The five W's

[Rob Seaman]

So, IS the "Who, When, Where, What, How" paradigm the correct one?

Arnold approaches an answer like this:

> The criterion for inclusion ought to be scientific significance, [,,,] 
>  And it would seem part of our job to agree on a canonical list of 
> items that are considered scientifically significant.  [...]  As a 
> first stab at what that information would be, at least as far as STC 
> is concerned, I would think: spatial position, time, spectral band, 
> position of the observatory - all as accurate as possible and with 
> errors and sizes/intervals/bandwidths.

As a (previously) outside observer, what is most remarkable about the 
VOEvent v0.3 and STC v1.21 specifications is how much overlap there is 
between the goals of the two nascent standards.  (See:  
http://www.ivoa.net/internal/IVOA/IvoaVOEvent/VOEvent-0.3.htm and 
http://hea-www.harvard.edu/~arots/nvometa)  Each starts from some 
expression of the scope of the phenomena that need to be supported and 
proceeds to a breakdown of metadata common to all.  For instance, here 
are just a few phenomena off the top of my head that should be 
supported (ideally):

     - SN - point source appears, brightens, dims, disappears
     - Variable star - point source brightens and dims periodically
     - Flare star - point source brightens and dims aperiodically
     - Asteroid - moving point source obeying orbital dynamics, may 
brighten and dim aperiodically
     - Comet - same as asteroid but with resolved structure
     - Solar flare - resolved structure that grows, shrinks and vanishes 
starting at a specific location on the Solar disk
     - Solar wind - may be related to a flare, has direct effect on 
Earth and spacecraft, non-positional?
     - Planetary disk - resolved changes to the observed character of a 
planet or moon
     - Gamma Ray Burst (GRB) - highly energetic flare of point source 
(position poorly determined?)

What we need to capture from these (and others); are the common 
parameters that tie the different classes of events together.  For 
instance:

     - Is this a point source event or, rather, an event involving a 
resolved (extended) source?
     - If the source is extended, is it fixed or variable in form and 
size?
     - Is the phenomenon located on the celestial sphere, or rather a 
planet, moon or the sun?
     - Is the source/phenomenon moving on the celestial sphere, planet, 
moon or sun?
     - If it is moving, have orbital (rotational) parameters been 
determined?  WRT what primary (e.g., Sun or Jupiter)?
     - Is the source fixed in flux (brightness, luminosity, etc), or is 
the flux varying?
     - If variable, are the variations periodic or aperiodic?
     - Have the amplitude, period(s) (frequencies) and shape(s) of the 
"light curve" been determined?
     - Does the reported event describe a detection(s) or rather 
inferred quantity(ies) of an identified (and perhaps cataloged) source?
     - Is a photometric, or rather, spectral characterization provided?
     - Photometric/spectral parameters, perhaps as a time series.

Note that my list does not start with characterizing the 
observatory/instrument.  This is implicit in any observation, but the 
signature of the instrument and observing site may well have been 
removed before the observation(s) was turned into an event(s).  I'm a 
bit distracted, typing this in the middle of an unrelated meeting, but 
removing the instrumental/observatory signature may be largely 
equivalent to converting from the report of a detection to the report 
of source behavior:

"Dear colleague, at Palomar on 1 Jan 2005 @ 12:34:56 UTC we noted the 
appearance of a B=12.5 point source at RA=01:23:45, Dec=+34:56:78.9 
(2000)."  versus "Dear colleague, a type I SN has been identified in 
M31.  See attached parameters."

(Note that "Dear colleague" is a rhetorical device - we're all aware 
that software agents form the appropriate audience for VOEvents :-)

Rob Seaman
NOAO