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How to generate the Spectra Energy Distribution of a source in an image

The analysis tools described in this suite of recipes are still in a development phase. As such, they are not intended to fully cover the whole possible astronomical needs. Some of their functionalities may be still at a prototype level, and not fully validated.

Thread content

This thread illustrates how to answer a typical VO question: do spectra in a given wavelength range exist for source in my field-of-view? Can I seamlessly build their Spectral Energy Distribution? The interoperability between Aladin (catalogue browsing, image visualization) and VOSpec (Spectral Energy Distribution visualization and analysis) allows you to answer these questions and accomplish these tasks with just a few mouse clicks.

The case

Let's assume that you are interested in mining UV spectral measurements of a source in the field of view of an X-ray (XMM-Newton/EPIC in the example) image. You would follow these steps:
  1. launch the Aladin applet
  2. click on Load. The Server Selector panel appears. Select
  3. [you may skip steps 4. to 7. below, if you already have an image on your local disk. Just click on and upload your image onto Aladin]
  4. fill the target name (NGC2273 in the example) and the search radius (14 arc-minutes in the example) in the Target and Radius widgets of the Server Selector, respectively
  5. tick the Images checkbox and SUBMIT. A list of all VO-compliant image servers is shown, which contain images of NGC2273
  6. expand the XMM-Newton Archive Interoperability System , and tick over the existing EPIC item


  7. SUBMIT. The requested XMM-Newton/EPIC image is loaded in the main Aladin panel.


  8. A few sources of comparable brightness are visbile close to the galaxy center. If you are unsure about their identification, you can try and use the NASA/IPAC Extragalactic Database (NED) to validate your choice. Click on in the Server selector panel. A new plane will be uploaded in Aladin, listing the NED sources in the field-of-view. Identify the AGN by moving the mouse over one of the small red diamonds: the source identification will appear in the bottom sub-panel, as shown in the next figure


  9. to limit the search cone for the UV spectra around the exact position of the AGN, click on Grab coor in the Server selector, move the mouse over the centroid of the AGN in the XMM-Newton image, and click the right button once the mouse is located in the correct position. The coordinates will be automatically transferred into the Target widget. Edit the Radius widget, if you wish to change the search radius.
  10. select Spectra (after de-selecting Images) and SUBMIT. A list of VO-compliant available spectral servers appears, which contain spectra around the selected sky position.


  11. Select VOSpec (ESAC) spectral analysis tool ... from the Tools menu of the main Aladin panel
  12. select the Spectra you are interested to display (in the example the IUE and FUSE spectra), and SUBMIT. The spectra will be displayed in the VOSpec panel.


If you now want to learn how to use VOSpec to modify the appearance of the plot, compare the observed Spectral Energy Distribution with theoretical models or line databases, or add more spectra, either extracted from VO-compliant spectra servers or located on your own local disk, you may refer to the specific VOSpec thread. If you wish to learn more about the wide Aladin capabilities, please refer to the Aladin thread.

last updated: 08-Feb-2010 co-funded project