Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001a%26a...367..577f&link_type=abstract
Astronomy and Astrophysics, v.367, p.577-581 (2001)
Astronomy and Astrophysics
Astrophysics
5
Stars: Individual: Grw+70O8247, Stars: Rotation, Stars: White Dwarfs
Scientific paper
Grw+70o8247 belongs to a small group of magnetic white dwarfs which despite repeated observations did not show any changes in their polarization over decades. The inferred rotation periods are of the order of hundred years which is not easy to understand if angular momentum is conserved during stellar evolution. An alternative possibility, which was to our knowledge never investigated, might be fast rotation with a period between some minutes and a couple of seconds. Assuming a mass of 1 M_sun and a radius of 1/100 R_sun the shortest possible period is about 10 s. In order to test this hypothesis the linear polarization of {Grw+70o8247} was measured at the 2.2 m telescope at the Calar Alto Observatory, Spain, with a time resolution of 3 s by trailing the linear polarized image of Grw+70o8247 over the CCD chip. The linear polarization was searched for periodicities in the range between 10 s and 4000 s. Investigations with synthetic polarized data using the same window function and an assumed sinusoidal variation showed that variations with amplitudes of 40% relative to the amount of average linear polarization should be detectable. However, no periodicities at this or higher levels of significance were found. This would be in accordance with a recent report on slow rotation of GD 229 and G 240-72, but fast variations with lower amplitudes could not be ruled out. Based on observations collected at the German-Spanish Astronomical Center (DSAZ), Calar Alto, operated by the Max-Planck-Institut für Astronomie Heidelberg jointly with the Spanish National Commission for Astronomy.
Friedrich Stefan
Jordan Stefan
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