The GHOST project commissioning has begun, with the Canadian and Australian teams able to travel to the summit following the easing of COVID-19 related restrictions. Optical bench assembly has begun, with alignment tests scheduled for late April. Twilight tests are to take place in mid-May. On-sky science commissioning is planned to take place in mid-late June, 2022.
The GHOST project continues to be on hold due to the pandemic and we do not expect to start the re-assembly and test of the instrument at Cerro Pachon this year. We are hopeful that the travel restrictions will ease in the first half of 2022 so this work can begin. In the meantime, we continue to make incremental improvements to our software and documentation, and order spare parts. Since our last report, the three containers of hardware stored at the base facility in La Serena were moved and unloaded for storage at Cerro Pachon. The rest of GHOST resides in storage at the NRC-Herzberg facility in Victoria, British Columbia, waiting for the green light for our Canadian and Australia teams to travel.
The project has been effectively on hold since the start of the COVID-19 pandemic, with the exception being progress on software and documentation. With the reopening of the Gemini South telescope, staff is now available to move the 3 containers from the base facility to be unloaded at the summit for storage until the remainder of the GHOST parts arrive. We expect the project to take another four months to complete once the Australian and Canadian crews are able to travel to Chile for the reassembly and test of GHOST at Cerro Pachón.
In January, comprehensive testing of the spectrograph subsystems was completed yielding excellent results, e.g. low scattered light and ghosting; wavelength coverage from 359 nm to beyond 1 µm with throughput exceeding requirements; high resolution mode median values of R = 81600 in the blue arm and R = 86100 in the red arm; a low resolution mode median value of R = 55500. In February, the spectrograph was disassembled and packed for shipping to Chile. Three 20 foot long sea containers carrying the enclosure, the optical bench, electronics cabinets, and assembly tools were shipped and then received in March, stored at the Gemini base facility due to the COVID-19 shutdown of the telescope. The optics were to be air-shipped shortly thereafter, but are being held in Victoria until the pandemic situation becomes more clear.
The northern hemisphere autumn saw multiple team members travel from Australia, Chile, and Hawai’i to converge on Victoria, British Columbia, at the NRC-H labs, to witness the completion of the spectrograph final assembly, and initiate acceptance testing. The Australian team bought along their science fiber optical cable and the slit viewer subassembly to be matched with the bench spectrograph for the testing. The mechanical alignment of the optical system went well, with the use of a FARO arm and laser tracker, achieving alignment within 100 µm. The outer enclosure final assembly was completed, and tested for temperature stability independently of the spectrograph, showing excellent results.
Bonding and mounting of the GHOST optics is well underway at the National Research Council of Canada, and both blue 4k × 4k and red 6k × 6k science detectors are assembled into their cryostats, ready to be tested.
Arriving at Gemini South is the first part of our new instrument "GHOST". The instrument consists of a unit mounted in the Instrument Support Structure in charge of 'capturing' the light of the telescope. The spectrograph will be installed in the pierlab connected by over 80 feet (24 m) of cable.
Australian Astronomical Optics at Macquarie University designed and built the Cassegrain unit, with software design coming from the Australian National University. Members of each organization traveled from Australia to Cerro Pachón to unpack, assemble, and test the unit with critical support from the Gemini South day crew, and from Gabriel Perez, Eduardo Toro, Cristian Urrutia, Steve Margheim, John Bassett, and David Henderson. The unit was then prepared and installed on the telescope to make the first checks on sky in early February.
The team had a very successful first night of testing. The instrument performed very well. A few of the accomplishments of the evening were confirming the coordinate systems and field center of GHOST are aligned within our measurements, and the probe map of the positioners is well behaved. The team were also able to map the coordinate systems to the sky and acquire targets repeated over the entire 7 arcmin FOV, and verify that target acquisition, both direct and via spiral search were working as expected in both the single target and two target modes. The team was enthusiastic about the performance of the GHOST unit and now await the arrival of the spectrograph from National Research Council Canada.
The build of the GHOST Cassegrain unit is nearly complete. In November, Gemini staff participated in weighing and inspecting the fully assembled unit at Australian Astronomical Optics (AAO) at Macquarie University lab in North Ryde, New South Wales. The unit is currently on its way to Chile. In December, Gemini representatives spent a week at the AAO testing the Integral Filed Unit (IFU) positioner and verifying the assembly and operation of the electronics and software of the Cassegrain Unit. Following 4 and a half days of inspections, tests, and demonstrations the positioner, electronics, and software were accepted for shipment to Gemini South. The electronics unit is expected to be shipped to Chile by year's end where the team will begin preliminary testing and debugging on the telescope in late January.
