GeminiFocus 2016 Year in Review | Page 38

July 2016
Figure 11 . A color mosaic of a region of the Pyxis globular cluster , produced from HST F606W and F814W images and a stack of GSAOI H-band frames . Disco-Stu was provided with one of the HST images and a source catalog constructed from that image ( culled of faint sources and objects outside the GSAOI fieldof-view ) but no further guidance was required .
Figure 12 . Gemini South ’ s shutters remained closed for most of May 2016 , due to persistent poor weather .
Image credit : Sandra Romero , Gemini from separate standard star observations redundant ( as every GMOS field will contain multiple sources with catalogued u ’, g ’, r ’, i ’ and z ’ magnitudes ), but in the interim we trust that the community will find this a useful resource .
Disco-Stu — GSAOI Image Reduction Simplified
Gemini has announced the release of a new standalone software package . Called Disco- Stu ( DIStortion COrrection and STacking Utility ), it is designed to help with the analysis of images taken with the Gemini South Adaptive Optics Imager ( GSAOI ). Disco-Stu takes images that have been reduced with the Gemini Image Reduction and Analysis Facility package for GSAOI and aligns them by matching sources with the aid of a lookup table that maps the instrument ’ s static distortion . Stacking is then performed with bad pixel rejection and , if desired , inverse-variance weighting . The astrometry can be tied to an external source catalog , and the output image can be made to share the world coordinate system of another image . Performing both these steps results in an image that is perfectly aligned with an existing image , either taken with a different instrument , or with GSAOI at a different epoch ( Figure 11 ).
Disco-Stu is written in Python and requires the NumPy and AstroPy packages ( which are part of the Ureka release ). SExtractor is also required for normal operation , although source catalogs can be prepared separately .
— Chris Simpson
July 2016
A Month to Forget
May 2016 may have been the worst month ever for weather at Gemini South on Cerro Pachón in Chile . In an average year , May is the first of five “ bad ” months , with weather loss usually on the order of 30 % ( see chart on page 41 ). By contrast , in May 2016 , we had 16 nights during which we observed nothing at all , and a further seven during which we observed for less than three hours ; in fact , weather interrupted observations every night to some degree during this period .
An extended and unusually poor weather period started in April and lasted well into June , with mainly high clouds as seen in Figure 12 ( but resulting in surprisingly little precipitation ). This could be an effect of the strong El Niño event that is gradually ending . Given that , on average , weather losses on Cerro Pachón peak in June and July , we can only hope that 2016 isn ’ t “ average ,” and that we will have better observing conditions in the following months . Obviously , the impact on observations has been significant . Bad weather wiped out most of the Phoenix visiting instrument run and greatly hindered
36 GeminiFocus January 2017 | 2016 Year in Review