GeminiFocus January 2018 - Page 24

which selected Band-1 programs are ex- tended for two full semesters after the con- clusion of their first, with a new rollover sys- tem, in which we allow all Band-1 programs to begin execution before their designated semester and continue executing through- out the entire semester after that. This proposal was discussed with the STAC, the data that led to it were described, and the STAC approved the proposal; their rec- ommendations can be seen on the Gem- ini website. It appears that the amount of time required to support this will be small enough that, at least initially, we will not topslice anything from the TAC process in a given semester. We will reassess after a year of operating this way. As with the formal rollover before it, this policy won ’t apply to Target of Opportunity programs, for which completion rate is not in our control, or for Large and Long Programs, limited-term partner programs, or programs using visit- ing instruments. Figure 1. A 19-arcsecond-wide field in globular cluster M15, imaged in half a minute with ‘Alopeke at 832 nm. The stacked raw frame (left) has seeing of approximately 1 arcsecond and significant elongation due to windshake. Point sources in the reconstructed image (right) have FWHM approximately 0.15 arcsecond. These commissioning data cover the central quarter of the `Alopeke field, but the technique should also be extensible to the full field. 22 ‘Alopeke Update ‘Alopeke (Hawaiian for “Fox”) arrived at Gemini North in October. It is a more so- phisticated variant of DSSI, the speckle camera which has been visiting Gemini since 2012. This new instrument occupies essentially the only spot on the telescope where it is possible to get light to it without disturbing other instrumentation — that is, in the small gap between the calibration GeminiFocus unit (GCAL) and the Instrument Support Structure (ISS). There’s not much room in there, but ‘Alopeke is small enough to fit. Therefore, although it’s a visiting instru- ment maintained and operated by a non- Gemini team, it is able to remain on the telescope at all times and thus offers much greater scheduling flexibility. ‘Alopeke has the usual speckle capabilities — two-color simultaneous speckle imaging over a 5 arcsecond field, significantly larg- er than was possible with DSSI, allowing diffraction-limited imaging in the visible — but now with a wide-field mode cover- ing 60 arcseconds with rapid (26 Hertz full- frame) readout. This, of course, enables fast, two-color photometry over the larger field- of-view and should be excellent for occulta- tion or high-speed photometry work. Interestingly, the early commissioning data show that the wider field may also be ame- nable to image reconstruction. The figure here shows a field in the globular cluster M15, taken in poor conditions (1 arcsecond seeing and very windy). Individual expo- sures were just 60 milliseconds with two sets of 500 images in each filter. Integrating all of the readouts produces, as expected, a blurry image consistent with the seeing, and with significant elongation due to wind- shake. From that rather uninspiring input, the team’s image reconstruction produces a remarkably sharp image, with 0.15 arcsec- ond point spread function. Strictly speak- January 2018