Further Progress on the SALT 11- meter telescope and the Prime Focus Imaging Spectrograph

Eric B. Burgh

SALT/PFIS Instrument Scientist

The Southern African Large Telescope

SALT is based on the Hobby-Eberly Telescope (HET)

•11 m segmented spherical primary

•Fixed altitude design

•Prime focus instrument package

9.8 meters(32.2 feet)

11.1 meters(36.4 feet)

• 11-meter diameter primary mirror constructed from 91 individual 1-meter hexagonal, spherical mirrors

Shack-Hartmann wavefront sensor

Course alignment with 91 element lenslet arrayFine alignment with 7 x 91 lenslet array• capture range ± 3 arcsec • can measure low-order Zernike terms for individual segments

- diagnose mount errors

PFIS

SAC

Rotation Stage and Cable Wrap

The Prime Focus Imaging Spectrograph

• First generation, all purpose spectrograph for SALT

• Optical Imaging 320 – 900 nm.

• All-refractive collimator and camera utilizing crystals for UV throughput

• Upgrade capability for infrared camera

• Optics:

– Fused Silica, CaF2 and NaCl

• Optomechanics

– All optics currently being mounted by The Pilot Group

The Prime Focus Imaging Spectrograph

Open Truss Structure

Grating Server

Articulation Rail

Camera Tube

Detector Dewar

Filter Server

Collimator Optics

Slit Mask Server

Fabry Perot Etalons

Waveplate Mechanism

• Open Truss structure• Welded Hollow Invar Box Beam

(Rutgers Machine Shop)

• Mass = 112 kg

PFIS Mechanisms

The Prime Focus Imaging Spectrograph

Niche Science

• Ultraviolet Spectroscopy

– to the atmospheric limit (~320 nm)

• Spectropolarimetry

• Fabry-Perot Spectroscopy

• High-time-resolution spectroscopy– 0.1 – 100 sec

• Volume Phase Holographic (VPH) Gratings

– High throughput, low scatter

– Tunable efficiency

} Rare on large telescopes

The Prime Focus Imaging SpectrographMulti-object Spectroscopy

• Laser-cut slit masks

• Unique mask cut for each individual observation

• Slit Server will hold 30 multi-object slit masks

• Studies of multiple objects in field of view

• Best utilizes CCD real estate• E.g. Chemical abundances and

kinematics of Planetary Nebulae in NGC 1399

The Prime Focus Imaging Spectrograph

Technical Challenges• Prime Focus:

– Weight/space constraints– Accessibility

• Wavelength coverage:– Crystals (CaF2 and NaCl)– Anti-reflection coatings (0.5% reflections)– High UV Quantum Efficiency CCDs (Marconi)

• VPH gratings:– Articulating Camera

• Multiple configurations:– Complex mechanisms/interfaces

} Similar to spaceflight instrumentation

The Prime Focus Imaging Spectrograph

Current Status

• All optics fabricated, coated, and being mounted now – delivery in two weeks.

• Most mechanisms built and tested:– Slitmask, Waveplate, Grating, Filter, Articulation, Etalon,

Focus, Beamsplitter

• Structure fabricated and heat treated, still needs machining and painting – delivery in a few weeks.

• Detector CCDs mosaiced and on-sky tests now – delivery in mid-May.

The Prime Focus Imaging Spectrograph

Upcoming Schedule:

• Assembly and alignment to begin upon arrival of structure and optics – lasts 3 months.

• Testing and calibration – lasts 3 months. • Shipping to South Africa in November 2004• Installation and commissioning – lasts 6 months