GeminiFocus 2013 Year in Review | Page 30

properties from the higher-mass M dwarfs to the L class. They also confirm W1906+40 as a magnetically active brown dwarf, despite the attribution of variability observed in some L dwarfs due to atmospheric variations, such as changing cloud distributions. Complete results are in press in The Astrophysical Journal; a preprint is available at arXiv 1310.5940. Figure 2. NICI observation of HD 100546 in the Ks band, processed to reveal multiple southern spiral arms (left), which are modeled (colored lines overlaid, right). monitoring with Kepler shows a regular brightness variation at the 1 percent level with a period of 8.9 hours. The team models this variability as the presence of a single “spot” of lower-than-average luminosity that moves in and out of view as the dwarf rotates. They suggest that a magnetic starspot could provide such cooler material, although they also consider the possibility of clouds in the atmosphere (similar to Jupiter’s Great Red Spot), which could also produce the same effect. Given their spectral characteristics, which include broadening of emission lines and a bluer or hotter continuum, the strong flares observed with Gemini (Figure 1) also have a magnetic origin. In contrast to the quiescent characteristic temperature of 2300 K, the flare corresponds to a temperature of 8000 K. These results show a continuity of flare Figure 3. Zooming in to the star’s central 3 arcseconds shows a candidate planet to the south, which may be responsible for producing the spiral arms. (The spot marked to the north of the star is an artifact of processing). 28 Spiral Patterns in a Protoplanetary Disk Spiral patterns measured in a protoplanetary disk offer an exemplary study aimed at accounting for the full process of planet formation. Planets are expected to form in the remains surrounding the formation of a star, called a protoplanetary disk. The star HD 100546 is an excellent candidate for such a detailed investigation, being young (age 5–10 million years), and showing excess infrared emission, which is characteristic of a dusty—potentially planet-forming—disk. The disk, which extends from the central star to distances of 80 times that between the Earth and Sun, has previously been resolved and some of its spiral patterns identified. In new work using archival observations obtained with the Near-Infrared Coronographic Imager on the Gemini South telescope, Anthony Boccaletti (Observatoire de Paris, France) and collaborators show additional detail of the spiral patterns in HD 100546 and uncover hints of a planet that may be responsible for producing them. Special data processing techniques of angular differential imaging reveal the subtle details of the spirals in the near-infrared, resolving the southern feature into multiple arms, and provide contrast at the level of 10-5 to 10-6 at distances of 1 and 2 arcseconds from GeminiFocus 2013 Year in Review January2014