Selection of zodi patches

Faint Zodi

• Primary positions: Location in the CVZ in order to be able to observe the same region throughout the mission. This would also allow us to follow the small (<10%) variation in the flux density of the high ecliptic latitude zodi during the year.
• Secondary positions: The regions of the MIPS deep field for which background (and most probably confusion) limited observations at longer wavelengths (70, 160 microns) will be available. These should help us identify any structure in the cirrus as well as faint sources (distant galaxies?) which may cause some concern. It should be noted though that at high ecliptic latitudes and within the IRS wavelength range, we do not expect to have any detectable influence in our lo-res and high-res flats due to the emission of the cold ISM. Only the higher sensitivity of the red PU camera may be potentially affected, but this remains TBD. Furthermore, it is considerably easier to create "superflats" for the PU camera by co-adding multiple short-low observations taken during and after IOC.
• Regions where cirrus structure was visible in the IRAS60 and IRAS100 maps were avoided. See
  • IRAS Maps of North CVZ
  • IRAS Maps of South CVZ
• Regions with stars brighter than 9mags in K (IRAS12=10mJy, IRAS25=3mJy) were avoided.

Taking into account the above we propose to use the following regions for low zodi measurements:

• Primary positions
  • CVZ-north (17:15:50, +65:25:37, J2000)
    No star with m_k < 10mag within a radius of 5arcmin. Check the 2MASS / IRSA search file here.
    Check the 2MASS J-band [fits, JPG] and K-band [fits, JPG] mosaics.
  • CVZ-south (6:16:40, -60:48:59, J2000)
    No star with m_k < 10mag within a radius of 5arcmin. Check the 2MASS / IRSA search file here.
    Check the 2MASS K-band [fits and JPG] mosaics.
• Secondary positions
  • Groth_NE (14:18:11.0, +52:29:46.4, J2000) : Visible Dec 04, 2002 - Jul 18, 2003
    IRAS Maps of region can be seen here
  • HDF-North (12:36:49.90, +62:12:58.0, J2000) : Visible Nov 03, 2002 - Feb 02, 2003
    IRAS Maps of region can be seen here

NOTE:The knowledge of the background at ~5microns (short low) is rather problematic. There is an offset of a factor of few between the model and the DIRBE maps. However, since we take a large number of PU images during IOC this will be the easiest module for which we can construct deep "super-flats" by combining various datasets.

Bright Zodi (updated Aug. 28th 2001)

• Brightness of zodi, that is proximity to the ecliptic plane and at 80 degrees solar elongation (calculated using JPL's Horizons) from the at any given period.
• Avoidance of the bright zodi lanes (name?) located ~8degrees from the ecliptic plane which are attributed to small grains and vary substantially (quantify?) with time.
• Main selection was based on the IRAS HCON4 maps from which a zodi model was subtracted.
• Rich fields were avoided using archival K-band date from the 2MASS survey. However, the selection of areas near the galactic plane remains problematic.

Using the regions specified in the above table I measured the infrared emission at 4.9, 12 and 25 microns (DIRBE maps e90ecl04.fits, e90ecl05.fits, and e90ecl06.fits respectively). In the four areas where no appropriate ecliptic latitude had been selected I used the value +1 degree, even though this needs to be revised. The measured flux densities as well as links to the 2MASS images are provided in the following table. We also provide the number of stars with K band magnitude brighter than 9 (for a K-giant m_K=8mag => IRAS12 = 30mJy, IRAS25=7mJy) found within a degree from the given position.

The information presented on table 2 were calculated using the IDL program zflux.pro, which takes as input the last two columns of Table 2 (also provided at: sun80.txt)