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Dear all,<br>
<br>
I have assembled photometric homogeneity table as part of the
release note:<br>
<a class="moz-txt-link-freetext" href="http://wiki.astro-wise.org/projects:kids:data_deliveries:internaldelivery2.0#photometric_calibration">http://wiki.astro-wise.org/projects:kids:data_deliveries:internaldelivery2.0#photometric_calibration</a><br>
I think column 3 can now be replaced with your results. <br>
That is more informative than current content: stdev in offsets of
KiDS vs SDSS for coadd as a whole.<br>
<br>
Is MAD(running median) representative (i.e., free of measurement
error) to quote?<br>
<br>
Best wishes, Gijs<br>
ps. I think the flatness allows us to proudly zoom in on +/-0.1 in
your plotting.<br>
<br>
On 11/30/2012 12:09 PM, Francesco La Barbera wrote:
<blockquote
cite="mid:CAOnmKXcDjVjC5R_aBrFBQRVGVC+ZJDjKUL1RF+_eBROq3zGRbQ@mail.gmail.com"
type="cite">
<div class="gmail_quote">On Fri, Nov 30, 2012 at 12:01 PM, Konrad
Kuijken <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:kuijken@strw.leidenuniv.nl" target="_blank">kuijken@strw.leidenuniv.nl</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF"> Hi all,<br>
<br>
indeed amazingly flat plots, Francesco!<br>
I suppose the conclusion from this is that we shouldn't use
petroMags for comparing stellar magnitudes, and that our
coadd photometry is pretty flat now.<br>
<br>
</div>
</blockquote>
<div><br>
</div>
<div>Yup, these are my conclusions too, Jelte ! </div>
<div>In any case, let's wait to hear also from Mario on Monday
morning. We should stick at using petromags for galaxies and
psfmags for stars, measuring KIDS mags accordingly. This is
also crucial to properly characterize the color terms.</div>
<div><br>
</div>
<div>Cheers,</div>
<div>Francesco</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF"> Cheers,<br>
Jelte
<div>
<div class="h5"><br>
<br>
<div>On 30/11/12 11:35, Francesco La Barbera wrote:<br>
</div>
<blockquote type="cite">Hi All,
<div><br>
</div>
<div>this is a "quick" test, showing the delta(mag)
stacked plots (i.e. overplotting all 13 fields),</div>
<div>when one adopts PSFmags from SDSS and KIDSCAT
large-diameter (8'') apertures.</div>
<div>I used the SDSS-KIDS matched catalogs produced by
Mario. </div>
<div>I didn't plot single values but only binned
trends. The x- and y-scales are the same as in
previous plots.</div>
<div>Amazing how the 2.5deg patterns disappear!!
Although in some cases (e.g. magenta curve for
g-band comparison), you can see some trend, we
should consider (IMHO) that PSFmags can still be
affected by systematics of the order of
0.01-0.02mag, and we are using an arbitrarely(!)
large aperture for KIDS data. Measuring mags in the
same (large) apertures would possibly solve any
residual aperture effect. </div>
<div>BTW, the amplitude of the trends is amazingly
small !! </div>
<div><br>
</div>
<div>Cheers,</div>
<div>Francesco</div>
<div><br>
</div>
<div> <br>
<br>
<div class="gmail_quote">On Fri, Nov 30, 2012 at
10:40 AM, Konrad Kuijken <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:kuijken@strw.leidenuniv.nl"
target="_blank">kuijken@strw.leidenuniv.nl</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0
0 .8ex;border-left:1px #ccc
solid;padding-left:1ex">
<div dir="auto">
<div>Hi all,</div>
<div>Beautiful work! Jelte and I looked at the
plots yesterday and indeed concluded that
the step functions correspond to the size of
the Sloan chips. The pattern in iband is 2.5
deg wide, exactly the width of a stripe in
Sloan. Two interleaved exposures, six chips
with large gaps each, similar to a 1d
version of the paw print pattern in vista,
would give the step pattern you find. </div>
<div><br>
</div>
<div>One thing to check: does the effect show
up if you use Sloan psf magnitudes?
