GMOS-S Photometric Standard Utilities
Have you ever received images of standard star fields from the Gemini Multi-Object Spectrograph at Gemini South ( GMOS-S ) and struggled to work out which stars are the actual flux standards ? Now , help is at hand , thanks to the Australian National Gemini Office and students from Macquarie University in Sydney .
For each photometric night on which GMOS-S imaging data are taken , the Gemini South queue observer also observes at least one standard star field . These standard star fields are taken from a list of 45 fields ( covering the range of right ascension and declination ) drawn from the ( unpublished ) catalog of J . Allyn Smith et al .’ s Southern Hemisphere u ’ g ’ r ’ i ’ z ’ Standard Stars . However , the task of identifying which stars from this catalog are within the GMOS field-of-view has , until now , been tedious .
Fortunately , Macquarie University operates a unique program known as PACE ( Professional And Community Engagement ), which offers opportunities for their undergraduate students to make long-lasting contributions to the community , while integrating practical experience into their degree . In 2014 PACE students Corine Brown and Dylan Harrison — under the supervision of the International Telescopes Support Office ( ITSO ) staff Stuart Ryder and Richard McDermid — conducted a project to construct finding charts for all 45 fields using the Gemini Observing Tool ( OT ), complete with magnitudes for each standard star present in the GMOS field-of-view .
The finders are available ( view here ), which give for each field an OT view of the field ( clickable for higher resolution ) and tables of magnitudes for each standard star ( Figure 10 ).
While this utility has been available via the GMOS photometric standards page for some time , it probably hasn ’ t received the attention it deserves . In due course , efforts such as the SkyMapper Southern Sky Survey and its shallow photometric survey should make deriving photometric zero-points
Figure 8 . Alejandro Gutierrez and Hector Swett ( Senior Electronics Technician and Electronics Engineer , respectively ) work on one layer of the A & G unit ’ s “ cake ” during the Gemini South shutdown .
Figure 9 . GMOS-S on-instrument wavefront sensor images from before ( left ) and after ( right ) the Gemini South shutdown . Each frame shows the image of a star from the four wavefront-sensor subapertures . The image at right was taken in very poor seeing , but the difference in quality of readout is clear . The “ noise ” in the worst parts of the “ before ” image is 150 analog-to-digital units ( ADU ) or more , although it was the systematic pattern which really caused problems with guiding . Now we consistently see only 10 - 12 ADU of truly random noise .
Figure 10 . Finding chart for the GMOS-S standard star field NGC 458-AB , a star cluster in the Small Magellanic Cloud , based on the OT Position Editor display .
January 2017 | 2016 Year in Review GeminiFocus
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