A white dwarf with a peculiar variability. The study: “Discovery of a magnetic white dwarf with unusual short-period variability” of A. Scholz (University of St. Andrews) published by RNAAS

The study of the variability of stars and compact objects is a powerful diagnostic to unveil their physical properties. For instance, it is typical not feasible to observe directly the presence of magnetic active regions on stellar surface, pulsations, very faint companions, or close circumstellar material. These properties, however, can be studied by the variability of the observed photometry or spectroscopic features.

 

The study “Discovery of a magnetic white dwarf with unusual short-period variability” of A. Scholz (University of St. Andrews), recently published by Research Notes of the American Astronomical Society with the collaboration of the astronomer Beate Stelzer of the Astronomical Observatory of Palermo, is focused on the variability of the pulsar SDSS 160357.93+140929.97, using data obtained from the camera EFOSC2@ESO/NTT, and the telescopes Lowell Observatory’s Discovery Channel Telescope and Large Monolithic Imager.

 

The white dwarf (with a surface temperature of about 10000 K and an average magnetic field intensity of 43 MG) shows a periodic optical variability, with a 110′ period, a color dependent amplitude, and a different phase shift in the observed bands. These properties, observed on a white dwarf for the first time, can be explained with two hypotheses. The star could host an unresolved brown dwarf companion, orbiting around the white dwarf in about 110 minutes, or it could have a magnetic cold spot on its surface, with a temperature of about 5000 K and a filling factor of 2%-3%. Future observations are necessary to discriminate between these two hypotheses.

 

The figure (link) shows the observed variability observed in the SDSS-g, SDSS-r, e SDSS-i bands.