Download Stellar Spectra - Montclair State University

A Spectrum: what it is and
what it can tell us
Mary Lou West
AAI, July 26, 2013
Our Theme
An alternation of experiment
and theory (new equipment and
new ideas) propels us to
understand the world better and
better.
My Goal
To show you some neat stuff,
and to have you begin to
understand it.
Are you ready?
Dispersion of white light by a
glass prism
Isaac Newton reversed the process in 1666.
Astronomy became
Astrophysics
• We learned about the stars’ make-up and
slow motions, opening up binary star
orbits, exoplanets, orbits in galaxies, and
cosmology.
• We knew about the types of visible light,
then we learned about other types of light.
Infrared Light
• William Herschel, February 1800
• Looking for good filters for the sun, to
observe sunspots
• Thermometer read hot
below “red”
Sunlight as white light,
thin dark lines found
In 1814 Joseph Fraunhofer invented
the spectroscope to characterize
types of glass more accurately.
In the 1820’s he saw the thin dark
lines in the solar spectrum.
Wilhelm Wien
• Explained how the color of a hot body
depends on its temperature in 1893
Colors of Stars
Stefan-Boltzmann Law
• 1879 Jozef Stefan and Ludwig Boltzmann
• total energy/surface area of light emitted
by a very hot solid object depends on the
temperature of the object to the 4th power
• Wow!
Spectrum of a hot gas
Hydrogen
Helium
Neon
Gas spectral lines
• In the 1850’s Gustav Kirchoff and
Robert Bunsen explained the dark
Fraunhofer lines in the sun’s
spectrum as absorption by the
chemical elements, each one with a
different “fingerprint”
Spectrum portions
Gamma Peg
The Sun
Spectra of Sun, Gam Peg
Gamma Peg
Gamma Peg Sivo 6
40 0
Gamma Peg Sivo 4
4000
Gamma Peg Sivo 8
5000
Sivo 2
4000
0
0
0
0
100
200
300
Pixel Number
400
500
600
0
100 200 300 400 500 600
Pixel Number
0
0
0 10 20 30 40 50 60
100
200
300
Pixel Number
400
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600
Calibration, hydrogen tube
Spectral Classification
• Annie Jump Cannon,
one of Harvard’s
“Computers”
• Classified thousands of
stars
• System started ABC..O
• But ended up as
OBAFGKM
Chemical Composition
• Cecelia Payne modeled the stars
• Found that they were mostly (70%)
hydrogen
• Very different from the Earth!
• They are also 25% helium
• There was only 5% for all the remaining
chemical elements
Emission Lines
• There are hot dense gas clouds (M42)
• There are dense winds around some stars
(Wolf-Rayet stars)
• There are planetary nebulae
• There are supernova
remnants
Doppler Shift
• Velocity:
• blue-shifted means approaching Earth
• Red-shifted means receding from Earth
• The amount of color shift indicated the
speed
• Some speeds are 20% the speed of light,
or more!
Hubble’s Law of Cosmological
Redshift
Types of spectroscopes
Sivo
•
Star Analyzer 100
Shelyak
Star Analyzer 100
• The star image is the zero-order, so
makes calibration easy
• Unfortunately, the resolution is poor
RSpec software
Projects to Try In the Solar
System
• Velocities of the rings of Saturn, calculate
the mass of Saturn itself
• Comets, as tails grow
• Asteroids, carbonaceous are farther out
Atmospheres of jovian planets,
especially ammonia at 643 nm in
Jupiter but not Saturn.
Projects with Stars
• Examples of spectral types of stars
• Wolf-Rayet stars, emission lines of dense
hot gas thrown out. Clumpy? Periodic?
• Colliding wind binaries, especially at
periastron
• Stars eclipsed by disks, clouds,…
• Young T Tauri stars, formation of planets
• Be stars with emission lines
More projects with stars
• Stars with variable lines, (Alioth)
• Modeling with synthetic spectra
• Stars with unusual elements, technicium,
europium
• Stars doing thermal pulses
• Planetary nebulae
• Novae
• Supernovae
Extragalactic Projects
• Different types of galaxies
• Velocity dispersion by line broadening
• Rotation curves of galaxies
• Quasars, red shift (3C 273, 16% c)
Inspiration at
the
Meadowlands,
yesterday
Inspiration from articles
• Field, Tom, Spectroscopy for Everyone,
Sky and Telescope, Aug 2011, p 68
• Hattenbach, Jan, Deciphering Starlight,
Sky and Telescope, Sep 2013, p 30
• Kannappan, Sheila, Fabricant, Daniel,
Getting the Most from a CCD
Spectrograph, Sky and Telescope, July
2000, p 125