2018/01/01 by Ingrid Pelisoli, S. O. Kepler, D. Koester
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Galaxy #Main sequence #Physics #Sky #Stars #Stellar, planetary, and galactic studies #Subdwarf #Surface gravity #White dwarf #astro-ph.SR
paper · pdf · doi:10.1093/mnras/sty011
Accepted for publication in MNRAS. 18 pages, 21 figures, 3 tables
arxiv created 2018/01/01 · openalex publication_date 2018/01/05 · arxiv updated 2018/01/24 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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 ELMs with similar properties to sdAs is known. Other possibilities include metal-poor A/F dwarfs, second generation stars, or even stars accreted from dwarf galaxies. In this work, we analyse colours, proper motions, and spacial velocities of a sample of sdAs from the Sloan Digital Sky Survey to assess their nature and evolutionary origin. We define a probability of belonging to the main sequence and a probability of being a (pre-)ELM based on these properties. We find that 7 per cent of the sdAs are more likely to be (pre-)ELMs than main-sequence stars. However, the spacial velocity distribution suggests that over 35 per cent of them cannot be explained as single metal-poor A/F stars.