Contributions by Gemini staff
News for Users
Figure 1.
Comparison of estimated
sky coverage for LGS+P1
(red) compared with
conventional LGS (black).
Note that sky coverage
refers to the percentage
of sky with guide stars
above elevation 40˚ at
Gemini North.
Many users are unaware of Gemini North’s powerful “Super Seeing”
capability, so this topic leads this edition of News for Users. Other
news includes an unscheduled shutdown at Gemini North to repair
serious issues with the lower shutter (while accomplishing the goals
of a subsequent planned shutdown), a scheduled shutdown that
went as planned at Gemini South, student work on GMOS standard
star field charts, and the release of Disco-Stu — a software package
designed to help with the analysis of images taken with the Gemini
South Adaptive Optics Imager.
The “Super Seeing” (LGS+P1) Mode
In 2012, Gemini commissioned a new observing mode for ALTAIR’s Laser Guide Star system (known as LGS + P1), which added
the option of using a peripheral wavefront sensor (PWFS1 or P1)
for the Natural Guide Star tip-tilt focus measurement. This mode
does not provide diffraction-limited resolution, but instead gives
“Super Seeing” by reducing the natural seeing point spread function Full-Width at Half-Maximum (PSF FWHM) by a factor of 2-3.
The major benefit of this seeing-improver mode is that it increases the LGS sky coverage to almost 100%. While the limiting magnitude of P1 is R = ~ 14 (less than the R = < 17 magnitude for the
conventional LGS mode), this is more than offset by P1’s much
larger patrol field. Figure X shows the predicted sky coverage as
a function of galactic latitude for the LGS + P1 configuration (red)
compared with the conventional LGS mode (black).
Currently, LGS + P1 has been commissioned with the Near-InfraRed Imager and spectrometer (NIRI) and Near-infrared Integral
10
GeminiFocus
October 2016