Global Calibration Solution

We analyze the data set of 24 northern calibration fields, observed from 05.21.97 to 07.15.98. The fields are listed in Table 1. We use the global calibration solution LS0

 

Table 1: Northern calibration fields. The coordinates are those of the fiducial standards.

Field	$\alpha$ (J2000)	$\delta$ (J2000)
90004	28.657154	+0.717208
90013	89.281275	+0.019769
90021	6.102505	-1.972259
90067	132.812917	+11.821944
90091	145.744583	+59.061944
90161	105.216667	+48.490000
90182	279.890417	+49.093889
90191	66.583156	+3.610611
90247	53.012500	+37.344444
90266	183.605833	+35.598611
90272	224.637917	+37.142500
90290	352.639167	+38.315833
90330	247.890000	+30.146667
90533	55.260000	+6.936944
90565	246.677917	+5.872222
90808	285.480833	-4.486667
90813	310.271250	-5.061944
90860	185.413750	-0.120278
90867	220.241667	-0.463056
90868	225.109925	-0.658013
90893	349.541667	+0.548889
92026	128.126694	-1.577265
92202	331.399018	-11.074560
92409	330.135417	+20.780972

(Weinberg & Nikolaev 1998, Nikolaev 1998) to establish the calibrated magnitudes of the fiducial standards. The difference between true and calibrated magnitudes of a standard is given by:

$$\Delta = m^K_{inst} - a_n - b_n \Delta t_n - A_K (X-1) - m^K_0,$$ (1)

where m^K_inst is the instrumental magnitude, a_n and b_n are nightly photometric constants, and m^K₀ is the true magnitude of the standard. The solution LS0 consists of the set of nightly photometric constants a_n, b_n for every night n and the single derived value of the atmospheric extinction A_K. Having solved for the difference $\Delta$ for each standard for all nights, we present the following runs of means:

1.

Temporal drift: nightly mean differences for standards as a function of time;

2.

Spatial drift: mean differences in calibration fields a function of the sky position ($\alpha$).