Fwd: TimeSeries of positions (Asteroid)

François Bonnarel francois.bonnarel at astro.unistra.fr
Fri Nov 23 10:53:55 CET 2018


This email sent yesterday to the three lists was apparently not sent to 
voevent. (Time domain maling list). I was apaprently not registered there.

For those on several lists, sorry for the SPAM



-------- Message transféré --------
Sujet : 	TimeSeries of position (Asteroid)
Date : 	Thu, 22 Nov 2018 21:51:19 +0100
De : 	François Bonnarel <francois.bonnarel at astro.unistra.fr>
Pour : 	dm at ivoa.net <dm at ivoa.net>, <dal at ivoa.net> <dal at ivoa.net>, 
voevent at ivoa.net

Der Dave, all,*

Before interop Dave asked me to provide how a TimeSeries of Asteroid
could look like with the current ts model proposal and Utypes serialisation.

> Someone recently described to me a use case that I haven't seen in our
>   discussions.
>   To help me understand how to use the new model, could you send me a
>   simple example of how a time series of position over time would look ?
>   For a single moving object we would get multiple ra/dec or Point
>   values plotted against time.
>   For a mode complex example, multiple position and magnitude values
>   plotted against time.

You can find a "dummy example" of this at this URL :


Could be from gaia for an Asteroid.

Then Dave gave more details for the second more complex example

> Two use cases from the Gaia meeting.
>   Exoplanets, the star will change both brightness and position by tiny
> amounts linked to the planet's orbit. Very small and slow changes in
>   both position and brightness, hard to detect above the noise.
>   Near earth asteroid will be travelling very fast, and change
>   brightness in response to distance from the sun, position relative to
>   the sun, and rotation and shape of the asteroid itself. Very large and
>   rapid changes in both position and brightness.
>   Both are valid cases for time series of positions and magnitudes.

This is an attempt for a Near Earth Asteroid

Data are dummy of course. but with about 1 magnitude amplitude and 1deg position change in 10 days !!!

/*Changes for the Exoplanets use case can be easilly done :*/

There will be no real "look and feel" change for the magnitudes.

For position, the best is probably to set the mid position of the star in the refPOsition of COOSYS (see note below)  and to have the lon and lat columns giving the deviation from this
  position along the ra and dec axes (and no more ecliptic longitude and latitude). The unit for these two columns will probbaly be "mas" instead of "deg".


COOSYS note : currently there is no "refPosition" attribute in COOSYS. We propose to add one , taking the opportunity of the change in VOTable schema required to introduce TIMESYS.

this attribute allows accurate distinctions of positions computed from BARYCENTER, TOPOCENTER, GEOCENTER, as well as definitions of standalone  "local" spatial frames to code   for
  very accurate  measurements.

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