The missing link in the evolution of magnetic cataclysmic ? 14 September 2007

An international team of astronomers might have periods longer than 3 hours and spin periods discovered the missing link in the evolution of the ranging from 33 seconds to 1 hour. so-called magnetic cataclysmic variable stars. They determined the spin and orbital periods of the In a cataclysmic variable system, both stars are so binary Paloma. They found that the Paloma close to each other (the whole system would match system has a weird way of rotating that fills the gap the size of our Sun) that astronomers cannot between two classes of magnetic cataclysmic distinguish one star from the other. For studying stars. Their results will soon be published in CVs, they rely on indirect observations: measuring Astronomy & Astrophysics. the variation in the brightness of the system, thereby estimating its characteristics ( size, Cataclysmic variables (CVs) are a class of binary period). stars made up of a and a normal star much like our Sun. Both stars orbit so close to Dr. R. Schwarz and his colleagues studied the each other that the white dwarf accretes matter candidate magnetic CV Paloma (also known as RX from the companion star. In most of the several J0524+42), which has not yet been characterised. It hundred CVs known, the matter spirals around the does not fit either of the known CVs categories. white dwarf, forming a disk, before being accreted The team presents both long- and short-term and incorporated into the star. About 20% of the monitoring of this stellar system, using several known CVs include a white dwarf with a strong European telescopes (1.2m OHP, 70 cm AIP, magnetic field of several million Gauss. They are 1.23m Calar Alto), over a period ranging from 1995 known as “magnetic CVs”. The magnetic field of to 2001. With this monitoring, they built the light the white dwarf can be strong enough to disrupt curves and estimated the periods of the system. the or even to prevent the disc from ROSAT observations of the system confirm that it forming. has a strong magnetic field and thus belongs to the magnetic CVs. Astronomers currently know two classes of magnetic CVs: From their observations, the team concludes that the faster white dwarf performs 14 spins around its -- Polars (also known as the prototype star AM own axis during 13 orbital revolutions. The weird Herculis) have a strong enough magnetic field to degree of synchronization of the system presents synchronize the spin period of the stars and the the characteristics that makes Paloma so of the system. A departure from interesting. This bridges the gap between the two synchronization is observed for four AM Herculis main classes of magnetic CVs: it spins much more stars, which are thought to be normal AM Herculis slowly than any known intermediate , but is too systems currently desynchronized by a recent much desynchronized to be an AM Herculis star. explosion. The difference between the spin Paloma thus revives the old idea that both classes period and the orbital period, that is, the degree of are evolutionarily linked together and that asynchronism, is less than 2% for these near- intermediate polars are the ancestors of the older synchronous polars. AM Herculis stars. Theoreticians predict that Paloma is in the process of synchronization and -- Intermediate polars (known as DQ Herculis should become a spin-locked AM Herculis star over stars) have a lower magnetic field, and the spin the next 100 million . period of the stars is shorter than the orbital period. The majority of the DQ Herculis stars have orbital Source: Journal Astronomy & Astrophysics

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APA citation: The missing link in the evolution of magnetic cataclysmic stars? (2007, September 14) retrieved 27 September 2021 from https://phys.org/news/2007-09-link-evolution-magnetic-cataclysmic- stars.html

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