Shown is the far-infrared spectrum of the molecular outer layers and shells of the famous AGB star IRC + 10 216 as measured by ISO-LWS. The wealth of molecular lines is dominated by the simple CO and HCN molecules. However, more carbon-bearing species are expected, and their lines may be detected through the higher spectral and spatial resolution of HIFI.
Figure adapted from J. Cernicharo et al., 1996, A&A 315, L201
Low resolution far-infrared spectra of objects in subsequent stages of post-AGB evolution. From top to bottom NGC 7027, CRL 618 and CRL 2688. CRL 2688 is a F-giant which has recently left the AGB. CRL 618 is a young planetary nebula ionized by a B-type central star, but still deeply embedded in the molecular envelope, created during the AGB phase. NGC 7027 has a hot central star whose ionizing photons have formed a compact planetary nebula. The low resolution spectra of these objects are dominated by strong CO lines of the gas heated by stellar photons and shocks. HIFI will enable us to to study the kinematics associated with the dominant cooling lines of the gas and thus study the physical conditions during the evolution of these types of objects.
Figure adapted from K. Justtanont et al., 1999, in "The Universe as seen by ISO", ESA SP-427, p.345.
A spectral survey for three sources in a high-mass star-forming region (W3), in one of the small windows of the submillimeter wavelength region observable from the ground .
The source in the top panel is undergoing infall from its parent molecular cloud and, at the same time, has a massive outflow. This is reflected in the spectrum through the prominence of sulfur-bearing molecules and a relatively small number of lines.
The star in the centre of the source in the middle panel has heated its environment. Complex molecules like alcohols have evaporated from the icy mantles of dust grains. Rotational lines from these molecules dominate the spectrum. The elevated temperature also causes many other molecular lines to be visible.
In the bottom panel, the star has broken free from its parent cloud and radiate from the back. The resulting spectrum shows few lines of mainly very simple molecules.
HIFI will open up the full submillimeter window from 480 to 1900 GHz to make a molcular inventory of regions of star-formation and thus enable us to determine their physical conditions, and probe their origin and evolution.
Figure taken from Van Dishoeck & Helmich, 1996, in Proc. 30th ESLAB Symp., ESA SP-388, p. 3
PhotoDissociation Regions (PDRs) are regions of predominantly neutral material where impinging far-ultraviolet photons heat the gas and ionize and dissociate the species. In PDRs, most of the hydrogen is in atomic form, while species with low-lying ionization potentials such as C, S, and Si are singly ionized. Traces of molecular species are also present. Deeper into a cloud, shielded from the FUV radiation, the gas will turn completely molecular. PDRs are bright in the finestructure lines of [CII] (1.9 THz), [CI] (492, 809 GHz), and [OI] (4.7, 2.0 THz) and the molecular rotational lines of CO and a variety of other molecules. Of course, the FUV photons are absorbed by dust and reradiated at longer wavelengths, so the far-infrared dust continuum of galaxies also originates from PDRs. Traditionally, PDRs are associated with regions of massive star formation where hot stars create HII regions or reflection nebulae. However, much of the physics and chemistry of the ISM is regulated by FUV photons as well and hence almost all of the interstellar gas is in PDRs of one sort or another.
The Orion Bar region is an excellent example of a PDR created by the UV photons of a massive star.
The B3-B4-B5 region allows us to study PDRs associated with molecular cloud interfaces, illuminated by the diffuse interstellar radiation field.
The coloured part in the top image shows the location of band 1-5 of HIFI.
The lower image shows a simulated spectrum for the Orion IRc2 region in which an enormous richness in molecular lines is expected. (Picture courtesy of Peter Schilke)
|HIFI BAND 1-5||HIFI Band 6||
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SRON’s scientific programme focuses on the evolution and history of the universe, on climate change and air quality on earth, and on the atmospheres of planets near other stars than our sun. SRON therefore has four programme lines: Astrophysics, Exoplanets, Earth, and Technology. These four programme lines are supported by two expertise groups: Instrument science and Engineering. SRON’s goals are to maintain its leading position in international space missions and to find answers to the big scientific and societal questions of our time.Read more →
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Halverwege de jaren vijftig van de 20ste eeuw - met name na de lancering van de Russische Sputnik-satelliet in 1957 - zien astronomen in dat de ruimtevaart kan helpen de grote vragen van het ruimteonderzoek te beantwoorden. Henk van de Hulst richt in 1960 de Commissie voor Geofysica en Ruimteonderzoek van de KNAW op; Kees de Jager volgt op 1 oktober 1961 met de Werkgroep Ruimteonderzoek van Zon en Sterren. Het is het begin van een ontwikkeling waarin Nederlandse sterrenkundigen wereldwijd een grote reputatie opbouwen.Read more →
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