Cool White Dwarfs Found in the UKIRT Infrared Deep Sky Survey

TL;DR

This paper reports the discovery of new cool white dwarfs in the UKIDSS survey, using combined infrared and optical data, with spectroscopic confirmation and analysis of their temperatures, ages, and kinematics.

Contribution

The study introduces a new method for identifying cool white dwarfs by combining UKIDSS infrared data with SDSS optical data, leading to the discovery of 20+ new objects and detailed characterization.

Findings

Seven white dwarfs with T_eff ~ 6000 K identified in 280 deg2.

Thirteen white dwarfs found in 1400 deg2 of sky.

White dwarfs have ages between 4.3 and 8.7 Gyr, with diverse kinematic properties.

Abstract

We present the results of a search for cool white dwarfs in the United Kingdom InfraRed Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS). The UKIDSS LAS photometry was paired with the Sloan Digital Sky Survey (SDSS) to identify cool hydrogen-rich white dwarf candidates by their neutral optical colors and blue near-infrared colors, as well as faint Reduced Proper Motion magnitudes. Optical spectroscopy was obtained at Gemini Observatory, and showed the majority of the candidates to be newly identified cool degenerates, with a small number of G- to K-type (sub)dwarf contaminants. Our initial search of 280 deg2 of sky resulted in seven new white dwarfs with effective temperature T_eff ~ 6000 K. The current followup of 1400 deg2 of sky has produced thirteen new white dwarfs. Model fits to the photometry show that seven of the newly identified white dwarfs have 4120 K <= T_eff <= 4480 K, and cooling ages between 7.3 Gyr and 8.7 Gyr; they have 40 km/s <= v_tan <= 85 km/s and are likely to be thick disk 10-11 Gyr-old objects. The other half of the sample has 4610 K <= T_eff <= 5260 K, cooling ages between 4.3 Gyr and 6.9 Gyr, and 60 km/s <= v_tan <= 100 km/s. These are either thin disk remnants with unusually high velocities, or lower-mass remnants of thick disk or halo late-F or G stars.