Cool white dwarf companions to four millisecond pulsars

TL;DR

This study presents photometric and spectroscopic observations of white dwarf companions to four millisecond pulsars, revealing their properties, cooling ages, and implications for pulsar companion evolution.

Contribution

First detailed spectroscopic analysis of white dwarf companions to multiple millisecond pulsars, providing new insights into their physical characteristics and evolutionary history.

Findings

Companion to PSR J0614-3329 is a DA white dwarf with Teff=6460 K.

White dwarf companions are cool (<4000 K) and old (>5 Gyr).

Thin Hydrogen envelopes and pulsar-driven mass loss influence white dwarf cooling.

Abstract

We report on photometric and spectroscopic observations of white dwarf companions to four binary radio millisecond pulsars, leading to the discovery of companions to PSRs J0614-3329, J1231-1411 and J2017+0603. We place limits on the brightness of the companion to PSR J0613-0200. Optical spectroscopy of the companion to PSR J0614-3329 identifies it as a DA type white dwarf with a temperature of Teff=6460+-80 K, a surface gravity log g=7.0+-0.2 cgs and a mass of Mwd=0.24+-0.04 Msun. We find that the distance to PSR J0614-3329 is smaller than previously estimated, removing the need for the pulsar to have an unrealistically high gamma-ray efficiency. Comparing the photometry with predictions from white dwarf cooling models allows us to estimate temperatures and cooling ages of the companions to PSRs J0613-0200, J1231-1411 and J2017+0603. We find that the white dwarfs in these systems are cool Teff<4000 K and old >5 Gyr. Thin Hydrogen envelopes are required for these white dwarfs to cool to the observed temperatures, and we suggest that besides Hydrogen shell flashes, irradiation driven mass loss by the pulsar may have been important.