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Behavior of Reddenings in the Color-Magnitude & Color-Color Diagrams of SDSS Filters

Behavior of Reddenings in the Color-Magnitude & Color-Color Diagrams of SDSS Filters. 김성수, 이명균. Estimating the Extinction. Photometric data in at least two bands CMD or CCD Color excess & extinction law --> Extinction People usually assume that the reddening vector is linear

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Behavior of Reddenings in the Color-Magnitude & Color-Color Diagrams of SDSS Filters

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  1. Behavior of Reddenings in theColor-Magnitude & Color-Color Diagramsof SDSS Filters 김성수, 이명균

  2. Estimating the Extinction • Photometric data in at least two bands • CMD or CCD • Color excess & extinction law --> Extinction • People usually assume that • the reddening vector is linear • a single reddening vector can be applied for all kinds of objects

  3. CMD

  4. CCD

  5. SED-Dependence & Nonlinearity of Extinction • Effective wavelength : • The effective wavelength varies for different SEDs. • The effective wavelength shifts toward the longer wavelengths as the extinction increases. • This effect is more significant for a filter with a larger bandwidth.

  6. Previous Studies • First studies on the nonlinearity • Blanco (1956, 1957) • Hiltner & Joihnson (1956) • Wildey (1963) • First thorough study on the SED-dependence • Grebel & Roberts (1995) • Called this “heterochromatic extinction”. • Infrared bands • Kim et al. (2005) : H-K colors • Kim, Lee & Figer (2006) : J-K colors

  7. SDSS Photometric Data • SEGUE is mapping the Milky Way on a regular grid extending through the Galactic plane. • SEGUE will observe many star clusters and galaxies in the zone of avoidance.

  8. Our Calculations • Isochrones • For star clusters in the Milky Way & nearby galaxies • Kurucz models for synthetic stellar spectra • Padova models for isochrones • Galaxies • For spatially unresolved galaxies • Bruzual & Charlot (2003) for the stellar population synthesis model • Buzzoni’s (2005) recipe for the galaxy build-up

  9. Reddening in Isochrones

  10. Our “Reference” Extinction Law • An extinction law calculated for • the average spectrum of stars in the 109 yr, solar-metallicity isochrone weighted with a Salpeter mass function

  11. Errors in DereddeningIsochroneCMDs (1/2)

  12. Errors in DereddeningIsochroneCMDs (2/2)

  13. Errors in DereddeningIsochroneCCDs

  14. Galaxy SEDs

  15. Errors in DereddeningGalaxyCMDs (1/2)

  16. Errors in DereddeningGalaxyCMDs (2/2)

  17. Errors in DereddeningGalaxyCCDs

  18. Errors in DereddeningGalaxyCMDs (109 yr, different redshifts)

  19. SDSS +GALEXGalaxyCMDs

  20. Summary • The SED-dependence and the nonlinearity are non-negligible for SDSS filters as well. • Extinction can be over- or under-estimated by up to 12% for Ai<5 mag. • Age is a more important factor than metallicity and redshift. • CMDs and CCDs involving the g’ filter have a much larger sensitivity. • CCDs are no better than CMDs. • Dereddening with the color that has a longer baseline is desirable. • Colors only from r’, i’, and z’ give stable reddening.

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