# Cool DZ white dwarfs I: Identification and spectral analysis

## TL;DR

This study identifies and analyzes 231 cool DZ white dwarfs with metal lines from SDSS data, revealing their properties and potential planetary system remnants, with 104 being newly discovered.

## Contribution

It provides an improved spectral analysis of DZ white dwarfs using updated models, extending the known sample and characterizing their properties and kinematics.

## Key findings

- Identified 231 cool DZ white dwarfs, including 104 new discoveries.
- Derived effective temperatures and metal abundances using improved models.
- Detected halo white dwarfs with high tangential velocities.

## Abstract

White dwarfs with metal lines in their spectra act as signposts for post-main sequence planetary systems. Searching the Sloan Digital Sky Survey (SDSS) data release 12, we have identified 231 cool (<9000 K) DZ white dwarfs with strong metal absorption, extending the DZ cooling sequence to both higher metal abundances, lower temperatures, and hence longer cooler ages. Of these 231 systems, 104 are previously unknown white dwarfs. Compared with previous work, our spectral fitting uses improved model atmospheres with updated line profiles and line-lists, which we use to derive effective temperatures and abundances for up to 8 elements. We also determine spectroscopic distances to our sample, identifying two halo-members with tangential space-velocities >300 kms-1. The implications of our results on remnant planetary systems are to be discussed in a separate paper.