Stellar variability in open clusters
II. Discovery of a new period-luminosity relation in a class of fast-rotating pulsating stars in NGC 3766 ⋆
Institute of Astronomy, University of Geneva, 51 chemin des Maillettes, 1290 Versoix, Switzerland
Received: 23 June 2016
Accepted: 27 September 2016
Context. Pulsating stars are windows to the physics of stars enabling us to see glimpses of their interior. Not all stars pulsate, however. On the main sequence, pulsating stars form an almost continuous sequence in brightness, except for a magnitude range between δ Scuti and slowly pulsating B stars. Against all expectations, 36 periodic variables were discovered in 2013 in this luminosity range in the open cluster NGC 3766, the origins of which was a mystery.
Aims. We investigate the properties of those new variability class candidates in relation to their stellar rotation rates and stellar multiplicity.
Methods. We took multi-epoch spectra over three consecutive nights using ESO’s Very Large Telescope.
Results. We find that the majority of the new variability class candidates are fast-rotating pulsators that obey a new period-luminosity relation. We argue that the new relation discovered here has a different physical origin to the period-luminosity relations observed for Cepheids.
Conclusions. We anticipate that our discovery will boost the relatively new field of stellar pulsation in fast-rotating stars, will open new doors for asteroseismology, and will potentially offer a new tool to estimate stellar ages or cosmic distances.
Key words: stars: variables: general / stars: oscillations / stars: rotation / open clusters and associations: individual: NGC 3766
© ESO, 2016