Calibration lamps witha SA?

[Gasman]

Hi guys

No doubt an overkill given the limited resolution achieveable with a Star Analyser but I`m wondering if its possible to use a reference lamp for calibrating spectra with slitless type spectro units like the SA. I`ve looked through both of Ken`s books but they only refer to using lamps with slit type instruments so its probably a non starter but being able to simply flick a switch to light a neon bulb for an instant calibration curve at the eyepiece quite appeals.

My C8 scope when focused on a stars spectrum will (presumably) be at or near infinity so to get an accurate reference spectrum to compare it with I`m struggling with how to get the same focus for a lamp?? If its possible where and how would it be introduced into the optical train of the scope/camera please?.

Regards

Steve

[Merlin66]

Steve,

You really do need a slit arrangement to be able to use a reference lamp.

The neon, or any other lamp, needs to be aligned with the spectrum being produced...with a SA100 in the converging beam, think of the zero star image as the defacto image of the entrance "slit" - the "actual" slit image would have to coincide with this zero order to allow even a rough calibration.

( The nearest I've come to your request is using the front perforated plate from a Hubble artificial torch, illuminated by a neon bulb placed about 10 mtr from the scope. The artifical (neon) star image produced is about 50 micron and can produce a spectrum with the same dispersion that you'd normally get with stars.

I assume this "reference spectrum" could then be superimposed on the actual target star spectrum during post-processing. I've never tried it, but it sort of sounds possible???)

[Gasman]

So all I need for an artificial `neon` star is a neon bulb behind a perforated disc with a small enough hole and at the same time bright enough to show in the camera and at an exact distance from the mirror to give the required dispersion...mmmmm!!!.

Steve

[Merlin66]

Steve,

I admire your courage....

IMHO the calibration you may achieve, due to the low resolution of the SA100 will be no better than that achieved using, say Vega, to generate a dispersion/ calibration curve for your set-up.

If you don't move any of the optical components then the dispersion will always remain the same.......

[chiltonstar]

You could of course point your scope with the SA100 at a distant streetlight (Na or Hg vapour) or even a houselight (if a modern low-wattage lamp is being used). I've tried the latter, and it works in the sense it produces a calibration spectrum, although as Merlin says, a star with clear spectral features might be more useful...

Chris

[robin_astro]

The easiest way to wavelength calibrate Star Analyser spectra is to use the Balmer lines in bright A type star. Taking one of these at the start of an observing run has the added advantages of allowing the system to be setup for optimum focus and also gives a standard star for instrument response correction before moving on to more challenging targets.

Cheers

Robin