English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Amongst the hydrogen-deficient accreting binaries known as the "AM~CVn stars"are three systems with the shortest known orbital periods: HM Cnc (321 s), V407Vul (569 s) and ES Cet (620 s). These compact binaries are predicted to bestrong sources of persistent gravitational wave radiation. HM Cnc and V407 Vulare undergoing direct impact accretion in which matter transferred from theirdonor hits the accreting white dwarfs directly. ES Cet, is the longest periodof the three and is amongst the most luminous AM CVn stars, but it is not knownwhether it accretes via a disk or direct impact. ES Cet displays strong HeII4686 line emission, which is sometimes a sign of magnetically-controlledaccretion. Peculiarly, although around one third of hydrogen accreting whitedwarfs show evidence for magnetism, none have been found amongst heliumaccretors. We present the results of Magellan and VLT spectroscopic andspectropolarimetric observing campaigns dedicated to ES Cet with the aim ofunderstanding its accretion structure. We find strong variability in ourspectra on the 620 s period. The lines show evidence for double-peakedemission, characteristic for an accretion disc, with an additional componentassociated with the outermost disc, rather than a direct impact, that isbroadly consistent with "S"-wave emission from the gas stream/disc impactregion. This confirms beyond any doubt that 620\,s is the orbital period of ESCet. We find no significant circular polarisation (below 0.1 %). The trailedspectra show that ES Cet's outer disc is eclipsed by the mass donor, revealingat the same time that the photometric minimum coincides with the hithertounrecognised eclipse. ES Cet shows spectroscopic behaviour consistent withaccretion via a disc, and is the shortest orbital period eclipsing AM CVn starknown.

Spectroscopy of the helium-rich binary ES Ceti reveals accretion via a disc and evidence for eclipse