Transcript Visual binaries

Journal 1/30/17
What do you think
life would be like if
we had more than
one sun?
Objective
Tonight’s Homework
To learn about star systems
with more than 1 star
Read “Binary Stars” on page
436 and 437. Do review 4, 7,
20 on page 442.
Binary Star Systems
There are 4 kinds of binary stars, and we classify
them by how we observe them.
Visual binaries are when we can see both
stars in the binary system visually with a
telescope. These are the hardest to see.
The brighter star is
called the primary.
Example:
Sirius A
Sirius B
Binary Star Systems
Visual binaries are rare. We can’t often
distinguish between multiple stars in single
images. There are a few examples, though.
Binary Star Systems
We see spectroscopic binaries by looking at
emission spectra lines. We look for small red and
blue shifts that tell us stars are moving around each
other.
Binary Star Systems
These are also fairly hard to observe. We have to
take very detailed spectra to see the shift.
Binary Star Systems
We see eclipsing binaries by looking at stars
in the sky and seeing if they change brightness.
This would mean the stars are going in front
and behind each other, blocking out some of the
light. We call what we see a “light curve”.
What it would
look like
What
astronomers
observe
Binary Star Systems
We see astrometric binaries when we look at
a star and can see it wobbling, but can’t see
any other stars near it.
Maybe the other star is too dim, but we can’t
see it. We can only see it’s effect from gravity
making the star we can see wobble.
Binary Star Systems
Some stars are in groups of 3, 4, or more, even
up to thousands of stars. These stars all have
complex orbits and can be very hard to predict
orbits.
The large groups of thousands have special
names: open clusters and globular clusters.
Binary Star Systems
Open clusters are one of the most common
types of multiple star systems. Open clusters
usually contain thousands of stars that all
formed at about the same time and are all orbit
around each other.
The average density in an open cluster is 500
times greater than the density of where we are.
Imagine 500 more times stars in the sky!
Binary Star Systems
Globular clusters are extremely tight clusters
with tens or hundreds of thousands of stars all
orbiting each other. They’re believed to be some
of the oldest things in the universe.
Globular clusters have very high densities.
Stars are packed in at least
twice as dense as in an
open cluster (1,000 times
denser than where we are!)
Exit Question
Which kind of binary star system is the hardest to detect?
a) Visual binaries
b) Spectroscopic binary
c) Eclipsing binary
d) Astrometric binary