# Virtual Observatory SAMP interface

SAMP is a messaging protocol, part of the Virtual Observatory, that enables astronomy software tools to interoperate and communicate. Skychart can connect to this other tools and send or receive coordinates position, FITS images and VO tables or selections.
Very useful tools to use with Skychart are Topcat and Aladin.

Skychart do not include a hub, so you need to connect to another software that include this piece.

### Initialization

To start to use SAMP with Skychart you can configure some options from the menu Setup -> General -> SAMP. This include how to connect to the hub, which function request to accept, and how to keep the data after the program is closed.

If you select to not connect automatically, or if the hub is not running when you start Skychart, you need to connect from the menu File -> SAMP.

From the same menu you can get the connection status and the list of clients.

### Messages Transmitted

For all this function you have the choice to broadcast the message to every client or to select a single destination client from a list.

##### Coordinates

To send coordinates use the right click menu SAMP send coordinates.

##### Table data

You can send a VO table data you get in Skychart from the VO catalog setup. Only VOtable format is supported.

##### Table selection

When you left click on the chart on an object that is part of a shared VO table the selected object is send as a selection. This is limited to single row selection.

##### Image

To send a FITS image use the chart right click menu Image list, the “Send image” button.

### Messages Received

Remember you can configure which message you want to receive and if you want a confirmation message before to take the action.
Also configure how you want to retain the data when the program is closed. This allow to make a complex data selection using Topcat for example and take the data offline for use with Skychart at the telescope.

##### Coordinates

Center the chart on the received coordinates and search for an object at this location.
If an object is found you can use all the function available in this case: show detailed information, slew the telescope, …

##### Table data

Add the table to the VO catalog list and display the objects on the chart. Only VOtable format is supported.
You can change the symbol, the color or the column selection with the Update button below the list.

##### Table selection

Mark the selected objects in green on the chart.

##### Image

Display the image and center the chart the same way as with a DSS image download. Only FITS format is supported.

### Example

We want to display on the chart the super-giant stars in the Hyades area using the XHIP catalog as the source of data. If you already know how to work with Topcat you can skip to the last three steps.

We use Topcat to get the data. So launch Topcat and Skychart, connect Skychart to the hub.

On Skychart make a chart centered on the Hyades with a FOV of 20°.

On Topcat click the menu VO → Vizier catalog service. Object name: hyades, click Resolve, enter 10 for the radius (degrees).
For “Output columns” select “all”.
For Catalog selection, click “By keyword”, for “Keyword” enter XHIP, click Search catalogues, select “V/137D” on the list. Click OK.

Send the table data to Skychart: Select the main table V_137D_XHIP in Topcat, open the menu Interop → Send table to .. skychart.

Create the Hertzsprung–Russell diagram in Topcat: open the menu Graphics → Plot, select Table=V_137D_XHIP, X Axis=B-V, YAxis=VMag (not Vmag!), click Flip on Y Axis.

Make a subset with a selection of the red giants branch.
From the graphic menu Subset → Draw subset region, then select the super-giant branch with the mouse.

Click the menu Subset → Finish drawing region. Give a name to your subset: “super-giant”, select “skychart” and click Transmit Subset.

This mark in green all the super-giant on the chart, with the other XHIP stars in red.

Click on Aldebaran in Skychart, this send a single row selection to Topcat. It highlight the Aldebaran position in the HR plot and in the table browser.

After you get this basic example working you can explore all the powerful function that Topcat can offer to produce the ideal catalog for the data you need. Start by the other options in the VO menu and also try the Joins menu to merge the data from many original tables.