A new extremely low-mass white dwarf in the NLTT catalogue

TL;DR

This paper reports the discovery and characterization of an extremely low-mass, hydrogen-rich white dwarf, NLTT 11748, providing insights into its properties, origin, and potential binary companion.

Contribution

It presents the first detailed analysis of NLTT 11748, a white dwarf with a mass below 0.2 solar masses, and discusses its implications for binary evolution models.

Findings

Mass of 0.167 solar masses derived from spectral fitting

Estimated progenitor mass between 0.87 and 0.93 solar masses

Potential binary companion yet to be identified

Abstract

We report on the discovery of the extremely low-mass, hydrogen-rich white dwarf, NLTT 11748. Based on measurements of the effective temperature (8540+/-50 K) and surface gravity (log g = 6.20+/-0.15) obtained by fitting the observed Balmer line profiles with synthetic spectra, we derive a mass of 0.167+/-0.005 M_solar. This object is one of only a handful of white dwarfs with masses below 0.2 M_solar that are believed to be the product of close binary evolution with an episode of Roche lobe overflow onto a degenerate companion (neutron star or white dwarf). Assuming membership in the halo population, as suggested by the kinematics and adopting a cooling age of 4.0 - 6.3 Gyrs for the white dwarf, we infer a progenitor mass of 0.87 - 0.93 M_solar. The likely companion has yet to be identified, but a search for radial velocity variations may help constrain its nature.