III. Recommended Elements of the On-Going Instrumentation Program

The scientific perspectives outlined above identified instrumentation capabilities for the ongoing instrumentation program. The rough mapping of science programs onto instrumentation capability is summarized in Tables 2 and 3. Table 2 attempts to summarize new instrumentation capabilities as derived from the scientific discussions, while Table 3 summarizes the capabilities that can be satisfied, at least in the near term, by upgrades to Phase I instrumentation or by the shared use of Michelle or Phoenix. The very strong overlap apparent in Tables 2 and 3 among the different scientific areas leads naturally to a broad consensus for the direction of the ongoing instrumentation program. The broad perspectives concerning the directions for future instrumentation for the Gemini telescopes:

Table 2 - Science Drivers for New Instrumentation Capabilities
SCIENTIFIC

PROGRAMS

A&G Polarization
Modulator
AOS IR Imager/
Coronagraph
IR MOS Hi Stab
Lab Spec
LGS

>0.4

NGS

>0.9

>3' FOV AO IFU
0.4-1µm 1-5µm 30K 5K 30k 5k 30k 5k 150k 300k 500k
A. Stars & Planetary System
--BD & giant planets       X X         X X X X  
--physics of nearby stars             X   X       X  
--stars in other galaxies     X   X   X   X   X      
--surface structure/active processes X X X                   X  
B. Star Formation & ISM
--initial mass function     X   X       X          
--molecular clouds & cores                            
--disks & envelopes   X X   X         X        
--young substellar objects     X   X           X X   X
C. Galactic Structure & Nearby Galaxies
--massive stars     X           X   X X    
--star clusters     X   X       X   X      
--galactic nuclei     X   X       X   X      
D. Formation & Evolution of Galaxies/Cosmology
--evolution of galaxies     X       X   X   X      
--studies of AGN's X X X   X       X   X      
--galaxies probes of HiZ structure     X       X   X          
--QSO's as probes of HiZ universe     X   X           X     X

Table 3 - Science Drivers for Upgrades to Phase I Instruments
SCIENTIFIC

PROGRAMS

UPGRADES SHARED INSTRUMENTS
HROS
R=120k
MK AOS
LB
GMOS NIRS MICHELLE PHOENIX
0.1" IFU 1-1.5µm R=25k IFU R~25k
A. Stars & Planetary System
--Brown Dwarfs & giant Planets X         X   X X
--physics of stars X               X
--stars in other galaxies X       X   X   X
--active stars               X X
B. Star Formation
--initial mass function   X              
--molecular clouds & cores             X X X
--disks & envelopes   X       X X X X
--young substellar objects   X X            
C. Galactic Structure & Nearby Galaxies
--massive stars X               X
--star clusters X X X   X X X X  
--galactic nuclei X X X   X X X X  
D. Formation & Evolution of Galaxies/Cosmology
--evolution of galaxies   X X X X        
--AGN's   X X X          
--galaxies as probes of structure   X X X X        
--QSO's & Hi-Z universe X X X X X     X X

1) The ability to obtain near diffraction-limited imaging capabilities at near IR wavelengths, on both Gemini telescopes, through implementation of adaptive optics (AO) is of paramount importance in effectively addressing key scientific issues over the whole range of topics outlined in Section II. Recent advances in the demonstration of the scientific utility of AO and of laser beacon capabilities have highlighted the timeliness of this capability. Efforts to maximize sky coverage by the implementation of Laser Beacon AO technology are of very high priority (see Figure 23). The Gemini telescopes will complement and extend HST performance at Near-IR wavelengths, and will provide spatial and spectral resolution capabilities in the 2-20µm atmospheric windows far superior to the capabilities of ISO and those planned for SIRTF. In the 10 and 20µm windows, the Gemini telescopes will provide diffraction-limited images even without AO.

Figure 23 2) Technological advances in Near-IR arrays enable new innovative instrumentation capabilities that will fully exploit the images delivered by the Gemini telescopes at wavelengths longward of one micron and allow new attacks on key scientific issues throughout the science program; e.g. detailed studies of star formation processes, and extending many extragalactic studies to higher redshift. The development of high performance 1kx1k and 2kx2k Near IR arrays open new possibilities for addressing many of the key scientific issues using Integral-field, multislit, and multi object spectroscopic capabilities at Near IR wavelengths.

