The ARAUCARIA project: Deep near-infrared survey of nearby galaxies. I. The distance to the Large Magellanic Cloud from

The ARAUCARIA project: Deep near-infrared survey of nearby galaxies. I. The distance to the Large Magellanic Cloud from K-band photometry of red clump stars ABSTRACT We have obtained deep imaging in the near-infrared J and K bands for 2 nearby fields in the bar of the LMC with the ESO NTT telescope, under exquisite seeing conditions. The K, J-K color-magnitude diagrams constructed from these data are of outstanding photometric quality and reveal the presence of several hundreds of red clump stars. Using the calibration of Alves for the K-band absolute magnitude of Hipparcos-observed red clump stars in the solar neigbourhood we derive a distance modulus to our observed LMC fields of 18.487 mag. Applying a correction for the tilt of the LMC bar with respect to the line of sight according to the geometrical model of van der Marel et al., the corresponding LMC barycenter distance is 18.501 mag. The random error on this result is +/-0.008 mag, whereas the systematic uncertainty on this distance result due to the photometric zero point uncertainty in our LMC K-band photometry, to the uncertainty of the Hipparcos-based absolute magnitude calibration of red clump stars in the solar neighborhood, and due to reddening uncertainties mounts up to +/-0.048 mag. If we adopt a K-band population correction of-0.03 mag, as done by Alves et al. 2002, to account for the difference in age and metallicity between the solar neighborhood and LMC red clump star populations, we obtain an LMC barycenter distance modulus of 18.471 mag from our data. This is in excellent agreement with the result of Alves et al., and of another very recent study 1 Based on observations obtained with the NTT telescope at the European Southern Observatory as part of project number 69.D-0352. – 2 – of Sarajedini et al. (2002) obtained from K-band photometry. However, we emphasize that current model predictions about the uncertainties of population corrections seem to indicate that errors up to about 0.12 mag may be possible, probably in any photometric band. Therefore, work must continue to tighten the constraints on these corrections. We also determine the mean red clump star magnitude in our LMC fields in the J band, which could be a useful alternative to the K band should future work reveal that population effect corrections for red clump stars in the J band are smaller, or more reliably determined than those for the K band.