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 Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

The binary fraction among extreme horizontal branch (EHB) stars in Galacticglobular clusters (GCs) is an order of magnitude lower than the binary fractionamong their counterparts, field hot subdwarfs. This casts serious doubt ontheir formation channels. In this {\em Letter}, I explain the differencebetween the field and the cluster EHB stars with the binary model of Han et al.(2002, 2003) for the formation of EHB stars. With the binary populationsynthesis code of Han et al. (2002, 2003), I follow the evolution of simplestellar populations resulting from single star bursts (note that Han et al.2002, 2003, adopted a constant star formation rate over the last 15 Gyr for theproduction of field EHB stars), and obtain EHB stars at different stellarpopulation ages. I found that the binary fraction among EHB stars decreaseswith the stellar population age. The fraction of EHB binaries with orbitalperiods $P<5 {\rm d}$ is $\sim 2.5%$ for a stellar population of 10 Gyr fromthe standard simulation set. The binary model of Han et al. (2002, 2003) isable to explain the lack of EHB binaries in globular clusters. I also proposethat the precise determination of the physical parameters of close EHB binariesin GCs can lead to the strictest constraint on common-envelope ejectionefficiency.

A possible solution for the lack of EHB binaries in globular clusters