centre. We also performed at least one sky dip per observing session to establish the sky temperature and opacity.

\[table:sources\]

  ---------------- ------- ----------------- ---------------- ---------- -------------- ------ ---------- ------- ----------- --------------- --------------- -----------
  Cluster          Src            RA               Dec                                                      Notes                                             
                   \#           (J2000)          (J2000)                                                                                                      
  A1835            1\*        14 01 02.1        02 52 41.0          39.3 $\pm1.6$            -               3.31 $\pm0.14$              2.93 $\pm0.18$       OB N
                                                                                                             2.88 $\pm0.07$                                   
                   2\*        14 01 00.5        02 51 53.0           1.6 $\pm0.1$            -               1.26 $\pm0.14$              1.33 $\pm0.07$       OB F
                                                                                                             1.36 $\pm0.08$                                   
  ZWCL1953         [1]{}    [08 50 07.8]{}    [36 04 21.7]{}    [19.4]{} ${\pm1.2}$          -                  -                    [0.79]{} [$\pm0.70$]{}   [GBT]{}
                   2          08 50 13.4        36 04 22.4          20.8 $\pm1.0$         19.0 $\pm4.0$      1.19 $\pm0.17$              1.28 $\pm0.16$       GBT OB
  ZW3146           1          10 23 37.2        04 09 06.4          31.5 $\pm1.0$            -               2.03 $\pm0.22$              2.35 $\pm0.81$       GBT OB
                                                                                                             2.12 $\pm0.15$                                   
                   2          10 23 39.6        04 11 15.4           7.1 $\pm0.5$            -               0.41 $\pm0.07$              0.33 $\pm0.07$       GBT OB
                   3          10 23 45.1        04 10 40.7          95.8 $\pm3.4$         42.0 $\pm7.0$      5.35 $\pm0.18$              5.27 $\pm0.11$       GBT OB
                                                                                                             5.70 $\pm0.10$                                   
                   4          10 23 45.2        04 11 39.7           3.6 $\pm0.4$            -               0.85 $\pm0.10$              0.80 $\pm0.10$       GBT OB
  RXJ1532.9+0005   1          15 32 47.4        30 18 46.0          18.0 $\pm1.0$            -                  -                        1.18 $\pm0.21$       GBT
                   2          15 32 50.7        30 