The Blazhko Project is an international collaboration, set up to join efforts in obtaining a better understanding of the Blazhko phenomenon in RR Lyrae stars. The project was founded in Vienna and started its activities in the autumn of 2003.


The starting point for improving the modelling is an extensive data of a limited sample of field RR Lyrae Blazhko and non-Blazhko stars: a few RRab Blazhko stars, in the northern and in the southern hemisphere, and also one RRc Blazhko target. Important is the inclusion of a few well-selected non-modulated RR Lyrae stars in the target list, of which similar data are being gained, to be compared with the Blazhko stars.


Figure1: The answer to the century-old Blazhko puzzle probably lies in the detailed study of the spectra of modulated stars. A suitable "magnifying glass" is needed to be able to detect the modes responsible for the modulation (see text).


The required data set consists of high-resolution R 40000, high-S/N (>100) spectroscopic data evenly spread over the Blazhko cycle for the target stars. A few very detailed snapshots (S/N > 200) are being (and will be) obtained with telescopes of the 8-m class, and will help to distinguish between different nonradial modes. Simulation studies reveal how much high-resolution data are minimally needed to be able to disentangle the modes, and what would be their optimal time spread. Additional radial velocities over a longer time base can be obtained with smaller telescopes, and provide essential information to interpret the line profile variations. Finally, photometric data gathered over a time base of at least a year, are needed to ensure the required frequency resolution. For the interpretation of the data we will use the available spectroscopic identification methods (described below), as well as combined techniques presently being developed (see Zima et al. 2004).


Figure 2: Comparison of the HIPPARCOS lightcurves of SU Dra, a non-modulated RR Lyrae star (first figure), and RR Lyr, a Blazhko star (second figure).



Click to find out the Actual Status of the Blazhko Project.
Click to see the collaborators who have contributed to the work done in the project.


Other work! not done by this project

This project is not the only one focused on a better understanding of amplitude and phase modulation in RR Lyrae stars. We want to point out the important work done by other astronomers both on the observational and the theoretical side since many years. Large-scale surveys such as MACHO, OGLE have contributed to precise statistics on the occurrence and phenomenology of the Blazhko effect (Alcock et al. 2000,2003; Moskalik & Poretti 2003; Soszynski et al. 2003). The photometry carried out at Konkoly observatory (Hungary) has yielded very important results over the past 10 decades (e.g., Szeidl & Kollath 2000) and especially in recent years after the refurbishment of the telescope (e.g., Jurcsik et al. 2005), important new results have been obtained. The spectroscopic and spectropolarimetric work of Chadid and collaborators (e.g., Chadid et al. 2004) has been crucial for a better understanding of the Blazhko effect. And there are undoubtedly many other contributors, professionals and amateurs, who are not mentioned here (yet). We apologize for incompleteness!