US Gemini Program

A New USGP Scientific Staff Member

We are pleased to welcome David Silva to the US Gemini Program as an Assistant Astronomer. Dave's previous position was NOAO Assistant Scientist with responsibility for the commissioning of the WIYN telescope. He has extensive experience with telescope operations and alternate observing modes. His major research interest is stellar populations in elliptical galaxies, which he has studied using many different techniques, including optical and IR spectroscopy, IR imaging, and theoretical modeling. Dave's expertise will be valuable as we gear up our program for the operations phase of Gemini.

A Workshop to Define US Instrumentation Priorities for Gemini

Planning is beginning for the instruments that will be designed and built for Gemini after the initial complement. Each of the Gemini partner countries has been asked to establish its interests and priorities for future instrumentation, and the lists will be compared and merged starting this fall. In the steady-state of Gemini operations, approximately $3.5 million per year will be available for instruments and facility upgrades; approximately one-half of that will be spent in the US.

In order to arrive at a community consensus about priorities for future Gemini instruments, the USGP has organized a small workshop in Tucson in early August. About 25 astronomers have been invited to discuss the science drivers for Gemini capabilities. An attempt is being made to place the Gemini program in the context of the many facilities available to US astronomers by including representatives of most of the other large telescopes and projects. Opinions and input have been solicited from the community at large through a discussion on the World-Wide Web. The conclusions of this upcoming workshop will be reported in the next Newsletter.

Science Drivers for the Gemini High-Resolution Optical Spectrograph

A meeting was held in early May in London to discuss the performance requirements and scientific motivations for the Gemini High Resolution Optical Spectrograph (HROS). This instrument will be one of the last delivered of the initial complement and will be installed at Gemini South. Its design and fabrication has been assigned to the UK, and the team working on it is based at University College London.

The goal of the meeting was to review the sorts of scientific problems that could be effectively attacked with a high resolution optical spectrograph in the southern hemisphere, and to ensure that the requirements that the team is designing to are consistent with that vision of the instrument's mission. Representing the US community at the meeting were David Meyer (Northwestern), Mario Mateo (Michigan), Mark Giampapa (NSO/NOAO), and Todd Boroson (USGP/NOAO).

The results of the meeting are best summed up by the performance requirements that were endorsed:

1. The baseline instrument will be mounted at the Cassegrain focus. The committee recognized that a bench mounted spectrograph fed with either a fiber bundle or a beam would address additional important problems, but this role might be better filled by a separate spectrograph.

2. HROS will have two resolutions, selectable by changing the camera. These resolutions (corresponding to 3 pixel sampling) are 50,000 and 135,000.

3. HROS will be usable over the range 300 to 1100 nm with complete coverage from 350 to 700 nm in a single exposure at the lower resolution.

4. The nominal slit widths will be 0.6" (low resolution) and 0.24" (high resolution). The slit width will be adjustable and a decker will provide a slit length up to 60". An image slicer will be available for the high resolution mode.

5. Fairly ambitious requirements are placed on throughput, image quality, scattered light, and flexure.

6. It is considered highly desirable to provide a multi-object capability. A number of very interesting problems could be addressed with even a small number of slits over a 30" x 60" field.

7. The ability to make spectropolarimetric measurements would be a desirable feature.

8. It was recognized that there is an important need for a stable spectrograph to measure radial velocities with a precision of 1 m/s between 400 and 1000 nm to search for planetary companions and for asterioseismology.

9. The scientific importance of spectroscopy at a resolution of order 1,000,000 in the spectral range 300 to 1000 nm was recognized.

Design work for this spectrograph is beginning, with a conceptual design review (CoDR) scheduled for late this year.

Near Infrared Instruments

Last year, the International Gemini Project Office asked the USGP to manage the IR instruments program for Gemini, since all of the Gemini construction-phase IR instruments are being built in the US. Current NIR USGP projects include the Gemini Near Infrared Imager (NIRI) built by the University of Hawaii, the Gemini Near Infrared Spectrograph ( GNIRS) built by NOAO, and the NOAO ALADDIN arrays and NIR array controllers for both of these instruments.

The NIRI completed its CoDR in March 1995 and held its Preliminary Design Review (PDR) at the end of June of this year. No major technical problems were uncovered at the PDR, and designs identified by the review committee as carrying technical risk are now being prototyped. NIRI is scheduled for delivery to Mauna Kea in September 1998 in time to serve as the commissioning instrument for the Gemini North Telescope.

The Institute for Astronomy has assigned an outstanding design team to this project: Klaus Hodapp (PI), Joseph Hora (Principal Astronomer and optics designer), Tony Young (lead mechanical engineer), Ev Irwin (electronics engineer), and Hubert Yamada (software engineer). USGP appreciates the hard work of these people and others in preparing and delivering the PDR. More on this instrument appears below.

