1. Behavior of Reddenings in the Color-Magnitude & Color-Color Diagrams of 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.

7. 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

8. 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.

9. Our Calculations Isochrones Galaxies
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

10. Reddening in Isochrones

11. 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 u’ g’ r’ i’ z’
Ai/A5500
1.5698
1.2000
0.8786
0.6738
0.4889

12. Errors in Dereddening Isochrone CMDs (1/2)

13. Errors in Dereddening Isochrone CMDs (2/2)

14. Errors in Dereddening Isochrone CCDs

15. Galaxy SEDs

16. Errors in Dereddening Galaxy CMDs (1/2)

17. Errors in Dereddening Galaxy CMDs (2/2)

18. Errors in Dereddening Galaxy CCDs

19. Errors in Dereddening Galaxy CMDs
(109 yr, different redshifts)

20. SDSS + GALEX Galaxy CMDs

21. 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.