TABLE 4.3 Comparison of Different Recommended Infrared Facilities

Facility

Most Important Attributes

SIRTF

Unequaled sensitivity for imaging and moderate-resolution spectroscopy

Broad wavelength coverage from 2 to 700 µm

7.5 (λ/30 µm) arcsecond imaging of faint sources at λ > 30 µm

Infrared-optimized 8-m telescope

0.7 (λ/30 µm) arcsecond imaging for λ < 30 µm

High-resolution spectroscopy in atmospheric windows for λ < 30 µm

Evolving instrumentation

SOFIA

High-resolution spectroscopy at λ > 30 µm

2.5 (λ/30 µm) arcsecond imaging at λ > 30 µm

Training of instrumentalists

have successfully completed preliminary design studies for SOFIA, drawing heavily on the technical heritage of the KAO. SOFIA could begin observations in 1998.

Table 4.3 compares the most important attributes of the three recommended infrared facilities, SIRTF, the infrared-optimized 8-m telescope, and SOFIA. One can see from this comparison that the three instruments are mutually complementary.

SIRTF has the highest sensitivity for photometry, for imaging, and for low- to moderate-resolution spectroscopy (~100 km s−1). Between 3 and 20 µm, SIRTF will be 10 to 40 times more sensitive than the infrared-optimized 8-m telescope. Despite advances in ground-based telescope design and detector technology, SIRTF will maintain fundamental advantages in sensitivity longward of 3 µm. SIRTF will also have the uninterrupted spectral coverage from 2 to 200 µm needed to detect important molecular and atomic spectral features.

The great strength of the infrared-optimized 8-m telescope compared with SIRTF will be its ability to operate at high spectral or spatial resolution, or both. The telescope, capable of subarcsecond resolution owing to its adaptive optics, will make maps with 100 times more spatial information than those made by the 0.9-m SIRTF telescope. Information on this angular scale will be critical for understanding the disks around young stars and the energy source of infrared-luminous galaxies. For spectroscopy shortward of 5 µm, and at resolving powers in excess of 100,000 from 2 to 20 µm, the infrared-optimized 8-m telescope will be more sensitive than a space-based one throughout the wavelength region accessible from the ground. The infrared-optimized 8-m telescope will make seminal contributions to problems requiring both high spatial and spectral resolution, such as probing the centers of dusty galaxies like our own to look for evidence of massive black holes.



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