30 Second People Study

• Imagine you are from an alien race who
live out their lives at an accelerated rate.
• Imagine you have discovered the planet
Earth with your advanced telescopes
which allow you to make observations of
Earth’s human population.
• After collecting data for about 30
seconds, what would you be able to say
about human physiology?


The Solar Spectrum

http://ess.geology.uﬂ.edu/ess/Notes/040-Sun/spectrum.GIF

Stellar Spectra

http://homepages.wmich.edu/~korista/phys325.html


Stellar Spectra

[Our Sun is type G2]

http://www.maryspectra.org/classical/
classical.htm


Stellar Spectra --
Composition

http://faculty.fortlewis.edu/tyler_c/classes/206/notes4.htm


Stellar Spectra--
Color and Brightness
Wien’s Law Stefan-Bolzmann Law

http://www.oswego.edu/~kanbur/a100/images/planck.jpg


HR Diagram:
Luminosity vs Temperature

http://outreach.atnf.csiro.au/education/senior/astrophysics/stellarevolution_hrintro.html

HR Diagram and Mass
Highest Mass:
about 150 Msun

Lowest Mass:
about 0.072 Msun
http://physics.uoregon.edu/~jimbrau/astr122/Notes/Chapter17.html

Low mass more common
than High mass

http://zebu.uoregon.edu/textbook/imf1.gif


The stars we see -- m vs M

Why
aren’t
they
mostly
M and K
type
stars?

http://www.astro.wisc.edu/~dolan/constellations/extra/brightest.html


Star Sizes

http://commons.wikimedia.org/wiki/Category:Star_size_comparisons

HR Diagram and Radius

http://abyss.uoregon.edu/~js/ast122/lectures/lec11.html

Stellar Mass and Lifetimes
0.07 Msun NOTE: This in not
last about an HR Diagram.
10,000,000,000,000 On an HR Diagram,
massive stars would be on
years the top left, not the
bottom right

150 Msun
last about
1,000
years

http://www.frostydrew.org/observatory/courses/astro/mass_life.gif

Main Sequence Turn-Off Point

H-R diagrams of two clusters, the open cluster M67 (a young cluster), and the globular
cluster M4 (an old cluster). The main sequence is signiﬁcantly shorter for the older
cluster; the luminosity and temperature of stars at the 'turnoff point' can be used to
date these clusters.

http://astro.berkeley.edu/~dperley/univage/univage.html

Hertzsprung–Russell diagram
LACC §16.2 16.3, 17.4
• Spectral Classes: O B A F G K M; blue (hot) --> red
(cool); Wien’s Law (λ ∝ 1/T); absorption features

• Luminosity Classes: I II III IV V; supergiant (I) -->
dwarf (V); Stefan-Bolzmann Law (Flux ∝ T4); size
(increases as you move up and right)
• distribution: (main sequence (90%), white dwarfs
(10%), blue giants (rare), red dwarfs (common), red
giants (dying), white dwarfs (dead)); masses &
lifetimes: blue m.s. (high mass, short life) --> red m.s.
(low mass, long life)
What is out there?

LACC HW: Franknoi, Morrison, and
Wolff, Voyages Through the Universe,
3rd ed.

• Ch 17, p. 392-393: 13 (expect test question(s) like this)

• Ch 18: Image Analysis Quizzes accessible
from: http://www.brookscole.com/cgi-brookscole/
course_products_bc.pl?
ﬁd=M20b&product_isbn_issn=9780495017899&discipline_number=19

Due beginning of next class period.


Stars
LACC §16.2 16.3, 17.4

• Spectroscopy
• Imaging
• Photometry

out there? How big is the universe?


