Letters of Intent received in 2017

LoI 2019-2015
Cataclysmic Variables and Related Objects

Topics

* White dwarf binaries as probes of compact binary evolution
* The diverse pathways towards supernovae type Ia
* Accretion disc dynamics and evolution
* Activity of the companion stars as mass-transfer modulator
* The physics of accretion in strong magnetic fields
* Ultracompact white dwarf binaries
* The impact of new state-of-the-art experiments: Gaia, JWST, and massive multi-object spectroscopy and time-domain photometry
* Links to related fields, including black hole binaries and accreting neutron stars

Rationale

Cataclysmic variables and related objects are by far the largest class of compact binaries, and provide us with the most detailed insight into the physics of accretion, both via accretion discs and in strongly magnetic environments, and offer the best statistical constraints on the complex processes of interacting binary evolution.

Key questions that this research field addresses are:

(1) What is the efficiency of common envelope evolution in extracting energy and angular momentum from binaries? This phase is of fundamental importance to all compact binaries, including stellar mass black hole binaries and milli-second pulsars.

(2) What mechanisms drive the long-term evolution of compact binaries? Magnetic wind braking plays an important role, but is so far still poorly understood, and different parametrisations span orders of magnitude in efficiency.

(3) Under what circumstances do white dwarfs grow in mass? Supernovae type Ia (SN Ia) are the gold standard cosmic distance beacons, yet we now know that there is diversity among the observational properties of SN Ia, which is probably linked to multiple underlying populations of progenitor systems.

(4) How does accretion disc dynamics vary over the relevant parameters space, disc size and accretion rate? Accretion discs are extremely important structures in many contexts, from star formation to AGN, yet the discs in cataclysmic variables are best suited for observational studies both in terms of time scales and the ability to image their sub-structures via Doppler tomography.

(5) How does the presence of strong magnetic fields affect accretion physics? While neutron stars have higher surface fields, accreting white dwarfs have won in terms of magnetic moment, and the discovery of the first white-dwarf radio pulsar in 2016 demonstrates that we are still in an exploratory phase of this area of physics.

(6) What are the properties of the Galactic population of ultracompact binaries, and what evolutionary paths produce them? Ultracompact white dwarf binaries are among the shortest binaries know, with periods down to a few minutes. They are expected to be among the strongest low-frequency gravitational wave signals, and a proper understanding of their population is very timely.

(7) The field of cataclysmic variables and related objects has seen transformational progress over the past decade, driven by new powerful instrumentation and large photometric time-domain and spectroscopic surveys. We now know several thousand cataclysmic variables and post common envelope binaries, spanning a very wide range in stellar and binary parameters. New state-of-the-art facilities are providing multi-wavelength information on their spectral properties and variability, and Gaia will have the largest impact by delivering accurate distances for the first time. Within a few years, we will be able to derive accurate space densities, luminosities, and accretion rates, essential ingredients to revolutionise our understanding of the evolutionary paths of compact binaries in general.

High-profile international meetings on the topic of cataclysmic variables have a long history within the framework of the IAU, with the last three meetings in 2002 (Magnetic Cataclysmic Variables, IAUC 190, Cape Town), 1995 (Cataclysmic Variables and Related Objects, IAUC 158, Keele), and 1986 (Cataclysmic Variables, IAUC 93, Bamberg). Considering the enormous progress of the field achieved over the last decade, and the large scientific potential that forthcoming state-of-the-art facilities will provide, the proposed IAU Symposium on Cataclysmic Variables and Related Objects is a very timely opportunity to bring together not only the international community working in this field, but also to attract scientists from neighbouring fields.