Figure 5.
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.
Credit: Gemini
Observatory/AURA/NSF
hot subdwarfs (Figure 5). The new pulsating
stars vary with amplitudes of 0.2 – 0.4 mag-
nitude, 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
conclusion that BLAPs form a new class of
variable stars. These characteristics have not
been observed in any known hot pulsators.
The very small number of BLAPs known so
far points to a rare, unexplored episode in
stellar evolution. This work is published in
the journal Nature Astronomy, and is avail-
able online (subscription required). The ar-
ticle is also on astro-ph.
The Little Star That Could …
Survive a Supernova Explosion
Astronomers have identified a white dwarf
star in our solar neighborhood moving fast-
er than the escape velocity of the Milky Way.
The international team, led by Stephane
Vennes (Astronomical Institute in the Czech
Republic), used telescopes in Arizona and
the Canary Islands, as well as the GRACES
(Gemini Remote Access to CFHT ESPaDOnS)
42
GeminiFocus
spectrograph atop Maunakea to study this
celestial speedster, which is thought to have
been expelled like shrapnel from a peculiar
Type Ia supernova explosion some 50 mil-
lion years ago.
The speedy white dwarf, known as LP40-365,
was first identified with the National Science
Foundation’s (NSF) Mayall 4-meter telescope
at Kitt Peak National Observatory in Arizona.
Over the next two years, the discovery team
received critical follow-up observations from
the Canary Islands and Maunakea, which
they analyzed using state-of-the-art com-
puter codes. The analysis proved the star’s
compact nature and exotic chemical com-
position, as well as its extraordinary Galactic
trajectory, which puts it on a path out of the
Milky Way with no return.
Astronomers once thought that nothing sur-
vives a Type Ia supernova, which occurs in a
binary system that includes a white dwarf.
However, a new class of models called “Sub-
luminous type Ia Supernova” (also known as
type Iax) can leave a partially burned rem-
nant that is instantly ejected at high velocity.
LP40-365 is the first observational evidence
that such high-velocity remnants of failed
January 2018 / 2017 Year in Review