Date: Tue, 25 Aug 1998 18:08:30 -0700 (PDT)
To: 2mass
Subject: IPAC 2MASS WG Meeting #161 Minutes
Cc: chas, stiening, bgreen
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-MD5: riN+DsiqcvjrsgGNlnVYLA==

           IPAC 2MASS Working Group Meeting #161 Minutes

Attendees: R. Cutri, S. Van Dyk, L. Fullmer, R. Beck, T. Evans, R. Hurt, 
           J. Fowler, G. Kopan, H. McCallon, J. White, D. Engler,
           R. Tam, D. Kirkpatrick, J. Mazzarella, W. Wheaton, T. Jarrett


1.) Project Update
2.) 2MAPPS 2.1 Update
3.) 2MASS Sampler
4.) QA Update
5.) ISIS Group Update


1.) Project Update

     Improvements will be made at the northern facility in early September.  
Further work on collimation and polar axis alignment will be carried out.  Since
there will always be some small axis misalignment, survey scans near the pole 
will always be taken without active tracking correction, and always in the 
poleward direction.

2.) 2MAPPS 2.1 Update

     W. Wheaton gave a short update of his work on the PSF problem.  He has
been studying PSF magnitude vs. aperture magnitude as the PSF changes, and
the results do not look too bad.  The observed scatter in his analysis could be
due to both crowding effects and seeing.  The chi^2 distribution for the south
is still diverging for high S/N ratio stars.  W. Wheaton suggested a more
thorough comparison with the effects occurring in the north.  This problem needs
to be solved soon, so that 2MAPPS 2.1 can be switched on.

     R. Cutri stressed that more southern nights must be processed.  The 
artifact identification, being handled by T. Evans, appears to be passing muster

     The PSF mag vs. aperture mag bias with cross-scan position is being studied
in depth by G. Kopan and L. Fullmer.  L. Fullmer is binning the scan-to-scan 
magnitude values for intercalibration periods, to analyze the magnitude bias as
a function of various parameters.  So far, a weak dependence on temperature and
focus (which, of course, are interrelated) may exist; also, a possible 
dependence on declination may apply.  Questions arose as to how this bias might
depend on positional (geometric) distortion.  J. Fowler offered that stacking
dithered frames with different relative distortion patterns could lead to a PSF
variation, thus leading to the magnitude bias with cross-scan position.  This
effect, he continued, could be worse in the south.  H. McCallon has the 
astrometric field data for the south, but has not yet generated distortion maps.

     R. Cutri summed up the discussion by saying that, although the ultimate
origin for the problem is still not fully understood, it is understood how to
provide a fix for it.  An empirical correction will be employed.  However, all 
of the ramifications of this correction have yet to be thought out.  Other 
issues, such as the crescent artifact and the "99.999" problem for magnitude 
output, need also to be addressed.

3.) 2MASS Sampler

     The final run on the 971116n scans is currently being done, so that these
results can be "frozen in place" for the 2MASS Sampler, now nominally a month
away or so.  It is important to go over the data thoroughly once the run is
complete.  The point source catalog generation will occur after that.  
Thresholds must be set for subsets of the various columns and rows in the 
catalogs for the Sampler.  

     T. Jarrett and T. Chester are generating the galaxy catalog.  T. Jarrett 
and R. Cutri pointed out that two kinds of extended sources, and therefore, two
branches of an extended source catalog, exist: galaxies and everything else that
is non-stellar.  A subset of rows and columns must be generated for the extended
source catalog as well.  The average community user will want to be able to pull
out, e.g., position, magnitudes, and shape and size parameters for a source.

     The primary catalog "view" will have a shortform format.  However, most of
the parameters for each source will be included in the catalog, and can be shown
with user-specified output formats.  T. Jarrett and T. Chester are developing 
the flags that will be used to cut from the extended source catalog, but this 
flag  format should be similar to that for the point source catalog.

     J. Fowler asked about the optical association "theta" values (i.e., the
point source position angle relative to catalog object) and the correction for 
this angle.  R. Cutri indicated that the correction will go into the catalog
generation, rather than the database.  H. McCallon must still apply corrections
for positional uncertainties; these corrections will be applied to the .cal
files, after calibration, rather than before.

4.) QA Update

     D. Kirkpatrick and R. Hurt discussed the troubles recently appearing in
flats and darks for some processed nights.  These nights may require some
reprocessing.  Problems with flats can be alleviated in processing by using 
nightly flats versus 5-night running-average flats, or by setting the averaging
window to something less than 5 nights.  The J-band linear correction is being
applied on a night-by-night basis, as required.  Currently, photometric 
fractions of nights are being accepted.

5.) ISIS Group Update

     R. Cutri and J. Mazzarella discussed ISIS interface with the 2MASS Sampler.
J. Mazz indicated that various bugs have been recently fixed.  For querying, it
may be necessary to redo the field groupings.  A question arose as to whether
a separate join of the point and extended source catalogs must exist, which R. 
Cutri and T. Evans indicated must be the case, since pointers exist between the
two catalogs.  The "views" of a catalog are virtual.

     As a closing note, R. Cutri reminded all team members that a mandatory
additional working group meeting would be held Friday at 4 PM.  (NB:  It turned
out to be a really grueling session.)