Draft note on STC in the Registry

[Arnold Rots]

I have mentioned this before.
A common positional query to catalogs basically asks three questions:
1. Is this location covered by the catalog?
2. If so, is there an entry associated with this location?
3. If so, what is that entry?

My understanding is that the MOCs associated with (most) catalogs
provide the coverage of the *records *in the catalog. As a consequence,
they can only give a definite response if the answer to the second
question is yes.
For the Chandra Source Catalog our coverage represents the union
of the fields of view of all the observations used to create the catalog.
This means that if a location is included in the coverage, but does
not correspond to a source, the user knows that there is a non-
detection at that location which, in many cases is as significant as
knowing there is a source.
If on the other hand, the coverage is solely based on the catalog's
records, a NO-answer is ambiguous; it may be:
*no, we had a non-*
*detection*; or: *we don't know since we didn't look there*.
I think that is a serious shortcoming. Non-detections are significant,
particularly in the context of SEDs and the time domain.

Cheers,

  - Arnold


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Arnold H. Rots                                          Chandra X-ray
Science Center
Smithsonian Astrophysical Observatory                   tel:  +1 617 496
7701
60 Garden Street, MS 67                                      fax:  +1 617
495 7356
Cambridge, MA 02138
arots at cfa.harvard.edu
USA
http://hea-www.harvard.edu/~arots/
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On Thu, Feb 1, 2018 at 5:27 PM, Pierre Fernique <
Pierre.Fernique at astro.unistra.fr> wrote:

>
> Le 30/01/2018 à 20:13, Arnold Rots a écrit :
>
>> Another issue is that MOCs generated
>> for catalogs generally reflect the distribution of the catalog's
>> records, not the true coverage of the catalog.
>>
>
> Arnold can you detail this point ? I'm not sure that I caught your
> argument.
> Thanks
> Pierre
>
>
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