Data Set Overview : This data set contains aperture photometry of Kreutz sungrazing comets that were observed by the Large Angle Spectrometric Coronagraph (LASCO) on NASA's Solar and Heliospheric Orbiter (SOHO) from 1996-2005. All photometry was calculated from reduced subimages which have previously been archived with the Planetary Data System (Knight 2008) [KNIGHT2008]. Scientific analysis of this photometry was published in (Knight et al. 2010) [KNIGHTETAL2010]. Please see these works for additional documentation.  Aperture photometry was calculated using the reduced subimages (Knight 2008) [KNIGHT2008] by centroiding on the brightest pixel using a two-dimensional gaussian. The flux was summed inside of circular apertures of radius 1, 2, 3...10 pixels, centered on the nucleus. The pixel scale is 11.9 arcsec/pixel for the C2 telescope and 56 arcsec/pixel for the C3 telescope (the telescope used is indicated in the file name of the PDS image).  Integrated fluxes from the aperture photometry were then converted to apparent visual magnitudes using the following relation  V : a - 2.5 * log_10(totcts/sec)  where a is the zero-point offset calculated by the SOHO team from F, G, and K type stars in the LASCO field of view, and totcts/sec is the integrated counts in a given aperture. Values of a for each telescope/filter combination used by SOHO are  Telescope Filter a --------- -------- ------ C2 Orange 11.867 C3 Blue 8.246 C3 Orange 9.472 C3 Clear 11.160 C3 Deep Red 9.546 C3 IR 8.217  although only C2 orange and C3 clear photometry are archived here. Note that the values in the above table differ from those given in Knight (2008) [KNIGHT2008]. The values given above were provided by Thernisien (private communication 2003; published in its entirety in the table above) and Llebaria et al. (2006) [LLEBARIA2006] and were used in Knight et al. (2010) [KNIGHTETAL2010].  The error in the magnitude was calculated using photon statistics and then converted to a magnitude through a propagation of errors. Any aperture for which the integrated flux was zero or negative (not uncommon due to variation of the background brightness on short timescales) was assigned an apparent magnitude of 99.99 and an error in magnitude of 99.99. Also, any magnitude error which exceeded 9.99 was set to 9.99.  Detailed filter information is archived with PDS in Knight (2008) [KNIGHT2008].

Confidence Level Overview : This data is a more basic version of that published in Knight et al. (2010) [KNIGHTETAL2010]. They differ in several ways: 1. Knight et al. (2010) [KNIGHTETAL2010] corrected the fluxes to unit SOHO-centric distance prior to conversion to magnitudes. 2. Knight et al. (2010) [KNIGHTETAL2010] corrected the magnitudes for the scattering properties of dust and the contribution of sodium emission to the scattered light. 3. Knight et al. (2010) [KNIGHTETAL2010] calculated upper/lower error estimates by adding/subtracting the error due to photon statistics from the integrated flux prior to conversion to magnitudes. The resulting difference in magnitudes was then then added in quadrature to additional sources of error (uncertainty in the comet-spacecraft distance, uncertainty in the dust scattering correction, and uncertainty in the zero-point scale). See Knight et al. (2010) [KNIGHTETAL2010] for further discussion of these differences.  Due to fluctuation in the sky background from image to image, there are a significant number of images where the photometry indicates negative integrated counts but the comet is clearly visible. These are recorded as having magnitude of 99.99 here but future users may wish to consult the images archived in Knight (2008) [KNIGHT2008] to perform their own photometry.