In the first spectroscopic campaign for a PG 1716 variable ( or long-period pulsating subdwarf B star ) , we succeeded in detecting velocity variations due to g-mode pulsations at a level of 1.0–1.5 km s ^ { -1 } , just above our detection limit .
The observations were obtained during 40 nights on 2 m class telescopes in Arizona , South Africa , and Australia .
The target , PG 1627+017 , is one of the brightest ( V = 12.9 ) and largest amplitude ( \sim 0.03 mag ) stars in its class .
It is also the visible component of a post-common envelope binary .
Our final radial velocity data set includes 84 hours of time-series spectroscopy over a time baseline of 53 days , with typical errors of 5–6 km s ^ { -1 } per spectrum .
We combined the velocities with previously existing data to derive improved orbital parameters .
Unexpectedly , the velocity power spectrum clearly shows an additional component at twice the orbital frequency of PG 1627+017 , supporting Edelmann et al. ’ s recent results for several other short-period subdwarf B stars , which they claim to be evidence for slightly elliptical orbits .
Our derived radial velocity amplitude spectrum , after subtracting the orbital motion , shows three potential pulsational modes 3–4 \sigma above the mean noise level of 0.365 km s ^ { -1 } , at 7201.0 s ( 138.87 \mu Hz ) , 7014.6 s ( 142.56 \mu Hz ) and 7037.3 s ( 142.10 \mu Hz ) .
Only one of the features is statistically likely to be real , but all three are tantalizingly close to , or a one day alias of , the three strongest periodicities found in the concurrent photometric campaign .
We further attempted to detect pulsational variations in the Balmer line amplitudes .
The single detected periodicity of 7209 s , although weak , is consistent with theoretical expectations as a function of wavelength .
Furthermore , it allows us to rule out a degree index of l = 3 or l = 5 for that mode .
Given the extreme weakness of g-mode pulsations in these stars , we conclude that anything beyond simply detecting their presence will require larger telescopes , higher efficiency spectral monitoring over longer time baselines , improved longitude coverage , and increased radial velocity precision .