1

2200+420 (BL Lac)

Coordinates (J2000):
R.A. = 22:02:43.290, Dec. = +42:16:39.98
z = 0.0686

Landessternwarte Heidelberg-Königstuhl

Field of view is 10’x10′

GASP suggested stars: B C H

Comparison stars

Star U B V R I
B 16.47 (~ 0.07) 14.68 (~ 0.04) 12.90 (0.04) 11.99 (0.04) 11.12 (0.05)
C 15.66 (~ 0.06) 15.20 (~ 0.05) 14.26 (0.06) 13.79 (0.05) 13.32 (0.05)
H 16.91 (~ 0.09) 15.81 (~ 0.06) 14.40 (0.06) 13.73 (0.06) 13.07 (0.06)
K 16.61 (~ 0.08) 16.36 (~ 0.07) 15.47 (0.07) 15.00 (0.07) 14.54 (0.07)

UB  from Bertaud et al. (1969, A&A 3, 436) 
VRI  from Fiorucci & Tosti (1996, A&AS 116, 403)

IMPORTANT: As specified since the first campaign targeting BL Lac in 2000, we recommend to use 8 arcsec for the aperture radius, and 10 and 16 arcsec for the radii of the background annulus. This allows us to optimize the subtraction of the host galaxy contribution in the following data analysis.