Superconducting tunnel junctions (STJs) may offer the possibility of very high efficiency low resolution spectroscopy from the atmospheric cutoff in the UV to near IR wavelengths. Pulse counting detectors with high quantum efficiency still offer significant advantages in extreme photon-starved problems.

High efficiency innovative grating developments would push the capabilities of the Gemini spectrographs to the faintest possible limits and immersed grating technology could extend the spectral resolution capabilities of GMOS and NIRS.

3) In general, although important scientific applications for wider fields than provided by Gemini's f/16 focus were identified, it is recommended that Gemini should concentrate its instrument development effort on exploiting the baseline f/16 focus. Innovative means for providing the Gemini communities access to wide field capabilities on other large telescopes, such as sharing time with other large telescope facilities, should also be explored.

The study of flickering phenomena in accretion processes requires 0.1 sec spectral sampling with <0.03 s dead time <1 ms absolute timing error on time scales of years.

A more detailed description of the recommended directions for the ongoing instrumentation program is presented in the following sections. The recommendations for new instrumentation capability are discussed first, followed by upgrades to the Phase I instruments and, finally, shared instrumentation.

A. Recommended New Instrumentation Capabilities

Table 4 summarizes the recommended new instrumentation capabilities and guidelines for performance requirements where appropriate.

Table 4 - Recommended New Instrumentation Capabilities
Instrument Capability Site Wavelength Range Pixel Scale FOV/Slit Length Spectral Resolution Other Capabilities
NGS/LGS AOS CP 1 - 2.5µm

0.5-5µm (goal)

SR > MK NGS AOS

SR> 0.9 @ 1.6µm (goal)

2'
feed to all inst ports

conjugate to optimum altitude?

Small Field Optimized Near IR Imager CP 0.8 - 5.5µm 0.01"

0.02"

0.05"

~10"x10"
Coronagraph
IR MOS CP


MK/CP

1 - 2.5µm

1 - 2.5µm

1 - 2.5µm

0.1" slits

0.05"

0.15"

~30" dia

5 - 10"

>3', 9' (goal)

~5 - 8k

~5 - 8k

~5 - 8k

IFU / coronagraph

multi slits

multi object

A&G Polarization Modulator MK/CP 0.4? - 5µm
TBD
Remote Modulator deployment

linear & circular

Hi Stability Lab Spectrograph CP 0.5-0.7µm

0.38-1.0µm

TBD less than or equal to1' 120k

300k

500k

absorption cell

1. Natural Guide star (NGS)/Laser Beacon (LB) AO System at Cerro Pachon

The Gemini-S facility will be a superb facility for Adaptive Optics observations. A combined NGS and laser beacon AO system will extend and complement the AO capabilities on Gemini North. The combination of AO implementation at Gemini-S, together with the Laser beacon upgrade and the Phase I NGS AOS for Gemini-N will constitute a powerful integrated AO program for the Gemini telescopes. These capabilities combined with the recommended optimized small field Near IR imager and near IR spectroscopic capabilities will enable new scientific programs throughout the whole scope of scientific issues addressed by the workshop.

When combined with a Near-IR WFS for tip/tilt and fast focus correction, a Laser Beacon AO system would enable high performance AO imaging and spectroscopic observations in dark clouds - one of Gemini's key science drivers. Adaptive Optics optimized for coronagraphic imaging and with high (>0.9) near-infrared Strehl ratios, is a key capability in the search for giant planets around nearby stars.

The Gemini-south site has not been adequately characterized regarding AO parameters such as Cn2(h) and wind velocity profiles. Specific site measurements, e.g. SCIDAR measurements aimed at characterizing these parameters, should therefore be initiated as soon as possible.

2. IR Imager at Cerro Pachon

1-5µm imaging will be a "workhorse" capability for Gemini, exploiting the superb image quality and extremely low emissivity of the telescopes. Furthermore, Gemini will be a unique platform for coronagraphic observations because of the exceptionally smooth primary mirror, rigorous mirror cleaning program, thin secondary vanes, etc. A small field imager with pixel scales and optics designed to exploit AO performance and t/t corrected images with optimized near-IR coronagraphic imaging capability will address a very wide range of science topics.

3. IR MOS, 1-2.5µm at Cerro Pachon

The continued development of large format Near-IR arrays (2kx2k HgCdTe arrays for the 1-2.5µm regime are under development and possibly buttable InSb arrays) provides an opportunity for three powerful new capabilities in the area of 1-2.5µm Multi-Object spectroscopy.

