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S617 triple star. Work to do...

MattJenko

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MattJenko

MattJenko

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Here is an attempt at getting the spectrum from a double star. This was a decent double available a couple of nights ago from my Essex garden. 

This is the double star S617 in Leo. It is a nice orange and white/blue affair with a separation of 35", which makes it just about possible to split into distinct spectrums (spectra?) that can be processed. The brighter orange star is mag 6.2 and is a spectroscopic double in its own right, but far too close for me to know or work out (yet?). The visual companion in the system is a hotter, but dimmer mag 8.7. They are 260 light years away.

The spectrum graph shows the 2 calibrated spectra with the same scale and overlaid, so you can see the differences. The red graph is the dimmer blue star :) and I had to do 60 sec exposures to try and get a decent spectrum, but it was still very dim and noisy as a result, but you can see that it peaks more to the blue side than the red line spectrum of the brighter orange star, which has all kinds of absorption lines, mainly the Hydrogen ones. Both spectrum were from the same exposure, which means in future, if I want to go down as far as mag 8+, I will need to concentrate on that alone, and do the brighter companions separately.

All taken with an AA115 with an Atik 414ex. RGB is 20 x 30 secs each RGB and then 120 x 60 sec exposures with the SA200 to trry and eek out that faint detail. There is work to do to get better and much to learn, but this kind of thing is fun!

 

S617_RGB.jpg

Spectrum.jpg

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robin_astro

robin_astro

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Very nice !   I had a look in Skiff's database to see what classification these two stars had been given.

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

The brighter one (HD 94363) is variously classified around late G / early K which agrees with your spectrum but there is only one classification documented for the fainter companion (BD-01 2458) as G0v which is clearly incorrect from your spectrum or the visual appearance so it could be interesting to try to get a less noisy spectrum.

Cheers

Robin

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MattJenko

MattJenko

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On 3/20/2017 at 01:34, Thalestris24 said:

Matt - now you've gone and got me interested in having a go....

Louise

There is a lot going for it. Entry level is cheap, as in just for the grating, given an existing imaging kit, and you don't need long exposure times to get the spectra, so no multi session, data gathering marathons. Whats not to like! I struggled with the various software options until I found RSpec, which is not free, but again, cheap in relation to astro imaging as a whole, but you may find the free options more accessible than I did. It is also ridiculously fascinating!

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Merlin66

Merlin66

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Louise,

100mm is too great a spacing with the grating.

Using the DSLR means the absolute minimum available would probably be at the front of a nosepiece connected to the T2 adaptor on the DSLR - this is probably around 80mm.

In this case I think a SA100 would be a better option.

I think you need around 40-60mm spacing for the SA200.

 

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Thalestris24

Thalestris24

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9 minutes ago, Merlin66 said:

Louise,

100mm is too great a spacing with the grating.

Using the DSLR means the absolute minimum available would probably be at the front of a nosepiece connected to the T2 adaptor on the DSLR - this is probably around 80mm.

In this case I think a SA100 would be a better option.

I think you need around 40-60mm spacing for the SA200.

 

Thanks! At the moment I have a reducer attached to the dslr so the filter drawyer has to go in front. I could use a non-reducing ff which would potentially allow a different mounting arrangement for the grating. Alternatively I could use the qhy8l ccd instead. I do have a lot of skyglow though so that might be limiting.... Not to mention near permacloud this year - so far :( 

Louise

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Merlin66

Merlin66

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This is my grating set-up...

A 200 l/mm (Baader) in a Neumann filter drawer, the ol' Meade flip mirror at the front to locate the target in the frame and a 10mm T thread spacer at the rear to mount the ATik 16ICs imaging camera.

 

grating arrangement.JPG

grating arrangement4.JPG

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MattJenko

MattJenko

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My SA200 is pretty close to be honest and under the 40mm mark. I have an Atik 414ex, which has a 13mm spacing from front to sensor, and then that screws directly into the filterwheel, so the total distance is about 25-30mm. This gives a ok rating from the calculator and it's estimated dispersion agrees with what I ended up calibrating my resolution to being of around 11 A/pixel.

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Thalestris24

Thalestris24

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Thanks guys. Looks like you're using small chip cameras and no field flatteners....  But I imagine with the 1.25" Star Analyser you'd only be concerned withe central part of the fov anyway? The Baader version doesn't seem to be available anymore?

