!!!Inter-instrument Offsets on Hinode

!! EIS to SOT

[Ken Dere|~KenDere] asked a fairly important question (comment moved here from [DataProAnalysis] ) :

''Alignment vs. FPP and XRT.
It is not too difficult to align EIS against XRT but it is more difficult agains FPP. Does anyone have a rough off set in the pointing of EIS vs FPP?
--[KenDere|http://null], 12-Oct-2007''

The rough number that we use here is that EIS's FOV centre is 50 arcseconds south of SOT's centre (assuming that they don't offset internally, though perhaps this is carried through their FITS files, as ours should be). Incidentally, space-craft centre is __defined__ so that it coincides with SOT FOV centre.

We assume that the telescope FOVs are co-centred in the east-west direction.

These values are based on the alignment work done by Hiro Hara in February of this year, after the EIS coarse mirror was moved (it has only been moved once since science observations began).

I have attached an image taken from Hiro's slide presentation on this subject (larger image also attached).

[InterInstrumentOffsets/HH_Offsets_Feb07small.png]\\\

You can see the inter-instrument offsets. Note that although EIS's centre is measured to be 3" west of SOT's, the difference is so small that we assume it to be zero.

!! EIS to XRT

As you can also see from the above image, XRT is centred about 43 arcseconds east of EIS, and 28 arcseconds north.

--[Dave Williams|DaveWilliams], 15-Oct-2007