Transcript Linking Asteroids and Meteorites through Reflectance Spectroscopy

Survey of the Universe
Tom Burbine
[email protected]
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HW #6
Due this Wednesday
You will make a quiz covering material up to April 8th
You need to have answers for each question
70 points
– Use a similar style to my previous quizzes
• Cumulative
• You can’t use (or be too similar to) previous questions
on quizzes
• You can’t use questions used by other students (no
collaboration with other students in making your quiz)
• I will use the “best” quiz as your next quiz
• If you are unhappy with any of your grades:
• You can write a 10 page paper on an astronomical
subject to replace it
• 12 point font
• Times New Roman font
• Double space
• No figures or plots
• Due by May 1st
• Star expands quickly
• Becomes more luminous because the star
becomes bigger
• Because the star is expanding, the energy coming
from the interior becomes more spread out
• The surface becomes cooler
Helium Fusion
• Helium can fuse into Carbon at temperatures
above 100 million kelvin
Degenerate gas
• Core compresses
• But can only compress so far since electrons can
not occupy the same space if they have the same
energy
• This is called a degenerate gas
• Stars less than 0.5 solar mass can’t compress any
more
• Stars from 0.5-2 solar masses get so compressed
that gravitational contraction and radiation from
the fusion shell releases energy that is absorbed
by some of the electrons
• The core can then compress more
• Helium fusion can occur
Variable Star
• Star whose luminosity changes over time
Lightcurves
• Lightcurves plot brightness of a star versus time
• Period is the interval of time where a pattern of
brightness repeats
Different Types of Variable Stars
• RR Lyrae Variables – Mass comparable to Sun
but ~40 times more luminous
• Mira Variables – Red cool supergiants that have
periods of many months to years
• Cepheid Variables –Yellow supergiants that are
more massive than the Sun and ~10,000 times
more luminous
• T-Tauri Irregular Variables – Pre-main sequence
stars that appear to brighten as material falls
sporadically onto the forming star
• Giant stars pulsate because their atmospheres trap
their radiated energy
• Heats their outer layers that expand
• The expanded gas cools and pressure drops
• Gravity then recompresses the gas
Cepheid Variables
• Obey a period-luminosity relation
• The more luminous a Cepheid is, the slower it
pulsates
Why is there a relationship?
• Larger Cepheid Variables have weaker surface
gravities than the smaller Cepheid Variables
• Gravity pulls Larger Cepheid Variables inward
slower than smaller Cepheid Variables
• So Larger ones pulsate slower
Cepheids as Standard Candles
• Can be used as standard candle
• So luminous that you can determine distances to
galaxies that are millions of light years distant
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You determine the pulsation period
You can then determine its luminosity
You can measure its brightness
Then determine distance from inverse-square law
B = L/4d2
• http://www.youtube.com/watch?v=iyisAjHdhas
Any Questions?