GeminiFocus April 2017 | Page 16

and pollution,” he says. “The brown dwarf was effectively hidden by the dust until we looked with the right instrument. But when we observed SDSS 1557 in detail, we recog- nized the brown dwarf’s subtle gravitation- al pull on the white dwarf.” From the Gemini data the team estimated that the white dwarf has a surface tempera- ture of 21,800 Kelvin (about 3.5 times hot- ter than the Sun) and a mass of ~0.4 solar masses; the brown dwarf companion has a mass of ~0.063 solar masses. The research is published in the February 27th online issue of Nature Astronomy. See the University College London press re- lease here. β Pictoris b: an Exoplanet with the Atmosphere of a Brown Dwarf Figure 3. Using advanced imaging techniques and the special capabilities of the Gemini Planet Imager (GPI), the light from β Pictoris has been suppressed in these images using GPI’s Y, J, H, K1, and K2 filters. The arrow indicates the location of the exoplanet β Pictoris b in in all but the left image. 14 A team of astronomers led by Jeffrey Chil- cote (University of Toronto) uses the Gemi- ni Planet Imager (GPI) at the Gemini South telescope in Chile to refine our understand- ing of the β Pictoris system. The system contains the ~ 13 Jupiter mass companion β Pictoris b, which is at the mass boundary sometimes used to distinguish between an exoplanet and a brown dwarf. Brown dwarfs are objects that are not massive enough for sustained nuclear reactions; and brown dwarfs less massive than 13 Jupiters cannot even start a nuclear reaction. GeminiFocus Based on the GPI data, combined with planetary evolution and atmospheric mod- els, Chilcote suggests a “hot-start” planet formation scenario for β Pictoris b, which has a surface temperature of about 1,724 K. He adds, “This is consistent with the disk instability formation mechanism for wide- orbit giant exoplanets.” However, the char- acteristics for the atmosphere of β Pictoris b found in this work best matches that of a low-surface-gravity (L2±1) brown dwarf, not a planet. The team studied β Pictoris b during the ver- ification and commissioning of the Gemini Planet Imager, and as part of an astrometric (position) monitoring program designed to constrain the orbit of the exoplanet (Figure 3). This work is also part of a Gemini Large and Long program. “With GPI, the Gemini Observatory is at the forefront of exoplanet exploration,” says Chilcote. He adds, “Direct imaging allows for the discovery of planets on solar-sys- tems-scale orbits, provides new insight into the formation and characteristics of extra- solar systems, and enables direct spectro- scopic observations of their atmospheres.” The full results are accepted for publication in The Astrophysical Journal Letters. A pre- print is available here. Peter Michaud is the Public Information Out- reach Manager of Gemini Observatory. He can be reached at: [email protected] April 2017