J. Plasma Fusion Res. SERIES, Vol.7 (2006) 358-360

Atomic and Molecular Databases in the Contextof Virtual Observatories
DUBERNET Marie-Lise and ROUEFF Evelyne
Observatoire de Paris-Meudon, LERMA/LUTH, 5 Place Janssen, 92195 Meudon, France（Received: 5 October 2004 / Accepted: 21 December 2005）

Abstract
Numerical and bibliographic Databases in Atomic and Molecular Physics are essential for both the modelling of various astrophysical media and the interpretation of astrophysical spectra provided by ground or
space-based telescopes. We report here on our current project concerning the access to Atomic and Molecular
Databases within the Virtual Observatories. This presentation aims at informing people about interoperability
matters, in order to put together the eﬀorts which have already started in this domain, to evaluate the needs
and requirements of the targeted interrelation between atomic and molecular data bases and VO projects.
Collaborations in this domain are welcome.
Keywords:
database, virtual observatory, interoperability
1．Introduction
Atomic and molecular databases are an example of
distributed resources which are used in numerous astrophysical applications. However, specific problems
raised by the access to these databases in the Virtual
Observatories paradigm have not yet been addressed. It
is important to make atomic and molecular data widely
available in interrelating databases with VO projects ;this would allow in particular uniqueness of data used in
astrophysical models and automatic access to these datafrom Web applications developed for spectrum analysis
or modelling.
2．Virtual Observatories
The Virtual Observatory can be defined as “an enabling and coordinating entity to foster the development of tools, protocols, and collaborations necessary
to realize the full scientific potential of astronomical
databases in the coming decade”. Since the first conference “Virtual Observatories of the Future”, June 2000,
various projects started in diﬀerent countries : Astrogrid (UK) [1], AVO (Europe) [2], NVO (USA) [3], JVO(Japan) [4] and more. An International Virtual Observatory Alliance (IVOA, Fig. 1) [5] started in 2002, its
aim is to facilitate international coordination throughagreeing upon common standards for data and interfaces. The alliance consists of representatives from all
funded international VO projects who meet on a regular basis to refine the roadmap and reach consensus on
choices for “the common ground” issues.

Fig. 1 The IVOA consortium

There is a collaborative Web [6] site with forum of
discussions and information on the diﬀerent groups thatdefine standards. The working groups are:
• Resource Registry: The Registry standard addresses the need for an astronomer to be able tolocate, get details of, and make use of, any resource
located anywhere in the IVOA space, ie in any Virtual Observatory.
• Data Modeling: addresses modeling of variousitems : Spectra, Quantity, Observations, Transforms, Interferometry, Simulations, etc...
C 2006 by The Japan Society of Plasma

Corresponding author’s e-mail: marie-lise.dubernet@obspm.fr

Science and Nuclear Fusion Research358

Atomic and Molecular Databases in the Context of Virtual Observatories• Unified Content Descriptors (UCD) : formal vocabulary for astronomical databases

semicolons (;). A word is composed of “atoms”, separated by periods (.). So the hierarchy is the following :atoms → words → composed words.
UCDs have been recently changed and updated, andwe participated to the new definition of UCD for atomic
and molecular physics. The first generation of atomic
and molecular physics did not follow any logical classification and is not complete. We adressed all thesepoints and provided a starting working sheet. We divided the field into 5 main topics: identification ofelements, identification of levels, radiative transitions
between bound states, photon-matter interaction, somespecific UCDs for various quantities. From this classification, some UCDs have been proposed and will bediscussed by the board working in the IVOA, here is anextract from the proposed list :Identification of elements:phys.at.element : atomic element• Data Access Layer: The task of the DAL working
group is to define and formulate VO standards forremote data access. Client data analysis software
will use these services to access data via the VO
framework; data providers will implement theseservices to publish data to the VO.
• VOTable: The VOTable format is a proposed XML(eXtensible Markup Langage) standard for representing tabular data in the context of the Virtual
Observatory.
• VO Query Langage : This working group has developped the Astronomical Data Query Langage(ADQL), which is an XML language for constructing queries. The mechanism of passing a query toa node is also developped in the VOQL working
group (SkyNode Interface).

• phys.at.name: name of the element [Actinium,Lead, ...]• Grid and Web Services, Standards and Processes.

• phys.at.number: atomic number [Z]Other groups of interest, such as VO Architecture,
VO Applications, GGF Astro-RG, Data Curation andPreservation, VOTheory are also established.
The VOTheory group is the group that will be active in working on the access of atomic and molecular databases within the VO. The aim of this group isto work out what should be added to the standards inorder to meet the requirements of theory. The themeof atomic and molecular data has been oﬃcially introduced in the IVOA during the September 2004 Interop
meeting in Pune (cf [6]). Even more recently the SpectralLinelists sub-group [7] has been created in the DAL
working group, its purpose is to provide a simple accessto spectral line lists.

• phys.at.symbol: [He, H ...]• phys.at.ion: ionisation stage [CII]• phys.at.isotopic: [9 Be, 10 Be]• phys.at.weight: atomic weight• phys.at.qn.I: nuclear spin quantum number (seebelow for explanation of phys.at.qn)
Identification of levels phys.at.level: atomic level• phys.at.term: atomic term
• phys.at.configuration: atomic configuration• phys.at.parity: parity

3．Unified Content Descriptors (UCD)The UCD was the first work that we undertook on
standards for atomic and molecular data. Each UCD
describes a concept, which is similar to classes in object oriented programming. The UCD concept vocabulary is restricted in order to avoid proliferation of terms
and synomyms, and controlled in order to reduce ambiguity as far as possible. UCDs play a central role inressource discovery and processing in the VO. Services
may publish the UCDs that describe their ouputs. Looking at these UCDs human users or machine agents canfind sources of information they are looking for. All
information on UCDs can be found at [8].
Definition in Version 0.2 : A UCD is a string whichcontains textual tokens called ”words”, separated by• phys.at.sweight: statistical weight• phys.at.lande: lande factor• phys.at.lifetime: lifetime• phys.at.qn: atomic quantum numbers– .S: electronic spin
– .L: electronic L– .J: resulting from coupling of S and L– .F: resulting from coupling of J and I359

Atomic and Molecular Databases in the Context of Virtual Observatories

4．Conclusion
Atomic and Molecular Databases are concernedwith the Virtual Observatories because their data
are used in tools for spectral analysis and in codes
simulating astrophysical objects. Those applications
will be made available for a large public throughWeb interfaces and will use VO standards. The
first step towards standardisation is to insure theuniquiness and a full documentation on the qualityof the atomic and molecular data that are used in
the applications. This first step could be done by
the various data centers, or could be carried out by
a dedicated service for specific applications. It isclear that the involvement of data centers would bepreferable. The next step is to work on the data model

for atomic and molecular data and to work on scientific“use cases”. We are currently involved in all these topics.

[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]

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References
http://www.astrogrid.org
http://www.euro-vo.org
http://us-vo.org
http://jvo.nao.ac.jp/index-e.html
http://www.ivoa.net
http://www.ivoa.net/twiki/bin/view/IVOA/
WebHomehttp://www.ivoa.net/twiki/bin/view/IVOA/
SpectralLineLists
http://vizier.u-strasbg.fr/UCD/