VizieR Online Data Catalog: Outer Solar System Origins Survey (OSSOS). I. (Bannister+, 2016)

The Outer Solar System Origins Survey (OSSOS) observations are acquired in blocks: contiguous patches of sky formed by a layout of adjoining multiple 0.90deg² MegaCam fields.

The OSSOS discovery and tracking program uses the Canada-France-Hawaii Telescope (CFHT) MegaPrime/MegaCam. In 2013 and 2014, the MegaPrime/MegaCam focal plane was populated by thirty-six 4612*2048 pixel CCDs in a 4 by 9 arrangement, with a 0.96°*0.94° unvignetted Field Of View (FOV) (0.90deg²) and 0.05'' Full Width at Half Maximum (FWHM) Image Quality (IQ) variation between center and edge. The plate scale is 0.184'' per pixel, which is well suited for sampling the 0.7'' median seeing at Maunakea. We observed our 2013 discovery fields in MegaCam's r.MP9601 filter (564-685nm at 50% transmission; 81.4% mean transmission) which is similar to the Sloan Digital Sky Survey (SDSS) r' filter. Our integration length was set at 287s. This exposure length achieves a target depth of m_r=24.5 in a single frame in 0.7'' median CFHT seeing. MegaPrime/MegaCam operates exclusively as a dark-time queue-mode instrument for CFHT. The OSSOS project thus has between 10 and 14 potentially observable nights each month, weather considerations aside. Through CFHT's flexible queue-schedule system we requested our observations be made in possibly non-photometric conditions (discussed in Section 3.5) with 0.6''-0.8'' seeing and <0.1mag extinction for discovery, and requested image quality of 0.8''-1.0'' seeing for follow-up observations. Images were taken entirely with sidereal guiding and above airmass 1.5. This aided the quality of the astrometric solution and the point-spread function, and retained image depth: median extinction on Maunakea is 0.10mag per airmass in this passband.

This paper covers OSSOS blocks that had their discovery observations in 2013A (2013 is the year that the discovery observations were successfully made, and A indicates the half-year semester of discovery opposition; A for Northern spring). Forthcoming papers will cover the subsequent discovery observations. The 2013A blocks were 13AE, centered at R.A. 14^h20^m, decl. -12°52' at discovery, spanning ecliptic latitude range b=0°-3°, and 13AO, centered at R.A. 15^h57^m, decl. -12°30' at discovery, spanning ecliptic latitude range b=6°-9°. The sky locations of the 13A blocks are at 44° and 30° galactic latitude. The 13AE discovery triplets were taken under some minor (<0.04mag) extinction and with IQ that ranged from 0.65'' to 0.84''. The 13AO discovery triplets exhibited no extinction and IQ that ranged from 0.49'' to 0.74''. Subsequent imaging to track the discoveries was acquired through 2013 August. Not all discoveries were observed in every lunation due to objects falling in chip gaps or on background sources on some dates, faint magnitudes, or variable seeing in the recovery observations. In much of 2013, poor weather conditions prevented observations in sufficient IQ for us to recover the faintest objects. To compensate, from 2013 November onward we used alternative 387s exposures in 0.8+/-0.1'' seeing for single-image passes on the block. For the seven February-August lunations that the blocks were visible in 2014, the 13AE and 13AO discoveries brighter than the characterization limit (Section 5) were observed with pointed recoveries; this was possible because the high-frequency cadence in the discovery year shrank the ephemeris uncertainty to a tiny fraction of the MegaPrime FOV. A handful of fainter objects not immediately recovered in the first pointed recovery images were targeted with spaced triplets of observations in subsequent lunations until recovery was successful on all of them (Section 6.1). Generally, two observations per object per lunation were made.

(2 data files).