This worksheet demonstrates some ways to retrieve and visualise astronomical images, spectra and catalogue data using AstroGrid.

To access AstroGrid services, launch the VO Desktop

Launch the Ddesktop, click on ''Start'' and select the All-VO Scope , an AstroGrid tool that allows you to find catalogues, images, spectra or time series which cover a given position or SIMBAD object, with the option of selecting by time period. It provides easy links to visualise the results and download data files either to your local machine or to your storage space on the Astrogrid system, called MySpace.

For example, enter the symbiotic star HM Sge as the Object, and use the default of all except Timed data and a Search Radius of 0.01 deg.

Select some data by double-clicking (e.g. the Catalogues 'Two Micron All Sky Survey' and 'INT-WFS DQC'). Actions on the left side now offers Download which will open up a destination browser for your local machine. Add instructions for saving to MySpace.

Tip: You are advised to start by selecting just one or a few items, and ensure that you have used the Clear selection button before later saving further data.

VO Explorer provides pre-selection of data, increasingly necessary now that tens of thousands of separate data collections and catalogues are published to VOs. The ****ADD HELP LINK explains how to use this to full advantage, but at the simplest, just click on + New Smart List and enter the name of a data set or a likely keyword, e.g. ''radio images'' or ''Symbiotic Star'', and then Create. Tip: This is not a positional search - that comes next - so if you enter HM Sge, you will only get catalogues etc. which have the source name in the metadata - usually more restrictive than you want.. You can then use the right-hand top down arrows to provide options for filtering the results, e.g. set Resource Type to Image Access (see the **HELP for full details).

You can now select an individual data set for Detailed data selection (see ** below) or select many data sets (shift-click on first and last items in the list) and click on Query on the left. This will open up a new All VO Scope which searches only the selected archives.

PLASTIC directly links AstroGrid and data visualisation and manipulation tools such as TopCat, Aladin, SPLAT, GAIA, VOSpec and VisiVO. The PLASTIC page provides web links which allow you to use webstart and/or download and run the compatible version. For details, see the Helper Applications.
documentation.

Start the visualistion tool(s) you want to use. After you have selected some data in All VO Scope, the icons for suitable tools will appear on the left - click to send the data to the chosen visualiser. You can also use any of these tools to load data directly from MySpace if you have the VO Desktop running. Tip: **ADD SOMETHING ABOUT MEMORY MANAGEMENT

FITS or JPEG images (including FITS cubes) can be dispalyed in GAIA or Aladin. Tip: You can send the images directly or you can send a table listing image properties to Aladin, so that you can make a more refined selection and avoid downloading many bulky images uneccesarily.

SPLAT and VOSpec are available. For example, after starting VOSpec and selecting a few spectra, click on the icon in AstroScope and the spectra will be displayed. You can do some basic manipulations such as change units, fit a black body, and save the spectra to your local disc.

IUE and ISO spectra displayed in VOSpec ovelaid with images created in Aladin after using the MERLIN Imager.

Virtual observatories and many other applications exchange tabular data in VOTable format. This can include lists of images with their URLs or simple spectra as well as lists of e.g. sources and properties. Aladin and VOSpec, described above, use VOTables and TopCat is a dedicated tool which lets you browse and plot tables, add new columns (including coordinate conversions) and exchange data with Aladin and any other tool which can see MySpace.

If you view the same table in Aladin and TopCat, a source selected in one application will be highlighted in the other.

The Astronomers' Data Query Language (ADQL) lets you select the columns you want within chosen ranges. Some of the accessible catalogues are listed in the VOExplorer Examples: Queryable database examples. When you select a suitable catalogue, e.g. hose the ''FIRST object catalogue'' (Faint Images if the Radio Sky at Twentyone cm, the Build ADQL button appears on the left. This opens up a Task Runer configured as the Query Builder. You can use the GUI Tree or enter SQL directly under the Adql/s tab. The following is an example:

 
SELECT * FROM catalogue AS T1 WHERE 
 T1.POS_EQ_RA > 186 AND T1.POS_EQ_RA < 188 
 AND T1.POS_EQ_DEC > 1 AND T1.POS_EQ_DEC < 3  
 AND T1.EXTENSION_FWHM_MAJ > 0.0 

Some data centres offer custom-made data products. For example, the MERLIN Imager produces an image to your specifications (or the nearest possible values of size and resolution) from radio interferometry data. Search for "MERLIN" in the Task Launcher. Fill in either the position or the object name and, optionally, other criteria, and the destination of the Output. At present only MERLIN names are recognised but you can check what sources have been observed by browsing the MERLIN Processed Data archive

If there are data anywhere within the field of view of an observation which match your criteria, the five best images will be made and supplied via a SIAP-like VOTable which can be loaded into Aladin or browsed with TopCat. The service uses ParselTongue, a python-based scripting language developed by RadioNet. It will be developed to link with SIMBAD, and other data products (e.g. spectra, time series) could be extracted in a simlar fashion from visibility data, X-ray event series etc.

AstroGrid's services can be run from scripts in python or other common languages, see Scripting.

At present these are best used as scripts, see examples above

**to follow