# 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.

## Key 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.