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Observing Campaign Details
Note: This Campaign is now Over.
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Amateurs Help Astronomers Unravel A Propeller Star - AAVSO Press Release (Spanish version)
- AAVSO Alert Notice 326 - Observing Campaign Announcement and Observing Instructions
- WHEN? - August 28/29 through September 1/2, with most of the observations occurring August 30/31, 2005
- WHY? - On August 30-August 31, 2005 two space-based and four professional ground-based observatories are scheduled to observe the cataclysmic variable star AE Aqr. Each of the observatories covers a different wavelength of light and amateur astronomers have been asked to help cover the visible-light portion.
- HOW? - Nightly observations should be made (see the Alert Notice for details) and then submitted to the AAVSO for processing. For more help on making observations, please see our Visual Observing Manual or CCD Observing Manual for help.
Background
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| Tri-color image of the novalike intermediate polar propeller system, AE Aqr. Image courtesy SDSS. | |
The variable star AE Aquarii is a unique object in the variable star
menagerie. It is a member of the class of binary stars known as
cataclysmic variables -- binary star systems composed of a normal star
and a white dwarf, where the white dwarf's gravitational field pulls matter
from its companion. Such stars can be spectacularly variable, and the
CVs have long been favorite targets for amateur observers and professional
researchers alike. However, the behavior of AE Aquarii has challenged our
understanding of cataclysmic variables for decades. While most CVs derive
their energy from matter being accreted onto the white dwarf itself,
the white dwarf in AE Aquarii actually throws matter away from itself,
often with incredible force. This strange behavior, described as a
"propeller", is caused by the rotation of the white dwarf and it's strong
magnetic field sweeping matter out of the system. The spectacular result is
variability at nearly every wavelength from radio waves to high-energy gamma
rays.
White dwarf stars are the leftover ashes of a sun-like star once it has used
up its entire store of nuclear fuel. These white dwarfs can sometimes have
incredibly strong magnetic fields, hundreds of millions of times stronger
than that of our Earth. Although white dwarfs themselves are only a few
thousand kilometers across, their magnetic fields can extend to hundreds of
thousands of kilometers into space. If the white dwarf rotates, the magnetic
field rotates along with it, sweeping around the star like a light house.
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| Artistic impression of an intermediate polar. AE Aqr is a type of intermediate polar called a propeller system. Unlike what is pictured here, the magnetic fields in a propeller system act like the blades of a fan and throw mass away from the white dwarf with great force!! Image by Mark A. Garlick | |
In ordinary, non-magnetic CVs, matter literally falls from the donor star
(known as the secondary) and spirals in toward the white dwarf through
an accretion disk, releasing lots of heat energy in the process. In
magnetic CVs, like the polars and intermediate polars, any matter
that gets pulled from the donor star by the white dwarf gets sucked in by the
strong magnetic field and funneled directly down to the white dwarf's surface,
unleashing huge amounts of energy as they do. But in AE Aquarii, the magnetic
fields act like the blades of a fan, and throw matter out of the system
entirely! The rotating magnetic field catches small blobs of matter falling
off of the donor star, and accelerates them to speeds exceeding the escape
velocity of the system. They're flung away from the white dwarf, escaping
its gravitational pull entirely. This is why AE Aquarii is called a
propeller system -- if we could see this star close up, it would look
like matter from the secondary was being blown off into space by the blades of
an invisible propeller. AE Aquarii does an incredibly efficient job of
dispersing matter this way; nearly 99% of the matter that gets pulled
off of the secondary gets flung out into space, rather than pulled onto the
white dwarf! In the process, these blobs of matter emit a broad spectrum of
radiation from a variety of physical processes.
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| AAVSO Observers have been contributing observations of AE Aqr since its discovery in 1944. This is a graph of 10-day means of the nearly 30,000 visual observations for AE Aqr found in the AAVSO International Database. |
Astronomers here on Earth have
used a variety of telescopes and astronomical satellites to better understand
this system. But despite nearly half a century of observations, there's still
more to learn about why the system behaves the way it does. Observations
with radio, infrared, optical, X-ray, and even gamma ray telescopes all
provide important clues about this enigmatic system. The amateur astronomers
of the AAVSO have been making observations of AE Aquarii since its discovery.
The AAVSO and its community of observers is pleased to contribute to this
exciting new campaign of discovery.
Other Magnetic Cataclysmic Variables of Interest
AM Herculis - Variable Star of the Month, June 2001
GK Persei - Variable Star of the Month, November 2000
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