Time Series Cube DM - IVOA Note

[Petr Skoda]

Dear All,

I have just returned from a holiday (without internet) and
have seen what interesting discussion is on-going.

As I was at the begining of this effort, which gradually was implemented 
during Jiri's master thesis and implemented in SPLAT-VO and DACHS, I want 
to make short comments the the whole philosophy.

The VO needed urgently standard for time series, a wealth of light curves 
as well as other time series (e.g. gravity wave) needs to be accessed .
We have proved the proposed concept works well and allows to fulfill most 
of uses cases we state (and in fact all which VO was able to imagine as 
summarised in Enrique's summary).

The new use case of Laurent is covered as well
so far we were just searching light curves drom Danish Dk154 telescope as 
I have  demonstrated multiple times using simple "cone search" in circle. 
Recent Obscore queries allows general ADQL shape (but very slowly as 
tested) We have crossmatched e.g. Landoldt cataloges from Visier directly 
wit the service implementing the presented standard in DACHS  using
TOPCAT and plotting light curves in (recently modified) SPLAT-VO as well 
as TOPCAT itself.

There are still some client adaptation necessary to have it smooth.
E.g. in TOPCAT would be nice to have feature that we already have 
discussed several times - which basically makes this:

If there is a accref in a displayed table  you display this link and on 
click it makes another table downloading this link.

  So far it must be done by copy this accref link to clipboard and using 
this link in opening new table.

This makes a magic (which is a core of our proposal) that you see the 
light curve in TOPCAT (you can plot it, filter, modify etc ...) as the 
accref is in fact just pointer to the TABLE where the time series is 
encoded using Jiri's suggestion.

You may send the table from SPLAT-VO as well as from ALADIN.
So the whole light curve is just a pointer to file (or in our case to the 
on-the fly generated query in database of photometric measurements) which 
is a light curve (time series) represented as a TABLE.

There is no need for special core data model with strange interpretation 
to fulfill almost all functionality.

I am afraid that the discussion I have briefly looked into (sorry for not 
reading in details) is running in a way which have killed many good 
attempts in IVOA - the fundamentalist's approch strictly based on complex 
data models which cannot incorporate all predictable application usage.
Strong words like "rewrite VO-DML" or sympathy to GOD-OBJECT is scaring 
me.

If we admit  the work of IVOA so far was not based of clear design concept 
(and the number of individual and inconsistent protocols shows this - e.g.
look how simple search in cone on sky looks in SSAP and SCS - same 
semantics RADIUS , COORDINATES ....) we still must see that in 20 years 
this inconsistence was still fruitful - look at number of publications 
using just Xmatching of catalogues.

The discussion here has shown the  way how to design future VO 
standards, but it is terribly complicated in sense of previous way of 
thinking.  I am afraid that some of you see in our small time series 
solution the way how to rewrite whole IVOA from scratch.
Sure the datacubes are new challenge complicated as the instruments 
providing it.

But we should deliver something useful to the community despite the fact 
of inconsistencies in different SCHEMAS ...

>From the point of view of client developers :

Please note that the propagation of strength of VO stands and fails with 
client applications - and in fact we have only few strong clients that 
everybody knows. So IMHO we must adopt the server side to the client 
writers (in fact who is going to write a new VO client?).

In astronomy the attempt to full standardisation despite the IAU effort 
always fails and people are naming object arbitrarily, using strange 
units, special variables etc ...

In using the 80/20 rule - we may not cover everything ...

So please keep this in mind - the time series is crucial part of 
astronomical research and having very simple applications to work with 
them despite uncomplete models would greatly improve the IVOA reputation 
in wide community (frankly - it is not terribly high ).

Concerning the coordinate system issues.

For most of X-matching the rough RA,DEC is just fine to be able to compare 
with catalogues in Vizier.

However many light curves are showing behaviour of objects which are 
hardly identified by coordinates .... You must use TARGET NAMES to clearly 
identify them. It is paradox , that the most interesting time series 
cannot give coordinates:

some use cases for this:

1) exoplanets - top  secret of PIs is their identification
they will not publish it but what to have many light curves to comape 
using just names a Tres1, Kepler 15, Myterestrialsurvey 5 etc ....

2) optical conterparts of gravitational wave - very uncertain and in fact 
unknown before the precise modelling is done - after long analysis..


3) time series of spectral behaviour of variable stars in general.
The telescopes points to given coordinates but at this there are 2 
separated spectra extracted from the same CCD frame.  Both objects have 
the same coordinates from the telescope and so the pipeline will write it 
in header.   Some manual effort and hacking headers is needed. - which is 
hardly done.

Most amateur astronomers just gives table of intensity dependence on time 
and say this is my target - XYZ    - I do not care where it is - I have used 
finding chart and I am sure it is what I want.   In their logs you will 
find only the one of many names of star - seldom coordinates...

An interesting job may be to identify the object which was really observed 
;-)


So the plotter mentioned earlier does not need to solve the coordinates at 
all !

Moreover using the current implementation I was able to use SAMP and send 
our lightcurve to Period04 and create e.g periodogram.

So all the basic use cases I can imagine can be already fulfilled.

Take this into account when creating the SuperGod objects or rewritting 
the VO-DML !

I hope I will have time in Shanghai to convince you .

Best regards,

Petr Skoda







On Wed, 22 Mar 2017, Laurent MICHEL wrote:
> - Looking for stars with more than N photometric points 5sigma higher than 
> the mean value.

>  An optical counterpart is not known. How can one get 
> lightcurves for all objects in the error-ellipse to look for variability and 
> thus possible counterparts to the blazar?
>
> - Plot the lightcurves of all SN Ia events together.


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*  Petr Skoda                         Phone : +420-323-649201, ext. 361 *
*  Stellar Department                         +420-323-620361           *
*  Astronomical Institute CAS         Fax   : +420-323-620250           *
*  251 65 Ondrejov                    e-mail: skoda at sunstel.asu.cas.cz  *
*  Czech Republic                             skoda at asu.cas.cz          *
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