Discovery of a compact companion to the hot subdwarf star BD+37 442

TL;DR

This paper reports the first X-ray detection of the hot subdwarf star BD+37 442, revealing pulsations that suggest the presence of a compact companion, likely a white dwarf or neutron star, accreting from the star's wind.

Contribution

First X-ray observation of BD+37 442 revealing pulsations, indicating a compact companion and providing insights into its accretion processes.

Findings

X-ray emission detected with flux ~3x10^-14 erg/cm^2/s

Pulsations with a period of 19.2 seconds observed

Spectrum well fit by blackbody and power law components

Abstract

We report the results of the first X-ray observation of the luminous and helium-rich O-type subdwarf BD+37 442, carried out with the XMM-Newton satellite in August 2011. X-ray emission is detected with a flux of about 3x10^(-14) erg/cm2/s (0.2-1 keV) and a very soft spectrum, well fit by the sum of a blackbody with temperature kT_BB = 45^(+11)_(-9) eV and a power law with a poorly constrained photon index. Significant pulsations with a period of 19.2 s are detected, indicating that the X-ray emission originates in a white dwarf or neutron star companion, most likely powered by accretion from the wind of BD+37 442.