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 Tools annual

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 monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

The physical nature of the sdA stars---cool hydrogen-rich objects withspectroscopic surface gravities intermediate between main sequence andcanonical mass white dwarfs---has been elusive since they were found in SloanDigital Sky Survey Data Release 12 spectra. The population is likely dominatedby metal-poor A/F stars in the halo with overestimated surface gravities, witha small contribution of extremely low-mass white dwarfs and their precursors,i.e., ELMs and pre-ELMs. In this work, we seek to identify (pre-)ELMs withradii smaller than is possible for main sequence stars, allowing even for verylow metallicity. We analyse 3891 sdAs previously identified in the SloanDigital Sky Survey using Gaia DR2 data. Our Monte Carlo analysis supports that90 of these are inconsistent with the main sequence. 37 lie close to or withinthe canonical white dwarf cooling sequence, while the remaining 53 lie betweenthe canonical white dwarfs and main sequence, which we interpret as likely(pre-)ELMs given their spectral class. Of these, 30 pass more conservativecriteria that allow for higher systematic uncertainties on the parallax, aswell as an approximate treatment of extinction. Our identifications increasethe number of known (pre-)ELMs by up to 50 per cent, demonstrating how Gaiaastrometry can reveal members of the compact (pre-)ELM subpopulation of the sdAspectral class.

The sdA problem - III. New extremely low-mass white dwarfs and their precursors from Gaia astrometry