Spectrophotmetry Web Service and Science Demonstration

• Francisco Valdes
• Jean-Michel Desert
• Paresh Prema
• John Bochanski

Abstract:

The Spectrophotometry Web Service takes VO accessible spectra and computes broadband fluxes, custom filter fluxes, line indices, and equivalent widths. It demonstrates making widely used code (in this case IRAF) accessible as a Web Service. The tie to the NVO is use of URLs and VOTables. Spectra of a class of sources is discovered with the VO and spectrophotometry is obtain using the web service. Filter profiles for standard filters are obtained from a VO service and applied to the spectra. Two client interfaces to the web service are demonstrated.

Vision:

Astronomers do SSAP queries to get a list of data references represented as VOTables. They define a band pass description in a client. This may involve finding broadband filter profiles from the VO. The data references and band pass descriptions are passed to a web service that does spectrophotometry on the specified data with the specified band passes. The results are returned to the astronomer.

Note that in this vision the spectral data, the band pass data, the compute server (web service), and the astronometer may be at different sites. In particular, the spectral data are not (necessarily) moved to the astronomer's site before being passed to the web service. Instead the web service fetches the data.

Required Components

Spectral data service

Spectrophotometry Web Service

We built this as an IRAF Web Service based using SBANDS (http://iraf.noao.edu/scripts/irafhelp?sbands) as the demonstration science application. In the process of defining this we realized that the service would really be a demonstration of a VO Space paradigm.

• Service methods
• Using the IRAF Web Service Generator

Spectrophotometry Client

The web service can be run manually with a command line interface. This interface is automatically provided by the IRAF Web Service generator. But it would be good to have a client that integrates getting the spectral data and band pass information, and sets and sends the band pass information in the form needed by the web service. We began sketching out a web interface modeled on the Wesix service. In this model the web page is a form that talks to a local client interface to the web service.

Science Demonstration

We wanted to demonstrate collecting a set of spectra and a filter profile from the VO. We identified where and how this could be done but we encountered various stumbling blocks that prevented us from reaching the point of a demo.

Instead we demo using some random data taken from the VO and demonstrated previously by Frank Valdes for a "VOSpec"-type client.

Queries

Get a list of the best sample OIII EW star:

In Openskyquery
SELECT TOP 10 o.objid, o.ra,o.dec,
s.restWave,s.ew,s.ewerr,s.continuum,s.specIndex, s.ew/s.ewerr as sigma
FROM
    SDSSDR3:Photoprimary  o, SDSSDR3:specline s
WHERE
     o.type=6
 AND
o.specobjid = s.specobjid
AND
s.restWave between 5008.2 and 5008.3
AND
s.ewerr  between 0.1 and 0.5
ORDER BY s.sigma DESC




194.78178783093,63.9742451556603
261.230728137583,53.5649499640872
170.828095141239,-3.04690051389261
218.815218907695,2.53933772357339
124.845194565007,3.30268146102654
160.488451830153,63.1171229095069

Take that and send it to:

http://voservices.net/spectrum Some problems:

DOBOS, Laszlo :dobos@pha.jhu.edu suggested:

http://test.voservices.net/spectrum2/search_form_cone.aspx

Get the VOTable with the references of the spectra....

Filter Service

• Couldn't use wget on URN from voservice.net
• Tried to use web service (SOAP) interface in Perl but didn't have time to complete it.