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ASTR 5610, Majewski [SPRING 2016]. Lecture Notes

ASTR 5610 (Majewski) Lecture Notes


CHEMICAL ABUNDANCE EFFECTS ON SPECTRAL ENERGY DISTRIBUTIONS


CHEMICAL NOMENCLATURE

Definition of "metallicity":


Abundances by weight:



Effects of Line Strengths on Broadband Colors: UBV Example

Metallicity effects play an important role on how the stars in a stellar population are distributed in a color-magnitude diagram (CMD).

Obviously, if we want to use CMDs to interpret the age/metallicity characteristics of a population, we need to understand how these metallicity effects change the colors and magnitudes of stars.

I will focus on one particular example, metallicity effects in the UBV system, not only to give flavor of how the CMD changes, but because this particular example plays an important role in Galactic astronomy/stellar populations studies.

In the following figure is shown the variation of the line-blocking coefficient (LBC) with wavelength for various types of stars.

You can think of the LBC as something like (1-emissivity), with the emissivity of a source defined as the ratio of true flux to that from a BB of same temperature.

Line blocking as a function of stellar type in top three panels. Bottom two panels shows change in the LBC for two stars of same spectral type but different metallicity. From Mihalas & Binney (1980).
From the figure notice that:

What is happening in above diagram?



Why Are There "Subdwarfs"?

It was noticed in the 1950s (perhaps earlier?), that stars with an ultraviolet excess also appeared to be subluminous with respect to normal Population I type stars.


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Filter curves taken from http://www.ast.cam.ac.uk/AAO/local/www/ras/rgo/appendix_c.html. All other material copyright © 2003, 2006, 2008, 2010, 2012, 2014, 2016 Steven R. Majewski. All rights reserved. These notes are intended for the private, noncommercial use of students enrolled in Astronomy 551 and Astronomy 5610 at the University of Virginia.