# Variable dust emission by WC type Wolf-Rayet stars observed in the NEOWISE-R survey

## TL;DR

This study used NEOWISE-R infrared data to identify and analyze dust emission variability in Wolf-Rayet WC stars, revealing new dust-making stars and episodic dust formation patterns.

## Contribution

It is the first to identify non-variable dust makers among early WC stars and to observe dust emission variability and episodic dust formation in a large sample.

## Key findings

- Identified 10 new dust-making WC stars, including early subtypes.
- Detected 11 stars with variable dust emission, including episodic dust makers.
- Confirmed and revised dust formation periods for several known Wolf-Rayet stars.

## Abstract

Photometry at 3.4 and 4.6 micron of 128 Population~I WC type Wolf-Rayet stars in the Galaxy and 12 in the Large Magellanic Cloud (LMC) observed in the WISE NEOWISE-R survey was searched for evidence of circumstellar dust emission and its variation. Infrared spectral energy distributions (SEDs) were assembled, making use of archival r, i, Z and Y photometry to determine reddening and stellar wind levels for the WC stars found in recent IR surveys and lacking optical photometry. From their SEDs, ten apparently non-variable stars were newly identified as dust makers, including three, WR 102-22, WR 110-10 and WR 124-10, having subtype earlier than WC8-9, the first such stars to show this phenomenon. The 11 stars found to show variable dust emission include six new episodic dust-makers, WR 47c, WR 75-11, WR 91-1, WR 122-14 and WR 125-1 in the Galaxy and HD 38030 in the LMC. Of previously known dust makers, NEOWISE-R photometry of WR 19 captured its rise to maximum in 2018, confirming the 10.1-y period, that of WR 125 the beginning of a new episode of dust formation suggesting a period near 28.3~y., while that of HD 36402 covered almost a whole period and forced revision of it to 5.1~y.