High resolution spectroscopy with the Subaru High Dispersion Spectrograph , and Swift ultraviolet photometry are presented for the pulsating extreme helium star V652 Her . Swift provides the best relative ultraviolet photometry obtained to date , but shows no direct evidence for a shock at ultraviolet or X-ray wavelengths .
Subaru has provided high spectral and high temporal resolution spectroscopy over 6 pulsation cycles ( and eight radius minima ) .
These data have enabled a line-by-line analysis of the entire pulsation cycle and provided a description of the pulsating photosphere as a function of optical depth .
They show that the photosphere is compressed radially by a factor of at least two at minimum radius , that the phase of radius minimum is a function of optical depth and the pulse speed through the photosphere is between 141 and 239 \mbox { km } \mbox { s } ^ { -1 } ( depending how measured ) and at least ten times the local sound speed .
The strong acceleration at minimum radius is demonstrated in individual line profiles ; those formed deepest in the photosphere show a jump discontinuity of over 70 \mbox { km } \mbox { s } ^ { -1 } on a timescale of 150 s. The pulse speed and line profile jumps imply a shock is present at minimum radius .
These empirical results provide input for hydrodynamical modelling of the pulsation and hydrodynamical plus radiative transfer modelling of the dynamical spectra .