adendum Re: hints and tips for DS 20

[Robert Creager <robert@carolinecreager.com>]

I noticed that the images in vdark/idark have an image
type of BIAS, but the EXPTIME appears to be correct.

---- Stupendous Man <richmond@a188-l009.rit.edu>
wrote:
> 
>   I'm working on some of the DS data right now, and
hope
> to write up a Tech Note sometime soon.  Let me
explain
> a few of the things I've noticed so far, since they
may
> help Michael Sallman or others to save a little
time.
> 
>       - the box flats on disks 2 and 3 are similar 
>             to night-sky flats derived from disk 6.
>             Large-scale differences are at most 3-4
percent.
> 
>       - the I-band flats show faint circular arcs
>             (probably the arcs mentioned by Michael
S.).
>             These are common in CCD chips at long
wavelengths:
>             I believe they are caused by small
variations
>             in the thickness of the silicon or
coatings.
>             The circular shape is a result of the
manufacturing
>             process.
> 
>       - the dark frames on disk 6 (only three for
each camera)
>             probably shouldn't be used for
reductions; 
>             I found what looks like a light leak in
the
>             V-band darks.  Strangely enough, I see
no hint
>             of this pattern in the V-band night-sky
images
>             for that night.
> 
>       - the night of disks 6, 7, 8 was not perfectly
clear.
>             I found that clouds came and went
throughout the
>             night.  A relatively clear patch runs
from
>             images 2239820 - 2239835, with the best
set of
>             3 consecutive images being 822,823,825.
> 
>       - the I-band data has a FWHM almost 1 pixel
larger than
>             the V-band data
> 
>       - when comparing Mark IV to Tycho-2
photometry, use only
>             stars in the range
>                        7.7 < V < 10.0
>                        8.0 < I < 10.0
>             The Mark IV data is saturated (or
nonlinear) at
>             brighter magnitudes, and the Tycho-2
data is ratty
>             at fainter magnitudes
> 
>       - it appears to me that the V-band camera is
very close
>             to standard Landolt V (color term approx
0.01);
>             the I-band camera has a color term of
about -0.17:
> 
>                    Landolt I  =  TASS I  - 
0.17*(TASS V - TASS I)
> 
>             (but this is preliminary)
> 
>       - the frames on disks 7,8 are centered at
RA=71.2 deg, Dec=7.4 deg,
>             which includes the middle of the shield
of Orion
> 
>       - the images drift by about 1.5 pix E/W and
0.5 pix N/S between
>             exposures on disks 7,8
> 
>   More later.
> 
>                                          Michael
> 
>            
>             
>             
> 
> 
>