Transcript Ha Line - azastro

Spectroscopy
for
Pre-Schoolers
2 October 2008
Jeff Hopkins
Hopkins Phoenix Observatory
(Counting Photons)
Member of SAC
What is Light?
In 1865
James Clerk Maxwell Said
Where:
The divergence of E (electric field) = 0
The divergence of B (magnetic field)= 0
The curl of E = -partial derivative of B with respect to time
The curl of B = m0 x e0 x partial derivative of E with respect to time
And There Was Light!
Maxwell’s Equations
These equations quite elegantly describe the
relationship between electric and magnetic fields and
thus electromagnetic radiation.
What these equations describe is the unit of
electromagnetic radiation called a photon.
Photons
Light consists of small packets of energy called
photons. Photons have no rest mass and always
travel at the speed of light, since they are light.
Depending on how a photon is measured it will
manifest itself as a particle or wave.
The frequency or wavelength of photon is a
function of it’s energy. The higher the energy,
the higher the frequency (shorter the
wavelength).
Wavelength (l
For Light
l= c / f
Where:
l is the wavelength in meters
c is the velocity of light, 299,792,458 meters/second
and
f is the frequency in Hertz (Hz)
For light frequencies, wavelengths are given in nanometers (nm) or
Angstroms (Å).
1 nm = 10 Å
Energy verse Intensity
To keep things straight, the intensity of light is
related to the number of photons and the energy
of light is related to the frequency or wavelength
of the photons.
The brighter a color, the more photons involved.
The higher the energy, the more toward the blue
end of the spectrum the photon is (higher
frequency, shorter wavelength).
Photon Energy
Where do photons come from?
Atoms consist of a nucleus surrounded by
electrons. The electrons are in specific energy
states or levels.
If an electron is raised to a higher energy state it
will soon fall back to its lower state and emit a
photon of energy equal to the difference in the
two energy states.
E=h*c/l
h = 6.62606896 x 10-34 J.s
Where:
E = Photon Energy
h = Planck’s Constant
C = Speed of Light
l = Wavelength
Absorbing Energy
A photon
interacts with
an orbital
electron and
raises it to a
higher energy
state. The
electron absorbs
the photon.
Emitting Energy
After a short time
the electron falls
back to its lower
energy state emitting
a photon with the
energy of the
difference between
the two energy
states
Electromagnetic Spectrum
The sensitivity of the human eye determines the
visible spectrum and is typically 380 nm to 750 nm
What is Color?
Newton’s Experiment (1670)
White light breaks
up into colors
Light colors combine
to white light
Single color does
not change
RGB Photons
Red, Green and Blue photons produce White for us to see.
There are no White Photons
Our Eye
Our eye has sets of light cones that are
sensitive to red, green and blue photons.
Color
Color is an illusion!
Different intensities of different energy
photons striking our eye produce all
the colors we see.
Sometimes our eyes fools us greatly.
Our Experiment
Each of you will have your own spectroscope so you can examine light.
This is yours to keep. It is a scientific instrument so treat it well!
Do Not
take it
apart!
Diffraction Grating
Slit
Your Spectroscope
Do Not
take it
apart!
What You See
Adjusting
If needed, hold the slit end with the slit vertical
and rotate the tube to see the above. The spectral
lines should be on the right and left.
White Light
White
You should see Red Green and Blue Lines
There are no White photons or lines.
Red Photons
Red Light
Red
You should see a Red Line
Green Photons
Green Light
Green
You should see a Green Line
Blue Photons
Blue Light
Blue Light
You should see a Blue Line
Yellow Light
Yellow
You should see Red and Green Lines
COLOR
IS
AN
ILLUSION
Red & Green Photons
Red and Green photons
produce Yellow for us to see.
Yellow Photons
There are also Yellow
photons as well as
photons of every color.
Demonstration
Pickle Light
A normal Pickle
A normal Pickle
with power
applied.
intense yellow
sodium D lines
light are
emitted
Incandescent Light
A continuous Spectrum
Fluorescent Light
A Emission Spectrum
Pickle Light Spectrum
You should see a Yellow Line
RGB
Three basic colors of visible light are RGB.
