Star Analyser setup or conventional slit spectrographs.   See the experiments by Uwe Zurmuhl for example in "Spektrum" editions 51 and 55

https://spektroskopie.vdsastro.de/journal-30.html

Resolution is not the only parameter in spectroscopy. You can go much fainter at low resolution  and there are lots of interesting targets for the simple Star Analyser including WR stars, bright novae and supernovae and even quasars. 

I would say attempting to see the difference between two almost identical spectral types (6,7 Lyr) which will only show the subtlest of differences is not the best place to start though.  Perhaps try Albireo instead. The hotter star A8v star would make a good calibration standard and is interesting as it is also a Be star. (Can you detect any H alpha emission line?) and the cooler K2ii star will have strong metal lines so would be a good test of how much you can resolve the features)

Cheers

Robin

[SteveBz]

11 minutes ago, robin_astro said:

Resolution is not the only parameter in spectroscopy. You can go much fainter at low resolution  and there are lots of interesting targets for the simple Star Analyser including WR stars, bright novae and supernovae and even quasars. 

Nice.  I'll look into that.  Actually, I'm quite pleased with the results and the setup.  I don't really want to go more complex at this stage. I automated the slide-off roof on my shed at the weekend with an old garage door opener I found on ebay, which makes things a lot easier.

As I mentioned before the reason I'm doing all this is that I'm also doing a project on binary stars with a colleague.  Theory is great, but actually looking at stars really helps to keep it real.  Even just chatting here with you about Zeta Lyrae brings clarity to the issue.  I saw the description 'binary star' on Zet01 Lyr, but not Zet02Lyr and I thought oh, they missed one, but your clarification about the 4.3 days and the spectral binary really helped shed light on the situation for me.

So it's all very well being theoretical, but looking at it in real life really brings a new dimension to ones understanding. 

Kind regards

Steve.

[robin_astro]

Steve,

If you want to see a binary in action in "real time" with the Star Analyser an eclipsing binary like U Cep is a good target.  Here by Mike Harlow with an objective prism but the Star Analyser should also show the changes in the spectrum well 

https://britastro.org/node/19199

Cheers

Robin