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