14 August 2014 sky & telescopeNews Notes
... Sun’s Newfound Chilly Neighbor
The Stingray Nebula, seen in this Hubble image, is the youngest known planetary nebula. Astrono-
mers think they’ve detected the central star passing through a transitional upheaval in its evolution.Infrared observations have uncovered
a cool brown dwarf that’s only about
7.2 light-years away. The object, WISE
J085510.83−071442.5, is the fourth-closest
stellar system to the Sun and the coolest
brown dwarf yet discovered.
Kevin Luhman (Penn State Univer-
sity) found WISE J0855−0714 using data
from NASA’s Wide-fi eld Infrared Survey
Explorer (WISE) and Spitzer Space Tele-
scope, as part of his ongoing search for
cool, nearby brown dwarfs. The object is
special for a few reasons.
First, at 7.2 light-years away (6.5 to 8
is the error range), it’s farther only than
the Alpha Centauri triple system (4.
light-years for Proxima and 4.3 light-years
for Alpha Cen AB), Barnard’s Star (5.
light-years), and the brown dwarf binary
WISE J1049−5319 known as Luhman 16(6.6 light-years; S&T: July 2013, p. 12). It
displaces Wolf 359, which lies 7.8 light-
years away.
Second, it’s moving fast. Part of that
movement is its high parallax, which
shows that WISE J0855−0714 is close toOort Cloud
(approximate
Sun outer edge)12345678Alpha
Centauri
systemBarnard’s
StarWISE
J1049–
5319WISE
J0855–
0714Wolf
359Distance from Sun (light-years)
This diagram illustrates the distances of the fi ve star systems closest to the Sun, with the newest
fi nd (WISE J0855−0714) bumping Wolf 359 to fi fth place. Two of the fi ve systems contain solely
brown dwarfs.
S&T: LEAH TISCIONEMATT BOBROWSKY / OSC / NASA
STELLAR I Helium-shell Flash in Action and...
The odd behavior of a star in the heart of
the Stingray Nebula (Henize 3–1357) pro-
vides tantalizing evidence that we might
be seeing an abrupt acceleration of nuclear
burning near the end of a star’s life.
This phase, called the helium-shell fl ash,
occurs after a low-mass star has fi nished
fusing its core hydrogen into helium.
Fusion continues in a surrounding layer of
hydrogen, raining down helium onto the
core. Eventually, the pressure and tempera-
ture build up enough to suddenly ignite
helium-shell fusion in the so-called fl ash.
This then leads to a thermal pulse during
which the star expands and brightens for a
short period of time.
Astronomers think that is what’s hap-
pening to SAO 244567, the star nestled
inside the Stingray. The Stingray is a young
planetary nebula in the southern constel-
lation Ara and was created when the aging
star blew off its outer layers. It’s only 0.
light-year across — one-tenth the size of
most known planetary nebulae and roughly
130 times larger than the average distancethe Sun. But the object’s parallax is small
compared with its proper motion: the
object traverses 8.1 arcseconds per year,
the third largest proper motion of any
object outside the solar system (trailing
only Barnard’s Star and Kapteyn’s Star).
In comparison, most of the brightest stars
have a proper motion of a few tenths of anSolar Neighborhood