RGB stands for Red, Green and Blue
Combinations of these colors with different
intensities (number of photons) can produce
all the colors we can see. RGB is an emission
color set meaning color of the emitted light as
opposed to reflected light.
TV sets and computer monitors use emitted
RGB light at different intensities to produce
desired colors.
Why RGB
While photons of the desired color could be used it
would mean we would need to be able to generate
millions of different colored photons for all the
colors.
Because our eye responds to RGB photons with the
effect of letting us see any color by just varying the
RGB intensities, we can generate all the colors with
just the three RGB colored photons.
RGB
(Single Colors)
Red
Green
Blue
RGB
(Combinations)
100% Green + 100% Blue = Cyan
100% Red + 100% Blue = Magenta
100% Red + 100% Green = Yellow
RGB
(Extremes)
0% Red + 0% Green + 0% Blue = Black
100% Red + 100% Green + 100% Blue = White
Technicolor
Colors seen on a movie screen, TV screen or
computer monitor are the results of a
combination of three basic colors, red, green
and blue.
Color film is a combination of three layers
(RGB) combined to produce a full color image.
We can produce a full color image by take
monochrome pictures through a red, green
and blue filter and then shinning white light
through each and overlapping them.
Taking Monochrome Images
Three Monochrome Images
Scene through Red Filter
Scene through Green Filter
Scene through Blue Filter
Red Filter Image
Green Filter Image
Blue Filter Image
Composite
CYMK
When an object is illuminated with white light, it
will reflect colors. The basic colors of reflection are
CYMK. CYMK stands for Cyan, Yellow, Magenta and
Black. The characteristic of the material determines
what colors are reflected.
CYMK is used to create color with ink and paints. It
is a reflective color creating set of basic colors.
Color pictures in magazines, and books use this. It
is known as a four-color process.
White light reflected from the paint or ink produces
the colors we see.
CYMK Reflection
White light reflected from the paint or ink produces
the colors we see.
CYMK Colors
Cyan
Magenta
Yellow
100% Cyan + 100% Magenta + 100% Yellow = Black
CYMK (Combinations)
100% Cyan + 100% Yellow =Green
100% Magenta + 100% Yellow =Red
100% Cyan + 100% Magenta =Blue
0%Cyan+0%Magenta+0%Yellow+0%Black=White
Types of Spectra
Continuous Spectra
Emission Spectra
Absorption Spectra
Continuous Spectrum
Continuous spectra are produced from a
high temperature source such as inside the
Sun or an incandescent light bulb
Emission Spectrum
Emission spectra are produced from a source with
excited atoms of an element, e.g., an LED, or
fluorescent light bulb or the Pickle Light
Absorption Spectrum
Absorption spectra are produced from a source
with a continuous spectrum and a gas between
the source and observer that absorbs photons with
the energy of the spectrum of the gas.The Sun’s
atmosphere absorbs lines for the elements in it.
Solar Spectrum
Solar Spectrum (detail)
Sun Spectrum
Fluorescent Tube Spectrum
LED Spectrum
Hydrogen Spectrum
Ha line 656.28 nm
Sodium D Lines
Absorption Lines
Emission Lines
The sodium D lines are at 588.9950 and 589.5924 nm
Galaxy 1 Spectrum
Ha Line 670 nm
At rest Ha line 656.28 nm
Galaxy 2 Spectrum
Ha Line 675 nm
At rest Ha line 656.28 nm
Galaxy 3 Spectrum
Ha Line 690 nm
At rest Ha line 656.28 nm
Galaxy Spectrums
Galaxy 1 Ha Line 670 nm
Galaxy 2 Ha Line 675 nm
Galaxy 3 Ha Line 690 nm
Doppler Shift
v = Dl x c / l
Dl is the change in wavelength due to motion
l is the stationary wavelength
v is the relative velocity
c is the velocity in the medium
(speed of light in a vacuum is 3 X 108 m/s)
To get just a 1% change in the frequency of light, a star has to be
moving 1,864 miles per second. For a blue light bulb to look red, it
would have to be flying away from you at 3/4 of the speed of light.
