New to Spectroscopy ... Very lost!

[legoman_iac]

Hi,

Recently bought the Star Analyser 100 after reading "Astronomical Spectroscopy for Amateurs" ... feeling overly confident I knew what I was doing I've tried capturing my first spectra of Sirius ( Alpha CMa ) and am incredibly lost trying to process it.

Is this a bad choice for a first spectra? If not, would I be able to post my results from using vspec to see where I'm going wrong? Tried following the tutorial in the book and some online, however they refer to other stars like Vega.

I'm concerned I'm not selecting the right dips in the graph for the hydrogen line when doing a 2 line calibration, then also that my camera response curve is not detailed enough. I manage to get a result that looks fairly flat then unsure how to read it, ie the bulk of the chemicals in Sirius, temperature of the stars, etc.

Keen to try other software. I looked at ISIS/IRIS but that seemed a steeper learning curve.

Kind Regards,
Daniel

[Merlin66]

Daniel,
I can help.
I would recommend you look at BASS project - easier than VSpec and very capable.
https://uk.groups.yahoo.com/neo/groups/astrobodger/info

Sirius (A1v) should show similar features to Vega (A0v), easily identifiable hydrogen lines.
Email me a copy of your raw spectral image, or upload here a bmp version.
You'll soon get the hang of it.
Ken

[legoman_iac]

Hi Ken,

Thanks for the link, will check it out.

If you're able to help with VSpec, I have made a little progress this morning, if not, I'll try out BASS tonight.

Main snag I was having with VSpec is I think there was something fishy in the VSpec a0iv.dat file I was using. I just tried using a0v.dat and things look a little better. Now I think I get it, and can identify the Hydrogen lines, though I only seem to get good data on two of them. My challenge now I think is building a correct continuum.

Below is the BMP version of the colour cropped spectrum:

http://sketchdigital.com.au/photos/alpha_cma/IMG_3286_cropped.bmp

Here are some of my working screenshots:

http://sketchdigital.com.au/photos/alpha_cma/alpcma_profile.jpg

Building the Continuum:

http://sketchdigital.com.au/photos/alpha_cma/alpcma_division.jpg

All mixed in together:

http://sketchdigital.com.au/photos/alpha_cma/alpcma_response.jpg

- Daniel

[Merlin66]

Daniel,
I think you've cropped too tightly around the spectral image. It's very noisy.
Ideally the crop should be 40-60 pixel high.
This then allows you to use the background removal function to improve the SNR.
I'll have a better look later, but I think your calibration is out.
Which camera are you using?

[Merlin66]

I can find a calibration with the H beta being the second "dip"
The dispersion comes out very high at 4.8A/pixel - a bit high, 10A/pixel would be better.
A longer exposure (or stacked exposure) will help the SNR.
The spectral shape looks odd???

What do you think?

[legoman_iac]

Noisy? Yeh, I tried stacking 5 subs in DSS but it could detect enough stars despite lowering the threshold and it detecting 65 stars.

Can post the raw frames (cropped larger) though it sounds like I should reshoot this first.

Was a quick setup. Using my canon 50d, 100mm macro and a dodgy home made card to hold the star analyser I my cokin filter holder. Yet to use my telescope.

[legoman_iac]

So the second dip is H beta (4861A)? That's what I told vspec and was getting 4.7-ish A/pixel. Might have to re-visit how I'm mounting the Star Analyser or try it in my scope perhaps?

Thanks for trying my file, sorry it's so odd.

- Daniel

[Merlin66]

Daniel,
I've corrected my message....
I had the wrong dispersion, 4.8A/pixel seems closer.
SimSpec shows about 5A/pixel with your 100mm lens.

[legoman_iac]

Hi Ken,

I wonder if my filter holder setup was not parallel to my sensor, then could this cause such an odd/distorted spectrum? Still wonder if using Sirius as a first object is a good starting point, being a binary and all, won't this change over time?

- Daniel

[Merlin66]

Daniel,
No, Sirius would make a good starting point.

[legoman_iac]

Hi Ken,

I joined the BASS group and downloaded the software. Will go through the tutorial and try my file, copying from your screen shot. Thanks again for your help, will let you know how I go.

- Daniel

[Merlin66]

Daniel,
I'm sure you'll quickly come to terms with BASS.
I use AstroArt to control all my cameras (and guiding etc.) I normally use AA5 to correct for darks any tilt before letting it stack my images (it has a "spectra stack" feature!) - I then take the final image across to BASS.....

[legoman_iac]

Hi Ken,

Thanks again for you help with all this. Unfortunately had a busy week and no time to experiment. Will probably be a few weeks before I get another chance to sit down and go through this. Will let you know how I go when I get back to it.

Thanks again,
Daniel

[sil]

Daniel, glad I'm not the only one getting lost with spectrum. I'm still trying to learn with what i captured over a year ago (before my stroke, capture is now too difficult for me).

Ken is very helpful and i keep rereading the threads picking up little gems (didn't realise AstroArt has a spectra stack feature, gave up using AA when I moved to Pixinsight, but feel my stacking could be much better still). Hoping the SA100 and ZWO is good enough to record usable data to get a handle on spectrum. Got a feeling this will be a never ending process trying to understand this better. getting distracted by minecraft doesn't help ;)
I'm more of a learning lurker with spectrum but i've learnt much from Ken and his book (just want to find time to reread and work through my own data together and take working notes etc), so thanks heaps Ken!