Search
Text Size:
Smaller Text Normal Text Larger Text

Facebook

Follow us on Twitter


ALFOSC UBVRI Zero Point Monitoring


In August 2000 we decided to start monitoring the UBVRI zero points for ALFOSC on each possible technical time occasion at the NOT in collaboration with the GL team at CUO (PI: Jens Hjorth). A data reduction pipe-line was made by Andreas Jaunsen who kindly has performed the photometric analysis.

The photometric standard cluster positions and exposure times we use.
Name RA (2000) DEC (2000) U#7 B#74 V#75 R#76 i#12
M92 17:17:03.82 43:02:03.2 60 40 30 20 20
NGC2419 07:38:16.00 38:55:32.0 120 60 20 20 20
NGC7790 23:58:27.70 61:13:01.0 30 30 10 10 10

Three photometric clusters were selected in order to cover visibility at an airmass < 2 at any time. They are all among the Stetson Photometric Standard Fields . M92 is preferred, though, because it has good U-band standards (from L. Davis, NOAO). Observations should be performed at 3 different airmasses in photometric conditions. Online catalogue is zpmon.cat. Sky flat fields and bias frames are needed, as well.

Results

Find below one table per filter with date of observations, cluster observed, and the derived zero point magnitude (zp) which is the magnitude for 1 ADU per second, the colour term (ct), and the atmospheric extinction coefficient (ext), all given with errors. Note that in some cases the extinction coefficients were not determined from the observations on that night, but fixed extinction values were used. The fitted zp, ct, and ext values were obtained with the following equations:

U = U_zp + u + U_ct * (U-B) + U_ext * X 
B = B_zp + b + B_ct * (B-V) + B_ext * X 
V = V_zp + v + V_ct * (V-I) + V_ext * X 
R = R_zp + r + R_ct * (R-I) + R_ext * X 
I = I_zp + i + I_ct * (V-I) + I_ext * X 

U-filter.
Date Field U_zp U_ct U_ext U_rms Comment
2000-Sep-11 NGC7790
 
 
 
 
no U-band standards.
2000-Oct-16 NGC7790
 
 
 
 
no U-band standards.
2001-Jan-14 NGC2419, M92 23.65 ± 0.02 0.09 ± 0.04 -0.462 0.026 fixed extinction
2001-Jan-14 NGC2419, M92 23.4 ± 0.2 0.09 ± 0.04 -0.3 ± 0.1 0.020 free fit (10 stars)
2001-Feb-08 NGC2419
 
 
 
 
no U-band standards
2001-Mar-08 NGC2419
 
 
 
 
no U-band standards
2001-Apr-07 M92 23.61 ± 0.01 0.10 ± 0.04 -0.462 0.031 fixed extinction
2001-Oct-04 NGC7790
 
 
 
 
no U-band standards

B-filter.
Date Field B_zp B_ct B_ext B_rms Comment
2000-Sep-11 NGC7790 25.704 ± 0.002 0.053 ± 0.002 -0.292 0.017 fixed extinction
2001-Oct-16 NGC7790 25.712 ± 0.002 0.062 ± 0.002 -0.292 0.019 fixed extinction
2001-Jan-14 NGC2419, M92 25.710 ± 0.006 0.032 ± 0.008 -0.292 0.037 fixed extinction
2001-Jan-14 NGC2419, M92 25.53 ± 0.02 0.050 ± 0.009 -0.18 ± 0.01 0.041 free fit
2001-Feb-08 NGC2419 25.60 ± 0.01 0.06 ± 0.02 -0.220 ± 0.007 0.023 free fit
2001-Feb-08 NGC2419 25.68 ± 0.02 0.08 ± 0.03 -0.292 0.040 fixed extinction
2001-Mar-08 NGC2419 25.62 ± 0.02 0.06 ± 0.02 -0.280 ± 0.006 0.030 free fit, 3-4" seeing
2001-Apr-07 M92 25.651 ± 0.005 0.057 ± 0.009 -0.292 0.027 fixed extinction
2001-Oct-04 NGC7790 25.423 ± 0.007 0.055 ± 0.002 -0.214 ± 0.005 0.018 free fit

