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
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Astrophysics, abstract
astro-ph/0111089
From: Janusz Kaluzny <jka(a)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(a)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(a)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).
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