download the fits images, then run !ds9 -minmax -histequ groundbig2.fits hstmatch.fits grounddiffbig.fits grounddiffbig2.fits & then you can blink and see for yourself the astronmetry
remember to adjust the ZEROPOINTS... istars = f814w stars +10-0.536 bstars = f475w stars +10 vstars = f606w stars +10+0.421
VEGAmag : SYNPHOT standard magnitude system, for which Vega by definition has magnitude 0 at
all wavelengths.
The vega magnitude of a star with flux F is -2.5 log10 (F/F_vega) where F_vega is the calibra
ted spectrum of
Vega in Synphot.
F475W 4744.356 1.808802E-19 420.11 25.757 26.068 26.168 g
F606W 5917.678 7.906457E-20 672.31 26.655 26.486 26.398 Broad V
F814W 8059.761 7.072360E-20 654.64 26.776 25.937 25.501 Johnson-Cousins I
Zero points are set to an aperture of 5".5 radius (infintie apeture)
Table 5 has aperture corrections from 0.5" to infinity
They recommend 4 pixel aperture to obtain highest S/n ratio
name pivot width photflam filter title
(erg sec-1 cm-2 A-1)
F435W 4317 293 3.14e-19 Johnson B
F475W 4744 420 1.80e-19 SDSS g'
F606W 5917 672 7.90e-20 Broad V
F814W 8060 654 7.07e-20 Broad I
Aperture correction from 0.5" pixels (10 pixels @ 0.05/pixel) to infinite
F475W 0.095 +/- 0.002 MAGS
F606W 0.088 +/- 0.001 MAGS
F814W 0.087 +/- 0.001 MAGS
Aperture correction from 4 - 10 pixels
F475W 0.0950 0.006052 MAGS
F606W 0.1050 0.012350 MAGS
F814W 0.1339 0.01763 MAGS
FINAL ZERO POINTS
photpars params.... = 26.068+0.095+0.095 = 26.258
26.486+0.088+0.105 = 26.679
25.501+0.087+0.134 = 25.722
2003-LMC-157
05:31:30.656 -70:47:26.03 sm75 3
http://darkstar.astro.washington.edu/2003-LMC-157/index.html
xy2rd
ct> xy2rd
>Input data file name (sn1987a_astrometric_image_rotated.fits): sm75.031201_0617.100_3.diff.f
its
>X pixel coordinate (785.68): 3220.08
>Y pixel coordinate (389.074): 318.68
RA = 5:31:30.7064, Dec = -70:47:25.843
ct>
imexam
3220.08 318.68 5:31:30.711 -70:47:25.812
xy2rd in my best centroid.
>Input data file name (sm75.031201_0617.100_3.diff.fits):
>X pixel coordinate (3220.08): 3220.244
>Y pixel coordinate (318.68): 318.597
RA = 5:31:30.6974, Dec = -70:47:25.865
!ds9 -minmax -histequ groundbig2.fits hstmatch.fits grounddiffbig.fits grounddiffbig2.fits &
final catalog of stars
remember to adjust the ZEROPOINTS...
istars = f814w stars +10-0.536
bstars = f475w stars +10
vstars = f606w stars +10+0.421
star 4500
F814W 490.417 465.170 15.107+10-0.536=24.571 ~+/- 0.08
F606W 490.097 466.100 14.918+10+0.421=25.339
F475W 490.530 466.506 15.888+10 =25.888
F475W-F606W = 0.55
F606W-F814W = 0.77
star 1
F814W 491.080 471.354 15.871+10-0.536=25.34 +/- 0.12
F606W 490.557 472.356 15.736+10+0.421=26.16
F475W 491.134 472.871 16.705+10 =26.71
F475W-F606W = 0.55
F606W-F814W = 0.82