GeminiFocus October 2017 - Page 14

Figure 1. Gemini South spectra for three BLAPs. Best fits of stellar atmosphere models are shown with red lines. Effective temperatures, surface gravities, and helium abundances derived for these stars are similar to the values obtained from spectra for the prototype object previously studied. This shows that all the newly discovered variables form a homogeneous class of objects. Image credit: Gemini Observatory/AURA/NSF 12 While knowing that very massive stars were exploding at that time is important, the team would now like to know the relative rate of superluminous supernovae to normal super- novae — to see if this atypical supernova is telling us something special about that time 10 billion years ago. It may be that at these earlier times in the Universe’s history, even high-mass galaxies, like our Milky Way, may have had a low enough metal content to cre- ate these extraordinary stellar explosions. Their findings appear in a paper published June 13th in the Monthly Notices of the Roy- al Astronomical Society. New Class of Variable Stars Confirmed Astronomers using the Gemini Multi-Object Spectrograph (GMOS) on the Gemini South telescope have confirmed a new class of variable stars. Called Blue Large-Amplitude Pulsators (BLAPs), they are significantly bluer than main sequence stars of the same lumi- GeminiFocus nosity, demonstrating that they are relatively hot. Pawel Pietrukowicz (Warsaw University Observatory, Poland) led the Gemini study, following the team’s discovery of 14 candi- date stars as part of the Optical Gravitational Lensing Experiment (OGLE) — a variability sky survey conducted on the 1.3-meter War- saw Telescope at Las Campanas Observa- tory, Chile. The team’s GMOS spectra on three of the candidate BLAPs confirmed that these stars are “low-mass giants” with helium-rich at- mospheres and high surface temperatures of about 30,000 K, comparable with hot sub- dwarfs (Figure 1). The new pulsating stars vary with amplitudes of 0.2 – 0.4 magni- tude, which is exceptionally high, given their short periods of only 20 to 40 minutes. This excludes the possibility that they are hot oscillating subdwarfs, leading to the conclu- sion that BLAPs form a new class of variable stars. These characteristics have not been observed in any known hot pulsators. October 2017