International Virtual Observatory Alliance

Difference: SourceDM (6 vs. 7)

Revision 72019-03-29 - JesusSalgado

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 Source DM: Call For Scientific Requirements 

During the spring 2018 Interop in Victoria, we had a hands-on session focused on the tools available to work with VO data models. The goal this session was to annotate data from different origins in order to make it inter-operable to eachother. The main concern expressed during this session was not related to the tools but to the lack of models for sources. 
 
After some discussions, it appeared that having a global model for all missions and all archives would lead to a very complex model not usable in practice. The reason is that such a global model would have to merge all quantities of all user-cases it is supposed to cover. 
 
It seemed to us more realistic to design a basic model, namely a core-model, with a reasonable set of quantities (ra, dec, ....) useful for all missions and to make it expendable with more specific components (e.g. parallax). So that a model aware tool could compare sources from different origins on the basis of the model components really instantiated. The data annotation process would also be simpler since only the core-model and some components of interest should be tagged.


The purpose of this page is to gather requirements from people involved in different missions and archives with the goal of proposing a draft in 2019. It is to be noted that Gaia people at ESA have already presented their own model proposal which is for us a good preliminary example of what is intended. 
 Core-model Components 
 
 ra : right ascension
  dec : declination
  name: source name
  flux:photometric measurement or magnitude in several bands ,
 
 LSST Specific Components 

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 EUCLID Specific Components 

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 CFIS Specific Components 

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 GAIA Specific Components
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+As described in https://wiki.ivoa.net/twiki/bin/view/IVOA/SourceDataModel, the basic mechanism of Gaia Sources can be described as follows:
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+- Detections are done. In this case, the basic source (detection) data model can be used for positions, identifiers and fluxes/magnitudes. Also, using spectrometric techniques, radial velocity or redshift can be derived. Also, as known, fluxes in one or more bands are also associated to the detections (e.g. to create and spectrum)

- Some properties (e.g. proper motions and parallaxes) require a cross-identification of source detections. This is the case of different main catalogues of astronomy (e.g. Gaia) where different transient observations of different detections are consolidated in a single instance adding extra information. Also, metadata can be combined from different catalogues. This kind of objects are called crossmatched sources in the present DM.

For this crossmatched objects as output of different detections, the extended data model is needed. Some of this properties are:

- parallax (it is, in a naive way, the inverse of the distance but catalogues use to provide parallax as there are some possible errors involved in the calculation of the distance). See, e.g. http://www.mpia.de/~calj/parallax.pdf

- proper motions (pm_ra and pm_dec) are also an output of the crossmatch of different detections what provides the displacement of the sources in the sky

- Extra flux/magnitudes measurements of the source at different times can produce a source time series. Depending on the data model to be used (spectral data model or time series data model), the connection between detections can be done only to the spectral data model for detections and crossmatched sources or to the time series data model (if any) for the crossmatched sources
  CDS Specific Components 

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 Exoplanet Specific Components 

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 Chandra Archive 

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