Petrosian mags might be a little seeing
dependent, psf mags should be optimal if
they have done their analysis right. </div>
<div><br>
</div>
<div>Thanks</div>
<div>Konrad
<div>
<div><br>
<br>
On 29 Nov 2012, at 12:15, Jelte de Jong
<<a moz-do-not-send="true"
href="mailto:jelte@strw.leidenuniv.nl"
target="_blank">jelte@strw.leidenuniv.nl</a>>
wrote:<br>
<br>
</div>
</div>
</div>
<div>
<div>
<blockquote type="cite">
<div> Hi Francesco and all,<br>
<br>
since I was quite intrigued by the
strange offsets in the SDSS vs. KiDS
comparison for stars (and not for
galaxies), I had a look at the DR8
data in the area of the 10 contiguous
tiles in INT-DR2.<br>
The problem here is of course that we
need an independent calibrator that we
are certain is constant over the
field-of-view, and the obvious thing
to me seemed to be the stellar locus.<br>
<br>
Here is what I did:<br>
- downloaded the DR8 petroMag data for
stars for (183.5 < RA < 186.5)
and (-2 < DEC < +2)<br>
- applied extinction correction (using
values included in DR8)<br>
- calculated the principle colors <br>
(FYI: from Ivezic et al, 2004, AN,
325, 583<br>
p2s = -0.249*u0 + 0.794*g0 - 0.555*r0
+ 0.234<br>
p2w = -0.227*g0 + 0.792*r0 - 0.567*i0
+ 0.050<br>
p2x = 0.707*g0 - 0.707*r0 -0.988<br>
p1s = 0.910*u0 - 0.495*g0 - 0.415*r0 -
1.28<br>
p1w = 0.928*g0 - 0.556*r0 - 0.372*i0 -
0.425<br>
p1x = 1.0*r0 - 1.0*i0<br>
)<br>
- for the stars with
r(petro,SDSS)<18 plotted the
principle colors p2s, p2w and p2x
(using only the part of the stellar
locus that is vertical in these
colors, e.g. see <a
moz-do-not-send="true"
href="http://wiki.astro-wise.org/projects:kids:photometry#sdss-style_principle_colors"
target="_blank">http://wiki.astro-wise.org/projects:kids:photometry#sdss-style_principle_colors</a>)<br>
<br>
In the p2s and p2x projections I
couldn't see anything specific, but in
p2w there does seem to be a variation,
corresponding to the same offsets seen
in the plots Francesco sent around.<br>
The attached plot shows the p2w color
vs. DEC for three different RA bins
(middle panel is full RA range, top is
low-RA half and bottom is high-RA half
of the area), with a running mean
plotted in red.<br>
I hope you can see (squinting might
help ;) there is a 'modulation' in the
top and middle panel, and the 'phase'
of it agrees with the offsets in the
SDSS vs. KiDS comparison!<br>
It seems this effect is stronger at RA
between 183.5 and 185, and is weaker
(or absent) at RA between 185 and
186.5; @Francesco: is this confirmed
by the SDSS vs. KiDS comparison?<br>
<br>
My interpretation on why this is only
obvious in the p2w color and not in
p2s and p2x, is that the 'problem' is
strongest in i-band (the offsets in
Mario+Francesco's plots seems larger
in i than in the other filters) and
p2w is the only principle color that
depends on i.<br>
Also, the fact that the effect is very
small in p2w (~1 %) is probably
because the calibration problem occurs
in all SDSS filters, meaning that the
colors are almost not affected.<br>
<br>
Perhaps there are other ways in which
to go deeper into this, but right now
I'm not sure exactly how. Perhaps
another independent calibrator can be
used... QSO's or something?<br>
<br>
In any case I have the feeling that
the offsets we see might very well be
due to a calibration issue in SDSS, or
at least in the SDSS petroMags for
stars.<br>
<br>
Cheers,<br>
Jelte<br>
<br>
<div>On 28/11/12 10:21, Francesco La
Barbera wrote:<br>
</div>
<blockquote type="cite">
<div>Dear All,</div>
<div><br>
</div>
<div>I summarize here the
comparison of KIDS to SDSS
photometry we</div>
<div>(Mario+me) have performed so
far for the 52 coadds of KIDS
INTR2. All</div>
<div>plots are included in the
attached archive.</div>
<div><br>
</div>
<div>Mario has also performed a
comparison to CFHTLS as well as
a first</div>
<div>attempt to characterize of
color terms using SDSS and CFHTLS
data, but</div>
<div>I'm not going to include it in
here (we didn't have much time to
look</div>
<div>at it in detail, so far).</div>
<div><br>
</div>
<div>We have matched the KIDSCAT
catalogs to SDSS DR8, separating
stars and</div>
<div>galaxies according to SDSS
classification.</div>
<div><br>
</div>
<div>The plots</div>
<div> <br>
</div>
<div>sdss_${SOURCE}_${BAND}_${FIELD}_full_DR8.png </div>
<div><br>
</div>
<div>show differences in magnitude
as a function of RA (upper
panel) and</div>
<div>DEC (lower panel), where </div>
<div>SOURCES -> gal/st refer to
galaxies and stars, respectively</div>
<div>BAND -> ugri</div>
<div>FIELD -> f135 plots the
three fields with RA~131, 135, and
139</div>
<div> f185 plots the ten
fields with RA~184, 185, and 186</div>
<div><br>
</div>
<div>We are using petromags from
SDSS (for both stars and
galaxies).</div>
<div>KIDSCAT mags have been
interpotaled to match the SDSS
4xPetroRad</div>
<div>(diameter) aperture for each
object. Lines are running
medians for</div>
<div>different bands/pointings (the
u-band comparison for galaxies is
quite</div>
<div>meaningless, considering the
low S/N of SDSS u-band data).
