GeminiFocus January 2019 | Page 13

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.] 11