Shake that Fibre

[Andrew Smith]

I know Christian has covered this before but the attached shows some flats I took without and with shaking the fibre optic cable to my echelle

Without movement

FlatA.png (93.98 KiB) Viewed 3998 times

With movement

FlatB.png (86.21 KiB) Viewed 3998 times

Regards Andrew

[Christian Buil]

Hi Andrew, this is a spectacular display of the modal phenomena in the optical fibers. A lot of ignored aspect by too many observers... The problem seem exist always at different degree, test similar to your experiment is a good idea for evaluation (and for tracking sources of pseudo-noise for max. SNR).

My eShel and VHIRES-MO fiber are always shaked.

Can you recall your setup Andrew: telescope aperture, diameter, type...

Very interesting !

Christian

[Andrew Smith]

Hi Christian, I have been commissioning a new telescope and echelle. The telescope is an Orion Optics (UK) ODK 16. It has a 400mm main mirror and works at F6.8. This is now mounted on a Paramount ME II using The Sky X to control it.

I use the Shelyak Fibre guide head with a 75 micron hole reduced for the 50 micron Fibre at F 4.5. The echelle is similar to the eShel in optical design but targeted at F4.0 and so has a bigger grating with a different spec. It gives R ~ 8000. I found I could not reduce the spectra using ISIS so have been on a journey to learn IRAF which once set up is no more complex that ISIS as you can run it via scripts.

I found the field of view of the guide head was too small for consistent plate solving (too few star or overwhelmed by a bright one) so I use an On Axis Guider to acquire the field before using the guide head to pull the target onto the hole and guide. Thus after opening the roof of the observatory I can run a Python program to control the mount and 3 CCD camera to get calibration and target frames for a list of targets.

I am experimenting with different designs of shaker as I need it enclosed otherwise it is too tempting for my Burmese cat!

Regards Andrew
PS This looks like a good summary of modal noise reduction http://eres-yale.science/pdfs/RyanPetersburg.pdf

[Andrew Smith]

Hi again Christian, did you edit your post last night or was I dreaming? I glanced at your post as I was going to bed and seemed to recall you mentioned 2x2 and 1x1 binning of the Atik 460 ex (I use the SX version). I also think I remember you were using you eShel. Maybe I hallucinated it all.

I had been using 2x2 binning but following a discussion and linked paper on the VdS forum was going to use 1x1.

Regards Andrew

[Christian Buil]

Hi Andrew, did not dream, I actually modified the message and reported the comment about binning 1x1 on this topic:

http://www.spectro-aras.com/forum/viewt ... f=5&t=1835

Yes, I suggest really to adopt Bin 1x1 mode when using échelle spectrograph for limit sampling noise, a more efficient cosmic defect removal procedure and a better definition of the Instrumental Line Spread (ILS) for scientific analysis.

The problem with the cat is unexpected... !

Christian