Moveable slit?

[Gasman]

Hi guys

Now this might be way out the ball park but bear with me .

Some time ago I watched a program about amateur astronomers in Britain. One such astronomer was Commander Henry Hatfield a well known Lunar cartographer and I believe former BAA president. Now Henry built his own spectrohelioscope so he could observe the sun in H alpha and part of Henry`s apparatus involved a slit mounted on springs which move side to side and apparently in doing so increased the resolution of the H alpha image.

I wondered if this could be adapted for stellar spectroscopy?. Take a slit say 0.25x FWHM for example and if it could be made to oscillate at right angles to the spectrum the fact that it is scanning more of those valuable photons with the same size slit would this enhance or degrade the final spectrum ??. I have no idea of the frequency needed for the oscillation or indeed if it could work at all but if the spectral resolution could be increased purely by making the slit move perhaps the effort involved would be worthwhile?

Just a thought.

Best

Steve

[Merlin66]

The needs of a spectrohelioscope for visual are different from stellar spectroscopy.

When you have a star image of say, 30 micron FWHM centred on a slit gap, the height of the spectrum will be 30 micron...

The resolution comes down to the effective width of the slit relative to the FWHM as does the transmission efficiency.

The guys at CAOS did a lot of work to evaluate different slits/ gaps (See "Astronomical Spectroscopy for Amateurs", p 136)

If you plug in your design slit gap to the SimSpecV4 spreadsheet, you'll immediately see the effect on resolution and transmission...

HTH

[Gasman]

Hi Ken

I can see how simspecV4 will work fine for a fixed slit. If your 30 micron FWHM star image shines through a fixed slit of width 0.25x FWHM (ie 0.25 x 30 = 7.25 microns) then you have a section of star light 30 microns high x 7.25 wide to work with but if that 7.25 micron slit can be made to move side to side scanning the whole 30 micron width wouldn`t the increased photons build up a higher resolution and wider image over the same length of exposure? Just thinking out the box

Steve

[Gasman]

Jeez its getting late 0.25 x 30 = 7.5 but you get the drift

Steve

[Merlin66]

The issue with spectroscope slits is that the resulting spectrum is a series of "images" of the width of the slit...that's where the resolution comes from.

If you move/ vibrate the slit gap in the direction of the dispersion, a couple of things - loss of resolution and loss of calibration.....

Now, if you were saying you could have "adaptive guiding" and move the slit to compensate for the seeing/ guiding errors and keep the "core" of the target star image in the entrance slit, without impacting on the resulting spectrum resolution - that would be interesting...........

[Gasman]

Point well made Ken! thanks. Adaptive spectroscopy mmmmm theres a thing.....

Steve