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Register a new userK-Band Red Clump Distance to the Large Magellanic Cloud
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Authors
David R. Alves
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The Hipparcos I-band calibration of horizontal-branch red clump giants as standard candles has lead to controversial results for the distance to the Large Magellanic Cloud (LMC). In an attempt to properly ascertain the corrections for interstellar extinction and clump age and metallicity, we analyze new multi-wavelength luminosity functions of the LMC red clump. Our photometry dataset in the K-band was obtained with the SOFI infrared imager at the European Southern Observatorys New Technology Telescope. In the V and I passbands, we employ data from WFPC2 onboard the Hubble Space Telescope. The LMC red clump is first identified in a K,(V-K) color-magnitude diagram. Our luminosity functions yield apparent magnitudes of K = 16.974, I = 18.206, and V = 19.233 (+- 0.009_r +- 0.02_s; random and systematic error, respectively). Compared directly to the Hipparcos red clump calibration (without a correction for age and metallicity), the LMC clump measurements imply a negative interstellar reddening correction. This unphysical result indicates a population difference between clumps. A modified calibration based on theoretical modeling yields an average reddening correction of E(B-V) = 0.089 +- 0.015_r, and a true LMC distance modulus of 18.493 +- 0.033_r +- 0.03_s. We reconcile our result with the short distance previously derived from OGLE II red clump data.
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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.
The structural parameters, like the inclination, i and the position angle of the line of nodes (PA_lon) of the disk of the Large Magellanic Cloud (LMC) are estimated using the JH photometric data of red clump stars from the Infrared Survey Facility - Magellanic Cloud Point Source Catalog (IRSF-MCPSC). The observed LMC region is divided into several sub-regions and stars in each region are cross identified with the optically identified red clump stars to obtain the near infrared magnitudes. The peak values of H magnitude and (J-H) colour of the observed red clump distribution are obtained by fitting a profile to the distributions and also by taking the average value of magnitude and colour of the red clump stars in the bin with largest number. Then the dereddened peak H0 magnitude of the red clump stars in each sub-region is obtained. The RA, Dec and relative distance from the center of each sub-region are converted into x, y & z 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. A reddening map based on (J-H) colour of the RC stars is presented. When the peaks of the red clump distribution were identified by averaging, an inclination of 25.7 +/- 1.6 and PA_lon = 141.5 +/- 4.5 were obtained. We estimate a distance modulus of 18.47 +/- 0.1 mag to the LMC. Extra-planar features which are in front as well as behind the fitted plane are identified which match with the optically identified extra-planar features. The bar of the LMC is found to be part of the disk within 500 pc. The estimates of the structural parameters are found to be independent of the photometric bands used for the analysis. We find that the inner disk, within 3.0, is less inclined and has larger value of PA_lon when compared to the outer disk.
High-precision (sigma < 0.01) new JHK observations of 226 of the brightest and nearest red clump stars in the solar neighbourhood are used to determine distance moduli for the LMC. The resulting K- and H-band values of 18.47pm0.02 and 18.49pm0.06 imply that any correction to the K-band Cepheid PL relation due to metallicity differences between Cepheids in the LMC and in the solar neighborhood must be quite small.
We present the most extensive and detailed reddening maps of the Magellanic Clouds (MCs) derived from the color properties of Red Clump (RC) stars. The analysis is based on the deep photometric maps from the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV), covering approximately 670 deg2 of the sky in the Magellanic System region. The resulting maps provide reddening information for 180 deg2 in the Large Magellanic Cloud (LMC) and 75 deg2 in the Small Magellanic Cloud (SMC), with a resolution of 1.7x1.7 arcmin in the central parts of the MCs, decreasing to approximately 27x27 arcmin in the outskirts. The mean reddening is E(V-I) = 0.100 +- 0.043 mag in the LMC and E(V-I) = 0.047 +- 0.025 mag in the SMC. We refine methods of calculating the RC color to obtain the highest possible accuracy of reddening maps based on RC stars. Using spectroscopy of red giants, we find the metallicity gradient in both MCs, which causes a slight decrease of the intrinsic RC color with distance from the galaxy center of ~0.002 mag/deg in the LMC and between 0.003 and 0.009 mag/deg in the SMC. The central values of the intrinsic RC color are 0.886 and 0.877 mag in the LMC and SMC, respectively. The reddening map of the MCs is available on-line both in the downloadable form and as an interactive interface.
We present Washington C, T1 CCD photometry of 21 fields located in the northern part of the Large Magellanic Cloud (LMC), and spread over a region of more than 2.52 degrees approximately 6 degrees from the bar. The surveyed areas were chosen on the basis of their proximity to SL 388 and SL 509, whose fields showed the presence of a secondary giant clump, observationally detected by Bica et al. (1998, AJ, 116, 723). From the collected data we found that most of the observed field CMDs do not show a separate secondary clump, but rather a continuous vertical structure (VS), which is clearly seen for the first time. Its position and size are nearly the same throughout the surveyed regions: it lies below the Red Giant Clump (RGC) and extends from the bottom of the RGC to approximately 0.45 mag fainter, spanning the bluest color range of the RGC. The more numerous the VS stars in a field, the larger the number of LMC giants in the same zone. Our analysis demonstrate that VS stars belong to the LMC and are most likely the consequence of some kind of evolutionary process in the LMC, particularly in those LMC regions with a noticeable large giant population. Our results suggest that in order to trigger the formation of VS stars, there should be other conditions besides the appropriate age, metallicity, and the necessary red giant star density. Indeed, stars satisfying the requisites mentioned above are commonly found throughout the LMC, but the VS phenomenon is only clearly seen in some isolated regions. Finally, the fact that clump stars have an intrinsic luminosity dispersion further constrains the use of the clump magnitude as a reliable distance indicator.
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