MagAO Imaging of Long-period Objects (MILO). II. A Puzzling White Dwarf around the Sun-like Star HD 11112

TL;DR

This study presents direct imaging of a white dwarf companion to Sun-like star HD 11112, revealing a high-mass white dwarf with a puzzling age discrepancy, offering insights into stellar evolution and white dwarf modeling.

Contribution

First direct imaging of a white dwarf companion to HD 11112, revealing a high-mass white dwarf with a unique evolutionary history and potential as a calibration benchmark.

Findings

White dwarf companion detected at 100 AU separation.

White dwarf mass estimated at 0.9-1.1 solar masses.

Age discrepancy suggests a complex progenitor history.

Abstract

HD 11112 is an old, Sun-like star that has a long-term radial velocity (RV) trend indicative of a massive companion on a wide orbit. Here we present direct images of the source responsible for the trend using the Magellan Adaptive Optics system. We detect the object (HD 11112B) at a separation of 2\fasec 2 (100 AU) at multiple wavelengths spanning 0.6-4 \microns ~and show that it is most likely a gravitationally-bound cool white dwarf. Modeling its spectral energy distribution (SED) suggests that its mass is 0.9-1.1 \msun, which corresponds to very high-eccentricity, near edge-on orbits from Markov chain Monte Carlo analysis of the RV and imaging data together. The total age of the white dwarf is $>2\sigma$ discrepant with that of the primary star under most assumptions. The problem can be resolved if the white dwarf progenitor was initially a double white dwarf binary that then merged into the observed high-mass white dwarf. HD 11112B is a unique and intriguing benchmark object that can be used to calibrate atmospheric and evolutionary models of cool white dwarfs and should thus continue to be monitored by RV and direct imaging over the coming years.