My 2nd spectra - Beta Car

[Slawomir (Suavi)]

Could not resist and continue tonight to experiment with taking star spectra. Definitely need to look into neater labelling of absorption lines... :-)

Thank you for looking!

[RickS (Rick)]

Looks just like a real one, Suavi

[Slawomir (Suavi)]

Thank you Rick.

I thought of testing the SA200 diffraction grating while I am waiting for another set of adapters for my flattener and for Riccardi reducer (the original ones seem to got lost in the mail...). Wanted to try spectroscopy for some time and somehow never got to that.

[Atmos (Colin)]

Looks great Suavi, the CFF looks to be doing a great job for you
I've been considering doing the whole spectroscopy thing for a while as well. Would also like to get a set of Johnson-Cousins UBVRI filters as well, prefer them over the Sloan.

[Merlin66 (Ken)]

Suavi,
Another good catch!
A couple of things:
I see the ripple on the profile...I'd guess this is due to recording the spectral image with a tilt across the CCD.....
When you rotate the image to the horizontal you typically get this "staircase" effect from the pixels.
Much better to set the camera/ grating to give a horizontal image on the CCD.
I think your focus is pretty good, but just remember to focus on the spectrum - ignore the zero order image.....
At 60000 ADU you're over exposed...around 40000 will probably be better.
Onwards and upwards.

[Slawomir (Suavi)]

Thank you Colin, yes, the CFF is certainly very very nice.
It's relatively inexpensive to get started with spectroscopy once you have a complete astro rig - just a SA100/200 and you are set! You might need to consider that large SX FW to fit all those filters in!

Thank you for your hints Ken - highly appreciate your help.

I was wondering about that staircase - will certainly better align the grating with the chip. Good to know about exposure as well, last night took also longer exposures on these target and 30s was certainly way too long. These are 5s exposures, so for bright stars like Beta Car may need to settle for 2-3s exposures. Focus should improve once I get an adapter for my flattener.

Suavi

[Merlin66 (Ken)]

Suavi,
You don't need a flattener with spectroscopy!
The dispersion angle from the grating is approx. 3.8 degrees/ 100 l/mm, so for the 200 l/mm grating the focal plane of the spectral image ( actually an arc) is spanning an arc that extends just over 7 degrees off axis.
(See http://users.erols.com/njastro/faas/articles/west01.htm)

The blue portion of the spectra will be "closer" to the zero order image focus and the red will require you to re-focus further inwards.
Hope this helps.

[Slawomir (Suavi)]

Good to know, thank you Ken.

I actually place the star to the left of the screen and try to position the spectra in the middle of the chip with its centre (green light?) roughly on the optical axis. I expect there will be some improvements with proper adapters, as at this stage I'm using thumb screws and flimsy extension tubes to hold the camera in the right place.

Happy days, the adapters have just arrived!

Okay, I'm back in business :-)

Suavi

[Merlin66 (Ken)]

Suavi,
Sounds good...
but just double check the "best" focus on the spectral image - deepest/ darkest absorption features.

[beren]

nice work Suavi