Mars Observations
When Mars is available, it is a good target for several important
tests.
- Instrumental polarization: Since Mars is an unpolarized
source, observing it with SPARO will give the combined
Viper/SPARO contribution to the polarization signal.
This is the most important of the "Mars tests".
- Beam shape: Mars, having an angular size of about 10 arcseconds, is
a point source to SPARO and thus can be used to do a more precise
mapping of the Viper/SPARO beam shape. Here, 1 degree scans each
way in elevation and azimuth should give enough information to
check the beam shape. See also the document on "moon scans".
- Off-axis polarization: we want to measure the instrumental
polarization by pointing SPARO at four half power points of Mars'
PSF.
Flux, angular size, and elevation information is given below for two dates,
along with integration times for a 1% detection (signal-to-noise = 100) of
Mars, denoted as t100.
| Date |
Angular Size |
Flux |
Zenith Angle |
t100 (tau=1.5) |
t100 (tau=1) |
| Aug. 20 |
8.3" |
3200 Jy |
70 degrees |
2.2 hours |
410 s |
| Oct. 5 |
6.8" |
2150 Jy |
65 degrees |
0.9 hours |
310 s |
A zenith opacity of 1.5 or 1 has been assumed in the above estimates, as well
as a surface temperature of 200K for Mars. It appears that the elevation of
Mars is the limiting factor in the integration time required for a 1%
detection.
Also note that if we know the integration time required for a signal-to-noise
ratio of N, then the time required for a S/N of M is
tN/tM = (N/M)2
1/18/00 update:
Calibration targets for Austral Summer/Winter 2000 and Austral Summer 2001.