GeminiFocus July 2013 | Page 16

compared to other AO systems: in one shot, the area of sky covered is 10- to 20-times larger than any previous AO system. This makes Gemini’s 8-meter telescope 10- to 20-times more efficient, giving astronomers the option to expose deeper, or explore more effectively with a wider range of filters. Globular Cluster NGC 1851: Going Fainter Another critical SV target was NGC 1851, a globular cluster located about 40,000 lightyears from our Sun (see Figure 3). Such a tightly packed city of starlight is a workhorse science case for MCAO; the AO corrections “deblend” multiple systems in crowded fields, allowing astronomers to access the cluster’s fainter stars, which are crucial in studies of star formation in these different environments. Figure 3. The globular star cluster NGC 1851 as imaged with GeMS/ GSAOI during System Verification we now see; the wakes shine like tracers due to the bullets piercing and heating the molecular hydrogen gas in the Orion Nebula. By comparing high-angular-resolution images of this region over several years (including observations at Gemini North with the Altair AO system obtained in 2006), the team, headed by John Bally and Adam Ginsburg (both of the University of Colorado), can actually measure a bullet’s motion. By mapping the proper motions of each, they can build a complete 3D dynamical model of the region. A single-pointing version of this new image also made headlines at the January 2013 meeting of the American Astronomical Society (held in Long Beach, California) and was featured in a press conference at the meeting. This remarkable image also illustrates the revolution brought by MCAO. The final mosaic, made by three GeMS/GSAOI pointings, covers a field-of-view measuring almost 4 x 3 arcminutes, resulting in one of the biggest AO-corrected images ever obtained. This is the main advantage of MCAO when 16 GeminiFocus Moreover, by delivering a uniform performance over fields that encompass most globular star cluster sizes, MCAO greatly improves the photometric precision on these crowded fields. By studying the MCAO observations of NGC 1851, Alan McConnachie from the National Research Council’s Herzberg Institute of Astrophysics and colleagues intend to precisely derive the different star populations that make up this cluster. By observing NGC 1851 over time, the team also expects to retrieve the cluster’s orbit within our Galaxy. In that case, GeMS/ GSAOI is also a perfect complement to the Hubble Space Telescope (HST): the image quality provided by the GeMS system in the NIR is very similar to that delivered by HST in visible light, which opens the possibility of combining these complementary data sets. Galaxy Cluster Abell 780: Better Sky Coverage to Go Deep The third SV target was Abell 780, a cluster of galaxies located at z = ~ 0.05 (see Figure 4). In July2013