Unequal Double Star Split Calculator - Chris Lord (1994) telescopic performance index algorithm for secondaries brighter than 13.0 magnitudes

K. Fisher fisherka@csolutions.net Rev. 2/3/2008

Calculator assumptions: Primary brighter than 9.0, the secondary is brighter than 13.0, the secondary is between 0 magnitudes and 7 magnitudes dimmer than the primary.

Math Appendix

• S = 1.033 * 10 ^ [ 1/n * ( Abs(delta mag) - 0.1 ) ] * rho
• where performance index n is the sum of three indices from the following table with a range between 4.0 and 12.0:
Table 2 - Performance indices for Lord's algorithm

Aperture Dmm	Aperture index	Obstruction ratio	Obstruction index	Seeing - suprious disk	Seeing index
<75	4	0	4	I<0.25p	4
75-150	3	0.1	3	II>0.25p	3
151-300	2	0.2	2	III<0.50p	2
301-450	1	0.33	1.5	IV<1.00p	1
451-600	0.5	0.4	1	V>1.50p	0.5
600	0.5-0.25	0.5	0.5

• where rho is Dawes criteria or rho = 116 / D_mm.

Although not explicited stated in Lord's 1994 paper, the following computational restrictions are added to this calculator for computational convenience and to assure valid results always are returned to the user:

• The secondary is at most 7.0 magnitudes dimmer than the primary; and,
• The primary is brighter than or equal to 9.0 and the secondary is brighter than or equal to 13.0. This is the approximate magnitude domain from which Lord constructed his performance index model.

References

Lord, Chris. 1994. Nomogram for Telescopic Resolution of Unequal Binaries. Brayebrook Observatory. http://www.brayebrookobservatory.org/BrayObsWebSite/HOMEPAGE/BRAYOBS%20PUBLICATIONS.html

Lord, Chris. 1994. A Report on the Analysis of the Telescopic Resolution of Unequal Binaries. Brayebrook Observatory. http://www.brayebrookobservatory.org/BrayObsWebSite/BOOKS/TELESCOPIC%20RESOLUTION.pdf

Lord, Chris. Jan. 2008. Personal Communication.

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Prepared K. Fisher fisherka@csolutions.net org. 7/2006 rev. 2/3/2008