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Astron. Astrophys. 363, 901-916 (2000)

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LMC and SMC Cepheids: combining OGLE with DENIS and 2MASS infrared data

M.A.T. Groenewegen

Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85740 Garching, Germany

Received 20 July 2000 / Accepted 9 October 2000


I cross-correlate the OGLE database of Cepheids in the Large and Small Magellanic Clouds (MCs) with the second incremental release of the 2MASS [FORMULA] survey, and the DENIS [FORMULA] point source catalog towards the MCs.

Of the 3384 Cepheids in OGLE in both Clouds, 1745 have a counterpart in the 2MASS survey within an 1" radius and good-photometry in all three bands. Only 173 have a counterpart in the DENIS survey within an 1" radius and good-photometry in all three bands. The reason for this difference is that the limiting magnitudes of the 2MASS survey are considerably fainter than for the DENIS survey.

The standard stars of the Carter IR photometric system are also correlated with the 2MASS survey to derive transformation equations from the natural 2MASS system to the Carter-system.

In order to describe to first order the geometrical configuration of the MCs a plane is fitted to the reddening-free Wesenheit index ([FORMULA]) and the inclination and position angle of the line-of-nodes are determined. For the LMC an inclination angle of 18 [FORMULA] 3o is derived, somewhat smaller that previous determinations. For the SMC a value of [FORMULA]o is derived in good agreement with previous determinations. These results are being used to take out the effect that some Cepheids are closer to the observer than others. For the LMC this effect is small over the area covered by the OGLE survey, but for the SMC PL-relations with a reduced scatter are derived in this way. Nevertheless, the dispersion in the PL-relation in W for the SMC is larger than that for the LMC, indicating a significant intrinsic depth of the SMC of about 14 kpc (front-to-back). The depth of the LMC is found to be small compared to the intrinsic scatter in the PL-relation.

Using single-epoch 2MASS data for the OGLE Cepheids PL-relations are fitted in JHK (on the Carter system) for both Fundamental mode (FU) and First-overtone (FO) pulsators, taking out the effect of the inclined disk. Because of the large number of stars available, this results in the most accurately determined slopes in the infrared up to now, and slopes for FO pulsators derived for the first time. This provides additional constraints for theoretical models.

The 16 derived PL-relations (in WJHK for FU and FO pulsators for LMC and SMC) are used to derive a relative distance modulus [FORMULA] assuming no metallicity correction. Two recent theoretical models predict different metallicity corrections, indicating a systematic uncertainty of up to 0.1 mag.

Using the database of Galactic Cepheids observed with HIPPARCOS and the method outlined in Groenewegen & Oudmaijer (2000), the zero points of Galactic PL-relations for FU pulsators in W and K are derived, using the newly derived slopes for LMC and SMC pulsators.

Combining the zero points of the Galactic and MCs PL-relations distance moduli of 18.60 [FORMULA] 0.11 (based on W) and 18.55 [FORMULA] 0.17 (based on K) to the LMC, and of 19.11 [FORMULA] 0.11 (W) and 19.04 [FORMULA] 0.17 (K) to the SMC are derived (without taking into account possible metallicity corrections).

Key words: stars: distances – stars: variables: Cepheids – galaxies: Magellanic Clouds – cosmology: distance scale

Send offprint requests to: Martin Groenewegen (groen@mpa-garching.mpg.de)

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© European Southern Observatory (ESO) 2000

Online publication: December 5, 2000