Workshop on Future Instrumentation for Gemini Telescopes

As announced in the last Newsletter, the USGP is beginning to plan for the ongoing Gemini instrumentation program. In the steady-state of Gemini operations, approximately $3.5 million per year will be available for new instruments and facility upgrades; one-half of that will be spent in the US. Each of the Gemini partner countries has been asked to identify its interests and priorities for future instrumentation. As a start to that process, the USGP held a workshop in Tucson in early August. About 25 astronomers from universities, research institutions, NOAO, and Gemini were invited to discuss the science drivers for Gemini capabilities. Representatives from most of the other large telescopes and telescope projects were there to put the discussion in the context of the total suite of facilities available to US astronomers. Input from the community at large was also received prior to the meeting via the World-Wide Web.

As preparation for the discussion, the group heard presentations on Gemini capabilities and its initial instrument complement as well as the instrumentation programs for the Keck, MMT-upgrade, Magellan, Hobby-Eberly, VLT, and Subaru telescopes. Short presentations were made on new technologies that might lead to instruments that could open up new research areas.

A general discussion of the philosophical principles for defining future instruments followed. Six considerations were agreed upon:

• Focus on combination of scientific issues and instrumentation. Remember that capabilities are more than the instruments alone.

• Emphasize Gemini's best attributes. Require performance that preserves Gemini's outstanding features.

• Duplicate capabilities can be justified by potential for scientific returns.

• Telescopes have to be effective in worse than median conditions.

• Bring US technology into Gemini; open new paths to facilitate this.

• Consider Gemini in the context of other large telescopes.

The general discussion of future Gemini capabilities was structured by dividing the participants into four groups, each charged to consider a (very broad) scientific area. The groups were:

1) Star Formation, Stellar Physics, and the ISM (chaired by Steve Strom),

2) Problems in Nearby Galaxies (chaired by Jay Gallagher),

3) Structure and Evolution out to z = 1 (chaired by Richard Elston),

4) Cosmology (chaired by Buell Jannuzi).

Each group was charged with developing a list of problems that they saw as important and addressable over the next ten years. For each problem, they were asked to list the required observations, the instrumental capabilities needed to make those observations, and some sort of benchmark for the capability.

The top problems identified by the four groups were:

1) The origin and early evolution of the stellar mass spectrum,

2) An understanding of the kinematics and structures of the nearest AGNs,

3) The local manifestations of large scale structure,

4) When (and where) did the progenitors of z = 1 ellipticals form their first significant population of stars?

These top problems give just a flavor of the discussions at the workshop; a large range of science and instrumental capabilities made it onto the four lists. Merging the four lists produced the following list of desired future instrumental capabilities for Gemini. Note that the order represents some measure of the overall importance of the capability, although the sequence in which instruments are built may be determined by other factors.

1) Laser Guide Star Adaptive Optics: A large fraction of the high priority programs require fairly high Strehl (> 0.5) AO at 2m over a small field (< 10"). Many of the objects are faint, requiring a laser beacon. It is recognized that this type of AO is far from being viable as a user facility, and that it is risky to base a large fraction of the science to be done on an undemonstrated capability. However, it was judged that within the constraints of the 3.5' IR field and the 10' optical field of Gemini, by far the most interesting and important science would capitalize on the diffraction-limited near-IR images of an 8-meter telescope. Thus, the recommended strategy is to pursue LGS AO (though not to fund development of major subsystems that are being worked on by other programs), and to concentrate early efforts within the ongoing instrumentation program on those instruments and upgrades that do not require AO.

2) Near-IR imager for Gemini-South: Several of the highest priority programs require near-IR imaging from both north and south sites. In general, the imaging applications tend toward AO, and so multiple pixel scales (from 0.01" or 0.02" to 0.1"-0.2"/pixel) would be effective.

3) Narrow-field multi-slit Near-IR Spectrograph: Those programs attempting to study distant galaxies or star forming regions in detail require a near-IR spectrograph optimized for use with the AO system outlined above. Some of these require multi-slits, some require a single slit, and some (most) require an integral field unit with spatial elements appropriate for the diffraction-limited 2µm images. Resolutions from 2000 to 10,000 are needed.

4) Wide-field multi-slit near-IR spectrograph: Many of the programs aimed at studying galaxies at high redshift require cryogenic multi-slit spectrographs. Those that wish to measure integrated properties require a few dozen slits over a field of several tens of arcminutes. The GMOS 1.5µm upgrade is seen as an interim solution, but a true cryogenic instrument will be necessary ultimately to address these problems. Resolution of several thousand is needed.

5) Ultra-high resolution optical spectrograph: Studies aimed at the next step in stellar physics were recognized as potentially yielding very important information and being well suited to Gemini. In addition, an ultra-high resolution (R ~ 500,000) spectrograph would open up new areas in studies of the interstellar medium. This would be a bench mounted (and probably fiber-fed) system in order to ensure high stability.

6) Integral Field Units for the existing spectrographs: Many of the programs require integral field spectroscopy, and some are in the spatial regime attainable with the initial instruments, GNIRS and GMOS. IFUs for these instruments having spatial scales of 0.1" or less could be used to attack some of these problems.

7) High-dispersion near-IR spectrograph: Two of the high priority programs require high-resolution near-IR spectra, one for studies of the abundances in distant absorption systems of QSOs and one for kinematic studies of circumstellar material. The proposed sharing of the NOAO instrument Phoenix would be cost-effective way of providing this capability.

8) Coronagraphic feeds: A number of the projects require blocking the light from a relatively bright object to study the faint or low-surface-brightness emission nearby. There are both imaging and spectroscopic applications that require a coronagraphic front-end; all of these are aimed at use with adaptive optics.

9) H-band extension for GMOS: Despite the fact that a multi-slit IR spectrograph with a cryogenic focal plane was seen as essential for a number of important programs, the possibility of extending the sensitivity of GMOS to 1.5µm by replacing the CCD array with a HgCdTe array is a good first step.

The workshop was deemed a success by all the participants, and the international Gemini project is organizing an international version with a structure quite similar to the US workshop to be held in England in January 1997. This Newsletter article is a condensation of the final report of the workshop, " Future Instrumentation for the Gemini 8-Meter Telescopes; The US Perspective," which is available from the USGP.

Participants in the workshop were:

Sam Barden (KPNO/NOAO)
Eric Becklin (UCLA)
Todd Boroson (USGP/NOAO)
Richard Elston (CTIO/NOAO)
Craig Foltz (MMT)
Christ Ftaclas (Michigan Technological)
Jay Gallagher (Wisconsin)
Fred Gillett (Gemini)
Richard Green (NOAO)
Lee Hartmann (Harvard)
Suzanne Hawley (Michigan State)
Buell Jannuzi (KPNO/NOAO)
Bob Joseph (Hawaii)
Pat McCarthy (OCIW)
Joe Miller (Santa Cruz)
Matt Mountain (Gemini)
Gerry Neugebauer (Caltech)
Phil Puxley (Gemini)
Larry Ramsey (Penn State)
Steve Ridgway (KPNO/NOAO)
Dave Silva (USGP/NOAO)
Steve Strom (Massachusetts)
John Tonry (MIT)
Mark Trueblood (USGP/NOAO)
Alistair Walker (CTIO)
Sidney Wolff (NOAO)

Todd Boroson