salt technology development lisa crause india-south africa astronomy workshop – saao 6 august 2012
TRANSCRIPT
SALT Image Quality
Large focus gradient, bifurcated stars seen in out of focus images, all seemed to be randomly
variable as well
Traced to problematic
interface ring transmitting
forces into the corrector &
disrupting the 4 SAC mirrors
The SAC Fix
Brought SAC down Replaced interface
with a pair of collars Developed Clean Room
Washed M5 & M3
SAC Alignment & Testing
Optically aligned & tested the mirrorsChecked system
performance at angle & over temp range
Re-installed SAC
On-Sky Testing
Used a bare CCD on an XY stage to tile the focal plane &
check the post-fix performance (also for direct comparison with
images taken before the fix)
SALTICAM was re-installed after its upgrade & it too
produced beautiful, uniform images over the full 10
arcmin field
Inductive Edge Sensors• Capacitive edge sensors were unsuitable
due to their sensitivity to humidity & dust• Contract signed with Fogale Nanotech in June
2012 for their inductive edge sensors• Excellent results obtained: insensitive to
humidity & consistent behaviour with temperature changes
• Maximum deviation of 30 nm over 5 days
• To be installed in situ & phased in, starting with the central 7 segments
Inductive Edge Sensors• 12 sensors/segment, each mounted to a
Clearceram L-bracket for a 3.5 mm gap• Primary mirror alignment should hold for
at least 5 days, longer if ΔT <20 C • Expect a substantial increase in
observing efficiency due to the alignment time saved & better overall IQ
• Full installation to take ~2 years
• Pathfinder for ELTs
Robert Stobie Spectrograph (RSS)
• Various problems with optics, mostly due to troublesome lens fluid
• Major overhaul of all mechanisms by SALT while the optics were being repaired
• Latest throughput issue traced to the collimator optics
• Keen to tackle the repair/replacement ourselves this time
RSS Near Infrared Arm• Being built by the University of Wisconsin• NIR to have most of RSS-Vis
functionality, but will operate from 0.8 to 1.7 microns
• Semi-warm design is an economical way to extend optical instruments into the near infrared
• Pre-dewar part kept @ -40 C & & dewar @ 120 K
RSS Near Infrared Arm• RSS spectroscopy from the atmospheric
cut-off (320 nm) to the H-band, in 1 shot!• Tracker weight budget is already being
exceeded so will need to upgrade its load capacity to make provision for NIR
• Tracker upgrade project is funded & will be carried out by SALT & SAAO staff
• Timescale: late 2014?
High Resolution Spectrograph• SALT HRS: fibre-fed echelle
spectrograph under construction at Durham’s Centre for Advanced Instrumentation
• Commissioning due to start towards the end of this year
• Blue & red beams to cover 370-555 nm & 555-890 nm
• λ/Δλ from 16000 to 67000 via 4 different modes
High Resolution Spectrograph• Pair of object & sky fibres for each
mode• Optics to be housed in a vacuum tank
& the whole instrument will be sealed in a thermally stabilised enclosure in the spectrometer room below the telescope
• Payload Fibre Instrument Feed for HRS designed & built at the SAAO