Design of the TMT mid-infrared echelle: science drivers and design overview

Abstract

We present a discussion of the science drivers and design approach for a high-resolution, mid-infrared spectrograph for the Thirty-Meter Telescope. The instrument will be integrated with an adaptive optics system optimized for the midinfrared; as a consequence it is not significantly larger or more complex than similar instruments designed for use on smaller telescopes. The high spatial and spectral resolution possible with such a design provides a unique scientific capability. The design provides spectral resolution of up to 120,000 for the 4.5-25 m region in a cross-dispersed format that provides continuous spectral coverage of up to 2% to 14 m. The basic concept is derived from the successful TEXES mid-infrared spectrograph. To facilitate operation, there are separate imaging channels for the near-infrared and the mid-infrared; both can be used for acquisition and the mid-infrared imaging mode can be used for science imaging and for guiding. Because the spectrograph is matched to the diffraction limit of a 30-m telescope, gains in sensitivity are roughly proportional to the square of the telescope diameter, opening up a volume within the Galaxy a thousand times greater than existing instruments.

Design concepts for a mid-infrared instrument for the Thirty-Meter Telescope

“…Optical layout of the image slicer unit A. Each image slicer unit has 11 slicing mirrors [1]. Because a slicing mirror is tilted from the neighboring one by 2.4 • , the light from each mirror is reflected to the different direction [2].…”

“…Several papers were published to show the scientific case, feasibility, and technical drivers. [1][2][3] The MIRES science focused on high-resolution spectroscopy as an unmatched capability in sensitivity and spectral-resolution for future mid-IR astronomy. In addition, a design study of a mid-IR adaptive optics (MIRAO) system was undertaken and published 4 since diffraction-limited spatial resolution is essential for MIRES.…”

“…Numerical characters beside the box represent slicer number. No [1][2][3][4][5][6][7][8][9][10][11]. are from unit A and B, respectively.…”

MIRAO: a mid-IR adaptive optics system design for TMT

“…At mid-infrared wavelengths ground-based observations are background-limited and the observing time to reach a fixed signal-to-noise ratio on point sources for a telescope at the diffraction limit decreases with the fourth power of the telescope diameter. At these wavelengths, the 30-meter TMT telescope can provide an increase in speed of 2 to 4 orders of magnitude over current ground-based capabilities permitting study of a variety of astronomical phenomena such as star and planet formation at unprecedented sensitivities at high spectral and spatial resolution (see Elias et al 2006).…”

Design tradeoffs for a high spectral resolution mid-infrared echelle spectrograph on the Thirty-Meter Telescope

“…One of the instruments being considered is the Mid-Infrared Echelle Spectrograph (MIRES). The detailed scientific rational and requirements of MIRES are discussed elsewhere at this meeting 3 . MIRES will provide a tremendous leap in sensitivity and speed for high-resolution spectroscopy and high-spatial resolution imaging in the thermal infrared (5-25 µm).…”