NOAO began work on the GNIRS last October and held the CoDR in March. The review committee was extremely impressed with the quality and quantity of work performed, which exceeded what they expected for a CoDR and was almost at a PDR level. The PDR will be held 3-4 October in Tucson and will be led by the GNIRS Project Engineer Dan Vukobratovich and Project Scientist Jay Elias. NOAO was fortunate to recruit the level of quality for this project exemplified by these two individuals, who have succeeded in keeping the project on schedule and within its budget. The GNIRS team also includes Nick Roddier (leading both electrical engineering and software) and Woon-Yin Wong (mechanical engineering), with substantial contributions by Gemini's Myung Cho (mechanical engineering and FEA modeling) and NOAO senior designers Randy Cuberly and Andy Kovacs. Jay described the spectrograph's science drivers, capabilities, and upgrade paths in the June Newsletter. GNIRS promises to exploit the full potential of the Gemini telescopes and to produce exciting science throughout its lifetime.

Both NIRI and GNIRS will use NIR arrays developed under NOAO's ALADDIN program and an upgrade of NOAO's Wildfire controller. NOAO is managing the arrays foundry run, the controller upgrade, and the integration of arrays and controllers into a working unit suitable for inclusion into each instrument. The first controller with an engineering grade array will be delivered to the NIRI team 15 July of next year, with the controller for the spectrograph following about a year later. As science grade arrays are produced, characterized, and selected, these will be integrated with each team's controller delivered previously and adjusted to optimize performance.

Proposals were received in early June by groups interested in performing conceptual design studies of a mid-infrared (8-25 m) imager for the Gemini telescope. A committee of qualified members from the community reviewed the proposals and made a recommendation for funding. The selected groups(s) will be announced in the next Newsletter. The next phase of the activity, the final design and hardware phase, is also an open competition. Proposals will be solicited from anyone in the US.

This initial conceptual design activity is useful to Gemini in gaining a better understanding of the cost and technical feasibility of obtaining an instrument which will meet the performance objectives.

Following the conceptual design work, the USGP will proceed with choosing a group for the complete design and fabrication of an instrument. Proposals for this work will be solicited from the entire US community. In order to propose, a group should have a design concept and analysis sufficient to address the types of performance questions listed in the Request for Proposals of the conceptual design study. Anyone wishing to receive this may request it from the USGP.

Gemini Near Infrared Imager

The Gemini Near Infrared Imager (NIRI) is being built by the University of Hawaii's Institute for Astronomy under contract to the International Gemini Project Office. This contract is being administered by IGPO contracts administrators, but the USGP acts as Technical Representative providing day-to-day oversight.

NIRI is designed to take advantage of Gemini's low IR emissivity, superb image quality produced by both active and adaptive optics (AO), large photon collecting area, and operating modes that can be adapted to observing conditions that vary rapidly over a wide dynamic range. The NIRI will operate as a camera with grism spectroscopy in the wavelength range 1.0 m through 5.5 m. The ALADDIN-style detector will have 27 m pixels with scales of 0.02" (20" field), 0.05" (51" field), and 0.12" (123" field). The 0.02" scale will be used primarily with AO, while the 0.05" scale will be used most often with tip-tilt enabled but AO disabled (e.g., when low emissivity is preferred over spatial resolution). Matching focal plane masks will be provided in the focal plane mask wheel. Grisms provide low resolution spectroscopy in the 1.0-2.5 m wavelength range using 120" slits. Extending low resolution grism spectroscopy to the 3 m window would be a desirable future option.

As shown in the isometric projection in Figure 1, NIRI's optics will be mounted on an optical bench inside a hexagonal dewar, with the science optics on one side of the optical bench and the NIR On- Instrument Wavefront Sensor (OIWFS) on the other side. Pickoff mirrors mounted on a turret reflect the science beam in the middle of the field and pass the surrounding guide field to the OIWFS. The science- beam-side layout is shown in Figure 2. The IfA is providing the OIWFS detector, a 1K x 1K Rockwell HgCdTe array operating in the range 1.0-2.5 m. Cryocooler heads and electrical connectors are all mounted on the central hexagon, for easy removal of the vacuum covers mounted on each side of the hexagon.

As with all true Gemini facility-class instruments, NIRI will be compatible with Gemini control systems, using the Experimental Physics and Industrial Control System (EPICS) software developed at US experimental high energy physics accelerators. This system provides a common framework for all Gemini enclosure, telescope, mount, and instrument control systems and guarantees they can all communicate with each other. Since the executable software is already debugged and operational (and has been for several years), all one does for a new system is populate a database specifying basic control algorithms and write a small amount of software to provide custom control features not found in EPICS. This speeds development and reduces overall software cost, but does require a substantial investment of a programmer's time to learn how to use effectively.

Watch this column for future articles on this critical Gemini instrument.

Todd Boroson, Mark Trueblood, Kathy Wood