Web databases’ interface – manual

Based on: “Web interface for star databases of the “Pi of the Sky” Experiment” by M. Biskup, K. Malek, L. Mankiewicz, M. Sokolowski, G. Wrochna


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 please contact Rafał Opiela or Małgorzata Siudek.

Figure 1. An average error vs. star magnitude.

Star search form

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”).

Figure 3. Web interface - sky map and variability diagram.

Figure 4. Interactive zoom on the Sky Map.

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

Star Page

A star page of the web interface (Figure 5) is shown when a user selects a star on the list of stars or on a plot. The main part of that page is a light curve, i.e. a plot of measured magnitude versus time. In the Pi of the Sky experiment the sky is divided into a number fields of observation. The measurements from different fields are marked with a different color on the light-curve. It is often necessary to distinguish different fields because observations of a star may have different characteristics (e.g. a different dispersion) on each field, depending for example on the position of the star on the CCD chip. For instance, measurements that are close to the center are more precise. The plot also shows the data of the other camera. Those observations are marked with small dots.

Figure 5. Star page.

Parameters of the light curve are controlled using a form below the plot (see Figure 5). Apart from changing the range of data for the plot, a user may also draw a phased light-curve – a light curve where the time axis is taken modulo a given period (the Period parameter in the form). On such a plot the points are repeated twice to show two lengths of the period. Phased light-curves are useful when studying periodic variables. It is also possible to plot averages of a given number of consecutive measurements (the Merge parameter in the form). This option may be used to remove the influence of statistical errors to reveal true changes in a light-curve. The form allows also some erroneous measurements to be skipped (the Skip options in the form) – turning on these options will cause measurements, which are marked in the database with an appropriate flag to be removed from the plot. The option Field may be used to choose one or more fields of observation, separated by a comma, from which the measurements will be shown. The light-curve is zoomable in the same way as the Sky Map and the Variability Diagram. After selecting a region, it will be magnified (Figure 6). Such a zoom corresponds to setting new range in the form.

Figure 6. Interactive zoom of a light curve.

The changes to a light-curve caused by setting different parameters in the form or by the interactive zoom are done asynchronously in JavaScript. The whole web page is not downloaded again from the web server – only the picture with the plot is reloaded. Such a solution speeds up browsing and reduces server loading. This solution does not destroy the browser’s back button functionality. Bookmarking however will not work directly and the whole web page should be reloaded with new parameters before saving the URL of the page. This can by done by clicking on the Reload Page button just below the light-curve (see Figure 5).

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.

Other star catalogs

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.

Bulk data download

Featured web interface has several ways to download bulk data to disk. In addition to the described above, the “Star Page” user has at their disposal button named “Get result pack”, so as shown in Figure 7. Clicking this button will start the download process of data found according to search criteria. The process of recording bulk data on computer disk is shown in Figure 8. Instead of giving the detailed search criteria, the user may also use the “List of Stars” button. It list all found stars, and then the user can choose which of these stars would be saved on the disc. This is done by clicking the checkboxes as is shown in Figure 9. The user can navigate between the pages with the results, and marked checkboxes remain remembered. Advanced options are available when you click the “Advanced result pack options” button. By clicking this button and selecting checkboxes, the user can specify the type of data archive to be used. It is also possible to choose the database fields to be included in the archive from the predefined list (checkboxes) or by explicitly specifying the database columns. In order to avoid too large data packs it’s also possible to specify the maximal size and number of stars in the archive. An additional, last option visible in Figure 10 allows to specify a file in two columns format respectively right ascension (HH:MM:SS) and declination (DD:MM:SS). This option allows to download light curves of objects which have coordinates listed in the file located within radius specifed in the field “radius”. The last figure (Figure 11) summarize all the options available for bulk downloading found data on user’s local computer.

Figure 7. Button "Get result pack" and its options.

Figure 8. The process of saving bulk data to a disk.

Figure 9. Downloading data via the direct selection.

Figure 10. Advanced options of downloading bulk data to a disk.

Figure 11. Overview of all options for bulk data download.

More advanced data reduction methods.

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)