GeminiFocus April 2016 | Page 10

planet directly. It would need to be actively accreting material to be bright enough to detect easily in future GPI observations. The Gemini website has some more information, and complete results are published in The Astrophysical Journal Letters. Figure 2. Limits on separation and magnitude for a binary companion to one of the Y dwarfs Opitz and colleagues observed using GeMS/ GSAOI. An equalbrightness companion is ruled out to within about 0.5 AU (0.04 arcsecond), and fainter companions are ruled out at somewhat larger radii. Seeking Companions of the Coolest Brown Dwarfs Examples of the coolest and least massive brown dwarfs, Y dwarfs, were first identified in 2011. Having temperatures just above those of the gas giant planets (around 250 K), they help bridge the gap from stellar objects to planets. The binary nature of any of these objects is linked to their formation process. Previous observations indicate that the frequency of multiplicity declines from around 65% (for solar-type stars) to 10–30% (for the slightly warmer and more massive L and T dwarfs). Does this trend continue to the Y dwarfs, or does it indicate only our observational limits? Also, some Y dwarfs show a spread of luminosity or otherwise seem overluminous. Are undetected companions the explanation? Daniela Opitz (University of New South Wales, Australia) and colleagues used the fine spatial resolution of the Gemini Multi-conjugate adaptive optics System (GeMS) and the Gemini South Adaptive Optics Imager (GSAOI) to begin to answer these questions, examining 8 GeminiFocus a small sample of five Y dwarfs. The delivered Full-Width at Half-Maximum was ~0.1arcsecond and the limiting angular separation was around 0.04 arcsecond. Although the observations were sufficiently sensitive to detect companions of roughly equal mass at separations of 0.5–1.9 astronomical units (AU), they did not find any evidence for binaries. Figure 2 shows the limits on separation and brightness for a binary companion to one of the Y dwarfs studied. At least one of the sources had previously been identified as “overluminous.” The presence of clouds in the atmosphere, rather than a companion, may account for the excess luminosity. The few cases observed here are a good start, not a definitive determination of the general trends. They do point to the extreme scenarios (separations less than 1 AU and extremely faint sources) that may arise in cases of Y dwarf binaries. This work is featured on the Gemini website, and complete results appear in The Astrophysical Journal. A Supermassive Black Hole That Wasn’t So Massive One sign of an extreme supermassive black hole at a galaxy’s core is a light deficit — the consequence of stars ejected from the central region. The brightest cluster galaxy of Abell 85 had been identified as such an example, claimed to host one of the most massive black holes ever detected in the Universe at around 1011 MSun. Juan Madrid, then a Science Fellow at Gemini South, along with Carlos Donzelli (Observatorio Astronómico de Córdoba, Argentina), used images obtained with the Gemini Multi-Object Spectrograph (GMOS) on Gemini South (Figure 3) to probe the galaxy’s center and demonstrate that the black hole’s mass is not so extreme. Rather than a deficit, data from their Director’s Discretionary Time program show the strong nuclear emission in the cen- April 2016