VOGCLUSTERS
Data Mining WebApp on Globular Clusters
Go to the Web Application (coming next)
The goal of the project VOGCLUSTERS is the design and development of a web application specialized in the data and text mining activities for astronomical archives related to globular clusters. Main services are employed for the simple and quick navigation in the archives (uniformed under VO standards and constraints) and their manipulation to correlate and integrate internal scientific information. The project has not to be intended as a straightforward website for the globular clusters, but as a web application. A website usually refers to the front-end interface through which the public interact with your information online. Websites are typically informational in nature with a limited amount of advanced functionality. Simple websites consist primarily of static content where the data displayed is the same for every visitor and content changes are infrequent. More advanced websites may have management and interactive content. A web application, or equivalently Rich Internet Application (RIA) usually includes a website component but features additional advanced functionality to replace or enhance existing processes. The interface design objective behind a web application is to simulate the intuitive, immediate interaction a user experiences with a desktop application.
The Science with Globular Clusters
Along with the progress of the instruments for astronomical investigation of our Galaxy, the amount of data available for each globular clusters in the Milky Way is also growing at a steady rate. Several project from earth and from space are working to improve our detailed knowledge of such object, which are of utterly importance for our understanding of the status and evolution of our Galaxy. Since some of the older object in the Universe are contained in globular clusters, they have a key role also in many cosmological topics.
The importance of globular clusters for a broad range of astronomical studies has already addressed by W.E. Harris (1996). In that seminal paper (that works as companion of the well known online parameter compilations for galactic globular clusters) he also stressed the importance of having “readily available up-to-date list of parameters for this unique objects”. After almost fifteen years, these words appear even more true: the amount of available data on globular clusters has increased at a steady rate, following closely the enhanced capability of the technical instrumentations. Not only we have new and more reliable parameters for a great part of the known clusters, but - thanks to modern surveys conducted in bands different from the visible, such 2MASS ((Skrutskie et al. 2006) - several other objects keep going to increase our list of Milky Way clusters (e.g., (Froebrich et al. 2007), (Bonatto et al. 2007)).
However, such data are inevitably scattered among the various papers and are reported in different (and for the most part not-homogeneous) web pages, so what is really needed is a simple way to have the relevant informations on a given cluster, or a range of clusters, in a single source and under a well defined standard. This is a necessary step to open a wide range of investigation: the more we gain new and more detailed information about parameters, the more we can make useful science investigating upon the correlations of those set of data.
To enable this perspective, however, it’s crucial to have tools that enable an efficient data mining between those parameters, as well as a coherent and coesive rapresentations of data, such as can be guaranteed by the adoption of standards of Virtual Observatory. This opens the possibilities of a wide range of studies, that take advantages from the analysis of distribution of given sets of parameters in respect to others. The inclusion of the properties of pulsars in our web app will will give boost to a young but very active field, which do represent a bridge among those high energy object with topics more connected to “classical” observational astronomy.
On the other side, the inclusion of M31 globular clusters properties will allow us to put our research in a broader context, making possible a lot of meaningful comparison. We can easily predict that similar studies can cast new light upon the formation and evolution of Milky Way, its “chemical” and “dinamical” history, as well as on the dependence of properties of variable stars and high energy objects from the environment.
Briefly, we are convinced that the developement of a coerent and homogeoeuos framework for the (galactic) globular clusters parameters is nowdays regarded as necessary from most of the researchers in the field (this is confirmed by the wide diffusion of the actual website “gclusters”, notwhitstanding it is a “classical” dynamical web site, which merely represent a much simpler prototype of our upcoming web application).
M. Castellani
In the Astrophysics environment a globular cluster (GC) is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers. The name of this category of star cluster is derived from the latin globules, a small sphere. A globular cluster is sometimes known more simply as a globular. An example is shown below (Messier 80)
Globular clusters, which are found in the halo of a galaxy, contain considerably more stars and are much older than the less dense galactic, or open clusters, which are found in the disk. Globular clusters are fairly common; there are about 150 to 158 currently known globular clusters in the Milky Way, with perhaps 10 to 20 more still undiscovered. Large galaxies can have more: Andromeda, for instance, may have as many as 500. Some giant elliptical galaxies, particularly those at the centers of galaxy clusters, such as M87, have as many as 13,000 globular clusters. These globular clusters orbit the galaxy out to large radii, 40 kiloparsecs (approximately 131,000 light-years) or more.
