The sdA problem - II. Photometric and Spectroscopic Follow-up

TL;DR

This study presents follow-up spectroscopic and photometric observations of sdA stars, confirming several as extremely-low mass white dwarfs and identifying a new pulsating ELM, advancing understanding of their nature.

Contribution

It provides new observational data confirming the nature of sdA stars and identifying additional extremely-low mass white dwarfs and pulsators.

Findings

Confirmed seven new extremely-low mass white dwarfs.

Identified one new pulsating ELM star.

Detected an eclipsing ELM star.

Abstract

Subdwarf A star (sdA) is a spectral classification given to objects showing H-rich spectra and sub-main sequence surface gravities, but effective temperature lower than the zero-age horizontal branch. Their evolutionary origin is an enigma. In this work, we discuss the results of follow-up observations of selected sdAs. We obtained time resolved spectroscopy for 24 objects, and time-series photometry for another 19 objects. For two targets, we report both spectroscopy and photometry observations. We confirm seven objects to be new extremely-low mass white dwarfs (ELMs), one of which is a known eclipsing star. We also find the eighth member of the pulsating ELM class.