SDSS-II SN Super-unofficial Hand-Scanning Guide

An attempted synthesis of information I found useful in getting up to speed for handscanning, culled from the mails of various members of the supernova-dp@fnal mailing list. Images are from the FNAL SN candidates handscanning page. Corrections/suggestions welcomed.

1. Decision Tree for Handscanning

Note the tree does not currently make use of g,r,i and delta_g, etc... magnitudes, nor does it discuss the SN-OTHER and SATURATED categories for which I do not have clear criteria.


2. Examples for various categories

For reference some examples are provided: (as usual, first frame is the search, second is the template, third is the difference).

SN Gold:

Note the history box: 0 previous objects. Clear separation from host galaxy and point-like candidate.

SN Bronze

No history of variability of the host. Candidate appears to be near the center of host (may be AGN etc...). Host should not obviously be stellar.


Object is moving (seen as clear change in position between g and r frames)


Diffraction spike or other obvious problem, e.g.


Roughly equal amounts of positive/negative flux in the subtracted frame


History of long-term variability (shown in the history box).

Note the history box shows the object significantly before (682.1 and 680.1 days before) with significant variation in the g/r magnitudes.


No apparent host and no recent, independent, history.

Note that although there is an entry in the history box, it is at zero lag. If the transient is moving it will not be seen again at this RA,DEC. If it is a SN, it will be seen again and will be reclassified as SN Silver. Often small amounts of motion are visible between g,r for transients.


3. Potential Ambiguous Cases

There are a couple of points at which the above classification scheme overlaps causing ambiguity:

Transient or SN Gold?

By unlucky chance a transient (e.g. asteroid) may be found close to, but nicely separated from, a ``host" galaxy in projection.

Variable or SN Bronze?

If history is missing (for some artificial reason), a variable may be classified as SN bronze. Conversely, host galaxies may appear stellar, giving rise to misclassification of SN as variables.

Bruce Bassett, v 0.1 (5 September 2005,