A discovery and surprising properties of the white dwarf radio pulsar in AR Scorpii

by Dr. Nazar Ikhsanov

Pulkovo Observatory, St. Petersburg, Russia

at Astrophysics and Cosmology Seminar

Wed, 20 Nov 2019, 11:10
Sacta-Rashi Building for Physics (54), room 207

Abstract

AR Scorpii is a 3.56h orbital period binary system composed of a M5V red dwarf and a white
dwarf which rotates with the period of 117s and manifests itself as a spin-powered radio pulsar.
The rapid spin-down of the white dwarf indicates that its surface magnetic field exceeds 150 MG
and prevents the surrounding material from penetrating to within its Roche lobe. Since the
cooling age of the white dwarf significantly exceeds its spin-down timescale the system could
not be formed in its current state. On the other hand, an attempt to model the origin of the system
in terms of accretion-driven spin-up scenario also encounters difficulties. Using currently
adopted disk accretion scenario one finds that a white dwarf with the surface field of 150 MG
could be spun-up to a period of 117s only if the mass accretion rate onto the white dwarf were in
excess of the Eddington limit. Otherwise, the centrifugal barrier at the Alfven radius would
prevent material from reaching the surface of the white dwarf well before its spin period reaches
the currently observed value. This may indicate that either the surface magnetic field of the white
dwarf during a previous spin-up epoch was buried by the accreted material or/and the inner
radius of the accretion disk was significantly smaller than the conventional Alfven radius. In my
talk I discuss both of these possibilities and show that similar corrections to the accretion
scenario may help to model the origin of the fast rotating white dwarf in AE Aquarii.

Created on 17-11-2019 by Zitrin, Adi (zitrin)
Updaded on 17-11-2019 by Zitrin, Adi (zitrin)