widowctrlFilters 

1.	1st proposed:notch filter with rejection at FWHM of 50 nm (leaving 20 nm for study)
•	bigoscillation in transmission that would have to be dealt with 
2.	company:Software Spectra Ltd. (useful modeling capabilities?) atwww.spectra.com/nf.html 
3.	2ndproposed:  band pass filter 
•	cavity = #high index low index in filter (more cavities = steeper sides at falloff) 
•	OD (opticaldensity) = -log(transmission) [i.e. 10% trans = 2 OD] 
•	advantages :10 nm bandpass,steeper sides at fall off 
•	disadvantages:  big $$ 
4.	3rd proposed:rejection filter (good rejection) at certain wavelengths 
•	these arestock (i.e. cheaper b/c they don’t have to be custom made) 

*  we may find that it is a budget trade-off(stock vs. custom made) 
*  notch filters are still viable 
*  for ~$500 we could have a rejection band of 20-30 nm; forbetter, there will be about a factor of 2-3        	times in cost
*  requests for more specs and prices from companieshave been made 

From reference of Absorptive OccultationStudies (see Dave’s reference email): 

•	Bestmeasurements (sensitivity) are when you work around 1 OD (tau = 1)
•	10% - 90%absorption is the window for good S/N (i.e. 63% absorption is best)
•	this means that we may notwant to use entire band and fit to it 
•	it is suggested that EVERYONE have a look at this reference

Gratings 

Transmission:
•	600 lines/mmabout the best 
•	lightweight
•	bonds to prism so that prismprovides the strength 
•	can beblazed to 55% efficiency to a specified order (which is good enough)
•	for weightissues:  lose the grating mass, but have to include prism and focusinglens 

Reflection: 
•	1200 lines/mmis common 
•	available inconcave 
•	attenuation fromreflection grating much less than for transmission grating 
•	eliminates an element if we haveto fold optics 
•	for weightissues:  only have grating mass (assuming concave grating) 

*  how much does the # of lines/mm help us? 
* what is the correlation between focal lengths to spectral resolutions?

For Hubi and Gene to do: 
•	For eachgrating, they will give a first rough cut of the optical set-up. 
•	Using thetransmission grating, the elements will be:  plane grating (50% in 1storder), prism (optional), focusing lens/mirror
•	Using the reflectiongrating, the elements will be:  plane or concave grating, (lens andmirror as required). 
•	Commonelements:  filter, intensifier, CCD (1-5 nm per pixel, 512x512) 

Miscellaneous 

*  effect ofkeeping zeroth order on the CCD:  high ruling = higher dispersion withthe zeroth and first 
	order = less CCD = less stars that yousee 

*  worries about spin of the instrument: 
•	if the spinis 1 Hz, we would have to take a picture every 8 ms - unachievable!
•	if thewavelength axis is parallel to the spin, there will be overlap ofspectrum from one measurement to the other 
•	if the wavelength axis isperpendicular to the star motion due to spin, then the spectrum willbe offset (i.e. first measurement on one row of CCD, second on thenext row) 
•	what happenswhen the swing of the instrument is added into this problem? 

*  definition: BAFFLE - using ‘knifeedges’ along the entrance to the detector in order to stopdirect light 
	from a contaminant source