Median</div>
<div>KIDS-SDSS offsets have been
subtracted off for each field.</div>
<div><br>
</div>
<div>On average, the agreement is
good, with no significant
variations</div>
<div>(larger than a few cenths of
mags) across the fields. This is
further</div>
<div>shown in the attached plots</div>
<div><br>
</div>
<div>cmp_${BAND}band_phot_ra_dec_${SOURCES}_errmag0.05.jpg</div>
<div><br>
</div>
<div>where </div>
<div><br>
</div>
<div>BAND->ugri</div>
<div>SOURCES-> stars/galaxies</div>
<div><br>
</div>
<div>plotting magntiude differences
as a function of RA and DEC with
all</div>
<div>fields overplotted (after
subtracting off the RA and DEC of
each coadd</div>
<div>center). Median magnitude
offsets have been removed (as
done for</div>
<div>previous plots), and only
objects with better SDSS
photometry</div>
<div>(petroerr_mag<0.05mag) have
been selected. Circles plot all
available</div>
<div>sources (for all 13 coadds in
each band). Curves are
median-binned</div>
<div>trends (each bin including the
same number of objects), with
different</div>
<div>colors corresponding to
different fields. Notice that the
u-band plot</div>
<div>for galaxies is not included,
for the reasons mentioned above.</div>
<div><br>
</div>
<div>Finally, the plots </div>
<div><br>
</div>
<div>off_${BAND}band_phot_ra_dec_${SOURCES}_errmag0.05.jpg</div>
<div><br>
</div>
<div>show the distribution of
median magnitude offsets for
all the 13</div>
<div>fields available in each band.
In general, the distributions
have a</div>
<div>width of a few cenths of
mags, but in one case
(KIDS_185.0_-0.5,</div>
<div>g-band) there is a large offset
of ~0.1mag. We think it's
important to</div>
<div>investigate why this happened.</div>
<div><br>
</div>
<div>I'm also attaching two tables
(produced by Mario, hopefully in
wiki</div>
<div>format) summarizing the the
median offsets, mad, and peak
to peak</div>
<div>amplitudes in RA and DEC (to
have an upper value to the
internal</div>
<div>photometric accuracy):</div>
<div><br>
</div>
<div>ov_sdss_gals.tab</div>
<div>ov_sdss_stars.tab</div>
<div><br>
</div>
<div>If necessary, I can provide
further details/info on the
comparison</div>
<div>during today's teleconf. We'll
try to put all this material on
the wiki as</div>
<div>soon as possible.</div>
<div><br>
</div>
<div>Cheers,</div>
<div>Francesco & Mario</div>
<div><br>
</div>
<br>
<fieldset></fieldset>
<br>
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</blockquote>
<br>
<pre cols="72">--
Dr. Jelte T. A. de Jong
Sterrewacht Leiden
Leiden University, Leiden, the Netherlands
E: <a moz-do-not-send="true" href="mailto:jelte@strw.leidenuniv.nl" target="_blank">jelte@strw.leidenuniv.nl</a>
T: <a moz-do-not-send="true" href="tel:%2B31-%280%29715275818" value="+31715275818" target="_blank">+31-(0)715275818</a>
W: <a moz-do-not-send="true" href="http://jelte.jdejong.net" target="_blank">jelte.jdejong.net</a>
</pre>
</div>
</blockquote>
</div>
</div>
<blockquote type="cite">
<div><DR8_p2w.eps></div>
</blockquote>
<div>
<blockquote type="cite">
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target="_blank">KiDS@astro-wise.org</a></span><br>
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<br>
</div>
</blockquote>
<br>
</div>
</div>
</div>
</blockquote>
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<br>
<br>
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