Las Cumbres Observatory Derived Data Product Collection

Data Abstract
=============

We obtained images of the NEO (65803) Didymos binary asteroid and
supporting calibration data with the Las Cumbres Observatory global
telescope (LCOGT) network through several filters. These images were
obtained in support of NASA's Double Asteroid Redirection Test (DART)
mission. The DART mission was a planetary defense mission designed to
test and measure the deflection caused by a kinetic impactor (the
spacecraft) on the orbit of Dimorphos asteroid around its primary,
Didymos. These ground-based observations were used to obtain light
curves of Didymos and time the mutual events of Dimorphos to determine
the period change caused by the impact of the DART spacecraft. This
collection consists of the Las Cumbres Observatory photometry summary
tables, which are a PDS4 derived product.

Data Set Overview
=================

The photometry of Didymos is measured from the calibrated frames (see
date_lcogtcal collection) using the NEOexchange or PHOTOMETRYPIPELINE
pipelines. Both perform source detection in the images using SExtractor
(Bertin, E and Arnouts, S. 1996. SExtractor: Software for source
extraction. A&AS, 117, 393), astrometric fits to the detected sources
based on the known positions of Gaia DR2 stars in the field using SCAMP
(Bertin, E. 2006.  Automatic Astrometric and Photometric Calibration
with SCAMP. ASPC, 351,112), photometrically calibrates the zero point
of the images based on the measured flux of field stars that have known
catalog magnitudes (typically from eithe the PanSTARRS or Gaia-DR2
catalogs), and then using these astrometric and photometric solutions
derives a calibrated magnitude for Didymos. The photometry tables
included in this collection are the output of these pipelines.


The photometry summary table is named according to the following convention: 
lcogt_<site>_<inst.>_<YYYYMMDD>_<request #>_<astname#>_photometry.tab
where:
* <site> is the LCOGT site code as defined in the table below,
* <inst.> is the LCOGT instrument code e.g. ‘fa15’ where the first letter
indicates CCD manufacturer (f=Fairchild), second letter indicates controller
manufacturer (a=Archon) and the 2 digits indicate serial number,
* <YYYYMMDD> is the date of the start of data collection for that night,
* <request number> is the unique LCOGT (integer) identifier assigned to the observation
request by the LCOGT Observing Portal
* <astname#> is the asteroid name and number in PDS-compatible identifier format i.e. all
lowercase

An example would be lcogt_lsc_fa15_20220730_2956963_65803didymos_photometry.tab
for a photometry file for (65803) Didymos from the fa15 instrument at
Cerro Tololo (site code 'lsc') from 2022-07-30.

The LCOGT site codes (which are based on the IATA code of the nearest
airport) are defined as follows:

LCOGT     Site 
Site code location description
--------- -----------------------------------------------------------------
ogg       Haleakala, Maui, HI, USA
coj       Siding Spring Observatory, NSW, Australia
lsc       Cerro Tololo Inter-American Observatory, Chile
cpt       South African Astronomical Observatory, Sutherland, South Africa
elp       McDonald Observatory, Texas, USA
tfn       Teide Observatory, Tenerife, Canary Islands, Spain
ngq       Ali Observatory, western Tibet, China
sin       Meta site for all Sinistro cameras in the network

Photometry data are stored as a PDS4 ASCII fixed-width table according to the 
following format. 

validity_flag: Flag whether this is a valid photometric datapoint, # indicates
probably invalid blended data due to asteroid interference with the star.
file: file name of the calibrated image where data were measured
julian date: Julian date of the exposure midtime
mag: Calibrated PanSTARRS r-band apparent magnitude of Didymos
sig: 1-sigma error on the apparent magnitude 
ZP: Calibrated zero point magnitude in PanSTARRS r-band
ZP_sig: 1-sigma error on the zero point magnitude
inst_mag:  Instrumental magnitude of Didymos 
inst_sig: 1-sigma error on the instrumental magnitude
SExtractor_flag: Flags associated with the Source Extractor photometry 
measurements, see source_extractor_flags.txt in the documents folder for this 
archive for more detailed description.
aprad: Radius in pixels of the aperture used for the photometry measurement


References
==========

E. Bertin and S. Arnouts., 1996. SExtractor: Software for source
extraction. A&AS, 117:393–404, June 1996. doi:10.1051/aas:1996164.
E. Bertin., 2006.  Automatic Astrometric and Photometric Calibration
with SCAMP. ASPC, 351:112. 2006ASPC..351..112B
T. Lister, et al, 2021.  NEOExchange - an online portal for NEO and
Solar System science. Icarus, 364, 114387. doi:10.1117/12.2314340
Proceedings of the SPIE, 10707, 107070K. doi:10.1117/12.2314340
Mommert, M., 2017. PHOTOMETRYPIPELINE: An automated pipeline for
calibrated photometry. Astronomy and Computing, 18, pp.47–53.
doi:10.48550/arXiv.1702.00834