This preview shows page 1. Sign up to view the full content.
Unformatted text preview: Some Uses of the H-R Diagram
• Cluster Fitting (more on this later)
– All stars at about the same distance, so
uncertainty in distance vanishes. Plot apparent
brightness as if it were absolute, then slide
diagram until it fits => distance determination
very accurate for a whole cluster, especially if
there are many stars. • Do the same thing with individual objects
=> “spectroscopic parallax,” but it isn’t
very accurate since it is based on one object. Star Formation Star Formation Facts
•Stars are constantly forming.
•Hot, blue stars are relatively young.
•Cool, red stars are relatively old.
•Stars form from otherwise stable gas clouds.
•Stars form in groups. Star Birth Where do stars form? Interstellar Dust
• Tiny solid particles
of interstellar dust
block our view of
stars on the other
side of a cloud
• Particles are < 1
micrometer in size
and made of
elements like C, O,
Si, and Fe Theory of Shock-wave
Triggered Star Formation
Since a gas cloud is stable, something
happens to it to cause stars to form.
A shockwave compresses the cloud.
As it compresses it, it fragments.
Within these fragments, stars are formed.
Within Contracting Protostar A protostar emerges from a fragment.
As gravity continues the contraction, its temperature increases.
The fragment is like a cocoon, in that the newly forming star is
protected from external effects. Protostar growth
Since gas clouds are usually
slowly rotating, a protostar forms
from a rotating disk.
The protostar emerges from the
center of the disk.
Planets may well form from the
View Full Document
This note was uploaded on 11/27/2011 for the course AST 301 taught by Professor Harvey during the Spring '07 term at University of Texas at Austin.
- Spring '07