Every galaxy of sufficient mass in the Local Group has an associated group of globular clusters, and almost every large galaxy surveyed has been found to possess a system of globular clusters. The Sagittarius Dwarf and Canis Major Dwarf galaxies appear to be in the process of donating their associated globular clusters (such as Palomar 12) to the Milky Way. This demonstrates how many of this galaxy's globular clusters were acquired in the past.
Although it appears that globular clusters contain some of the first stars to be produced in the galaxy, their origins and their role in galactic evolution are still unclear. It does appear clear that globular clusters are significantly different from dwarf elliptical galaxies and were formed as part of the star formation of the parent galaxy rather than as a separate galaxy. However, recent conjectures by astronomers suggest that globular clusters and dwarf spheroidals may not be clearly separate and distinct types of objects. Globular clusters are generally composed of hundreds of thousands of low-metal, old stars. The type of stars found in a globular cluster are similar to those in the bulge of a spiral galaxy but confined to a volume of only a few cubic parsecs. They are free of gas and dust and it is presumed that all of the gas and dust was long ago turned into stars.
The diagram above is an example of the Hertzsprung-Russell diagram (HR-diagram) that is a graph of a large sample of stars that plots their visual absolute magnitude against their color index. The color index, B-V, is the difference between the magnitude of the star in blue light, or B, and the magnitude in visual light (green-yellow), or V. Large positive values indicate a red star with a cool surface temperature, while negative values imply a blue star with a hotter surface.
When the stars of a particular globular cluster are plotted on an HR diagram, in many cases nearly all of the stars fall upon a relatively well defined curve. This differs from the HR diagram of stars near the Sun, which lumps together stars of differing ages and origins. The shape of the curve for a globular cluster is characteristic of a grouping of stars that were formed at approximately the same time and from the same materials, differing only in their initial mass. As the position of each star in the HR diagram varies with age, the shape of the curve for a globular cluster can be used to measure the overall age of the star population. The scientific investigation of GCs is based on the possibility to compare existent tabular data (GC archives) and on the internal information interoperability wide spread into these databases. The knowledge process is made by cross-matching correlation between GC physical parameters, bibliographic notes and references, statistical overlapping and analysis of data, images and spectra, etc.
The VOGCLUSTERS web application is hosting an integrated specialized toolset in the DAME Program. In particular its integration deals with technological solutions adopted, derived from DAME Web Application Suite strategy and requirements. For example, concerning the user access security policy, the VOGCLUSTERS shares the DAME user archive and, being on top of pre-existing CLOUD-GRID hybrid architecture, all inherited integrity and security levels. This includes the embedded S.Co.P.E. project policy tools for the safety and traceability of processes and registration/accounting information about connected users. Finally, as in DAME, all VOGCLUSTERS authorized users are protected against privacy and data consistency violations.
The VOGCLUSTERS is based on the following software layers, (see the scheme above):
- Data Layer (DL): it manages the project data consistency. It inherits the user archive and data base;
- Data Access & Process Layer (DAPL): it handles interactions with the data persistent system (database). It permits the safe and reliable information retrieval mechanism. It is internally composed by two subsystems, respectively, VOGCACCESS for the saving and retrieval of data and PSA (Plot Statistics and Analytics) exposing runtime configurable graphical tools;
- Service Layer (SL): it is the business logic layer, including all internal application services and information flow dispatch system (SERVER component);
- Frontend Layer (FL): it includes all interaction logic between users and application. It is composed by two subsystems, respectively, the WEB APP implementing all core applications and dynamical pages and User Interface, that has the role to render the views of services to the end users.
As previously remarked VOGCLUSTERS deal with GCs. The user has the possibility to visualize and navigate the GC archives (galactic and extra-galactic objects), locally registered (by merging worldwide distributed VO databases and registries). A GC is made of observational parameters, sometimes including an history of the research evolution on its values. So far the user has the possibility to integrate/update these parameters with own values and reports (new values, comments, images, diagrams, references etc.).
Regarding the users, the web application foresees three different categories of users, respectively, the administrators, qualified (or equivalently registered) and generic users (see diagram above). The main differences between these user categories are related to the information manipulation rights. In particular the web application can be passively navigated by all users (generic category), can be integrated/updated by registered users (already authenticated within DAME Suite) in terms of own data management and can be re-engineered by administrators (typically DAME working group members). In principle all generic users can become qualified by submitting a registration form to administrators, by obtaining account information (login and password).
In terms of internal communication between DAME Suite and VOGCLUSTERS (essentially to share user accounting information) there is a specific mechanism based on the XML-type document exchange, as shown above, between DAME Framework (FW) component and VOGCLUSTERS SERVER component.