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

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.

9 pages, 7 figures, MNRAS in press

References in corpus (5)

• EVEREST: Pixel Level Decorrelation of K2 Light curves
• Post-merger evolution of carbon-oxygen + helium white dwarf binaries and the origin of R Coronae Borealis and extreme helium stars
• White-dwarf red-giant mergers, early-type R stars, J stars and lithium
• Polyaromatic disordered carbon grains as carriers of the UV bump: FUV to mid-infrared spectroscopy of laboratory analogs
• Direct imaging of a massive dust cloud around R Coronae Borealis

Cited by in corpus (3)

• Catalogue of central stars of planetary nebulae: Expanded edition
• TESS photometry of extreme helium stars PV Tel and V821 Cen
• On the optical properties of Resonant Drag Instabilities: Variability of Asymptotic Giant Branch and R Coronae Borealis stars