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

The well-studied carbon star, V Hya, showing evidence for high-speed,collimated outflows and dense equatorial structures, is a key object in thestudy of the poorly understood transition of AGB stars into asphericalplanetary nebulae. Using the STIS instrument onboard HST, we have obtained highspatial-resolution long-slit optical spectra of V Hya that show high-velocityemission in [SII] and [FeII] lines. Our dataset, spanning three epochs spacedapart by a year during each of two periods (in 2002-2004 and 2011-2013), showsthat V Hya ejects high-speed (about 200-250 km/s) bullets once every ~8.5 yr.The ejection axis flip-flops around a roughly eastern direction, both in andperpendicular to the sky-plane, and the radial velocities of the ejecta alsovary in concert between low and high values. We propose a model in which thebullet ejection is associated with the periastron passage of a binary companionin an eccentric orbit around V Hya with an orbital period of ~8.5 yr. Theflip-flop phenomenon is likely the result of collimated ejection from anaccretion disk (produced by gravitational capture of material from the primary)that is warped and precessing, and/or that has a magnetic field that ismisaligned with that of the companion or the primary star. We show how apreviously observed 17-year period in V Hya's light-cycle can also be explainedin our model. Additionally, we describe how the model proposed here can beextended to account for multipolar nebulae.

High-Speed Bullet Ejections during the AGB to Planetary Nebula Transition: HST Observations of the Carbon Star, V Hydrae