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The project started in the autumn of 2003. The first observations were gathered from Michigan State University. In 2004 we devoted an international combined photometric and spectroscopic campaign to the brightest and probably most studied Blazhko star RR Lyrae. Photometric data are being gathered from Michigan, Arizona, Greece, Turkey, Austria, and Belgium. Spectroscopic data are gathered from Texas, Canada, the Czech Republic and La Palma. This campaign continued until December 2004. An overview of the collaborators, the gathered data and some results:
The results of this campaign have been published: K. Kolenberg, H. Smith, K.D. Gazeas, A. Elmasli, M. Breger, E. Guggenberger, P. Van Cauteren, P. Lampens, P. Reegen, P.G. Niarchos, B. Albayrak, S.O. Selam, I. Özavci, and I. Aksu, 2006: The Blazhko Effect of RR Lyrae in 2003-2004, 2006, A&A 459, 577. A photometric follow-up campaign on RR Lyrae was carried out in 2006. Besides looking back at RR Lyr, we selected another target deserving special attention: XZ Cyg, also showing a changing Blazhko period.
As part of the multisite summer observations, three students at the University of Vienna set up a campaign to bring observational astronomy closer to the public. The observations were carried out from Lower Austria during the first three weeks of September 2006. Here is a link to the campaign website, in German.
Starting in the autumn of 2004, some interesting winter Blazhko targets were selected to be observed photometrically from Vienna. Soon the Belgian observers joined the campaign. In the meantime data are also being gathered from Turkey, Michigan, Kansas, Athens, Barcelona, Vienna and Beersel, Belgium. All people interested, professionals as well as amateurs, are welcome to join in this multi-site campaign.
At the beginning of 2004 a photometric campaign started from the South African Astronomical Observatory (SAAO), dedicated to the observation of southern Blazhko stars. This campaign allowed us to select the best targets for a spectroscopic study. In the summer of 2005 (July-September) a big simultaneous photometric campaign was carried out from SAAO (South Africa) and SSO (Siding Spring Observatory, Australia). An overview of the observations:
From the theoretical side, line profile variations are being studied for stars pulsating in a radial mode, modulated by nonradial components with close frequencies. These experiments also serve to determine the optimal time spread for the observations, in order to make efficient use of telescope time.
Our extensive photometric campaigns allow for a study of the changes in the light curve shape at different phases in the Blazhko cycle. A confrontation of the derived Fourier parameters with those resulting from hydrodynamical pulsation codes such as the ones developed by Feuchtinger (1999), allows us to conclude that it is very hard to model the observed light curve variations with only radial modes (Pikall, private communication).
Since an application of spectroscopic mode identification techniques to RR Lyrae stars is not so straightforward due to the strong nonlinearity of the radial mode, we are also investigating the possibility and discriminating power of a photometric mode identification method making use of amplitude ratios and phase differences related to data gathered in different photometric filters (e.g., Johnson B,V, I).
Finally, spectroscopic mode identification methods and their applicability are being tested in a Vienna-Leuven collaboration (Zima et al. 2004, Communications in Asteroseismology 144).
Kolenberg, K.: "The Blazhko Effect: Facts, Figures and Future work", 2004, Communications in Asteroseismology, vol. 145, 16
Zima, W., Kolenberg, K., Briquet, M., Breger, M.: "Moment Method and Pixel-by-Pixel Method: Complementary Mode Identification I. Testing FG Vir-like pulsation modes", 2004, Communications in Asteroseismology, vol. 144, 5
Kolenberg, K.: "New approaches to solve the old Blazhko puzzle in RR Lyrae stars",The A-Star Puzzle, IAU Symposium, No. 224, held in Poprad, Slovakia, July 8-13, 2004. Edited by J. Zverko, J. Ziznovsky, S.J. Adelman, and W.W. Weiss, Cambridge, UK: Cambridge University Press, 2004, 367
Zima, W., Kolenberg, K., Briquet, M., Breger, M.: "Limits for the application of spectroscopic mode ID methods",The A-Star Puzzle, IAU Symposium, No. 224, held in Poprad, Slovakia, July 8-13, 2004. Edited by J. Zverko, J. Ziznovsky, S.J. Adelman, and W.W. Weiss, Cambridge, UK: Cambridge University Press, 2004, 780
Kolenberg, K.: The Blazhko Project: "Joint Efforts in Solving a Century-old Problem", The Light-Time Effect in Astrophysics, Proceedings of ASP Conference Series, Vol. 335, held in Brussels 19-22 July 2004. Edited by C. Sterken. San Francisco: Astronomical Society of the Pacific, 2005, 16
Kolenberg, K., Guggenberger, E., Lenz, P., Van Cauteren, P., Lampens, P., Wils, P.: "OV And, a new field Blazhko star?", 2005, Communications in Asteroseismology, vol. 146, 11
K. Kolenberg, H. Smith, K.D. Gazeas, A. Elmasli, M. Breger, E. Guggenberger, P. Van Cauteren, P. Lampens, P. Reegen, P.G. Niarchos, B. Albayrak, S.O. Selam, I. Özavci, and I. Aksu: "The Blazhko Effect of RR Lyrae in 2003-2004", 2006, A&A 459, 577
Kolenberg, K., 2006: The Blazhko Project: "Unravelling the Mysteries of Amplitude Modulation", Proceedings of the conference "Solar and stellar physics through eclipses" (Side, Turkey, March 2006), ASP Conf. Ser., in press
Breger, M., & Kolenberg, K., 2006: "Equidistant frequency triplets in pulsating stars: the Combination Mode Hypothesis", Astronomy & Astrophysics, in press
Guggenberger, E., & Kolenberg, K., 2006: "A photometric study of the bump in SS For and RR Lyr", Communications in Asteroseismology, vol. 148, p. 21
Kolenberg, K., & Guggenberger, E., & the Blazhko collaboration, 2006, Proceedings of the Workshop on the Future of Asteroseismology, "Photometry of Blazhko stars: Results of the Blazhko Project so far", Communications in Asteroseismology, 150, in press
Kolenberg, K., Guggenberger, E., Medupe, T., Lenz., P., Schmitzberger, L., Shobbrook, R.R., Lub, J., Breger, M., Beck, P., 2006: "A photometric study of the southern Blazhko star SS For", submitted to the Monthly Notices of the Royal Astronomical Society
Guggenberger, E., & Kolenberg, K.., 2006, Proceedings of the Workshop on the Future of Asteroseismology:"RR Lyrae stars: the changing light curve shape during the Blazhko cycle", submitted to the Communications in Asteroseismology
Kolenberg, K., & Guggenberger, E., & The Blazhko Collaboration, 2006, Proceedings of the Workshop on the Future of Asteroseismology: "Photometric Campaigns by the Blazhko Project", submitted to the Communications in Asteroseismology
Guggenberger, E., & Kolenberg, K., 2006: "Features in the light curves of Blazhko stars", submitted to the Communications in Asteroseismology
Kolenberg, K., Guggenberger, E., Lenz, P., Schmitzberger, L., Medupe, T., Shobbrook, B., Beck, P., Breger, M., 2006: "UV Oct, the brightest southern Blazhko star", in preparation
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!