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Transcript
Part 2
2015
WIRO and Spectral Analysis
RESEARCH ON STARS, GALAXIES & QUASARS
Emission &
Absorption Lines
WIRO Telescope
When heated every element gives off light.
When this light is decomposed using a prism it is
found to be made up of a series of ``lines'', that
is, the output from the prism is not a smooth
spectrum of colors, but only a few of them
show up. This set of colors is unique to each
element and provides a unique fingerprint: if you
know the color lines which make up a beam of
light (and you find this out using a prism), you
can determine which elements were heated up in
order to produce this light.
Similarly, when you shine white light through a
cold gas of a given element, the gas blocks some
colors; when the ``filtered'' light is decomposed
using a prism the spectrum is not full but shows
a series of black lines (corresponding to the
colors blocked by the gas); see Fig. 8.3. For a
given element the colors blocked when cold are
exactly the same as the ones emitted when hot.
The University of Wyoming's 2.3-meter telescope is located at the Wyoming Infrared
Observatory (WIRO) about 25 miles southwest of Laramie, WY on the summit of Jelm Mt.
and at an altitude of 9656 ft. (Elev.: 2943 m; Long: 105d 58m 35s.5 west; Lat: 41d 05m 49.4s).
This site (469 Jelm Mtn. Road) was chosen because: (1) the dryness of the air, an important
consideration for infrared astronomy since moisture strongly absorbs infrared radiation, (2)
comparatively low turbulence in the air above the mountain, (3) a dark night sky, (4) close
proximity to the University of Wyoming, and (5) pre-existing road, electricity and phone lines
since Jelm was formerly used by the US Forest Service and BLM as a fire lookout station.
The wavelength of the emission or absorption lines
depends on what atoms are molecules are found in
the object under study.
What atoms or molecules exist depend on:
temperature
chemical composition.
Kirchhoff's Laws
The spectrum of an object is the variation in the intensity
of its radiation at different wavelengths.
Objects with different temperatures and compositions emit
different types of spectra. By observing an object's
spectrum, then, astronomers can deduce its temperature,
composition and physical conditions, among other things.
Kirchhoff's Laws are:
A hot solid, liquid or gas, under high pressure, gives off a
continuous spectrum.
A hot gas under low pressure produces a bright-line or
emission line spectrum.
A dark line or absorption line spectrum is seen when a
source of a continuous spectrum is viewed behind a cool
gas under pressure.
Harvard ComputersWomen Astronomers
American astronomer whose painstaking
classifications included an important early
catalog of stellar spectra, and whose work
assisted Ejnar Hertzsprung in his verification
of a distinction between dwarf stars and giant stars..
How far to that galaxy?
Galaxy Spectra
The overall spectrum of a galaxy is simply the combined spectrum of all the stars and other
radiating matter in the galaxy. As galaxies vary in structure and relative composition of star
type and gas their spectra will vary. The classification scheme for galaxies developed by Edwin
Hubble and based on photographic images of the shape of galaxies is now supplemented by
comparison of their spectra.
Stellar Spectra
There are many key aspects of stellar
Researchers
spectral graphs that indicate whether the
N
ICHOLE BUCZYNSKI-- CHEYENNE WY
object is a single star, a galaxy, or a quasar
CAROL FOLEY – UNITY NH
(or something else, like a binary star
JOE MEYER– LANDER WY
system, etc.) Below this is explained and
illustrated.
FINDINGS
Antonia Maury 1866 - 1952)
Types of
Astronomical
Spectra
OVERVIEW
L.A.S.S.I.
Thicker “black body” look (data distribution looks
thicker) indicates the object is a star. The spectrum of
a star (one shown a the right from our data collection
at WIRO) without an atmosphere would be a smooth
curve. Photons from star core heat up gas in star’s
atmosphere. Electrons in the gas increase energy
levels, but eventually decrease energy levels, which in
essence changes the direction of the photons from
the core. So what we are able to “view” is absorption
of photon energy, whereas in reality the energy was
simply redirected. A lot of drops in a spectral graph
means a lot of absorptions, and indicates the presence
of a star versus a galaxy or quasar.. Absorption
wavelength locations indicate elements in star,
according to what cooler stuff in atmosphere of star
is made of. In summary, a star’s hot core causes
absorption in the cooler stellar atmosphere.
LASSI: Launching Astronomy:
Standards & STEM Integration
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Flux/brightness (ergs/sec/cm^2) vs. wavelength
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The overall spectrum of a galaxy is simply the
combined spectrum of all the stars and other
radiating matter in the galaxy.
Emission spike means gas in galaxy has been
heated up by many stars, indicating galaxy.
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To measure the distance to a galaxy, we try to find stars in that
galaxy whose absolute light output we can measure. We can then
determine how far away the galaxy is by observing the brightness of
the stars. Such stars can help us measure the distance to galaxies 300
million light years away.
If a galaxy is too far away for us to distinguish individual stars,
astronomers can use supernovae in the same manner, because the
light output of supernovae at their peak brightness is a known fact.
Supernovae can be used to measure the distance to galaxies as far as
10 billion light years away.
When light passes through a prism, it separates into the colors that make it up. White light
changes to a swath of colors. This rainbow is called a spectrum. You can make spectra (the plural
of spectrum) in many ways: with a prism, with drops of water (as in a real rainbow), or with
gratings (like in the glasses you can get). Scientists build special instruments to separate light,
usually with gratings. These instruments are called spectrographs.
When astronomers pass the light of a star through a spectrograph, they get a spectrum of the
star. The spectrum looks like a regular rainbow of colors—except that there are dark lines in it.
Flux/brightness (ergs/sec/cm^2) vs. wavelength
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Flux/brightness (ergs/sec/cm^2) vs. wavelength
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Emission lines/spikes indicate super heated gases,
and many different emission spikes mean multiple
elements present, indicating quasar. Quasars consist
of a galaxy with a black hole in middle of it, causing
GPE to turn into KE, and the KE coming out as
pure light. Spectral emission lines are WIDER
because energies emitted move toward and away
from us as a quasar’s stellar objects revolve about the
center of the black hole, causing blue and red
shifting, creating wider/thicker emission lines.
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