There are two independent observing projects going on in Warsaw which have cosmological implications.

Janusz Kaluzny of CAMK discovered (with his associates) a number of detached eclipsing binaries in several globular clusters. These are ideal objects to measure the ages, far superior to the traditional "isochrone fitting" method, which suffers from uncontrollable errors due to lack of understanding of convective envelopes (mixing length "theory". The method used by Kaluzny is based on the very robust mass-luminosity relation for stars near the main sequence turn-off point. Enclosed is the abstract of a relevant paper: astro-ph/0111089. This is the most reliable (so far) determination of the age of any globular cluster. More work will be done soon by Janusz Kaluzny and his collaborators.

Another project is OGLE, and enclosed are two papers by its leader, Andrzej Udalski of the Warsaw University Observatory. The project provides the best (so far) determination of the distance to the Large Magellanic Cloud, which is the first step towards the determination of Hubble constant by the HST Key Project and other groups. OGLE will keep refining the LMC distance determination using variety of methods - stay tuned.

Bohdan Paczynski

------------------------------------------------------

Astrophysics, abstract astro-ph/0111089

From: Janusz Kaluzny jka@camk.edu.pl Date: Mon, 5 Nov 2001 15:46:09 GMT (123kb)

Photometry and Spectroscopy of Eclipsing Binaries in omega Centauri

Authors: J. Kaluzny, I. Thompson, W. Krzeminski, A .Olech, W. Pych, B. Mochejska Comments: 5 pages, 3 figures, newpasp.sty, to appear in the "Omega Centauri: a Unique Window into Astrophysics" (Cambridge, Aug. 2001), ASP Conf. Ser. edited by F. van Leeuwen, G. Piotto,and J. Hughes

Detached eclipsing double line spectroscopic binaries are accurate distance indicators. They can be used for the direct determination of distances to globular clusters in which such systems can be identified. The results of major photometric surveys aimed at identification of variable stars in omega Cen are summarized. Over 43 eclipsing binaries have been identified so far in the cluster field of which only 8 objects are true detached systems. Distance and age determinations are presented for the system OGLEGC-17. The apparent distance modulus is (m-M)_{V}=14.09\pm 0.04 and the age of this binary is tau=11.8\pm 0.6 Gyr.

------------------------------------------------------

Astrophysics, abstract astro-ph/9910167

From: Andrzej Udalski udalski@astrouw.edu.pl Date (v1): Fri, 8 Oct 1999 16:33:32 GMT (33kb) Date (revised v2): Sun, 10 Oct 1999 11:58:20 GMT (33kb) Date (revised v3): Fri, 14 Jan 2000 15:35:00 GMT (36kb)

The Optical Gravitational Lensing Experiment. Red Clump Stars as a Distance Indicator

Authors: A. Udalski Comments: 11 pages. Latex+psfig. Accepted for publictation in ApJ Letters. Major revision: 30% larger sample of Hipparcos red giants with spectroscopic metallicities and extended photometry of the LMC field red clump stars (9 lines-of-sight). Due to journal space limitation, sections on comparison of the LMC red clump distance modulus with previous determinations and relations between the color indices and metallicity removed from this version

We present relation of the mean I-band brightness of red clump stars on metallicity. Red clump stars were proposed to be a very attractive standard candle for distance determination. The calibration is based on 284 nearby red giant stars whose high quality spectra allowed to determine accurate individual metal abundances. High quality parallaxes (\sigma_\pi / \pi < 10%) and photometry of these very bright stars come from Hipparcos measurements. Metallicity of the sample covers a large range: -0.6<[Fe/H]<+0.2 dex. We find a weak dependence of the mean I-band brightness on metallicity (about 0.13 mag/dex). What is more important, the range of metallicity of the Hipparcos sample partially overlaps with metallicity of field giants in the LMC, thus making it possible to determine the distance to the LMC by almost direct comparison of brightness of the local Hipparcos red clump giants with that of LMC stars. Photometry of field red clump giants in nine low extinction fields of the LMC halo collected during the OGLE-II microlensing survey compared with the Hipparcos red clump stars data yields the distance modulus to the LMC: (m-M)_LMC=18.24+/-0.08 mag.

------------------------------------------------------

Astrophysics, abstract astro-ph/0010151

From: Andrzej Udalski udalski@astrouw.edu.pl Date: Sat, 7 Oct 2000 09:34:13 GMT (161kb)

The Optical Gravitational Lensing Experiment. Stellar Distance Indicators in the Magellanic Clouds and Constraints on the Magellanic Cloud Distance Scale

Authors: A. Udalski Comments: 26 pages, 8 figures (3 in 'jpg'format), LaTex Journal-ref: Acta Astronomica, 50, 279

BVI photometry of the Magellanic Clouds collected during the OGLE-II microlensing experiment makes it possible to study in detail photometric properties of the "major" stellar distance indicators in the Magellanic Clouds. In addition to Cepheids, RR Lyr and red clump stars, which photometry was presented in the earlier OGLE papers, we present the so far most accurate determination of brightness of the tip of the red giant branch in the LMC and SMC. We analyze the ratios of brightness of all four distance indicators in the LMC and SMC. Additionally, we include in our analysis, when possible, photometric data of the distance indicators in the metal poor Carina dwarf galaxy for which photometry was also collected during the OGLE-II experiment. The analysis is largely differential, free from zero point and extinction uncertainties. The main conclusion is that the distance scales resulting from all four stellar distance indicators are fully consistent with each other. Therefore the distance scale problem is not a problem resulting from different distances yielded by distance indicators, but rather a problem of the proper zero point of this common distance scale. All four stellar distance indicators have to be treated as an ensemble, and any determination of the zero point for one of them must predict reasonable luminosities of the others. This puts strong constraints on many proposed calibrations of distance indicators. For example, very bright calibrations of Cepheids or RR Lyr can practically be ruled out. (Abridged).

------------------------------------------------------