Figure 1. Average error vs star magnitude.
This is the data base of Pi of the Sky measurements taken from 2006 to 2009. Instrumental data have been reduced using standard photometric pipeline. This raw analysis gives a typical rms accuracy for a 8 mag star of order of σ ~ 0.05 mag and astrometric accuracy of order of 20 arc sec. Various corrections which have been worked out by our Data Analysis Group allow to significantly increase accuracy to σ around 0.015 mag. For details contact rafal.opiela@fuw.edu.pl and malgorzata.siudek@fuw.edu.pl
Figure 1. Average error vs star magnitude.
The search form allows a user to search a star catalog for stars of given parameters. A user fills in the search form presented in Figure 2. It is not necessary to provide all parameters. The checkbox on the left of the each parameter may be checked or unchecked dependently on whether the parameter is to be used for searching. There are also advanced search options (hidden in Figure 2) for searching stars of a specified type, e.g. RR Lyrae variable stars. After filling in the form, a user has to choose how the results will be presented by clicking one of the buttons "List stars", "Show map", "Count stars", or "Get Results Pack". The first choice will output a list of stars, as presented in Figure 2. The list is limited to the number of stars chosen from the "Stars per page" dropdown button. The complete list can be browsed by using the "next page" and "previous page" buttons, which cause fetching the next and previous portion of stars from the server. This limit was introduced for efficiency reasons. The table can be sorted in several ways, e.g. by magnitude, number of measurements, star's name. The order can be chosen from the "Sort by" dropdown button (Figure 2). Clicking on an identifier of a star brings in the page of the star (see section "Star page").
Figure 2. Web interface - search form with a list of stars.
If the user clicks on the "Show map" button, the server will generate two plots (Figure 3): a Sky map - a plot with celestial coordinates Ra and Dec on the axes - and a Variability Diagram - a plot of the standard deviation of magnitudo measurements of stars versus their average magnitudo. These plots contain also a limited number of stars. Browsing and sorting can be done in the same way as in the case of the list of stars. Both plots are interactive. If the user selects an area by drawing a rectangle with a mouse, the plot will be zoomed in, i.e. a new query with new parameters will be executed on the server. The new coordinates will also be put into the search form (Figure 4). It is also possible to click on a star on the plots. If there are other stars close to the point where the user clicked, in the range of a few pixels, the plot will be zoomed in and centered on that point. If, however, there is no ambiguity which star was selected, the page of this star is presented (section "Star page").
Finally the third option on the search form returns just the total number of stars found. The reason for separating this option from the other two is efficiency. If the number of records found in the database is large (millions) it is faster to retrieve a portion of data than to compute the total number of rows found.
Warning: large queries are disabled for safety reasons and we recommend to narrow down your search using available search parameters. If you still need to make large querries, we recommend that you obtain a copy of our data base on a hard disk. Please contact malgorzata.siudek@fuw.edu.pl.
The data from the plot can be exported in a few file formats: as a HTML table, in a Comma Separated Values (CSV) file and as a ROOT macro. The CSV file contains also the metadata of a plot, for instance the values of the parameters of the form. The ROOT macro is a macro of the ROOT framework [10] that plots the light curve in a nice, ready-forpublication way. A user may chose to export only a basic data - time and value - or also additional information of each observation - the celestial coordinates, the coordinates on the CCD chip, the field, etc. Apart from the light-curve, the star page contains detailed information about a star. For instance there is a link to the same physical star from the other camera and a link to stars in external databases (see section "Other star catalogs"). Advanced properties are initially hidden. They will be shown after the user clicks on the Advanced button. Showing and hiding of these properties is done in JavaScript and does not involve any communication with the server.
It has been mentioned before that the web interface can be used with other star catalogs, provided that the database scheme is the same. The data of ASAS, Tycho and GCVS catalogs have been loaded into such databases. Together with the Pi of the Sky data they form a large system, which allows the catalogs to be changed easily. First of all the user can switch between databases by choosing a database from the DHTML popup menu on the star search form (Figure 2 - upper left corner). Also on a star page there are links to the page of the same star in other catalogs (provided that this star has been correctly identified in other catalogs - the identification is stored in the superstar table). There is also a link, which presents results of searching for stars in the range of 2 arc minutes around the position of the current star.
The data of each catalogue differs a bit. For instance in the Tycho and GCVS catalogs there are no brightness measurements. Also the variability types in GCVS and ASAS are different. The web interface is fully configurable and such changes can be described in configuration files, without any modification to the source code.
ASAS: G. Pojmanski, 2002, The All Sky Automated Survey. Catalog of Variable Stars. I. 0h - 6h Quarter of the Southern Hemisphere. Acta Astronomica, 52, 397.
Tycho: E. Hog et. al.,The Tycho-2 catalogue of the 2.5 Milion Brightest Stars, Astronomy and Astrophysics, v.355, p.L27- L30 (2000)
GCVS: Kholopov et. al., Combined General Catalogue of Variable Stars, 4.1 Ed (II/214A). (1998)