What is GHOST
GHOST, the Gemini High-resolution Optical SpecTrograph is the next Gemini facility instrument and will provide world-class, high-resolution spectroscopic capabilities to the Gemini community. GHOST will provide a wide simultaneous wavelength coverage at high observational efficiency, enabling astronomers to investigate a broad range of science from the composition of the first stars to the characterization of exoplanetary systems. A data reduction pipeline will be delivered with the instrument. Australian Astronomical Optics at Macquarie University leads the GHOST team which includes the National Research Council Herzberg (NRC-H) for the construction of the spectrograph and the Australian National University (ANU) for instrument control system and data reduction software.
GHOST Science Cases
Designed to be a workhorse instrument, GHOST’s world-class efficiency, resolution, wavelength coverage, and stability will enable a broad range of science by the Gemini community. Scientific expertise and guidance for the development of GHOST is provided by the Combined Science Team, jointly led by Alan MacConnachie (NRC-H), Michael Ireland (ANU) and Verne Smith (NOIRLab).
Characterization of exoplanet systems
Extremely metal-poor stars in the Milky Way and nearby dwarf satellites
Follow-up of GAIA targets
Radial velocity confirmation of transiting planet candidates, particularly from TESS
Abundance studies of extra-galactic globular clusters
GHOST Instrument Design
GHOST provides simultaneous wavelength coverage from 363 nm to 950 nm. It has two selectable spectral resolution modes: standard-resolution mode with R > 50000 and high-resolution mode with R > 75000. The instrument will obtain a limiting magnitude of 17.5 at 450 nm (30 sigma per resolution element). GHOST will spatially sample each target object over a field size of 1.2 arcsec, well matched to the wide range of seeing conditions at the observatory.
In standard-resolution mode, GHOST will have the capability to observe 2 targets simultaneously over a 7.5 arcmin diameter field of and provide a radial velocity precision of 600 m/s over the full wavelength. GHOST will have the capability to provide a radial velocity precision of 10 m/s over the wavelength range from 430 nm to 750 nm in the high-resolution mode, which can utilitze a simultaneous ThXe calibration source.
GHOST consists of three primary components; the cassegrain unit mounted on the telescope, the spectrograph bench located in the pier lab, and a fiber cable connecting the two. The cassegrain unit contains the positioning arm system, the object and sky fiber IFUs, and mini-ADCs. The bench spectrograph is isolated in the telescope pier lab for image and wavelength stability.
The GHOST spectrograph is an echelle white-pupil design, using VPH grating for cross-dispersion. A slit unit camera provides for object acquisition and active monitoring of the slit illumination. The bench uses active thermal stabilization to help provide the image and wavelength stability necessary for operation efficiency and radial velocity precision.
The GHOST Team
- Vladimir Churilov, Mechanical Engineer
- Tony Farrell, Software Engineer/Project manager
- Yuriy Kondrat, Mechanical Engineer
- Richard McDermid, Project Scientist
- Gordon Robertson, Instrument Scientist
- Lew Waller, Electronics Engineer
- Ross Zhelem, Optical Engineer
- Michael Ireland, Project Scientist
- Lance Luvaul, Software Engineer
- Jon Nielsen, Software Engineering Technical Lead
- Rob Sharp, Instrument Scientist
- Marc White, Data Reduction Programmer
- André Anthony, Mechanical Engineer
- Greg Burley, Detector Engineer
- Edward Chapin, Software Engineer
- Adam Densmore, Project Manager
- Jennifer Dunn, Project Management and Software Engineer
- Colin Ganton, Fabrication Lead
- Brian Hoff, Mechanical Engineer
- Jordan Lothrop, Mechanical Technologist
- Scott MacDonald, Optical Engineer
- Alan McConnachie, Project Scientist
- John Pazder, Project and Optical Engineer
- Ivan Wevers, Mechanical Technologist
Software Design Ideas
- Peter Young, Software Engineer
- John Basset, Systems Engineer
- Andrea Blank, Project Support
- Manuel Gomez, Instrumentation Engineer
- David Henderson, Project Manager
- Venu Kalari, Project Scientist
- Kathleen Labrie, Data Reduction Software Engineer
- Steve Margheim, Project Scientist
- Gabriel Perez, Mechanical Engineer
- Pablo Prado, Science Operations Specialist
- Juan-Font Serra, Project Scientist
- Eduardo Toro, IT Engineer
- Cristian Urrutia, Software Engineer