Dqher Dq Herculis stars

- Another group of stars usually considered a subdivision of the novalike cataclysmic variables, DQ Her stars are also known as "intermediate polars." These binary systems contains a non-synchronously rotating, magnetized white dwarf and a cool companion that is near the main sequence. Accretion occurs in the outer regions and forms a disk. Close to the white dwarf, the accretion disk is disrupted by the magnetic field and mass flows by way of an accretion column towards the star's magnetic

Observation Key

Foint stars g?] Small amplitudes r\ Short periods <®> CCD or PEP

Figure 5.3. Light curve

Jam Her. Dole provided by (he VSNET Used with pinni»«*1

Figure 5.3. Light curve

Jam Her. Dole provided by (he VSNET Used with pinni»«*1

poles. Light variations are caused by eclipse effects and by the rotationally modulated accretion effects. Several intermediate polars have undergone nova explosions, not recognized within the GCVS

Although not officially listed as a group of variable stars within the GCVS, astronomers recognize DQ Her stars as an important group of variable stars. DQ Her stars are also known as intermediate polars (IP) and display strong magnetic fields surrounding the white dwarf star of the binary system.

An accretion disk has formed around these stars, but it is disrupted close to the primary (white dwarf) star because of the magnetic field. In the case of intermediate polars, the magnetosphere is not strong enough to synchronize the orbits of the rotating white dwarf with the orbital period of the system, such as is observed in AM Her stars.

The Intermediate Polar Homepage, a Web site dedicated to the study of these stars, can be found at <http://lheawww.gsfc.nasa.gov/users/mukai/iphome/iphome. html>. You will find a list of intermediate polar candidates and basic information pertaining to the stars, including where to obtain finder charts and references.

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