One key Near-IR MOS mode would be a high spatial resolution IFU that adequately samples AO corrected images, possibly equipped with coronagraphic capability. More than one IFU may be required to work in the three Near IR bands. An IFU with a FOV of 5-10" and 0.05-0.1" sampling was identified as being required for studies in crowded regions and of galactic nuclei.

A second mode would be the capability to select numerous objects for spectroscopic study within a FOV consistent with AO isoplanatic patch size, about 20-30" dia. Many applications for this type of MOS will be in crowded complex fields, so multi-slits or even multi-2D capability would be required.

The third key capability is simultaneous spectroscopy of objects over a FOV comparable to that of GMOS at the f/16 focus, particularly for studies of the distant universe. It is noted that over a 9' FOV the telescope emissivity increases by only 1%, making a truly wide field instrument possible.

For many science applications the spectral resolution needs to be optimized to work between the OH airglow lines, between 5000 and 8000, while abundance measurements will require spectral resolutions around 30,000. This capability supports a range of scientific applications, many of which follow the themes of GMOS science to higher redshift or probe dusty environments.

The cryogenic MOS slit masks or other object selection mechanism would have to be changeable during an observation session without warming the spectrometer, or significantly interrupting operations. Similarly the changeover between IFU and MOS operation should not require warming the instrument. A minimum array format for these capabilities is 2kx2k, with a goal to achieve 4kx4k pixels.

Given the complex issues surrounding implementation of the wide range of scientifically compelling MOS capabilities in the near IR, which include the possibilities of implementing upgrades to GMOS and NIRS, the Workshop suggests the following course of action:

4. A&G Polarization Modulator / Optical & IR - Mauna Kea & Cerro Pachon

Polarization measurements will require implementation of a polarization modulator in the A&G unit above the bottom port. The NIRI and NIRS Phase I instruments can accomodate Wollaston prism polarization analyzers, however, implementation of polarizing capability in GMOS and HROS will require upgrades to the Phase I instruments.

5. High Stability Lab Spectrometer - Cerro Pachon

The High stability Lab in the telescope pier provides a stable environment for precision radial velocity measurements. A fiber-fed, bench-mounted optical spectrograph with R=120,000, usable with an absorption cell in 500-600 nm range, would provide the greatest sensitivity currently for detection of low mass companions. A higher resolution mode, R>300,000 over the 380 to 1000 nm range, would enable many studies in stellar physics, including convection and magnetic fields, and also sufficient resolution for detailed studies of the ISM.

B. Recommended Upgrades to Phase I Instrumentation Capabilities

The recommended upgrades to Phase I instruments are shown in Table 5, along with guidelines for performance requirements.

Table 5 - Recommended Upgrades to Phase I Instruments
Instruments Upgrade Options Site Wavelength Range Pixel Scale FOV/Slit Length Spectral Resolution Other Capabilities Note
AOS Laser Beacon MK           1
GMOS NIR MK 1 - 1.5µm ~0.08" ~3'   IFU 2
NIRS IFU MK   ~0.05" ~1" x 2.5"     3
        ~0.15" ~3" x 7.5"      
GMOS Grating Impr MK/CP       ~25,000 improved grating efficiency 4
Notes:
1) -- goal is to increase sky coverage at similar performance levels as for a Bright natural guide star
2) -- long wavelength cutoff due to room temperature background needs further investigation
   -- compatibility with mass, volume constraints on GMOS needs further investigation
3) -- initial step toward ultimate weapon - gain experience in use and demonstrate science performance
4) -- grating efficiency is currently the major limitation in GMOS throughput
   -- an immersed grating may provide increased spectral resolution
   -- AO correction may allow use of <0.2" slits, thus achieving higher spectral resolution, possibly down to 0.4µm

1. Laser Beacon AO System Upgrade - Mauna Kea

A Laser Guide Star upgrade to the NGS AOS would boost AO sky coverage at moderate Strehl ratios in the near-IR very substantially. The intent is to be able to upgrade the initial NGS AOS for use with a Na Laser beacon in order to achieve moderate Strehl ratios (around 0.5) in the near-IR over most of the sky. Lasers are currently forbidden on MK as are the currently FAA required radar-based aircraft protection schemes. Intensive efforts are underway, led by Keck, to obtain approval for Na laser beacons on MK and FAA approval of alternative passive aircraft detection schemes.

