An estimate of the structural parameters of the Large Magellanic Cloud using red clump stars

Abstract

The structural parameters of the disk of the Large Magellanic Cloud (LMC) are estimated.We used the red clump stars from the VI photometric data of the Optical Gravitational Lensing Experiment survey and from the Magellanic Cloud Photometric Survey for the estimation of inclination and position angle of line of nodes of the LMC disk. The dereddened peak I magnitude of the red clump stars in each subregion is used to obtain the relative distances and hence the z coordinate. The RA and Dec of each sub-region is converted into x & y cartesian coordinates. A weighted least square plane fitting method is applied to this x,y,z data to estimate the structural parameters of the LMC disk. We find an inclination of i =23.0 plus or minus 0.8 and PAlon = 163.7 plus or minus 1.5 for the LMC disk using the OGLE III data and an inclination of i=37.4 plus or minus 2.3 and PAlon= 141.2 plus or minus 3.7 for the LMC disk using the MCPS data. The effect of choice of center, reddening and area covered on the estimated parameters are discussed. Regions in the north west, south west and south east of the LMC disk are warped with respect to the fitted plane. We also identify a symmetric but offcentered warp in the inner LMC.We identify that the structure of the LMC disk inside the 3 degree radius is different from the outside disk such that the inner LMC has relatively less inclination and relatively large PAlon. The 3D plot of the LMC disk suggests an offcentered increase in the inclination for the north-eastern regions which might be due to tidal effects. We suggest that the variation in the planar parameters estimated by various authors as well as in this study is because of the difference in coverage and the complicated inner structure of the LMC disk. In the inner LMC, the stellar and HI disk are found to have similar properties.