Find RR Lyrae

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Goal 1: To find RR Lyrae in the bulge

Figure 1: Optical colour-magnitude diagram for bulge RRab (crosses), showing the sequence belonging to the Sgr dwarf galaxy (circles) located behind the bulge (Alcock et al. 1997, 474, 217). Differential reddening is very significant even in the bulge clear windows. The direction of the reddening arrow illustrates that the optical sample of RR Lyrae quickly becomes incomplete. There are about 2000 RR Lyrae known in the unreddened windows of the bulge, while the total population is estimated to be an order of magnitude larger than that.
which will allow to: determine periods and amplitudes, measure accurate mean magnitudes, make the Bailey diagram, interpret the results of the variability analysis in terms of stellar pulsation and evolution models, and compare the pulsation properties of bulge variables with those of similar variables in the halo and nearby dwarf galaxies[1]. The distances measured and RR Lyrae counts can be compared with the clump giants, which are excellent tracers of the inner bar[2]. This would define the geometry of the inner bar and of additional structures[3], and explore the radial dependence of the density[4], or trends with Galactic latitude-longitude, to finally unveil the structure of the bulge. The microlensing surveys that we have been involved in (OGLE and MACHO) have discovered about 10% of the existing bulge RR Lyrae stars[5]. Our final survey will find more than 50% of the bulge RR Lyrae.


  1. e.g. Catelan 2006, astro-ph/0507464
  2. Stanek et al. 1994, ApJ, 429, L73
  3. like a potential second bar; Nishiyama et al. 2006, ApJ, 621, L105
  4. e.g. Minniti et al. 1999, ASP, 165, 284
  5. e.g. Figure 2, see Alcock et al. 1998, ApJ, 492, 190; Udalski et al. 2002, AcA, 52, 129
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