never wanders more than 0.13 kpc from the
Galactic plane. This makes the binary the
most metal-poor star system yet discovered
within the thin disk. Moreover, the study es-
timates that the age of the system exceeds
13 billion years, which would suggest that
the thin disk may be considerably older
than generally believed. However, the age
is based on isochrone fitting to the primary
star and is subject to systematic uncertainty.
In addition to setting astronomical records,
2MASS J18082002–5104378 B is a diminu-
tive star with big implications. The study
argues that the existence of this low-mass
object, as well as a known brown dwarf
within an EMP system, implies that low-mass
primordial-composition stars could form
as members of binaries via fragmentation
within the protostellar disks of the supposed
high-mass Pop III stars. If this is the case, al-
though the primary stars would have long
since burnt themselves out, the liberated
low-mass Pop III secondaries could still be
wandering inconspicuously about our Gal-
axy, just waiting to be discovered.
Gemini’s Role in the Discovery
of the Young Planet PDS 70b
This past July as Gemini Observatory was
preparing for its triennial Science Meeting,
our colleagues at the European Southern
Observatory (ESO) announced the discov-
ery of a planet caught in the act of forma-
tion within the transition disk (a debris disk
with a central gap) surrounding the young
low-mass star PDS 70. The star was targeted
because it was known from previously pub-
January 2019
lished Gemini and Subaru observations to
host a transition disk with a large central
gap, suggestive of ongoing planet forma-
tion. PDS 70 belongs to the Scorpius-Cen-
taurus association at a distance of 113 par-
secs (determined from Gaia Data Release 2).
It has an estimated age of 5.4 million years
and a mass of about 0.8 M B . The discovery,
based on observations obtained at the Very
Large Telescope (VLT) and Gemini South,
was published in the September 2018 issue
of Astronomy & Astrophysics.
This is the first time that a young planet
has been caught in the act of plowing out
the central region of a transition disk. “Disks
around young stars are the birthplaces of
planets, but so far only a handful of obser-
vations have detected hints of baby planets
in them,” said Miriam Keppler of the Max
Planck Institute for Astronomy. Keppler led
the large team of over 100 astronomers who
made the discovery. Using the Spectro-Po-
larimetric High-contrast Exoplanet REsearch
instrument (SPHERE) on the VLT, the team
detected a point source about 22 astronomi-
cal units from PDS 70 within the gap of the
surrounding disk. The detection was con-
firmed at five different epochs using three
different instruments at wavelengths rang-
ing from 1.6-3.8 μm (Figure 3). The astrome-
try from the multiple epochs shows that the
object has a very similar motion to that of
PDS 70, and thus is likely a bound planetary
companion.
The crucial first epoch was provided by an
archival L’-band image taken in March 2012
with the Near-Infrared Coronagraphic Im-
ager (NICI) on Gemini South. Although the
GeminiFocus
Figure 3.
Direct images of the
exoplanet PDS 70b, from
left to right: Gemini/NICI
L’-band (2012-03-31),
VLT/SPHERE H2H3-band
(2015-05-03 and 2015-
05-31), VLT/SPHERE
K1K2-band (2016-05-14),
and VLT/NACO L’-band
(2016-06-01). North is up
and east is to the left in
all images.
[Figure from Keppler et
al., A&A, 617: A44, 2018.]
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