Louise

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robin_astro

robin_astro

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Hi Louise,

Using the Star Analyser as  an objective grating in front of a DSLR lens is an interesting arrangement as it generally gives  a sharper  spectrum compared with mounting behind a telescope. It is good for some extended objects too like comets for example as they appear star like so the spectrum can be recorded. It is only for brighter objects though as the effective aperture is very small ~25mm. It helps if you can track so you can take longer exposures. You can see a description of the technique on my website

 http://www.threehillsobservatory.co.uk/astro/spectroscopy_11.htm

and a discussion on the relative adavantages of the SA100/SA200 using this arrangement here

http://www.threehillsobservatory.co.uk/astro/spectroscopy_17.htm

and  there are some comet spectra taken using this type of arrangement included in a talk I did for the BAA comet section a while back here (eg slides 6-8 Not my observations, credit to the original observers is on the slides)

http://www.britastro.org/projectalcock/RL spectroscopy_BAA_comet_section_may13.pdf 

Cheers

Robin

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robin_astro

robin_astro

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18 hours ago, Thalestris24 said:

Hi Matt

Can I ask how far your SA200 is from the Atik sensor? I have a 115mm scope with a filter drawyer (which is currently about 100mm from a dslr sensor) but the online sa200/100 calculator didn't like the numbers :(

Louise

Hi Louise,

If you can get the grating far enough away from the sensor then the SA100 works better than the SA200 in any case because the aberrations and shift in focus along the spectrum is less.  (I developed the SA200 specifically for situations where you cannot get the grating far enough away from the sensor, like in a filter wheel for example.) 100mm distance with a Star Analyser 100 and DSLR should be fine.  (What warnings did you get on the calculator?)  You can see more about the discussion of SA100 v SA200 on my website here.

http://www.threehillsobservatory.co.uk/astro/spectroscopy_16.htm

Cheers

Robin

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robin_astro

robin_astro

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18 hours ago, Merlin66 said:

In spectroscopy Sky Glow is normally a non-issue (!!) it can be easily removed during the spectral processing.

 

Hi Ken,

This is not entirely true. While it is true you can subtract the sky background, it still adds noise in the spectrum and particularly in slitless systems like the Star Analyser, ultimately dictates how faint you can go.  The limiting magnitude with the Star Analyser with my reasonably dark skies is ~mag 14. By using  a slit spectrograph (which keeps most of the sky background out) I can get to ~mag 17 at the same resolution eg

http://www.threehillsobservatory.co.uk/astro/spectroscopy_20.htm

Cheers

Robin

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Thalestris24

Thalestris24

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1 hour ago, robin_astro said:

Hi Louise,

If you can get the grating far enough away from the sensor then the SA100 works better than the SA200 in any case because the aberrations and shift in focus along the spectrum is less.  (I developed the SA200 specifically for situations where you cannot get the grating far enough away from the sensor, like in a filter wheel for example.) 100mm distance with a Star Analyser 100 and DSLR should be fine.  (What warnings did you get on the calculator?)  You can see more about the discussion of SA100 v SA200 on my website here.

http://www.threehillsobservatory.co.uk/astro/spectroscopy_16.htm

Cheers

Robin

Thanks Robin :) I'm a bit conflicted because the sa100 won't quite fit in my filter drawyer but maybe I could use either version just with a dslr+200mm lens (or 55mm kit lens)? (possibly on a Star Adventurer). I have that option plus either an 80mm f6 APO or 115mm f7 (f5.5 with reducer) with either a full-spectum 1100d or maybe a qhy8l cooled osc ccd. I can't remember exactly what errors I got as I was keying in various combos... AsI'll try again when I get a minute :) mentioned before, I have a filter drawyer in front of a reducer attached to the 1100d on the 115mm which gives a distance of around 105mm to the sensor though maybe I could rearrange things :) 

Louise

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Thalestris24

Thalestris24

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1 hour ago, robin_astro said:

Hi Ken,

This is not entirely true. While it is true you can subtract the sky background, it still adds noise in the spectrum and particularly in slitless systems like the Star Analyser, ultimately dictates how faint you can go.  The limiting magnitude with the Star Analyser with my reasonably dark skies is ~mag 14. By using  a slit spectrograph (which keeps most of the sky background out) I can get to ~mag 17 at the same resolution eg

http://www.threehillsobservatory.co.uk/astro/spectroscopy_20.htm

Cheers

Robin

I'm in an urban red zone so have bad skyglow, especially to the east. To the west is slightly better. But lp everywhere really :(

Louise

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Thalestris24

Thalestris24

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4 minutes ago, Merlin66 said:

Louise,

Don't let the Skyglow situation deter you. For basic bright star spectra you'll manage OK.

As Robin says when you start to push the limits it can become an issue..

Hi

Don't worry - I'm determined to have a go! I just need to work out the best way :)

Louise

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MattJenko

MattJenko

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I was on a course this week, so missed out on some clear skies earlier this week, but managed a session last night. Here is a spectrum of the B companion with 5 minute exposures, which worked much better and I managed 20 of them. It still appears to be more an F star than a G star as per the catalog entry.

What do you guys suggest going forwards to try and nail down what this star actually is?

 

S617B.jpg

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