Instituto de Física y Astronomía

February 18, 2015- IFA News.

Adam Hardy, a PhD student at  IFA, and his supervisor Matthias R. Schreiber have led a team who have published the first science results with a groundbraking new instrument. The Spectro-Polarimetric High-contrast Exoplanet REsearch instrument, or SPHERE, has been installed on ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile, and its main goal is to find and characterise substellar objects such as brown dwarfs and giant planets orbiting nearby stars by direct imaging. This is an extremely challenging task as such objects are both very close to their parent stars in the sky and also very much fainter.
The team observed with SPHERE the close binary star V471 Tau aiming for a final confimation of the circumbinary brown dwarf that has been predicted around V471 Tau for more than twenty years. V471 Tau is an eclipsing binary star consisting of a white dwarf and a normal main sequence star with an orbital period of 0.5 days. When the main sequence star passes in front of the white dwarf, the light emitted from the white dwarf gets blocked and the system appears to be fainter, but the resulting eclipse signal has been found to periodically vary, and this has been interpreted as evidence for a circumbinary brown dwarf orbiting the stars every 30 years.
The observations performed with SPHERE by the IFA team now show that the brown dwarf does not exist. This result has potentially far reaching consequences, as circumbinary planets or brown dwarfs have become the standard explanation for eclipse timing variations in close binary stars.

The damaging evidence for the circumbinary brown dwarf interpretation of V471 Tau provided by the SPHERE observations shows that at least in this system, and maybe in the others too, another mechanism is driving the eclipse timing variations. The paper has appeared in the Astrophysical Journal Letters and a press release has been released by ESO.

Associated links: Press Release from European Southern Observatory -  Article in Astrophysical Journal Letters - News in National Geographic