NOTES on UKIDSS REFERENCE PAPER-II

"The WFCAM/UKIDSS Photometric System", 

Hewett, Warren, Leggett, Hodgkin, et al.


1. Introduction 
--------------- 



This is UKIDSS Reference Paper II. This describes the WFCAM 
photometric system that will be used for UKIDSS (Lawrence et al., 
UKIDSS Reference Paper I). V brief description of UKIDSS. 

Goal of paper is: description of the photometric system, synthetic 
calculation of colours of objects (examples), colour equations 
relating filters to other systems, and conversion Johnson to AB. Point 
to web page where the tables will be. A future paper (Hodgkin et 
al.), will provide on-sky measured colour equations. 


2. Method of calculation 
------------------------ 

2.1 Formal procedure i.e. integral of no. photons in bandpass. 
Assemble required data, incl. filter curves (discuss choice of Z and 
Y), array response, atmos. transmission. Justify airmass and water 
vapour adopted. Tabulate and plot system response curves adopted, as well as 
effective wavelengths. Point to location of model Vega spectrum. Spell 
out how anyone can reproduce our results. [I'm unclear here whether we 
want to produce absolute response curves (i.e. someone could do a S/N 
calcuation) or normalised response curves. I don't really see the need 
for absolute response curves.][I don't think we need technical details 
of filters here? Refer to WFCAM paper to be prepared by Casali.] 


2.2 Discuss history of UKIRT faint standards to justify accuracy to 
which this is tied to Vega, since synthetic mags specifically use 
Vega. Additional brief discussion of how Z and Y bands will be 
calibrated. Discuss accuracy of model Vega spectrum as a 
representation of Vega. Then draw conclusions on accuracy of synthetic 
mags, compared to mags calibrated to UKIRT faint standards. Finally 
discuss accuracy of absolute calibration of Vega, and so draw 
conclusions of accuracy of conversion from Johnson to AB mag. [We need 
to define our AB system, which is I assume -48.60 as Fukugita96, rather 
than V(Johnson-5480)=V(AB-5480).] 


3. Results 
---------- 

3.1 BPGS results and colour equations. Some of these are simple 
e.g. J-J2 v J-H, H-H2 v H-K, K-K2 v H-K. But the others are a bit 
trickier e.g. Z-z' and Y-Z (or Y-J). It seems to me we need to plot 
these against things we can observe, which means Y-Z, Y-J, Z-J. [I 
think we should accept z' as standard at present, but I'd like to 
think that people might start manufacturing Z filters like ours, and 
it might one day become standard. Unfortunately the above will involve 
a comparison of our calc for z' and Fukugita's.]. Tables and 2-colour 
diags. 


3.2 Colours of other objects. Tables and 2-colour diags. 

3.2.1 Other Galactic targets 

3.2.2 ExtraGalactic targets 

4. Summary/conclusions/discussion 
---------------------------------