Space Infrared Astronomy

Rotational spectroscopy and microwave astronomy are the most accurate way to identify a molecule in space but there are two atmospheric windows for infrared astronomy in the region 1-5 im between the H2O and CO2 absorptions in the atmosphere and in the region 8-20 xrn. Identification of small molecules is possible by IR but this places some requirements on the resolution of the telescope and the spacing of rotational and vibrational levels within the molecule. The best IR telescopes, such as the UK Infrared Telescope on Mauna Kea in Hawaii (Figure 3.13), are dedicated to the 1-30 xm region of the spectrum and have a spatial resolution very close to the diffraction limit at these wavelengths. 

Astronomy. The potential of using the infrared portion of the electromagnetic spectrum for investigating celestial bodies and interstellar space has been considered by some astronomers for a number of years. This concept was first proposed by William Herschel. It has only been within the last few decades, however, that serious experiments in infrared astronomy have been made. 

NASA s Infrared Astronomy Satellite (IRAS), which was launched in 1985, consisted of a liquid-helium cooled telescope (60-cm mirror) and produced the first all-sky maps of the infrared universe at 25, 60, and 100 pm wavelength. IRAS was followed in 1996 with another cooled telescope in space, the Infrared Satellite Observatory (ISO), an ESA mission, which was a true observatory that could carry out follow-up observations of the IRAS sources. In 2003, NASA s Spitzer Space Telescope, with an 85-cm mirror, achieved major advances in sensitivity, image quality and field-of-view over ISO. Although its mirror was only slightly larger than ISO s 60-cm mirror, the use of new, sensitive, and large-area infrared array detectors has permitted this new view of the infrared universe. 

In this Thesis an instrument simulator for a Far Infrared space interferometer is presented, as well as a test bed implementation of the technique intended to be used to achieve high spectral and spatial resolutions from space. In this Introduction the motivation for this system is given from a general view of the Far Infrared astronomy and the possible science cases, through the past and present Far Infrared instruments, to FIRI, the concept of a space based Far Infrared Interferometer. 

There are two basic reasons for the appropriateness of a substantial space effort in infrared astronomy at this time ... 

Cosmic Radiation Gravitational Wave Astronomy Infrared Astronomy Neutrino Astronomy Pulsars Solar Physics Supernovae Ultraviolet Space Astronomy X-Ray Astronomy... 

Source Ericksen, E. R, SOFIA Stratospheric observatory for infrared astronomy in next generation infrared space observatory, in Next Generation Infrared Space Observatory (B. Burnel, Ed.), pp. 62. Kluwer Academic Publishers, The Netherlands (1992) with kind permission from Kluwer Academic Publishers. 

As we have seen above, infrared space missions are quite elaborate and expensive, both in time and in money. Throughout the history of infrared astronomy there has been a quest to gain some of the benefits of space missions but with less expense and with more frequent access than provided by space missions. As discussed earlier, the best observatory sites are on very high, very dry mountains, but this still leaves a large part of the infrared spectrum blocked from ground viewing. The obvious alternative has been observations from aircraft and high-altitude balloons. We will discuss some of these observations below. 

Love et al. (2000) Infrared Detectors for Ground-Based and Space-Based Astronomy Applications , by P. Love, K. Ando, J. Garnett, N. Lum, J. Rosbeck, M. Smith, and K. Sparkman, Proc. SPIE 4008, 1254-1267. 

Abstract. This paper describes the status of NASA s Space Infrared Telescope Facility (SIRTF) program. SIRTF will be a cryogenicaily cooled observatory for infrared astronomy from space and is planned for launch early in t next decade. It will be the first cryogenic space observatory to make extensive use of the powerfrd infrared detector array tednology discussed at this conference. We summarise a newly developed SIRTF mission concept and show how the availability of detector arrays has shaped the scientific rationale for SIRTF, and how the arrays themsdves have become part of the definition of the SIRTF misaon. 

Two 256X256-pixel arsenic-doped-silicon (Si As) impurity band conduction (IBC) hybrid detector arrays developed by Hughes Technology Center have been evaluated for space-based astronomy applications. Potential applications include instrumentation on orbiting astronomy platforms such as the Space Infrared Telescope Facility (SIRTF). 

Identification of molecules in space, even small molecules, by IR astronomy requires a rotational progression in the spectrum to be measured and resolved by the telescopes. For the transitions in the simpler molecules such as CO the telescope must be capable of aresolution of 2150/1.93 1114, which is within the resolution limit of the UK Infrared Telescope (3000-5000). However, the rotational constant for CO is rather large and many molecules, especially polyatomic species, will have a rotation constant ten times smaller than this, placing the observation of a resolved rotational progression beyond the resolution of the telescopes. Confidence in the identification of the molecule is then severely dented. The problem is worse for visible astronomy. 

The FIRI laboratory testbed is the the result of an effort by Cardiff University, the Rutherford Appleton Laboratory (RAL) and UCL to develop an instrument to demonstrate the feasibility of the Double-Fourier technique at Far Infrared (FIR) wavelengths, which in a long term basis is expected to be the precursor of the space-based Far Infrared Interferometer (Helmich and Ivison 2009). It is currently located at the Physics and Astronomy Department of Cardiff University. This system is in constant development, and here the current design and issues, the latest results and the future planned improvements are presented. 

Astronomy, Astrophysics, and Cosmology. Astronomy is an observational science. Observations are made by a variety of instruments, including optical telescopes, radio telescopes, infrared and ultraviolet telescopes, and gamma-ray and X-ray telescopes. However, instead of simply taking photographs to study, modern astronomers measure spectra, intensities, and many other properties to understand the olgects of their study. Some of the instruments they use are located at ground-based observatories with lai e telescopes, and others are located in orbit around Earth in space-based observatories, the most famous of which is the Hubble Space Telescope. 

The Symposium on Infrared and Submillimeter Astronomy was held in Philadelphia, Pennsylvania, U.S.A., on June 8-10, 1976, as an activity associated with the Nineteenth Plenary Meeting of the Committee on Space Research (COSPAR). The Symposium was sponsored jointly by COSPAR, the International Astronomical Union (lAU) and the International Union of Radio Science (URSI). 

This particular Symposium was unique in many ways. It is the first symposium on the subject of infrared and submillimeter astronomy to be held at a COSPAR meeting. It was also one of the rare occasions in which an international group of infrared astronomers, primarily interested in space astronomy, has gathered together to exchange ideas and information. The number of astronomers that attended the Symposium is another indication of the rapid growth and importance of space astronomy in the infrared and submillimeter region of the spectrum. 

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