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Improving the Local Distance Scale from Empirically Calibrated Stellar Isochrones

by An, Deokkeun

Abstract (Summary)
Many outstanding problems concerning the formation and evolution of the Galaxy require accurate distances, but currently available photometric parallax relations for main-sequence (MS) stars often have an unacceptable accuracy of > ~20%. To overcome this, a method for empirically calibrating theoretical color-temperature relations was developed, with emphasis given to the critical assessment of the accuracy of the MS-fitting technique in the Johnson-Cousins-2MASS filter system. It is demonstrated that isochrones with empirical corrections accurately match the shape of the MS for nearby well-studied open clusters and provide internally consistent distances in several color indices. The resulting error in distance is estimated to be ~2% when there exists a good metallicity estimate. The distance to the Pleiades is in excellent agreement with several geometric distance measurements. Furthermore, the Cepheid period-luminosity (P-L) relation derived from Milky Way open clusters yields a distance to the maser-host galaxy NGC~4258 that agrees with the geometric measurement. These results suggest that a self-consistent local distance scale, estimated from trigonometric parallaxes, MS-fitting method, and Cepheid P-L relations, is now within reach. Photometric parallax relations in the Sloan Digital Sky Survey (SDSS) griz system are also presented to exploit the full capabilities of the SDSS imaging survey. For this purpose, SDSS imaging data for 17 globular and 3 open clusters are reduced with the DAOPHOT/ALLFRAME suite of programs. Theoretical isochrones are tested over a wide range of metallicity using the photometry and fiducial sequences for these clusters. It is demonstrated that the models are in satisfactory agreement with the data for [Fe/H]
Bibliographical Information:

Advisor:

School:The Ohio State University

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:distance scale stellar evolution open clusters and associations globular

ISBN:

Date of Publication:01/01/2008

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