Proper Motion (Imaging)

http://csep10.phys.utk.edu/astr162/lect/motion/proper.html

Radial Velocity using Doppler
Shift (Spectroscopy)

http://spiff.rit.edu/classes/phys301/lectures/doppler/doppler.html

Spectroscopic Binaries
(Spectroscopy)

http://csep10.phys.utk.edu/astr162/lect/binaries/spectroscopic.html

Eclipsing Binaries
(Photometry)

http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap17/FG17_21.jpg


Light curve of 2MASS
J05352184–0546085 at 0.8 m

http://www.nature.com/nature/journal/v440/n7082/ﬁg_tab/
nature04570_F1.html

Stellar Because of the size and proximity of this star
it has the third largest angular diameter as
Diameters: viewed from Earth, smaller only than the Sun
and R Doradus.
Betelgeuse [Betelgeuse] is one of only a dozen

(Imaging) or so stars telescopes have imaged
as a visible disk....The distance to
Betelgeuse is not known with precision but if
this is assumed to be 640 light years, the
star's diameter would be about 950 to 1000
times that of the Sun. Betelgeuse ... is
thought to have a mass of about 20 solar
masses.

Though only 20 times more massive than the
Sun, this star could be hundreds of millions
times greater in volume (as with a beach
ball compared to a large stadium). Betelgeuse
http://www.lesia.obspm.fr/ was the ﬁrst star on which starspots were
~titania/results.html resolved in optical images by a telescope,


Stellar Diameters
(Photometry)
The occulted star, a K0
giant, has an angular
diameter of 0.55
mas (not 1.11 mas, as
indicated erroneously on
the ﬁgure, to be
corrected), corresponding
to 7.5 km projected at
Titania.

The star being at 170 parsecs from the Earth, this yields a stellar
radius of 10 solar radii, a reasonable value for this kind of stars.
http://www.lesia.obspm.fr/~titania/results.html


Brown Dwarfs
Astronomers have found many
types of objects in orbit around
stars. These range from other full-
sized stars like our sun (binary star
systems) to Jupiter sized planets
(never directly imaged but inferred
from radial-velocity
spectroscopy). The relative sizes
of these various types of bodies
are shown above for comparison.
Even though a brown dwarf
can be similar in diameter
to a Jupiter sized planet,
brown dwarfs are 13-75
times more massive and they
can appear on the order of
100-1,000,000 times brighter than
a Jupiter sized planet at infrared
wavelengths when they are studied
with telescopes. Credit: Gemini
Observatory/Artwork by Jon
Lomberg

http://www.spaceﬂightnow.com/news/n0205/22closest/

Radius-Mass Ratios

http://www.astrophysicsspectator.com/topics/overview/SizeStarsPlanets.html


Radius-Mass Ratios
The material inside a degenerate object like Saturn is softer than in
the smaller planets; unlike the solid rock of Earth, the material at the
center of Saturn gives when it is squeezed. This means that as
the mass of a degenerate object increases, which increases the
pressure required to counter the object's self-gravity, the density
also increases. The consequence is that the radius can decrease
as the mass increases. For cold bodies of the same composition,
the radius goes as the inverse of the cube root of the mass. For bodies
with some internal heat—and generally there is some internal heat left
over from the creation of the body—the radius decreases more slowly
than for the cold bodies as the mass rises. This residual heat causes
Jupiter to be slightly larger than Saturn, and it causes most of the known
brown dwarfs to be about the size of, rather than much smaller than,
Jupiter.

http://www.astrophysicsspectator.com/topics/overview/SizeStarsPlanets.html


Brown Dwarfs: Sizes

http://homepages.wmich.edu/%7Ekorista/stargal-images/sunMLTJ_visseq.jpg


Stars
LACC §16.2 16.3, 17.4
• Spectroscopy: Temperature, Composition,
Radial Velocity, Age of a Cluster, Binary
Systems (Spectroscopic Binaries)
• Imaging: Diameters, Proper Motion, Binary
Systems (Visual Binaries) Clusters (Open vs
Globular)
• Photometry: Variable Stars, Diameters, Binary
Systems (Eclipsing Binaries); light curves
out there? How big is the universe?


LACC HW: Franknoi, Morrison, and
Wolff, Voyages Through the Universe,
3rd ed.

• Ch 16, pp. 371-372: 6.

• Ch 19: Image Analysis Quizzes accessible
from: http://www.brookscole.com/cgi-brookscole/
course_products_bc.pl?
ﬁd=M20b&product_isbn_issn=9780495017899&discipline_number=19

Due beginning of next class period.


A1 16 Stars

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