[guide-user] Comets/WDS2000/darks and flats

Bill J. Gray Feb 28, 2000

Hi folks,

Hans, regarding comet display: you may not want to turn comets "on",
because there are a _lot_ of comets. If you do this, Guide will insist
on showing comets dating back a thousand years ago, currently at mag 50
or so. It may be better just to set the limiting comet magnitude faint
enough to get the objects you want, while leaving out the "old" comets.

You also asked about evading duplicate asteroids. A month ago,
you couldn't do this. However, the 30 January version added a way
to suppress Guide's built-in asteroid data. You have to add this
line to GUIDE.DAT:

ASTFILTER=b

Full details on how the asteroid filtering works are given at

http://www.projectpluto.com/update7.htm#asteroid_filtering

Andrea, you're right: click anywhere on the lunar disk, and Guide
finds the moon first. This is intentional. Otherwise, you can run into
an unfortunate situation where it's nearly impossible to click on the moon,
because you get craters instead.

The penalty, as you noticed, is that you have to use 'next' to actually
get the crater/lunar feature you wanted.

WDS 2000:

I've posted a new .TDF file for display of this dataset. See:

http://www.projectpluto.com/extras.htm#WDS

REQUEST FOR COMMENTS:

(Those of you who don't do astrometry can safely ignore the rest of
this e-mail.)

I'm contemplating adding a new feature to Charon: a simple ability to
use dark and flat images. Provide a dark image, and Charon could just
subtract that from any image provided. (Provide _many_ dark images, and
Charon would create a "median" dark image.)

If you also provide a flat image, Charon would use that to flat-frame
adjust any image provided. And again, given many flat images, it would
make a "median" flat image and use that.

Dark-subtraction would be almost trivial for me to do (in fact, I
wrote most of the code to do it, in about five minutes, yesterday.)
Flat-fielding is slightly trickier, but not too much so. I don't really
want to rewrite MaximDL, but it seems to me that a few simple functions
of this sort could lead to _much_ better astrometry. (Many of the images
sent to me for testing look as if dark-subtraction alone would improve
them immensely. Flat-fielding appears to be less important, and getting
good flats is harder to do; still, those with vignetting or doing
photometry would probably like this feature.)

Before I get too enthusiastic about this, though, I'd like to get some
comments from Charon users as to whether you would use something like this.

-- Bill