My main current interest and effort is in the work related to the Optical Gravitational Lensing Experiment (OGLE). This is a collaborative project with the team from the Warsaw University Observatory (Andrzej Udalski, Marcin Kubiak, Michal Szymanski, and their students). The new instrument is the 1.3 meter R/C Warsaw telescope recently built at the Las Campanas Observatory of Carnegie Institution of Washington. The primary goal of the project is to detect all kinds of variable objects, among them microlensing events, of which some may be related to dark matter. However, as CCD data is taken in the standard B, V, I bands, the photometric results are useful for a very broad range of topics. The new system has began operation on January 6, 1997, and it is described by Udalski, Kubiak & Szymanski (1997, Acta Astronomica 47, 319 = astro-ph/9710091 . The current OGLE-II phase of the project will be terminated at the end of September, 2000. The system will be upgraded to OGLE-III with the new mosaic CCD camera with 8k x 8k pixels, under construction by Dr. Andrzej Udalski. OGLE-III will become operational in 2001.
Another observing project I am associated with is the All Sky Automated Survey (ASAS) carried out by Dr. Grzegorz Pojmanski of the Warsaw University Observatory with the automated instrument located at the Las Campanas Observatory. The ultimate goal of the project is to monitor variability of all stars in the sky down to the magnitude limit we can afford. The description of the first instrument can be found at astro-ph/9712146 . The most recent results: about 3,900 bright and very bright variable stars found in 300 square degrees of the sky can be found at ASAS archive and at astro-ph/0005236. The system has been upgraded by Dr. G. Pojmanski, and the data rate has increased by a factor 30 in the second half of 2000. The new system has the name ASAS-3, and all details can be found at ASAS archive. The reasons why it is interesting to monitor all sky for variability are described in: "The Future of Massive Variability Searches", (1997, proceedings of 12th IAP Colloquium: "Variable Stars and the Astrophysical Returns of Microlensing Searches", Paris, Ed. R. Ferlet, p. 357 = astro-ph/9609073) and in: "Monitoring All Sky for Variability", (2000, PASP, 112, 1281 = astro-ph/0005284).
If you would like to contact Bohdan Paczynski, you can do so at:
The red clump giants are core helium burning stars, a high metallicity equivalent of the better known horizontal branch stars. Near the sun they form a very compact, well populated cluster in the Hipparcos color - magnitude diagram, as shown in the following figure. The potential of these stars as distance indicators was pointed out by Paczynski and Stanek,(1998, ApJ Lett., 494, L219 = astro-ph).
A very compact red clump is also clearly apparent in almost all galaxies that have been studied. For example, it is very dramatic in the low extinction part of the Small Magellanic Cloud. The following color - magnitude diagram has appeared in Paczynski et al. (1999, Acta Astronomica, 49, 319 = astro-ph). It is based on the OGLE data, made public domain by Udalski et al. (1998, Acta Astronomica, 48, 147 = astro-ph). The data is at OGLE-II SMC fields.
The most recent empirical calibration of distance determination using red clump giants, its metallicity dependence, and comparison with other distance indicators was published by A. Udalski (2000, ApJ, 531, L25 = astro-ph; 2000, Acta Astronomica, 50, 279 = astro-ph.