GeminiFocus 2013 Year in Review | Page 37

Figure 11. J104915.57 - 531906 in the WISE data. He then recovered the object in other earlier surveys to obtain a more accurate distance measurement. The outstanding question remained: “What is this object?” Director’s Discretionary Time enabled spectroscopy with the Gemini Multi-Object Spectrograph (GMOS) on Gemini South to provide an answer, and more. Luhman classified the object as an L8 dwarf, showing good agreement with a template spectrum. For ages less than 10 billion years, the temperature is well below that of the hydrogen burning limit. Also, considering the strong lithium absorption, Luhman concludes that the object is a brown dwarf. As an unexpected bonus, the acquisition image resolved the source into two components (Figure 11). The pair, separated by 1.5 arcseconds, corresponds to 3 astronomical units at the object’s determined distance. Examination of earlier, archival images does not show either source at their present location, arguing that they form a common binary system. The secondary is only about half a magnitude fainter than the primary, which suggests that it is also a brown dwarf and near the L/T spectral class transition. Brown dwarf models are sensitive to age, so a binary system offers robust tests of models and potentially strong constraints on mass, assuming the objects formed at the same time. The GMOS observations were obtained on February 23, 2013, and the full paper is published in The Astrophysical Journal, available at: http://arxiv.org/abs/1303.2401, as is more information from http://www.gemini.edu/node/11966. WISE J104915.57 - 531906 appears as a single object at the center of the larger image from WISE. The inset shows higherresolution observations using GMOS-South, which revealed its binary nature (inset) and enabled classification of the brown dwarf pair. Light Echoes Show the Asymmetric Explosion of SN1987A Observations of light echoes — reflections of a transient event in the surrounding material — allow astronomers to change perspective. Rather than being effectively fixed to a viewpoint on Earth, light echoes reveal the source object from a variety of viewing angles. Brendan Sinnott (McMaster University) and colleagues used light echoes from supernova 1987A (SN1987A) to conclude that this Type II event was asymmetric, with an elongated 56Ni structure. The strongest asymmetry they measure is in the Ha line, and this asymmetry aligns well with the observed axis of ejecta. The five fields the team observed with GMOS on Gemini South probe the supernova emission over its first 300 days. Figure 12 shows the prominent light echos, which appear as nearly circular rings, along with the slit positions on the GMOS fields. Variations in spectra obtained at different locations alone do not imply asymmetry in the supernova emission. The source spectrum itself changes, so the reflected light depends not only on the dust properties and its dis- January2014 2013 Year in Review GeminiFocus 35