V-filter.
Date Field V_zp V_ct V_ext V_rms Comment
2000-Sep-11 NGC7790 25.660 ± 0.002 -0.059 ± 0.002 -0.179 0.019 fixed extinction
2000-Oct-16 NGC7790 25.684 ± 0.002 -0.061 ± 0.002 -0.179 0.025 fixed extinction
2001-Jan-14 NGC2419, M92 25.672 ± 0.005 -0.074 ± 0.005 -0.179 0.037 fixed extinction
2001-Jan-14 NGC2419, M92 25.54 ± 0.01 -0.050 ± 0.004 -0.107 ± 0.007 0.032 free fit
2001-Feb-08 NGC2419 25.62 ± 0.01 -0.061 ± 0.006 -0.135 ± 0.005 0.025 free fit
2001-Feb-08 NGC2419 25.68 ± 0.01 -0.060 ± 0.009 -0.179 0.035 fixed extinction
2001-Mar-08 NGC2419 25.62 ± 0.01 -0.062 ± 0.008 -0.164 ± 0.006 0.037 free fit, 3-4" seeing
2001-Apr-07 M92 25.624 ± 0.004 -0.046 ± 0.005 -0.179 0.022 fixed extinction
2001-Oct-04 NGC7790 25.44 ± 0.01 -0.063 ± 0.002 -0.108 ± 0.007 0.023 free fit

R-filter.
Date Field R_zp R_ct R_ext R_rms Comment
2000-Sep-11 NGC7790 25.493 ± 0.004 -0.047 ± 0.007 -0.136 0.030 fixed extinction
2000-Oct-16 NGC7790 25.515 ± 0.004 -0.067 ± 0.006 -0.136 0.033 fixed extinction
2001-Jan-14 NGC2419, M92 25.499 ± 0.004 -0.089 ± 0.009 -0.136 0.036 fixed extinction
2001-Jan-14 NGC2419, M92 25.41 ± 0.01 -0.06 ± 0.01 -0.088 ± 0.008 0.035 free fit
2001-Feb-08 NGC2419 25.48 ± 0.01 -0.09 ± 0.02 -0.086 ± 0.005 0.033 free fit
2001-Feb-08 NGC2419 25.55 ± 0.01 -0.09 ± 0.02 -0.136 0.043 fixed extinction
2001-Mar-08 NGC2419 25.47 ± 0.02 -0.04 ± 0.02 -0.140 ± 0.010 0.043 free fit, 3-4" seeing
2001-Apr-07 M92 25.497 ± 0.005 -0.09 ± 0.01 -0.136 0.027 fixed extinction
2001-Oct-04 NGC7790 25.33 ± 0.01 -0.071 ± 0.005 -0.095 ± 0.008 0.025 free fit

I-filter.
Date Field I_zp I_ct I_ext I_rms Comment
2000-Sep-11 NGC7790 24.866 ± 0.003 -0.033 ± 0.003 -0.079 0.027 fixed extinction
2000-Oct-16 NGC7790 24.850 ± 0.003 -0.042 ± 0.003 -0.079 0.033 fixed extinction
2001-Jan-14 NGC2419, M92 24.930 ± 0.005 -0.109 ± 0.005 -0.079 0.035 fixed extinction
2001-Jan-14 NGC2419, M92 24.80 ± 0.01 -0.082 ± 0.005 -0.008 ± 0.007 0.032 free fit
2001-Feb-08 NGC2419 25.14 ± 0.03 -0.056 ± 0.006 not derived 0.026 free fit
2001-Feb-08 NGC2419 24.888 ± 0.009 -0.059 ± 0.007 -0.079 0.032 fixed extinction
2001-Mar-08 NGC2419 24.89 ± 0.01 -0.057 ± 0.007 -0.116 ± 0.005 0.038 free fit, 3-4" seeing
2001-Apr-07 M92 24.943 ± 0.007 -0.046 ± 0.008 -0.079 0.029 fixed extinction
2001-Oct-04 NGC7790 24.73 ± 0.01 -0.043 ± 0.003 -0.060 ± 0.009 0.030 free fit


Back to top Last modified: 04-Jun-2007