SED serialization

[Paolo Franzetti]

Dear all,

we are working on new tools for redshift measurement and SED fitting (EZ and GOSSIP respectively)
which will be available to the astronomy community as soon as possible.
We are just adding the VO compliant facilities, and so we have taken a look at the new
"Spectral Data Model" document (V 1.0 RC 1 Rev 2).


We have got some doubts and proposals.

One doubt is about the FITS serialization. Reading the draft, we understand that we must consider
each binary table row as a single segment where the columns types are variable length arrays.
In this case, a single spectrum will be represented as a single table row while a SED as many
rows (for instance one row is a K band photometric point, another is a R phot. point,
the next one is a spectrum, and so forth). Is this right?
If it is right, we don't understand the instance example at 9.4 paragraph, which describes
a single spectrum as a simple FITS binary table with wavelenghts in one column, flux in
another etc. Also this seems to be the format used by all the available SSA services.



We have seen that there are two unsolved issues which are very important for our applications

1. The photometric points given in magnitudes.
How to handle them? Surely it is needed to know the filter transmission curve. There are many
different approaches proposed in this mailing list; we would like to know at which point
the discussion is now and also if and how we can contribute to it.
Our idea is to define a metadata linked with the single segment, which contains an instrument
filter unique identifier which can be used by the applications to download, for instance from
the http://www.voservices.net/filter service, the filter profile in a well defined data
format (model).

2. The SED data model and the serialization formats.
In the Spectral Data Model document is cited the "Spectral Associations Document"
which shoul describe SEDs and other groupings.
Which is the state of this document? Can we retrieve it and/or collaborate to its writing?




Finally we think there are some mistakes within the Schema. We think that this:

<xs:complexType name="positionParamType">
<xs:complexContent mixed="false">
<xs:extension base="xs:anyType">
<xs:element minOccurs="2" maxOccurs="2" name="value" type="doubleParamType" />
</xs:complexContent>
</xs:complexType>

should be

<xs:complexType name="positionParamType">
<xs:sequence>
<xs:element minOccurs="2" maxOccurs="2" name="value" type="doubleParamType" />
</xs:sequence>
</xs:complexType>

This

<xs:complexType name="spectralFrameType">
<xs:complexContent>
<xs:extension base="coordFrameType">
<xs:element minOccurs="0" maxOccurs="1" name="redshift" type="doubleParamType" />
</xs:extension>
</xs:complexContent>
</xs:complexType>


should be

<xs:complexType name="spectralFrameType">
<xs:complexContent>
<xs:extension base="coordFrameType">
<xs:sequence>
<xs:element minOccurs="0" maxOccurs="1" name="redshift" type="doubleParamType" />
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>

And this

<xs:complexType name="timeFrameType">
<xs:complexContent>
<xs:extension base="coordFrameType">
<xs:element minOccurs="0" maxOccurs="1" name="Zero" type="doubleParamType" />
</xs:extension>
</xs:complexContent>
</xs:complexType>

should be

<xs:complexType name="timeFrameType">
<xs:complexContent>
<xs:extension base="coordFrameType">
<xs:sequence>
<xs:element minOccurs="0" maxOccurs="1" name="Zero" type="doubleParamType" />
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>



Thanks in advance.

Paolo Franzetti
Luigi Paioro


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