GeminiFocus 2016 Year in Review | Page 30

April 2016
Figure 14 .
Radially scaled polarized intensity in the J-band shows the variation of dust density distribution in the disk of TW Hydrae .
The coronagraph blocks light in the central region . Comparison with simulations suggests that the gap around 23 AU could be cleared by a planet of mass about 0.2 M Jupiter
.
Figure 15 . 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 .
April 2016
Traces of Planet Formation in a Stellar Disk
Planets form in the disks around young stars , and the relatively nearby TW Hydrae is an excellent candidate in which to observe this process . In polarimetric observations with the Gemini Planet Imager ( GPI ) on the Gemini South telescope , Valerie Rapson ( Rochester Institute of Technology , New York ) and collaborators probe the disk of TW Hya — from about 80 astronomical units ( AU ) to within 10 AU of the central star —
at a resolution of about 1.5 AU and detect structure . The observations show a gap located around 23 AU that is about 5 AU wide , suggesting the presence of a forming planet ( Figure 14 ).
The researchers deduce the properties of the possible ( proto ) planet comparing with simulations . They find good agreement with a planet of mass 0.16 M Jupiter located at 21 AU from the star , about the distance of Uranus from the Sun . Details of the differences between the model and observations suggest that more complex distributions of dust in the disk ( radially and vertically ) may be relevant .
The authors acknowledge other processes that can create gaps and rings , such as grain fragmentation and ice condensation fronts . A definitive test would be to observe the 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 .
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 ?
28 GeminiFocus January 2017 | 2016 Year in Review