The sdA problem – I. Physical properties

@article{Pelisoli2018TheSP,
  title={The sdA problem – I. Physical properties},
  author={Ingrid Pelisoli and S. O. Kepler and Detlev Koester},
  journal={Monthly Notices of the Royal Astronomical Society},
  year={2018},
  volume={475},
  pages={2480-2495}
}
The so-called sdA stars are defined by having H-rich spectra and surface gravities similar to hot subdwarf stars, but effective temperature below the zero-age horizontal branch. Their evolutionary history is an enigma: their surface gravity is too high for main sequence stars, but too low for single evolution white dwarfs. They are most likely byproducts of binary evolution, including blue-stragglers, extremely-low mass white dwarf stars (ELMs) and their precursors (pre-ELMs). A small number of… 

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