R Coronae Borealis: Radial-velocity and other observations, 1950-2007

TL;DR

This comprehensive study of R Coronae Borealis over 57 years presents extensive radial-velocity data, revealing complex atmospheric behavior and turbulent mass ejections linked to brightness declines, without evidence of coherent periodicity.

Contribution

It provides the longest and most detailed radial-velocity dataset for RCB stars, analyzing atmospheric turbulence and mass ejection mechanisms over decades.

Findings

No coherent periodicity in radial velocity series.

High-velocity components associated with atmospheric turbulence.

Mass ejection likely triggers brightness declines.

Abstract

Radial-velocity observations made on more than a thousand nights are presented for the type star of the R Coronae Borealis (RCB) class. There are four principal sources: the Lick Observatory (1950-1953), the original Cambridge radial-velocity spectrometer (1968-1991), and the Haute-Provence and Cambridge Coravels (1986-1998 and 1997- 2007, respectively). In the case of the last set the size (equivalent width) and width (expressed as if Vsin(i)) of the Coravel cross-correlation ('dip') profiles are also given, and the variation and complexity of those profiles are discussed. Although there is often evidence of cyclical behaviour in radial velocity, no coherent periodicity is found in any of the series. From time to time, and especially over 100 days before the great decline of 2007, the atmosphere was highly disturbed, with evidence of high-velocity components. We suggest that those are associated with large turbulent elements and result in mass ejection to sufficient distances for the formation of soot and other solids and thus the initiation of RCB-type declines. We associate the changes in light and radial velocity near maximum light primarily with the combined effect of such turbulent elements, and not with coherent pulsation. There is some evidence for a variation in the mean radial velocity on a time scale of about ten thousand days.