The International Virtual Observatory Alliance – ivoa

The next generation of powerful millimeter/submillimeter observatories (ALMA, Herschel) require extensive resources to help identify spectral line transitions and suitable calibration sources. We describe the compilation of a spectral line catalogue and calibration source database. The Calibase is an extensible repository of measurements of radio and submm calibration sources, building on the SMA, PTCS, VLA and VLBA lists. The Splatalogue is a comprehensive transition-resolved compilation of observed, measured and calculated spectral lines. Extending the JPL and CDMS lists, and updating the Lovas/NIST list of observed astrophysical transitions, it adds atomic and recombination lines, template spectra, and is completely VO-compliant, queryable under the IVOA SLAP standard.

The International Virtual Observatory Alliance – www.ivoa.net

Salgado et al., 2006, SLAP (Simple Line Access Protocol) v.0.5

Dubernet et al., Atomic and Molecular Line Data Model

The Cologne Database for Molecular Spectroscopy - www.cdms.de

Müller, Schlöder, Stutzki & Winnewisser, J. Mol. Struct. 742, 215 (2005)

Müller, Thorwirth, Roth & Winnewisser, A&A 370, L49 (2001)

Submillimeter, Millimeter & Microwave Spectral Line Catalogue (JPL) - http://spec.jpl.nasa.gov

Pickett, Poynter, Cohen, Delitsky, Pearson & Müller, J. Quant. Spectrosc. & Rad. Transfer 60, 883 (1998)

NIST Recommended Rest Frequencies for Observed Interstellar Molecular Microwave Transitions - F.J. Lovas - http://physics.nist.gov

PTCS – ftp://ftp.cv.nrao.edu/NRAO-staff/jcondon/

VLBA – http://www.vlba.nrao.edu/astro/calib/

SMA – http://sma1.sma.hawaii.edu/callist.html

Holdaway, Carilli, Weiss & Bertoldi, 2005, ALMA Memo 543

Both these services have two major modes of operation - one user-friendly, the other application-friendly. The former is a PHP based web interface, from which most of the output presented here came. The latter returns results of IVOA-compliant queries in VO-table XML. XML is not a concise form of data transfer, but it is a standard and will enable software to be written that queries the splatalogue and/or calibase in a consistent manner. At least in the case of spectral lines, there is a developing standard (SLAP) for querying such databases. As far as I know, the splatalogue is the first to implement it. By way of example, an excerpt of the XML returned from the splatalogue for a query of a single line of the SiO molecule is given below.

The services are also designed to be fully extensible. The interaction between the splatalogue and the ALMA Archive is under development, but extension from within the astronomical spectroscopy community itself will also be possible and encouraged.

Currently, neither the splatalogue nor calibase is publicly available. We anticipate this launch in 2006 Q4. The splatalogue will certainly become live at www.splatalogue.net – watch that space.

The splatalogue in particular is an attempt to collate, rationalize and extend existing resources. The JPL, CDMS and Lovas/NIST line lists provide an enormous amount of data – just throwing them together generates over 3.5 million transition data entries across almost 700 molecular species. The JPL and CDMS databases do not describe the transitions in a user-friendly way, and where the catalogues overlap, the descriptions have to be compared and resolved to be consistent. The Lovas/NIST list tabulates observed interstellar transitions, but it somewhat out-of-date. One of this project’s goals is to update it - the splatalogue will contain at least one example of every detected line. All the linelists on which the splatalogue builds are primarily ordered by species then frequency. The splatalogue is different – it is ordered by species then transition, which is more sensible. In this way, every observation, calculation or measurement is cross-referenced against that table. So you can ask for e.g. CH3CN 43-33 and see all the entries for that species/transition, be they observation, measurement or calculation.

Example XML output for SiO v=3 1-0

Note: another good reason why such databases shouldn’t index on line frequency… the VO data model.

Describes upper state

Lower state description snipped

Species: note VO data model requires initial and final species

Frequency

Example detection reference

Note: this block not part of the VO model

Below are two examples of the ‘human readable’ interface output from the splatalogue. Using SiO v=0 10-9 as an example (lines 28-30 below left), the need to index the database on species and transition becomes obvious. There are entries listed in each of the main 3 sources (JPL, CDMS, Lovas) but with slightly different frequencies. In these cases in general we will ‘prefer’ the Lovas number since it comes from an astronomical observation. For molecules like SiO, resolving the transitions is trivial since they are few and simple to describe. For more complex non-linear molecules, though, the process is much harder.

Here I asked the splatalogue to show the lines of SiO v=0 which lie in the specification ALMA receiver bands….

…. and here I asked it to list the transitions labelled ‘1-0’ which ALMA will be able to observe.

Here is a brief look at a calibase online PHP query. Clearly in this case the XML service is more flexible, but it just doesn’t look so good on a poster….

Unit

Various header info snipped

Accuracy

Note: the VO has a ‘quantity’ data model