Lecture 12
HR diagram, luminosity/color/temp/radius/lifetime of stars
Tuesday July 22, 2008
Introduction to different types of stars, from the OBAFGKM (hottest to coolest)
main sequence stars, to the bloated red giants and tiny white dwarfs. Powerpoint
is on Angel. Here is an HR diagram simulator
you might enjoy playing around with. The HR diagram in one sentence:
hotter main sequence stars are bluer, much more luminous, somewhat larger and more massive, have
much shorter lifetimes, and are rarer than cooler main sequence stars.
Concepts:
- Hydrostatic equilibrium: Balance between pressure and gravity that keeps star from collapsing or blowing up
- Flux/luminosity: Flux is apparent brightness, proportional to luminosity divided by distance squared
- Main sequence: "Normal" stars, ranging from cool red K to yellow G (like sun) to hot blue-white O stars
- Red giants: Very large (as in, could extend past the Earth) red and cool stars.
- White dwarfs: Very small (as in, roughly size of Earth) hot stars. We'll learn more about these and red giants in a few days
Vocabulary:
- Apparent/absolute magnitude: Corresponds to flux/luminosity. Log scale, higher numbers are dimmer, absolute is defined as apparent at 10 pc
- Malmquist bias: Selection effect that biases flux-limited survey towards high luminosity objects. Volume-limited sample is preferable
- Spectroscopic parallax: Not really parallax; method of measuring distance assuming luminosity of star is known (e.g., because it is on main sequence)
Activity:
Reviewed midterm results. Here is the curve.
Random link:
Excerpt from Scientific American article titled "Meet Makemake, the fourth dwarf planet"
Astronomers have upgraded a distant rock discovered in 2005 to the category of dwarf planet, the controversial designation created two years ago by the International Astronomical Union (IAU) to deal with planetlike bodies far out in the solar system. The IAU decided at a meeting last week that the object formerly known as 2005 FY9 (or unofficially, "easterbunny") will henceforth be known as Makemake (pronounced MAH-kee MAH-kee) for the Polynesian god of fertility and creator of humanity. That makes it the fourth dwarf planet, joining Ceres, Eris and Pluto, and the third "plutoid," or dwarf planet beyond Neptune.
Updated July 22, 2008