# ROAD and K2 photometry of V348 Sgr: probing the pulsation dust connection

## TL;DR

This study investigates the pulsation and dust production connection in V348 Sgr, a peculiar star exhibiting RCB variability, through extensive multicolour and space-based photometry, revealing small-amplitude pulsations potentially triggering dust episodes.

## Contribution

It provides new continuous space-based photometry data and analyzes pulsation-dust interactions in V348 Sgr, a star with unique properties among RCB and helium stars.

## Key findings

- Detected small-amplitude pulsations at maximum light.
- Observed dust extinction events similar to cooler RCB stars.
- Reddening properties suggest scattered light dominates at minimum light.

## Abstract

V348 Sgr is simultaneously an active hot R Coronae Borealis (RCB) variable, a peculiar extreme helium star, and the hydrogen-deficient central star of a planetary nebula. Explaining the RCB-type variability has been difficult since the star spends much of its time at minimum light. We present new ground-based multicolour photometry covering 5 observing seasons and 80 days of continuous photometry from space. The latter demonstrate small-amplitude (< 0.01 mag.) variability at maximum light on timescales typical for strange-mode pulsation in hot helium supergiants. These could provide a trigger for frequent dust-production episodes; other mechanisms must also be considered. Multi-colour photometry probes the reddening properties of extinction events from minimum to maximum light. The latter are comparable with extinction events due to carbonaceous grains seen in cooler RCB stars. Minimal reddening at minimum light is indicative that starlight scattered from circumstellar dust into the line of sight dominates transmitted light.