Sher 25: pulsating but apparently alone

TL;DR

This study detects pulsations in the blue supergiant Sher25 through radial velocity variations, challenging the binary companion hypothesis and highlighting stellar pulsations as the likely cause of observed spectral changes.

Contribution

It provides the first clear evidence of pulsations in Sher25, linking stellar variability to nebular morphology and rejecting the binary companion explanation.

Findings

Radial velocity variations of ~12 km/s over 6 days detected in Sher25.

No significant velocity variations observed in similar stars SBW1 and HD 168625.

Pulsations are identified as the likely cause of spectral variability in Sher25.

Abstract

The blue supergiant Sher25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula, which shows similarities to the triple-ring structure seen around SN1987A. From optical spectroscopy over six consecutive nights, we detect periodic radial velocity variations in the stellar spectrum of Sher25 with a peak-to-peak amplitude of ~12 km/s on a timescale of about 6 days, confirming the tentative detec-tion of similar variations by Hendry et al. From consideration of the amplitude and timescale of the signal, coupled with observed line profile variations, we propose that the physical origin of these variations is related to pulsations in the stellar atmosphere, rejecting the previous hypothesis of a massive, short-period binary companion. The radial velocities of two other blue supergiants with similar bipolar nebulae, SBW1 and HD 168625, were also monitored over the course of six nights, but these did not display any significant radial velocity variations.