TITLE:   GCN CIRCULAR
NUMBER:  9221
SUBJECT: GRB090423: Y-band field calibration
DATE:    09/04/24 12:43:12 GMT
FROM:    Myungshin Im at Seoul Nat U  <mim@astro.snu.ac.kr>

  M. Im, Y. Jeon, C. Choi, W. Park, I. Lee Seoul National Univ),
  Y.-B. Jeon (KASI) and Y. Urata (NCU) on behalf of EAFON team.

  We took a series of Y-band photometry calibration data
  for the field of GRB090423 using the 1.0m telescope at
  Mt. Lemmon (Arizona, US) operated by the Korea Astronomy
  Space Science Institute.

   For the Y-band photometry standards, we used P239-C and
  GD140 from UKIRT faint standards, and HIP 50459, a A0V star
  from Hipparcos catalog. The zero points obtained for
  these standards are applied to our observation of
  the GRB090423 field, yielding Y-band photometry (Vega) for
  objects in the GRB field down to Y(MKO) ~ 17.5 magnitude at 10-sigma.
  The expected zero point accuracy is ~0.1mag.
  To derive AB mag, add 0.63 mag to the values listed in
  the catalog.

  The calibration data and finding charts are available at
  http://astro.snu.ac.kr/~mim/grb/readme
  http://astro.snu.ac.kr/~mim/grb/grb090423_ycal.dat
  http://astro.snu.ac.kr/~mim/grb/yobj.reg
  http://astro.snu.ac.kr/~mim/grb/chart.gif

  We thank the LOAO operator, J. Yoon for his assistance for this
  observation.