Well, I am now beginning to look at a bit of success with my foray into spectroscopy, and I am quite pleased.
Last night, while it was clear, and before the equipment got foggy, I was able to have a go with my Star Analyser on three targets - Acrux (B class), Alpha Centauri (G class) and Sirius (A class). I was aiming to get an A and an M class. The telescope was a Megrez90 and the CCD was an Atik 314L+.
In the attached composite, I can at least see some banding. And they appear different with each of the three objects. So I figure I have finally captured my first spectrographs. I realise now that my focus was the issue. I had been focusing on the stars and not the spectra.
I am hoping someone might be able to answer a few questions for me, regarding what I have captured.
First, notice that there is a large "white strip" from the star to the first band (the blazed first order?). There are no features in here. Is this normal?
Second, notice that to the right, the spectra of Acrux fades to black quite quick, while AlphaCent has a pale line and Sirius is quite bright with some features. Is this simply a function of the brightness of the star (the Zero order?) coupled with my exposure time?
Well, I am now beginning to look at a bit of success with my foray into spectroscopy, and I am quite pleased.
Last night, while it was clear, and before the equipment got foggy, I was able to have a go with my Star Analyser on three targets - Acrux (B class), Alpha Centauri (G class) and Sirius (A class). I was aiming to get an A and an M class. The telescope was a Megrez90 and the CCD was an Atik 314L+.
In the attached composite, I can at least see some banding. And they appear different with each of the three objects. So I figure I have finally captured my first spectrographs. I realise now that my focus was the issue. I had been focusing on the stars and not the spectra.
I am hoping someone might be able to answer a few questions for me, regarding what I have captured.
First, notice that there is a large "white strip" from the star to the first band (the blazed first order?). There are no features in here. Is this normal?
Second, notice that to the right, the spectra of Acrux fades to black quite quick, while AlphaCent has a pale line and Sirius is quite bright with some features. Is this simply a function of the brightness of the star (the Zero order?) coupled with my exposure time?
Thanks
Darrell
Well done.
This is a great start. You have certainly achieved spectra of these stars. I will try to explain what I can see. The zero order image of the star is to the left of each image. This then has the first order spectra to the right. This is the white strip you describe. The violet end of the spectra is closest to the left and the red end is to the right. The long tail past the end of the spectra to the right is the beginning of the second order spectra.
There are no details in most of the spectra because the image is saturated. I have put a line profile of the image of sirius below. It shows that most of the image is saturated. Try taking a much shorter exposure to then get details in the brighter part of the spectra. Sirius is an A0V star. I have attached a spectra of Delta Vela which I have taken for comparison. It is a A1V star so quite similar. You should be able to display similar lines.
Cheers
Terry
I have now done as suggested and reduced the exposure times. Sirius was the target. I tried quite a range of exposures. The original effort was at 3 seconds.
The attached has my attempt from last night. I bracketed from 2 seconds down to .002sec. I have include what appear to me to be the "better" results - .5, .05, and .08sec. With the .08 image being the best. I can see some detail in the violet end of the spectra, so I think I am heading in the right direction.
My question now is, does this look like focus is still an issue? It does still appear to be fuzzy at that violet end. Or is that fuzziness brought about by the exposure do you think?
Guys
I have downloaded the trial version of RSpec and run up the Sirius spectrograph. See attached. I haven't calibrated the software yet, but does this look roughly correct?
I have pulled out my three spectro books;
Spectroscopy: The Key to the Stars (Robinson)
Practical Amateur Spectroscopy (Tonkin)
Stars and Their Spectra (Kaler)
and if the weather is poor this weekend, I will go through them again and try to deciper all that I have done.
Darrell,
Sorry I missed this post...
As mentioned you need better exposures and double check the focusing on the spectrum, not the zero order star image (this will end up slightly out of focus)
The shape of the spectrum shows the typical "fishtail" associated with non apo telescopes....getting the UV into focus at the same time as the red is impossible with achromats. You can take separate images re-focused for the different regions to overcome this.
The book missing from your collection is "Grating Spectroscopes - How to use them" available thru Amazon/ Springer ;-)
As Terry said, try cutting your exposure times down. Look forward to seeing your next batch!
