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Variable Stars:
Stepping Stones To The
Universe
Albert Holm
Computer Sciences Corporation & Space Telescope
Science Institute,
Retired
STScI Public Lecture Series
April 4, 2011
Fireflies?
No, RR Lyrae-type variable stars
Copyright J. Hartmann, Harvard U., and K. Stanek, Ohio State U.
RR Lyrae-Type Variable Stars
Discovered by Williamina Fleming in
1893 in Omega Centauri
RR Lyrae-Type Variable Stars
Discovered by Williamina Fleming in
1893 in Omega Centauri
Change their brightness
by pulsing like the air in a
pipe organ
RR Lyrae-Type Variable Stars
Discovered by Williamina Fleming in
1893 in Omega Centauri
Change their brightness
by pulsing like the air in a
pipe organ
About 40 times brighter
than the sun
Pop Quiz
RR Lyrae stars are interesting because they…
1. Are fun to watch change from hour to
hour, even minute to minute
2. Provide clues about what happens in
the interior of stars
3. Provide clues about how stars age
4. Help determine the size and shape of
the Milky Way galaxy
5. All of the above
How can we use a candle?
To determine distances
The big sisters of RR-Lyrae stars are …
RR Lyrae
Our Sun
The big sisters of RR-Lyrae stars are Cepheid variables
RR Lyrae
Our Sun
Delta Cephei
Delta Cephei, the prototype Cepheid Variable
Delta Cephei, the prototype Cepheid Variable
John Goodricke
Cepheid Variables: Measuring the Universe
Henrietta Leavitt
Cepheid Variables: Measuring the Universe
Henrietta Leavitt
Cepheid Variables: Measuring the Universe
Henrietta Leavitt
Cepheids – Key
to Edwin
Hubble’s
Discoveries
Cepheid Variables: Measuring the Universe
The Expansion and Age of the Universe
We can identify variable stars
by how the light we see from
them changes with time
1. Stars that vary in brightness
2. Time scales of seconds, hours,
days, years or centuries
How to make a light curve
How to make a light curve
How to make a light curve
How to make a light curve
How to make a light curve
Light Curves … Fingerprints of
Variable Stars
Light Curves … Fingerprints of
Variable Stars
Light Curves … Fingerprints of
Variable Stars
Light Curves … Fingerprints of
Variable Stars
Light Curves … Fingerprints of
Variable Stars
Light Curves … Fingerprints of
Variable Stars
Light Curves … Fingerprints of
Variable Stars
Light Curves … Fingerprints of
Variable Stars
Astronomers don’t have time
to look at the sky!
The Solution:
People who love to look at the sky!
Why Are Amateur Astronomers’
Observations Crucial for HST Science?
• A scientist has requested observations of an
object that could become so bright that it could
damage the Instrument
Why Are Amateur Astronomers’
Observations Crucial for HST Science?
• A scientist has requested observations of an
object that could become so bright that it could
damage the Instrument
• Operations staff insert commands to cancel the
observation automatically unless overridden
Why Are Amateur Astronomers’
Observations Crucial for HST Science?
• A scientist has requested observations of an
object that could become so bright that it could
damage the Instrument
• Operations staff insert commands to cancel the
observation automatically unless overridden
• Amateur astronomers determine whether the
object is safe to observe
Why Are Amateur Astronomers’
Observations Crucial for HST Science?
• A scientist has requested observations of an
object that could become so bright that it could
damage the Instrument
• Operations staff insert commands to cancel the
observation automatically unless overridden
• Amateur astronomers determine whether the
object is safe to observe
• Operations staff bypass the fail safe commands
What was V455 Andromedae doing when
Dr. Szkody wanted to observe it?
What might V455 Andromedae have been
doing?
Another way that amateurs
enable scientists to get data
Provide alerts
when something
interesting occurs
Dwarf Nova Model
Another way that amateurs
enable scientists to get data
Dr. Peter Wheatley’s
observations of
SS Cygni
People who love to look at the sky! The American
Association of Variable Star Observers
www.aavso.org
People who love to look at the sky! The American
Association of Variable Star Observers
www.aavso.org
People who love to look at the sky! The American
Association of Variable Star Observers
www.aavso.org
American Association of
Variable Star Observers
AAVSO
100 years old this year!
1918 Photo of AAVSO
1918 Photo of AAVSO
Edward C. Pickering
1918 Photo of AAVSO
Anne S. Young
www.aavso.org
20,000,000 observations freely available!
www.aavso.org
And there are short essays telling about many
of these stars and why they are interesting
www.aavso.org
Eclipsing Variables
• Eclipsing variables
are not intrinsically
variable
• The change in
brightness is due
to a line of sight
effect
A mysterious eclipsing binary
What’s the answer?
Here’s one idea
Epsilon Aurigae
Stay tuned for the next
discoveries be announced
about Epsilon Aurigae
Moving on to Supernovae
The Ultimate Variable Stars
Is the
expansion of
our universe
speeding up?!!!
Contents of the Universe
- 72% dark energy
- 23% dark matter
- 5% ordinary matter
Our substance comes from Supernovae
Our substance comes from Supernovae
Our substance comes from Supernovae
Our substance comes from Supernovae
Our substance comes from Supernovae
Our substance comes from Supernovae
Iron
Calcium
Gold
Uranium
Thank you,
variable stars!