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 Change their brightness by pulsing like the air in a pipe organ Discovered by Williamina Fleming in 1893 in Omega Centauri

RR Lyrae-Type Variable Stars Change their brightness by pulsing like the air in a pipe organ About 40 times brighter than the sun Discovered by Williamina Fleming in 1893 in Omega Centauri

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

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

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

People who love to look at the sky! The American Association of Variable Star Observers

People who love to look at the sky! The American Association of Variable Star Observers

American Association of Variable Star Observers AAVSO 100 years old this year!

1918 Photo of AAVSO

Edward C. Pickering

1918 Photo of AAVSO Anne S. Young

20,000,000 observations freely available!

And there are short essays telling about many of these stars and why they are interesting

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

Iron Calcium Gold Uranium

Thank you, variable stars!