The Konkoly Blazhko Survey: is light-curve modulation a common property of RRab stars?

A systematic survey to establish the true incidence rate of Blazhko modulation among short-period, fundamental-mode, Galactic field RR Lyrae stars has been carried out. The Konkoly Blazhko Survey (KBS) was initiated in 2004. Since then, more than 750 nights of observation have been devoted to this project. A sample of 30 RRab stars was extensively observed, and light-curve modulation was detected in 14 cases. The 47 per cent occurrence rate of the modulation is much larger than any previous estimate. The significant increase of the detected incidence rate is mostly a result of the discovery of small-amplitude modulation. Half of the Blazhko variables in our sample show the modulation with such a small amplitude that they would definitely have been missed in previous surveys. We have found that the modulation can be very unstable in some cases; for example, RY Com showed regular modulation during only one part of the observations, and had a stable light curve with abrupt, small changes in the pulsation amplitude during two observing seasons. This type of light-curve variability is hard to detect in the data from other surveys. The higher frequency of the light-curve modulation of RRab stars makes it even more important to find an explanation for the Blazhko phenomenon. The validity of the [Fe/H](P, ϕ31) relationship using the mean light curves of Blazhko variables is checked in our sample. We found that the formula gives accurate result for small-modulation-amplitude Blazhko stars, and this is also the case for large-modulation-amplitude stars if the light curve has complete phase coverage. However, if the data for large-modulation-amplitude Blazhko stars are not extended enough (e.g. fewer than 500 data points from fewer than 15 nights), the formula may give false result owing to the distorted shape of the mean light curve used.

[1]  C. Alard.  Image subtraction using a space-varying kernel , 2000 .

[2]  A. Layden.  The metallicities and kinematics of RR Lyrae variables, 1: New observations of local stars , 1994 .

[3]  M. Weber,et al.  The Blazhko behaviour of RR Geminorum I , 2008 .

[4]  G. Preston.  The RR Lyrae Stars , 1964 .

[5]  E. Schmidt,et al.  The Behlen Observatory variable star survey: finding charts and light curves for the first ninety-three stars , 1993 .

[6]  A. Henden,et al.  An extensive photometric study of the Blazhko RR Lyrae star MW Lyr – I. Light‐curve solution , 2008, 0807.0534.

[7]  M. Weber,et al.  The Blazhko behaviour of RR Geminorum I - CCD photometric results in 2004 , 2004, astro-ph/0410119.

[8]  Horace A. Smith,et al.  RR Lyrae Stars , 1995 .

[9]  E. Poretti,et al.  Fourier decomposition and frequency analysis of the pulsating stars with $P < $ 1 d in the OGLE database - II. Multiperiodic RR Lyrae variables in the Galactic Bulge , 2002, astro-ph/0211296.

[10]  G. Hajdu,et al.  An extensive photometric study of the Blazhko RR Lyrae star DM Cyg , 2009, 0904.4129.

[11]  K. E. McGowan,et al.  Northern Sky Variability Survey: Public Data Release , 2004, astro-ph/0401217.

[12]  A. Drake,et al.  The MACHO Project Large Magellanic Cloud Variable Star Inventory. XI. Frequency Analysis of the Fundamental-Mode RR Lyrae Stars , 2003, astro-ph/0308019.

[13]  C. Sturch.  Intrinsic UBV colors of RR Lyrae stars , 1966 .

[14]  Samus,et al.  General catalogue variable stars , 2001 .

[15]  O. Regev,et al.  Multimode stellar pulsations , 1982, Astrophysics and Space Science.

[16]  A catalogue of RR Lyrae stars from the Northern Sky Variability Survey , 2006, astro-ph/0601432.

[17]  Multiperiodic Galactic field RR Lyrae stars in the ASAS catalogue , 2007, astro-ph/0701068.

[18]  Michael Perryman,et al.  Astronomical Applications of Astrometry: The Hipparcos and Tycho Catalogues , 2008 .

[19]  A. Henden,et al.  An extensive photometric study of the Blazhko RR Lyrae star MW Lyr – II. Changes in the physical parameters★ , 2008, 0811.3095.

[20]  N. Suntzeff,et al.  Summary of Delta S Metallicity Measurements for Bright RR Lyrae Variables Observed at Lick Observatory and KPNO between 1972 and 1987 , 1994 .

[21]  I. D'ek'any,et al.  The Shortest Modulation Period Blazhko RR Lyrae Star: SS Cancri , 2006, astro-ph/0603496.

[22]  P. Beck,et al.  A photometric study of the southern Blazhko star SS For: unambiguous detection of quintuplet components , 2008, 0812.2065.

[23]  J. Jurcsik,et al.  The Blazhko behaviour of RR Geminorum II Long-term photometric results , 2007, 0704.3337.

[24]  D. Fabrycky,et al.  Catalog of Fundamental-Mode RR Lyrae Stars in the Galactic Bulge from the Optical Gravitational Lensing Experiment , 2006, astro-ph/0601137.