# Disk or Companion: Characterizing Excess Infrared Flux in Seven White Dwarf Systems with Near-Infrared Spectroscopy

**Authors:** Dylan Owens, Siyi Xu, Elena Manjavacas, S. K. Leggett, S. L. Casewell, Erik Dennihy, Patrick Dufour, Beth L. Klein, Sherry Yeh, B. Zuckerman  
**arXiv:** [2303.16330](https://arxiv.org/abs/2303.16330)  
**Date:** 2023-03-28  
**Summary page:** https://www.summarizepaper.com/en/paper/2303.16330v1/

## Key points

- White dwarf stars emit excess infrared flux
- Excess infrared flux can originate from a dusty debris disk or a cool companion
- Near-infrared spectroscopic observations were conducted on seven white dwarfs with previously identified infrared excesses
- Dust disks were confirmed around four white dwarfs and two new white dwarf brown dwarf pairs were discovered
- Near-infrared metal emissions (Mg I, Fe I and Si I) were detected from the gaseous component of the disk in three of the dust disk systems for the first time
- A new Markov Chain Monte Carlo framework was developed to constrain the geometric properties of each dust disk system
- In three systems studied by the team, both the dust disk and gas disk appear to coincide spatially
- Broad molecular absorption features typically seen in L dwarfs were identified in two brown dwarf white dwarf pairs
- The origin of infrared excess around Gaia J0723+6301 remains unknown
- Near-infrared spectroscopy can be used to determine sources of infrared excess around white dwarfs
- Findings provide valuable insights into understanding these mysterious objects' formation and evolution processes.

## Summary

White dwarf stars are known to emit excess infrared flux which is believed to originate from either a dusty debris disk or a cool companion. In this study, the authors present near-infrared spectroscopic observations of seven white dwarfs with previously identified infrared excesses using Keck/MOSFIRE, Gemini/GNIRS and Gemini/Flamingos-2. The team confirmed the presence of dust disks around four white dwarfs (Gaia J0611-6931, Gaia J0006+2858, Gaia J2100+2122 and WD 0145+234) as well as two new white dwarf brown dwarf pairs (Gaia J0052+4505 and Gaia J0603+4518). They also detected near-infrared metal emissions (Mg I, Fe I and Si I) from a gaseous component of the disk in three of the dust disk systems for the first time. To constrain the geometric properties of each dust disk system they developed a new Markov Chain Monte Carlo framework. Interestingly in three systems studied by the team both the dust disk and gas disk appear to coincide spatially. Furthermore broad molecular absorption features typically seen in L dwarfs were identified in two brown dwarf white dwarf pairs. However, the origin of infrared excess around Gaia J0723+6301 remains unknown. This study highlights how near-infrared spectroscopy can be used to determine sources of infrared excess around white dwarfs which has been detected photometrically in hundreds of systems so far. The findings provide valuable insights into understanding these mysterious objects' formation and evolution processes.