Gemini South Shutdown
Figure 4.
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 wavefrontsensor 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.
Gemini South was shut down for two working weeks from August 16-25, to carry out
annual maintenance on the Acquisition and
Guidance (A&G) unit and, specifically, to address issues with the Gemini Multi-Object
Spectrograph (GMOS) on-instrument wavefront sensor, which had become very noisy
and affected our ability to guide on faint stars.
— Andy Adamson and Michiel van der Hoeven
Figure 5.
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.
12
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.
GeminiFocus
For each photometric night on which GMOSS 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the range of right ascension and declination) drawn from the (unpublished) catalog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.
While this utility has been available via the
GMOS photometric standards page for some
time, it probably hasn’t received the atten-
October 2016