Fwd: Light curves in the IVOA

[Arnold Rots]

The Timescale is missing; one would hope that it is TDB...

I did see a comment on "Modified heliocentric Julian Date";
let me be clear: that is not an acceptable term, as it is woefully
ambiguous and ill-defined.

  - Arnold

Roy Williams wrote:
[ Charset windows-1252 unsupported, converting... ]
> 
> 
> -------- Original Message --------
> Subject: Re: Light curves in the IVOA
> Date: Wed, 16 Jun 2010 07:52:08 -0700
> From: Roy Williams <roy at cacr.caltech.edu>
> To: Raul Gutierrez Sanchez <raul at cab.inta-csic.es>
> CC: Doug Tody <dtody at aoc.nrao.edu>, Rob Seaman <seaman at noao.edu>
> 
> Raul
> I would like to start launching and interoperating light curve services, 
> and what you have done is a most of the work that is needed, so I am 
> very happy about your real live services!
> 
> Perhaps we can think about writing a real document about what a light
> curve service should look like? That way we can ensure that they real
> interoperate. I have a few small questions and concerns about what you
> have implemented, and I wonder if I could ask if there could be slight
> modifications to your services? Please find attached the two files
> (lightcurve-menu.xml and light-curve-instance.xml), where the first is a 
> listing of links, and the second is a light curve.
> 
> (1) I see in both of the attached files that you have GROUP containing
> GROUP. This recursion in VOTable is something that is difficult for many 
> parsers and code-binders, and I fought against it when it was introduced 
> into the VOTable specification. Would it be possible to just delete 
> GROUPS altogether, since the utype of the PARAMs already reveals its 
> position in the hierarchy. The GROUPs seem like a lot of extra
> complication that adds no information!
>         <GROUP utype="sed:Segment.Frame">
>          <GROUP utype="sed:Segment.Frame.Sky">
>             <PARAM utype="sed:Segment.Frame.Sky.Type" ??./>
> 
> (2) I see that time is represented by barycentric MJD as in the types
> and values below. I am not clear on the meaning of your MJD -- it is
> 1300 days from which reference point? But I do not see much of the STC
> technology that has been crystallizing in the IVOA with the efforts of
> Demleitner (*). Do you think it would be possible to modify your service 
> to report something more like that?
> 
> sed:Segment.Frame.Sky.Equinox value="2000.0"
> sed:Segment.Frame.Time.Type value="MJD"
> sed:Segment.Frame.Time.RefPos value="BARYCENTRIC"
> sed:Segment.Coverage.Location.Time.Value value="1305.88"
> sed:Segment.Coverage.Region.Time.Start value="1305.87"
> sed:Segment.Coverage.Region.Time.End" value="1305.89"
> 
> (*) http://www.ivoa.net/Documents/latest/VOTableSTC.html
> 
> 
> (3) I see that some of your data values have "99.0" for the flux value,
> which obviously means missing data. But is there any way in the SSAP or
> VOTable specification to say in the metadata "whenever you see 99.0 it
> means missing data".
> 
> Thank you
> Roy Williams
> 

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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 head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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