A&A Press Release: The missing link in the evolution of magnetic cataclysmic stars? (14 Sept 2007)
- Published on 13 September 2007
A&A press release
Released on September 14th, 2007
The missing link in the evolution of magnetic cataclysmic stars?
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)
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 . 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.
• Intermediate polars (known as DQ Herculis stars) have a lower magnetic field, and the spin period of the stars is shorter than the orbital period. The majority of the DQ Herculis stars have orbital periods longer than 3 hours and spin periods ranging from 33 seconds to 1 hour.
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,
Dr. R. Schwarz and his colleagues  studied the candidate magnetic CV Paloma (also known as RX J0524+42), which has not yet been characterised. It does not fit either of the known CVs categories. The team presents both long- and short-term monitoring of this stellar system, using several European telescopes (1.2m OHP, 70 cm AIP, 1.23m Calar Alto), over a period ranging from 1995 to 2001. With this monitoring, they built the light curves and estimated the periods of the system. ROSAT observations of the system confirm that it has a strong magnetic field and thus belongs to the magnetic CVs.
From their observations, the team concludes that the faster white dwarf performs 14 spins around its own axis during 13 orbital revolutions. The weird degree of synchronization of the system presents the characteristics that makes Paloma so interesting. This bridges the gap between the two main classes of magnetic CVs: it spins much more slowly than any known intermediate polar, but is too much desynchronized to be an AM Herculis star. Paloma thus revives the old idea that both classes are evolutionarily linked together and that intermediate polars are the ancestors of the older AM Herculis stars. Theoreticians predict that Paloma is in the process of synchronization and should become a spin-locked AM Herculis star over the next 100 million years.
Fig. 1 - Artist's illustration of an intermediate polar. Copyright M.A. Garlick.
 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.
 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.
 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?
by R. Schwarz, A.D. Schwope, A. Staude, A. Rau, G. Hasinger, T. Urrutia, and C. Motch
Astronomy & Astrophysics, 2007, 473, p. 511. Full article available in PDF format
Dr. R. Schwarz
Astrophysikalisches Institut Potsdam
An der Sternwarte 16
D-14482 Potsdam, Germany
Email: schwarz (at) aip.de
Phone: +49 (0)331 7499 286
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© Astronomy & Astrophysics 2007