SHARCII Observing Time Calculation

Darren Dowell -- (626)395-6675 (office), 796-8806 (FAX)

Last modified Wednesday, 09-Apr-2003 18:44 PST
cdd@submm.caltech.edu

Instrument Characteristics

SHARC II nominally has 384 pixels in a 12x32 format. Approximately 85% of them work well. Each pixel has an extent of 4.85 arcseconds, resulting in a 2.59 arcminute x 0.97 arcminute field of view. (Pixel scale updated Feb. 2003.)

The beam size with good focus and pointing is 8-9 arcseconds (full-width, half-maximum) at 350 microns.

Time Calculation Basics

Deep SHARC II integrations require tau(225 GHz) <= 0.05. Statistically speaking, this happens 10% of the time in "summer" (May - November) and 27% of the time in "winter" (December - April). During tau(225 GHz) = 0.05, the NEFD at 350 microns at 1.3 airmasses is 1 Jy s^1/2 At 450 microns, we expect a similar NEFD. Here are some example sensitivity estimates for 1 field of view, assuming the stated weather and airmass, and assuming 50% loss of time due to overheads (writing data, pointing, calibration, filling in bad pixels):

time   1-sigma rms
-----  -----------
 1 hr    24 mJy
 3 hr    14 mJy
10 hr     7 mJy

The NEFD in other conditions can be estimated by:

NEFD = 1 Jy s^1/2 * exp(25*tau₂₂₅*airmass - 1.6)

Go to SHARC II home page...