Galaxy Doppler Shift
v = Dl x c / l
Thus for the galaxies
Galaxy 1:
Galaxy 2:
Galaxy 3:
Dl = 670 nm - 656 nm = 14 nm
Dl = 675 nm - 656 nm = 19 nm
Dl = 690 nm - 656 nm = 34 nm
Galaxy 1: v = 6.4 x 106 meter/sec
or 3,974 miles per second
Galaxy 2: v = 8.7 x 106 meter/sec
or 5,403 miles per second
Galaxy 3: v = 15.5 x 106 meter/sec
or 9,656 miles per second
Spectroscopy
Spectroscopy is the detailed measure of an
electromagnetic spectrum.
A device used to display and measure an
astronomical optical spectrum is known as a
spectrograph.
This device may also go by the name of
spectrometer, spectroscope and spectrum analyzer.
These terms are sometimes interchanged.
Spectroscope
A spectroscope may use either a prism or grating,
but is used visually.
Spectrometer
A spectrometer usually uses a prism or diffraction
grating with an electronic or photographic detector.
Spectrograph
A spectrograph uses a diffraction grating with an
electronic or photographic detector.
Lhires III Spectrograph
Lhires Diagram
HPO Spectroscopy
Raw Spectrum
No pretty rainbow because a monochrome
camera was used. If the spectrum was in color
it would be all red. The dark line near the middle
is a hydrogen alpha absorption line.
Spectrum Profile
By summing the ADU values of pixel columns a
spectrum profile can be generated.
Ha Line
Why the interest in the Ha Line?
When a gas discharge tube containing hydrogen
gas is excited by passing a current through it, the
gas glows red. There are several spectral lines
produced, but the most prominent is the hydrogen
alpha (Ha) line at 6,562.8 Å.
Most stars are made of mainly hydrogen so the Ha
line provides an excellent reference line with
which to explore details about a star’s spectrum.
Star Ha Lines
Stars burn hydrogen and produce a continuous
spectrum.
Some stars produce a large Ha emission line
superimposed on the continuum. This is seen as a
bright line in the continuum.
Some stars have an atmosphere of hydrogen gas
that absorbs the Ha radiation and thus produces a
hole or dark line in the continuum.
Ha Line Detail
Shifted toward the blue
Shifted toward the red
Be Stars
Be stars are nonsupergiant B-type stars
whose spectra have, or
had at some time, one
or more Balmer lines in
emission. The mystery
of the "Be phenomenon"
is that the emission,
which is well understood
to originate from a
flattened circumstellar
envelope or disk, can
come and go
episodically on time
scales of days to
decades.
Be Stars (continued)
This has yet to be explained as a predictable consequence of stellar
evolution theory, although many contributing factors have been
discussed, including:
*
*
*
*
*
rapid rotation
radiation-driven winds
nonradial pulsation
flarelike magnetic activity
binary interaction
Observations indicate that all Be stars are rotating rapidly, at up to
90% of the velocity at which gravitational force is balanced by
centrifugal force at the star's equator (~400 km/s). In effect, material
at the surface of the star is almost in orbit, so that only a slight
additional force is necessary to move it into the circumstellar disk.
Be Stars Ha Line
Near 100% Ha
Ring Emission
Some Absorption of
Star Ha Emission
Lower Ha Emission
Greater Ha Absorption
A
Mysterious
Star System
Auriga
N
Epsilon Aurigae
While Epsilon Aurigae is not a Be star it is a most interesting
star system.
It is an eclipsing binary system and has the longest
known period of 27.1 years.
It also has the longest known eclipse of nearly 2 years.
The main star is an F supergiant with a diameter of 200 times
that of the Sun, one of the largest stars known.
The unknown companion has a diameter of 2,000 times
that of the Sun. The companion has been likened to a
round paving brick with a hole in it.
The next eclipse starts next summer.
Epsilon Aurigae System
Epsilon Aurigae Timing
Epsilon Aurigae Ha
Out-of eclipse Ha is most interesting
Things To Do
Use your spectroscope to look at:
Stars at night
Street lights
Different kinds of light in your home
Fires
Anything that glows
Have Fun and Learn!
Advertisement
New Book
Epsilon Aurigae
A Mysterious Star System
Special!
Normally $29.95 + S&H
Tonight
$25.00
The End