2. GMOS Near IR Upgrade - Mauna Kea

Upgrade GMOS-N with the addition of a 2kx2k HgCdTe array under development at Rockwell International, to provide high performance multi-object spectroscopy over a roughly 3 arcmin dia field in the 1-1.5µm region. The same camera could also be fed with an IFU. This upgrade provides near term capability for near infrared, full field, MOS capability. A variety of scientific applications were identified that require this capability: studies of lenses and lensed objects, AGNs and normal galaxy nuclei, the properties clusters of galaxies as a function of z and the study of galaxies close to QSO lines of sight. Many of these applications call for a J-band IFU on GMOS.

A significant constraint on the upgrade path is to preserve the optical spectroscopy and imaging capability in the GMOS.

3. Near IRS IFU Upgrade - Mauna Kea

The NIRS is designed to have significant space in front of the cold slit for an Integral Field Unit (IFU). Because of the "small" 1kx1k format of the NIRS detector, an image slicer concept for the IFU, which maps slices of the image plane into a single long slit, would provide efficient use of the array and require no additional blocking filters. This concept is expected to yield roughly a 20x50 spatial element sampling. We encourage investigation of two plate scales; around 0.15 arcsec/spatial element for non-AO use and around 0.05 arcsec/spatial element for use with AO.

The initial NIRS IFU implementation should be kept relatively simple, since this is a new capability, with little experience concerning implementation or use. Switching between IFU plate scales and between IFU and long slit use should not require warming of the dewar.

Optical design and conceptual implementation work should be initiated as soon as possible.

4. HROS R=120,000 - Cerro Pachon

This capability is required to disentangle the effects of temperature and velocity in absorbing clouds along the line of sight to quasars. The recommended bench mounted R=120,000 capability could also provide for much of the science drivers for this upgrade.

5. Grating Improvements (GMOS) - Mauna Kea and Cerro Pachon

The largest single source of throughput loss in GMOS is the grating efficiency (at 65-70%). Possible high efficiency innovative grating developments would push the capabilities of GMOS to the faintest possible limits. Grating developments to allow spectral resolutions of 20,000 to 30,000 would also fill the gap between the baseline GMOS and HROS capabilities would allow for detailed abundance studies in nearby galaxies.

C. Shared Instrumentation

The recommended shared instruments are listed in Table 6, together with their performance characteristics.

Table 6: Recommended Shared Instruments
Instruments Wavelength Range Array Format Pixel Scale FOV/Slit Length Spectral Resolution Other Capabilities
MAUNA KEA
MICHELLE 8 - 25µm ~256 x 256

Si:As IBC

0.18" 46" R~200, 1k, 20k  
    0.10" 26" x 26" filters  
CERRO PACHON
PHOENIX 1 - 5µm 512 x 1024

InSb

0.09" 14" 100k (2 pix) pupil, viewing
          imaging mode

1. Mid-IR Spectrograph (MICHELLE) (shared with UKIRT) Mauna Kea

A Mid-IR spectrometer under development at ROE for use at UKIRT and proposed for shared use on Gemini-N. It will provide spectral resolution from 200 to 30,000, and diffraction limited imaging capability in the 8 - 28µm range. Under the proposed shared-use agreement, MICHELLE would be available at Gemini-N 50% of the time.

It would be very desirable to have MICHELLE available for use at the start of scientific operations on Gemini-N.

2. Near-IR HRS (PHOENIX) (shared with NOAO) - Cerro Pachon

The shared use of PHOENIX at Gemini-S and possibly Gemini-N should be pursued. Because of the initial scarcity of science instruments on Gemini-S, It would be very desirable to have Phoenix available for scientific use on Gemini-S late in the commissioning period and during early operations of Gemini-S.

Ultimately this spectroscopic capability will be needed with a much larger simultaneous wavelength coverage than can be provided by Phoenix, however Phoenix would offer an adequate capability for the short term. The provision of a new instrument for that would provide extended wavelength coverage in a single exposure should appear later in the on-going instrumentation program

3. NIRS Clone (Gemini-S)

NOAO is considering cloning the NIRS for use on the SOAR telescope. The decision to proceed with the duplication of NIRS, hinges on details surrounding the SOAR telescope project. Without SOAR, NOAO cannot use NIRS on any of the NOAO telescopes, and thus would have little interest in cloning NIRS.

The NIRS would be a basic "workhorse" instrumental capability with wide ranging scientific capability on Gemini-South extending into the thermal IR.


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