Herschel telescope

The first example is the 4-m class William Herschel telescope, at la Pakna, whose optical specifications, drafted by D. Brown, were expressed in terms of allowable wavefront error as a function of spatial frequencies matching those of atmospheric turbulence. 

Fig. 12.5. Parts of the spectra of two QSOs (with emission redshifts 2.9 and 3.3 respectively) taken with the 4-m William Herschel Telescope on La Palma with a resolution of about 50kms 1 showing Lyman-a lines with damping wings (column densities N(H i) 2 x 1021 cm 2 or 6M0pc-2 and 8 x 1020 cm-2 or 2.4 Mq pc-2 respectively). After Pettini et al. (1997).

Figure 2. The strong absorption feature centred near 3375 A in the near-ultraviolet (UV) spectrum of the bright QSO Q1331+170 is a good example of a damped Lya line, in this case produced by a column density of neutral hydrogen atoms 1V(H I) = 1.5 x 1021 cm-2. This spectrum was recorded in the early 1990s with the Image Photon Counting System on the ISIS spectrograph of the 4.2 m William Herschel telescope on La Palma (Pettini et al. 1994).

The presence of reactive ions like CH in the diffuse interstellar medium has been a challenge for interstellar chemistry since CH is easily destroyed by reactions with H2 but slow to form under the known physical conditions of the diffuse interstellar medium. It now appears that a warm chemistry can develop in the tiny dissipative structures of the interstellar turbulence, enabling the formation of transient species like CH and SH [43], The opening up of the sub-millimetre sky by the Herschel telescope has led to the discovery of several new reactive ions, enabling a better characterization of their chemistry. In the future, these tracers should bring interesting constraints on the properties of the interstellar turbulence. 

Fig. 2.7 Image of a fraction of the Rosette nebula obtained at far infrared wavelengths with the Herschel telescope. The colours correspond to the three monochromatic images that have been combined, with blue coding for the shortest wave- length (60 pm) and red for the longest wavelength (500 pm) [45]. Regions with the warmest dust appear in blue while the cold dust regions, further away from the heating sources, appear in red...

Reflecting telescopes would, however, still compete with refracting ones, mostly for their feasibility in much larger diameters. Herschel s telescopes,... 

On the last three decades, several space experiments with parts at very low temperatures have been flown. Among these, we mention IRAS (Infrared Astronomical Satellite) launched in 1983 (see Fig. 14.1), COBE (Cosmic Background Explorer) launched in 1989, ISO (Infrared Space Observatory) launched in 1995 and Astro-E (X-ray Observatory), launched in 2000 with instrumentation at 65 mK [35], Some cryogenic space missions are in the preparation or in final phase in Europe, USA and Japan. For example, ESA is going to fly Planck (for the mapping of the cosmic background radiation) and Herschel (called before FIRST Far Infrared and Submillimetre Telescope ) [36], These missions will carry experiments at 0.1 and 0.3 K respectively. 

The Education and Public Outreach section of the Spitzer Space Telescope mission is known as Cool Cosmos 13). It has a wealth of information and links for teachers including details on reproducing how Sir Frederick William Herschel discovered IR radiation, now known as The Herschel Experiment. This is an experiment for younger students, perhaps up to middle school. 

NASA s Spitzer space telescope (Werner et al. 2004), and more recently ESA s Herschel space observatory, both provide large area survey atlases across this FIR wavelength range. However, for most science cases, neither telescope has sufficient angular resolution to probe individual targets of interest in detail, and thereby study the physical processes which govern these sources. 

Fig. 1.4 FIR instruments in chronological order from left to right IRAS (1983), 0.6-m dish cooled at 2K and operating at 12, 25, 60 and 100 xm ISO (1995), 0.6-m dish cooled at 2-3 K operating in the band 3-200 p.m Spitzer (2003), 0.85 m dish cooled at 4 K operating in the band 3-180 xm Herschel (2009), 3.5-m dish cooled at 80 K operating in the band 55-670 xm. [Credit, respectively NASA/JPL ESA NASA/JPL-Caltech ESA/AOES Medialab, background from Hubble Space Telescope image (NASA/ESA/STScI)]...

Figure 1.4 shows, in chronological order, the satellites just presented. IRAS (1983) was provided with a 0.6 m telescope cooled at 2 K, operating at 12,25,60 and 100 p,m. ISO (1995) had only a single dish telescope of 0.6 m cooled at 2-3 K but operating in the band 3-200 gm. Spitzer (2003) increased the dish size to 0.85 m and was cooled to 4 K, still operating in a similar band as ISO (3-180 p,m). Finally Herschel (2009) represented a huge increase of spatial resolution due to its 3.5m telescope diameter cooled at 80 K. Its band of operation was from 55 to 670 ptm. 

The purpose of this module is to compute the emissivity and transmission of the 3 components of each telescope. The emissivity of the primary (Ml) and secondary (M2) is assumed to be the same and is based on Herschel mirror sample measurements, with a wavelength-dependent emissivity based on the results of Fischer (Fischer et al. 2004) who give the following equation for the best fit to the... 

J. Fischer, T. Klaassen, N. Hovenier, G. Jtikob, A. Poglitsch, O. Sternberg, Cryogenic far-infrared laser absorptivity measurements of the herschel space observatory telescope mirror coatings. Appl. Opt. 43(19), 3765-3771 (2004). doi 10.1364/A0.43.003765. http //ao.osa.oig/abstract. cfm URI=ao-43-19-3765... 

The excellent imaging capabilities of the Herschel space telescope have revealed, with unprecedented detail, the structure of molecular clouds and the regions where dense cores are formed. It is now clear that dense cores form within the ubiquitous filamentary structure of interstellar clouds, as localized density and column density maxima. There is a threshold in gas colunm density for dense core formation, estimated to be at extinctions of seven magnitudes from the analysis of either deep extinction images [15] or dust sub-millimetre emission maps [16], With such a threshold, the dense cores will be commOTily well shielded from the far ultra violet (FUV) radiation, with some exceptions in massive star forming regions or in photodissociation regions (PDRs) where dense molecular gas becomes directly exposed to FUV radiation. 

One must distinguish two phases which is the specificity of this task. A first phase, lasting a very short time, just a few minutes, which starts from the ignition of the launcher up to the orbital injection of the payload (telecom. Earth, and deep space observation satellites, spatial telescope like recently Herschel and Planck, the automated transport vehicle [ATV] from Astrium Space Transportation baptized symbolically Jules Verne). This is followed by a second phase, of a very long duration, 15 years of orbital fife for telecom satellites. 

Herschel (formerly known as FIRST, Far InfraRed and Sub-millimetre Telescope) was successfully launched on 14 May 2009 by ESA. The telescope was named after Sir W. Herschel who proved the existence of IR radiation. Herschel carries a 3.5 meter diameter passively cooled telescope. Herschel (Fig. 9.8, see also Doyle, Pilbratt, and Tauber, 2009, [111]) is the only space facility dedicated to the submillimeter and far infrared part of the spectrum (55 to 672 pm range). The main tasks of Herschel are ... 

Doyle, D., Pilbratt, G., Tauber, J. The Herschel and Planck space telescopes. IEEE Proc. 97, 1403-1411 (2009)... 

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