Subdwarf A stars vs ELM WDs radial velocities

The two classes of objects are confused in low-resolution spectroscopy. However, colors and proper motions indicate that sdA stars are cooler and more luminous, and thus larger in radius, than published ELM WDs.

We demonstrate that surface gravities derived from pure hydrogen models suffer a systematic ~1dex error for sdA stars, likely explained by metal line blanketing below 9000K. A detailed study of five eclipsing binaries with radial velocity orbital solutions and infrared excess establishes that these sdA stars are metal-poor ~1.2M_{sun}_ main sequence stars with ~0.8M_{sun}_ companions. While WDs must exist at sdA temperatures, only ~1% of a magnitude-limited sdA sample should be ELM WDs.