Stray Light and TAUVEX performance

1. The Limiting Magnitude Table

   This table summarize the effect of different Stray Light levels of the limiting magnitude of TAUVEX in some representative filters. Each of these limiting magnitudes were calculated for Signal To Noise= one under which no detection can be made (look at more realistic signal to noise = 5).
   The observing time for all the calculation was 1e4 sec.
   The different PST were calculated for the BBF filter after the level of stray light was set arbitrarily to cover the range of stray light from 0 to the current level of 2.18e6 e/sec. and then were used to predict the stray light level of the other filters.

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   	BBF		SF3		SF2		NBF 3
   PST	Stray Light	Limiting Magnitude	Stray Light	Limiting Magnitude	Stray Light	Limiting Magnitude	Stray Light	Limiting Magnitude
   	0	26	0	24	0	25	0	23.4
   5e-11	40,000	19.2	6500	18.5	3400	19.2
   1e-10	80,000	18.6	13,000	18.1	6700	18.8	1600	18.4
   1.53e-10	120,000	18.2	20,000	17.8	10,000	18.5
   2.12e-10	166,000	17.7	27,000	17.6	14,000	18.2
   3.2e-10	250,000	16.9	41,600	17.3	21,500	18	5080	17.6
   4.47e-10	350,000	16.1	58,000	17.0	30,000	17.8
   6.38e-10	500,000	14.9	83,000	16.7	43,000	17.5	10,000	17.3
   2.8e-9	2.18e6	---	364,000	14.0	188,000	15.8	44,500	16.3

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2. Event rate for a Sun-like star in the different filters

   BBF	SF3	SF2	NBF 3	SF1
   7.8e14 e/sec	1.3e14 e/sec	6.72e13 e/sec	1.59e13 e/sec	2.0e12e/sec

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3. Limiting Magnitude in BBF for tracking.

   The limiting magnitude in the table are different Counts/sec options. The current value is about 100.

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   Stray Light	100	50	20	10
   0	11.29	12	13	13.7
   40,000	11.04	11.7	12.7	13.4
   80,000	10.68	11.4	12.4	13.2
   120,000	10.4	11.2	12.2	13
   166,000	10.1	10.95	11.9	12.6
   250,000	9.5	10.3	11.3	12.1
   350,000	9.0	9.7	10.7	11.4
   500,000	8.0	8.6	9.7	10.42

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4. Number of stars in TAUVEX field of view

   From UVC (the new version Liliana has) the color - color transformation in TAUVEX BBF (for models of stars only) was used in the Galactic model code. The use of real IUE data force us to cut the BBF under 3200A which inroduce an error of 6.4% (underestimation). The different count prediction is presented in here. The results were scaled to the TAUVEX field of view (0.63 square Deg.) and a Poisson probability function was used to estimate the probability that for a given averaged number of stars in TAUVEX field we will find at least one star. The results are summarized in the next table.
   

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   Limiting Magnitude	Num of Stars up to mag #	Probability of more than one star
   12	2.07	0.87
   11.5	1.5	0.77
   11.0	1.1	0.66
   10.5	0.8	0.54
   10.0	0.6	0.44
   9.5	0.45	0.35
   9.0	0.33	0.28
   8.5	0.25	0.22
   8.0	0.18	0.16

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5. SUMMARY of results

   To summarize these results the probability of observing at least one star in TAUVEX field of view is presented in different PST's and decreasing required number of counts for tracking.
   The probability was calculated under the asumption that TAUVEX will half of it's time observe targets in forward angle and half of the time the stray light is 0 (backward angle). All the calculation is done for azimith angle phi=0, for phi=10 deg. the PST is about an order of magnitude worse.
   

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   PST	BBF (Stray Light)	100 events/sec	50 events/sec	20 events/sec
   0	0	0.7	0.87	0.98
   5e-11	40,000	0.68	0.83	0.97
   1e-10	80,000	0.65	0.82	0.95
   1.53e-10	120,000	0.62	0.73	0.94
   2.12e-10	166,000	0.58	0.76	0.92
   3.2e-10	250,000	0.52	0.69	0.84
   4.47e-10	350,000	0.49	0.63	0.79
   6.38e-10	500,000	0.43	0.55	0.69