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

• Autorzy: Udalski A.
• Języki publikacji: EN

Abstrakty

EN

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. At present, the most likely calibration of the zero point of the common distance scale, which would be consistent with observations of all four distance indicators, is that resulting from faint calibration of RR Lyr stars or calibration of the red clump stars. With the OGLE-II photometry it leads to the distance moduli of (m-M)_LMC=18.24 mag, (m-M)_SMC=18.75 mag and (m-M)_CAR=19.94 mag for the LMC, SMC and Carina dwarf galaxy, respectively. The systematic uncertainty is of the order of 0.07 mag, while the standard deviation of four determinations of only 0.02 mag. We also analyze the difference of distance moduli between the SMC and LMC. The average value is Δ(m-M)_SMC-LMC=0.50±0.03 mag from four independent measurements. This very good agreement allows us to draw conclusions on the interstellar extinction in the Magellanic Clouds. Our photometric data also provide constraints on the properties of red clump stars. Finally, the differential comparison of brightness of Cepheids with brightness of other distance indicators in the Magellanic Clouds, and preliminary observations of Cepheids in the IC1613 galaxy indicate no dependence of the zero point of Cepheid Period-Luminosity relation on metallicity.

Słowa kluczowe

EN

Magellanic Clouds; galaxies: distances and redshifts; distance scale

• Wydawca: Copernicus Foundation for Polish Astronomy
• Czasopismo: Acta Astronomica
• Rocznik: 2000
• Tom: Vol. 50, No. 3
• Strony: 279--306
• Opis fizyczny: Bibliogr. 59 poz., tab., wykr.

Twórcy

autor

Udalski A.

• Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland

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