Got RSpec

Hmmm.

I still think the large dip you show may be atmospheric at 7600A

Hello

Without buying a new camera, I am a little chalenged in resolution with my setup.  Has anyone tried to do the following?

Increase the spacing sufficient to get the first order and say half the spectra of typical stars.  Then calibrate on say the Hbeta or other feature, which will now be near the right hand side of the chip.  This calibration should be fixed for a fixed setup, if I am understanding this.  Then reposition and center the complete spectra on the chip, giving acces to Ha and the red end.  This would allow me to get from my present 18.4 A/px to somewhere near 10, which is what most folks seem to use.  While there is no free lunch (the calibraton at the red end is extrapolated which is not a accurate as interpolation), this might give a more satifying result, with more detail over all the spectra.

Anyone using 18-20 A/Px and happy with it?  

And no, I am not going to go to a separate Spectra setup at this time.  I really like the simplicity of the SA200 and don't want to compromise my PT setup.  Just looking to optimize things.

Comments?

Gary Walker

WGR

gary,

Any A type star will show good Balmer lines.

I think your problem may well be a common problem experienced by members who already have a dedicated set-up and don't want to change it to accommodate spectroscopy.

Inevitably this will probably lead to less than optimum results. It really depends what you want to achieve with the grating.

Get some experience with the set-up you have, even at low resolution and then assess what improvements are possible..........

Ken,

 It is important when steering beginners to speak from experience and not make assumptions. 

You will not see strong Balmer lines clearly in supergiants like Deneb at the Star Analyser resolution (R~100). They are just too narrow and H alpha is partially in emission. See my posts in the "first steps" thread for more information on this. Try it and you will see what I mean. Deneb is a difficult target for the Star Analyser. An A or late B star of luminosity class iv or v  should be selected as a test target for strong Balmer absorption lines are desired.

Robin

Why are we still going round in circles?  Unbelieveable !

One more time......

There is nothing wrong with this setup. The Star Analyser is a very low resolution spectrograph and you need to chose targets suited to it. Deneb is a difficult target. The very narrow lines in supergiants do not show up well at this resolution. I have already suggested some targets will work well.

For a start, why not turn your telescopes to Delta and Gamma Cas and duplicate what I did almost 10 years now with a much cruder setup than anything  being discussed here.

http://www.threehillsobservatory.co.uk/astro/spectra_12.htm

Robin

First I think I should apologise for my rather tetchy posts above. No excuse, but me and the family are all suffering from the flu and we are not in the best of spirits.

Re the 18A/pixel dispersion. It is true that for most systems a lower A/pixel (typically10-15A) gives higher resolution but if I recall correctly your pixels are untypically large at 24um compared with a more typical figure of say around 6-8um these days.

To get the maximum available resolution out of a Star Analyser setup (~40A) you need to:- 

a)  Have at least 2 pixels covering 40A in the spectrum - which you have met (2 x 18.4 = 36.8A)

b)  Ensure the size of the in focus star image (FWHM) is smaller than 40A in the spectrum. This is where your large pixels really count and why most users with smaller pixels need a lower A/pixel to meet this criterion. In your case with 1.6 arcsec/pixel and 3 arcsec seeing the star image size covers 1.9 pixels or 35A in the spectrum.

Perfect !

I will give some thought to a top 10 list of practical tips for getting the most out of the Star Analyser. A good idea -  the things they dont tell you in the books ;-)

Robin