1. Spiral arms in the milky way galaxy and cosmic rays
Smadar Levi
The Hebrew University of Jerusalem
International School of Cosmic
Ray Astrophysics
July 2004
Work in progress in collaboration with Nir Shaviv

2. A typical galaxy ~15Kpc ~0.5Kpc The disk The Central Bulge
The disk is characterized with stars that move in nearly circular orbits around the galactic center.
The Central Bulge is characterized with stars with large random motions. Therefore its distribution is ellipsoidal.
The star in the disk has a differential velocity, meaning the star nearer to the center has a shorter period of motion.

3. Density Waves The Lin Shu Hypothesis
Spiral structure is: Quasi – steady density wave.
The arms are a region where the star density is the highest.
The Star velocity is different than the arms velocity.
The spiral arms represent the places where the stars spend more time than in an equivalent area of space elsewhere in the galaxy.

4. Spiral wave – the moving traffic jam
Stars=cars spiral arm=jam t1 t2 t3
Direction of movement

5. Finding the arms velocity
We wish to work in a frame of reference which rotates with the arms.
We denote as the circular velocity of the stars.
And is the circular velocity of the arms, which we call: pattern speed .
is the measured angle
At first we simplify the analysis by assuming that the orbits
are circular. Hence:

6. Analysis Open clusters. From Loktin & Dias catalogs.
Fitting the data to a logarithmic arm with 500pc thickness.
3 parameters to find.
a – the slope.
b – the interjection point with the r axis.
- the pattern speed

7. Analysis

10. Analysis
Fitting 500pc logarithmic arm to the data points: Finding a minimum to a weight function.
Bootstrap: Replacing ~37% random data points by ~37% different random points.
Extracting the
significant minima's
and finding the errors.
Bootstrap:
The term derives from the phrase to pull oneself up by one's bootstraps (Adventures of Baron Munchausen, by Rudolph Erich Raspe).

11. Looking for minimum
Two sets of arms!!

12. In The Milky Way .... Two sets of arms!! ? ice age Every ~125
million years
higher CR flux
Nir Shaviv [2003]
ice age
Improving the position limits ?
future work:
Density profile