Figure 4.
The relative position of
the companion object
PDS 70b. The blue points
show the measured
positions from the
Gemini and VLT data.
The red points (labeled
“BG”) show the positions
that would have been
expected in the VLT data
if the object detected
in the first-epoch NICI
observations had been
a distant background
object, for which the
relative position would
follow the plotted curve.
The offset in position
between the NICI and
later observations is con-
sistent with the expected
orbital motion.
[Figure from Keppler
et al., A&A, 617: A44,
2018.]
derived from the VLT observations taken in
2015 and 2016 (Figure 4). This is likely due
to orbital motion over the four-year baseline
spanned by the Gemini and VLT observa-
tions analyzed in the discovery paper. The
inferred orbital motion is clockwise, which is
in the same direction as the disk rotates. A
second study adds an additional SPHERE ob-
servation from early 2018 and finds a best-fit
circular orbit with a period of 118 years.
The multi-band photometric analysis com-
bining the VLT and Gemini data indicates
that PDS 70b is likely a gas giant with a
mass a few times that of Jupiter and a
temperature of about 1,200 K. Additional
observations of PDS 70b should allow test-
ing of theoretical predictions of the role of
planet-disk interactions in the evolution of
young planetary systems.
OCTOBER 2018
Fast Outflows in the Echoes of
Eta Carinae’s Great Eruption
Students of the history of solar astronomy
and telecommunications will be familiar
with the Carrington Event, named for the
English astronomer Richard Carrington who
witnessed a brilliant solar flare erupt from a
cluster of sunspots one September morn-
ing in 1859. The flare was associated with
the largest coronal mass ejection on record,
which traveled at a speed of about 2,000 ki-
lometers per second (km/s) and reached the
Earth less than 18 hours later. Although the
explosion on the Sun’s surface lasted only
about a minute and involved a negligible
fraction of an Earth mass of material, the
blast of charged particles impinging on the
Earth’s magnetosphere wreaked havoc with
telegraph lines across Europe and North
America and produced stunning auroral dis-
plays visible even in the tropics.
Around the same time, stellar astronomers
were witnessing the final stages of a far
more energetic and sustained eruption by
the southern star Eta Carinae (then known
as Eta Argus). Formerly a 4th-magnitude
object, Eta Car brightened to 1st magni-
tude in the late 1820s and underwent a
series of luminosity spikes during which it
occasionally rivaled Canopus, a convenient
comparison star located in the same con-
stellation. The star then entered a plateau
phase when it stayed above 0th magnitude
from 1843 to 1858, before rapidly fading
below naked-eye visibility in the 1860s. The
extended period from the 1830s through
the 1850s is called the Great Eruption.
Eta Car is now known to be a binary star
with an orbital period of 5.5 years, a dis-
tance of 2.3 kiloparsecs (kpc), and a com-
bined mass of at least 250 solar masses.
The pre-1845 luminosity spikes appear to
coincide with periastra of the binary orbit
26
GeminiFocus
January 2019 / 2018 Year in Review