title: An accurate geometric distance to the compact binary SS Cygni vindicates accretion disc theory.
abstract: Dwarf novae are white dwarfs accreting matter from a nearby red dwarf companion. Their regular outbursts are explained by a thermal-viscous instability in the accretion disc, described by the disc instability model that has since been successfully extended to other accreting systems. However, the prototypical dwarf nova, SS Cygni, presents a major challenge to our understanding of accretion disc theory. At the distance of 159 ± 12 parsecs measured by the Hubble Space Telescope, it is too luminous to be undergoing the observed regular outbursts. Using very long baseline interferometric radio observations, we report an accurate, model-independent distance to SS Cygni that places the source substantially closer at 114 ± 2 parsecs. This reconciles the source behavior with our understanding of accretion disc theory in accreting compact objects.
authors.affiliation: International Centre for Radio Astronomy Research, Curtin University, Perth, WA 6845, Australia. james.miller-jones@curtin.edu.au
authors.forename: J C A
authors.initials: JC
authors.lastname: Miller-Jones
authors.forename: G R
authors.initials: GR
authors.lastname: Sivakoff
authors.forename: C
authors.initials: C
authors.lastname: Knigge
authors.forename: E G
authors.initials: EG
authors.lastname: Körding
authors.forename: M
authors.initials: M
authors.lastname: Templeton
authors.forename: E O
authors.initials: EO
authors.lastname: Waagen