Paris Astronomical Data Centre

Observatoire de Paris

Science using the VO

Tutorial organized by VO-Paris Data Centre, build and framed by Ivan Zolotukhin and Igor Chilingarian.


In our day-long tutorial we would like to present several bright scientific use-cases of the Virtual Observatory that have recently served as a basis for different peer-reviewed publications in main astronomical journals. Following the comprehensive VO introduction, we will show three step-by-step demonstrations devoted to the key subjects: optical identification of X-ray sources, proper motions of open clusters and compact galaxies studies. All demos are organized in a way that the audience is able to follow them in place using own laptops connected to the Internet (be sure to check the Requirements section in advance), probably even getting unique scientific results. Two tutors will be ready to help, should you encounter any problem. The learning curve is adopted for scientists not really familiar with the VO concepts, however more experienced users will have a chance to carry out advanced tasks as well.


Tutorial 1: Proper motions of the open clusters

Using the very recent UCAC3 survey and Virtual Observatory interfaces to access its data we are able to perform important scientific measurements just within the VO environment without necessity to develop custom software using rich built-in capabilities of the Aladin+TOPCAT tools bundled together by means of SAMP intercommunication protocol. We will take the catalog of ~200 new Galactic open clusters (Glushkova et al., 2009) and examine several yet unstudied clusters both in 2MASS and UCAC3 data. 2MASS gives a clue about color-magnitude diagram of the cluster and its features (e.g. giants branch), whereas UCAC3 provides proper motion measurements for the brightest stars of the cluster. Using only the VO applications it is possible to distinguish between background stars and cluster members determining the average proper motion of the cluster which essentially contributes to our understanding of the Galaxy dynamics and e.g. to its rotation curve.

Tutorial 2: H-alpha emitters in X-ray surveys

Many objects with hydrogen-rich accretion discs which are active in X-rays besides that demonstrate a bright H-alpha emission line. Since there are several H-alpha photometric surveys became available recently and several are planned in coming years this important piece of information can be exploited to identify X-ray objects with large positional uncertainties. The input X-ray catalog of Sugizaki et al. (2001) contains ~100 unidentified X-ray objects in the Galactic Plane with positional errors about 1 arcmin. We will explore some of these sources (preselected to maximize probability for the source to demonstrate H-alpha emission) in the INT Photometric H-Alpha Survey (IPHAS) in order to find any objects with H-alpha emission excess among hundreds of the background stars that fall in the positional uncertainty. For the candidates found we will then try to discover an unpublished X-ray data in the Virtual Observatory which can help to pinpoint the proposed counterparts. This tutorial clearly showcases the workflow based on the VO advances that one can easily set up in the existing VO environment to bring the scientific value for the permanently actual problem of X-ray sources identification.

Tutorial 3: Compact elliptical and ultracompact dwarf galaxies

Using imaging and spectroscopic data from large surveys (SDSS, UKIDSS) available in the Virtual Observatory, HST images from the Hubble Legacy Archive, and the Vizier catalogue access services to get information on small samples of objects from individual research papers, we will search for candidates to a very rare galaxy types, compact elliptical and ultracompact dwarf galaxies. Using TOPCAT and Aladin software, we will identify the candidate galaxies based on different criteria (colour, compactness or half-light radii from SDSS) and will search for complementary such as spectra, high-resolution HST images (using footprint capabilities of Aladin and HLA), literature measurements of redshifts. This will be the generalisation of the cE discovery workflow published recently in the Science magazine (Chilingarian et al. 2009).


The tutorial will make use of typical VO environment available under any modern operating system. The key ingredients are working network connection and a couple of pre-installed components, Java (JRE version 1.6 by Sun Microsystems is recommended, but any version newer than 1.4 should work) and a web browser (Firefox is recommended, but Chrome, Safari, Opera or Internet Explorer is OK as well). It is desired, that your browser understand Java WebStart files. To check this and your Java installation, please launch two most common VO tools we are going to use in a course of the tutorial:

If you see Aladin and TOPCAT windows and are able to make simple manipulations with these applications after clicking on the above links, you are ready for the tutorial. If you cannot make it work, please follow the instructions at and to download and install the standalone Aladin and TOPCAT applications. If you feel unable to obtain the applications, we will provide you the copy during tutorial; but please be sure you have at least working Java installation by clicking on the following link:

Those, willing to ensure their ultimate performance during the tutorial, please follow the instructions given at web-page and check that all features available there are working in your setup.