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A&A press release Released on September 14th, 2007
Based on the article “Paloma (RXJ0524+42): the missing link in magnetic CV evolution?”, by Schwarz et al. (Published in Astronomy & Astrophysics, volume 473-2, p. 511)
An international team of astronomers might have
discovered the
missing link in the evolution of the so-called magnetic cataclysmic
variable stars. They determined the spin and orbital periods of the
binary star Paloma. They found that the Paloma system has a weird way
of rotating that fills the gap between two classes of magnetic
cataclysmic stars. Their results will soon be published in Astronomy & Astrophysics.
Cataclysmic variables (CVs) are a class of binary stars made up of a
white dwarf [1] and a normal star much like our Sun. Both stars orbit
so close to each other that the white dwarf accretes matter from the
companion star. In most of the several hundred CVs known, the matter
spirals around the white dwarf, forming a disk, before being accreted
and incorporated into the star. About 20% of the known CVs include a
white dwarf with a strong magnetic field of several million Gauss [2].
They are known as
“magnetic CVs”. The magnetic field of the white
dwarf can
be strong enough to disrupt the accretion disk or even to prevent the
disc from forming.
Astronomers currently know two classes of magnetic CVs:
• Polars (also known as
the prototype star AM
Herculis) have a strong enough magnetic field to synchronize the spin
period of the stars and the orbital period of the system [3]. A
departure from synchronization is observed for four AM Herculis stars,
which are thought to be normal AM Herculis systems currently
desynchronized by a recent nova explosion. The difference between the
spin period and the orbital period, that is, the degree of
asynchronism, is less than 2% for these near-synchronous polars.
In a cataclysmic variable system, both stars are so close to each other
(the whole system would match the size of our Sun) that astronomers
cannot distinguish one star from the other. For studying CVs, they rely
on indirect observations: measuring the variation in the brightness of
the system, thereby estimating its characteristics (orbit size,
period).
[1] A white dwarf is a dying star that has exhausted most of its
nuclear fuel. It is extremely dense (1 ton per cm3),
with about the
mass of the Sun and the size of the Earth. Our Sun will become a white
dwarf in about 4.5 billion years.
[2] For comparison, the Sun's magnetic field is about 50 Gauss and the magnetic field inside a nuclear medical imaging device is about 10000 Gauss. [3] The Earth-Moon system illustrates the case for synchronization in astronomy: from the Earth, we always see the same side of the Moon because the spin period of the Moon is the same as its orbital period around the Earth. [4] The team includes R. Schwarz, A.D. Schwope, A. Staude (Astrophysikalisches Institut Potsdam, Germany), A. Rau (CalTech, USA), G. Hasinger (MPI, Garching, Germany), T. Urrutia (UC Davis, USA), and C. Motch (Observatoire Astronomique, Strasbourg, France).
Paloma (RXJ0524+42): The missing link in magnetic CV evolution?
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Home  Press releases A&A Press Release: The missing link in the evolution of magnetic cataclysmic stars? (14 Sept 2007)
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