[vsnet-campaign 62] NGC 4151 ASCA-VSNET multiwavelength campaign: photometry guideline

[Taichi Kato <tkato>]

NGC 4151 ASCA-VSNET multiwavelength campaign: photometry guideline

   We recommend to use one or a few of the following comparison stars.

                     (J2000.0)        V    B-V  U-B   spec  name
   ===============================================================
   GSC3017.903  121043.76 +391925.3  9.83 0.59 -0.01  G0
   GSC3017.1484 121031.35 +392641.2 11.47 1.00  0.80        sq1_2
   GSC3017.1357 120955.95 +392825.7 11.22 1.02  0.83        sq1_5
   GSC3017.1470 121012.41 +391934.3 12.58 0.65  0.22        sq1_4
   GSC3017.1645 121038.53 +392029.3 12.79 1.22  1.40        sq1_3

   For small telescopes with wide FOVs, the first comparison star would
provide the best statistics and the suitable color.  The second or third
comparison star would be suitable for smaller FOVs.

   Some notes:

   (1) Please use the fixed aperture size to minimize the effect of galaxy
       comtamination.

   (2) PSF-fitting photometry might yield less contamination, but the
       nucleus is bright enough for usual aperture photometry.

   (3) Multicolor photometry is strongly encouraged.

   (4) Please make observations on as many possible nights in order to
       make sufficient zero-point adjustment between observers.
       Single-night observation is usually useless.

   (5) No dense time-series is necessary.  However, several points during
       one night would help when correlating observations.

   (6) Report your observations in differential magnitudes to these
       comparison stars (or fully reduced magnitude), with UT, bands and
       other information.

   (7) The expected variation would be smaller than errors of visual
       observations.  However, there was an occasion when the rise reported
       by visual observers coincides with the spectroscopic change in the
       broad line.  According to the reports to VSNET, the source has been
       on a stready decline from the 1995 bright state.

Regards,
Taichi Kato
VSNET Collaboration team

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