Impact of a Smaller ARISE Antenna

Impact of a Smaller ARISE Antenna

There occasionally has been discussion of building a space telescope for ARISE that has a solid central surface that operates at 86 GHz, with the outer sections working only at lower frequencies. If such an antenna were built, and a 3-meter central portion had an aperture efficiency of 0.5, its SEFD at 86 GHz would be Jy, a factor of 11 worse than the nominal value. The number of detectable sources is given in Table 5. This table shows that such a small antenna would be inadequate at any feasible data rate for a baseline to a VLBA antenna, but might be able to observe a satisfactory number of sources if large amounts of time on the GBT were available. Of course, imaging would be very difficult with such a large disparity between the sensitivities of the space telescope and the ground telescopes, so the actual situation is probably worse than that depicted in Table 5.

Table 5. Sources for 3-meter ARISE Telescope
Assumed K
Data Rate	VLBA Antenna		GBT
(Gbit sec)	Threshold	Number	Threshold	Number
8	400 mJy	37	87 mJy
4	570 mJy	26	124 mJy	210
2	800 mJy	16	175 mJy	140
1	1130 mJy	8	247 mJy	83