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

I cross-correlate the OGLE database of Cepheids in the Large and Small Mage llanic Clouds (MCs) with the second incremental release of the 2MASS J H K- s survey, and the DENIS I J K-s 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 go od-photometry in all three bands. The reason for this difference is that th e 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 2 MASS system to the Carter-system. In order to describe to first order the geometrical configuration of the MC s a plane is fitted to the reddening-free Wesenheit index (W = 1 - 1.55 x ( V - I)) and the inclination and position angle of the line-of-nodes are det ermined. For the LMC an inclination angle of 18 +/- 3 degrees is derived, s omewhat smaller that previous determinations. For the SMC a Value of i = 68 +/- 2 degrees is derived in good agreement with previous determinations. T hese results are being used to take out the effect that some Cepheids are c loser to the observer than others. For the LMC this effect is small over th e area covered by the OGLE survey, but for the SMC PL-relations with a redu ced 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 si gnificant intrinsic depth of the SMC of about 14 kpc (front-to-back). The d epth of the LMC is found to be small compared to the intrinsic scatter in t he PI-relation Using single-epoch 2MASS data for the OGLE Cepheids PL-relations are fitted in JHK ton the Carter system) for both Fundamental mode (FU) and First-ove rtone (FO) pulsators, taking out the effect of the inclined disk. Because o f 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 de rived for the first time. This provides additional constraints for theoreti cal models. The 16 derived PI-relations tin W J H K for FU and FO pulsators for LMC and SMC) are used to derive a relative distance modulus Delta (SMC-LMC) = 0.50 +/- 0.02 assuming no metallicity correction. Two recent theoretical models predict different metallicity corrections, indicating a systematic uncerta inty of up to 0.1 mag. Using the database of Galactic Cepheids observed with HIPPARCOS and the met hod outlined in Groenewegen & Oudmaijer (2000), the zero points of Galactic PI-relations for FU pulsators in W and K are derived, using the newly deri ved slopes for LMC and SMC pulsators. Combining the zero points of the Galactic and MCs PL-relations distance mod uli of 18.60 +/- 0.11 (based on W) and 18.55 +/- 0.17 (based on K) to the L MC, and of 19.11 +/- 0.11 (W) and 19.04 +/- 0.17 (K) to the SMC are derived (without taking into account possible metallicity corrections).