Research Note

Gravitational excitation of high frequency QPOs

¹ Institute of Physics, Faculty of Philosophy and Science, Silesian University in Opava Bezručovo nám. 13, 74601 Opava, Czech Republic e-mail: [zdenek.stuchlik;stanislav.hledik]@fpf.slu.cz
² Centre for Theoretical Studies, Indian Institute of Technology, Kharagpur 721 302, India e-mail: sushan.konar@googlemail.com
³ SISSA, International School for Advanced Studies and INFN via Beirut 2–4, 34014 Trieste, Italy e-mail: miller@sissa.it
⁴ Department of Physics (Astrophysics), University of Oxford, Keble Road, Oxford OX1 3RH, UK e-mail: jcm@astro.ox.ac.uk

Received: 5 January 2007
Accepted: 13 August 2008

Abstract

We discuss the possibility that high-frequency QPOs in neutron-star binary systems may result from forced resonant oscillations of matter in the innermost parts of the accretion disc, excited by gravitational perturbations coming from asymmetries of the neutron star or from the companion star. We find that neutron-star asymmetries could, in principle, be effective for inducing both radial and vertical oscillations of relevant amplitude while the binary companion might possibly produce significant radial oscillations but not vertical ones. Misaligned neutron-star quadrupole moments of a size advocated elsewhere for explaining limiting neutron star periods could be large enough also for the present purpose.