adding information about new metadata in v1.28.4

docs/UserGuide.md

@@ -179,8 +179,19 @@ If you want to generate a light curve rather than an integrated value, pass the
 
 For any command, you can always request more information be printed to the terminal by setting the `--verbose` or `-v` flag to a number between 1-3 (defualt is 0) where larger numbers indicate increasing levels of output. Setting `-v 3` will print out complete SQL commands and should really only be used for debugging.
 
+####Lightcurve Header Definitions
+Setting the `--addhdr` keyword when calling gAperture from command line or `addhdr=True` when called as a Python module will induce gAperture to prefix several rows of additional information to each lightcurve file. This information includes the parameters used for the call as well as the software version number. If called from the command line, the header will include a reconstruction of the command line call used.
+
+There are three additional header parameters related to possible contamination of the observation by outside sources:
+
+&nbsp;&nbsp;**n_apersources** - The number of MCAT coadd sources in this band that are located inside of the aperture. You would usually want this number to be <=1.
+&nbsp;&nbsp;**n_bgsources** - The number of MCAT coadd sources in this band that are located inside of the background annulus (if applicable). You probably want this number to be small, but a large number is not necessarily bad.
+&nbsp;&nbsp;**max_bgmag** - The AB magnitude of the _brightest_ MCAT coadd source located within the background annulus. You probably want this to be significantly dimmer (i.e. bigger magnitude) than the object of interest.
+
+Remember to always check the images for contamination.
+
 ####Lightcurve File Column Definitions
-**NOTE:** The column definitions for the .csv output from _gAperture_ are in flux. These are the column definitions as of the v1.27.1 build.
+**NOTE:** The column definitions for the .csv output from _gAperture_ are in flux. These are the column definitions as of the v1.28.4 build.
 
 **NOTE:** The columns are not necessarily written to the output file in the order given. Nor are the columns necessarily fixed in order at all. You should parse the lightcurve file on the column _name_ and not the column number.
 
@@ -334,7 +345,7 @@ The individual photon events used in the creation of a light curve can be option
 
 _gMap_ is the image creation tool. It can generate integrated count, intensity, and response (equivalent to GALEX _cnt_, _int_ and _rrhr_) maps of arbitrary size<sup>+</sup>, shape and depth, including coadds across epochs and survey designation. It can also create "movie" (time-binned, multi-plane) versions of such maps. _(Note that in v1.23.0, image creation is quite slow because it uses an older method of interpolating the response map from the flat rather than the new and faster method used by gAperture of weighting the photons directly by the flat. This will be fixed in v1.24.0)_
 
-_gMap_ writes all image files in the Flexible Image Transport System (FITS) standard, which is an uncompressed archival data format favored by many astronomy applications (and was used by the GALEX mission for archival products). FITS images generated by _gMap_ have headers which describe the World Coordinate System (WCS) information defining their orientation on the sky as well as effective exposure time and other metadata for the observation as a whole. For multi-frame images (movies), the per-plane information is described in a table in the FITS secondary HDU; this table describes start time, stop time, and effective exposure for each frame (within appropriately labelled columns).
+_gMap_ writes all image files in the Flexible Image Transport System (FITS) standard, which is an uncompressed archival data format favored by many astronomy applications (and was used by the GALEX mission for archival products). FITS images generated by _gMap_ have headers which describe the World Coordinate System (WCS) information defining their orientation on the sky as well as effective exposure time and other metadata for the observation as a whole. The headers also contain `EXPSTART`, `EXPEND`, and `EXPTIME` parameters that are defined precisely as they are in mission produced products; notably, `EXPTIME` is _uncorrected_ for deadtime and shutter effects. For multi-frame images (movies), the per-plane information is described in a table in the FITS secondary HDU; this table describes start time, stop time, and effective exposure for each frame (within appropriately labelled columns).
 
 <sup>+</sup>Caveat emptor. "Arbitrariness" is limited by your available patience and RAM.