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Willem Jellema

Other affiliations: Max Planck Society, ASTRON, Kapteyn Astronomical Institute  ...read more
Bio: Willem Jellema is an academic researcher from Netherlands Institute for Space Research. The author has contributed to research in topics: Spica & Heterodyne. The author has an hindex of 23, co-authored 117 publications receiving 2653 citations. Previous affiliations of Willem Jellema include Max Planck Society & ASTRON.


Papers
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Journal ArticleDOI
Th. de Graauw1, Th. de Graauw2, Frank Helmich2, Thomas G. Phillips3  +176 moreInstitutions (20)
TL;DR: The Heterodyne Instrument for the Far-Infrared (HIFI) was launched onboard ESA's Herschel Space Observatory in May 2009 as mentioned in this paper, which is a set of 7 heterodyne receivers that are electronically tuneable, covering 480-1250 GHz with SIS mixers and the 1410-1910 GHz range with hot electron bolometer mixers.
Abstract: Aims. This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods. The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480-1250 GHz with SIS mixers and the 1410-1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s-1. Results. After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations.

828 citations

Journal ArticleDOI
Pieter R. Roelfsema1, Frank Helmich1, D. Teyssier, Volker Ossenkopf1, Volker Ossenkopf2, Patrick W. Morris3, Michael Olberg1, Michael Olberg4, R. Shipman1, Christophe Risacher1, M. Akyilmaz2, R. Assendorp1, I. M. Avruch5, I. M. Avruch1, D. A. Beintema1, N. Biver6, Adwin Boogert3, Colin Borys3, J. Braine7, J. Braine8, M. Caris9, Emmanuel Caux10, Emmanuel Caux11, José Cernicharo12, O. Coeur-Joly11, O. Coeur-Joly10, Claudia Comito9, G. de Lange1, B. Delforge8, Pieter Dieleman1, L. Dubbeldam1, Th. de Graauw, K. Edwards13, Michel Fich13, F. Flederus1, C. Gal2, A. M. di Giorgio14, Fabrice Herpin8, Fabrice Herpin7, D. R. Higgins15, A. Hoac3, R. Huisman1, Christopher Jarchow9, Willem Jellema1, A. de Jonge1, Dominicus Kester1, T. Klein9, Jacob Kooi3, C. Kramer2, W. M. Laauwen1, Bengt Larsson16, Christian Leinz9, S. D. Lord3, A. Lorenzani14, W. Luinge1, A. Marston, Jesús Martín-Pintado12, C. McCoey13, M. Melchior17, M. Michalska18, R. Moreno6, Holger S. P. Müller2, W. Nowosielski18, Yoko Okada2, Piotr Orleanski18, Thomas G. Phillips3, J. C. Pearson19, D. Rabois11, D. Rabois10, L. Ravera11, L. Ravera10, J. Rector3, Miriam Rengel9, Hideo Sagawa9, W. Salomons1, E. Sánchez-Suárez12, Rudolf Schieder2, F. Schlöder2, F. Schmülling2, Marco Soldati17, J. Stutzki2, B. Thomas1, Alexander G. G. M. Tielens20, Charlotte Vastel10, Charlotte Vastel11, K. Wildeman1, Q. Xie3, M. Xilouris, C. K. Wafelbakker1, N. Whyborn, P. Zaal1, Tom Bell3, Per Bjerkeli4, E. De Beck21, Thibault Cavalié9, Nathan R. Crockett22, Pierre Hily-Blant8, Mihkel Kama23, Mihkel Kama1, Tomasz S. Kaminski18, Bertrand Lefloch8, Robin Lombaert21, M. De Luca6, Z. Makai2, M. Marseille1, Z. Nagy5, Z. Nagy1, S. Pacheco8, M. H. D. van der Wiel1, M. H. D. van der Wiel5, S. Wang22, Umut A. Yildiz20 
TL;DR: In this paper, the calibration and in-orbit performance of the Heterodyne Instrument for the Far-Infrared (HIFI) is described based on a combination of ground and in flight tests.
Abstract: Aims. In this paper the calibration and in-orbit performance of the Heterodyne Instrument for the Far-Infrared (HIFI) is described. Methods. The calibration of HIFI is based on a combination of ground and in-flight tests. Dedicated ground tests to determine those instrument parameters that can only be measured accurately using controlled laboratory stimuli were carried out in the instrument level test (ILT) campaign. Special in-flight tests during the commissioning phase (CoP) and performance verification (PV) allowed the determination of the remaining instrument parameters. The various instrument observing modes, as specified in astronomical observation templates (AOTs), were validated in parallel during PV by observing selected celestial sources. Results. The initial calibration and in-orbit performance of HIFI has been established. A first estimate of the calibration budget is given. The overall in-flight instrument performance agrees with the original specification. Issues remain at only a few frequencies.

309 citations

Journal ArticleDOI
TL;DR: In this paper, the physical state and energy balance of cool matter in space were measured in the infrared wavelength domain, enabling the detailed study of the processes that govern the cooling process.
Abstract: Measurements in the infrared wavelength domain allow direct assessment of the physical state and energy balance of cool matter in space, enabling the detailed study of the processes that govern the ...

122 citations

Journal ArticleDOI
TL;DR: In this paper, the authors performed a sensitive search for the ground-state emission lines of ortho- and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI instrument.
Abstract: We performed a sensitive search for the ground-state emission lines of ortho- and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI instrument. No strong lines are detected down to 3sigma levels in 0.5 km/s channels of 4.2 mK for the 1_{10}--1_{01} line and 12.6 mK for the 1_{11}--0_{00} line. We report a very tentative detection, however, of the 1_{10}--1_{01} line in the Wide Band Spectrometer, with a strength of T_{mb}=2.7 mK, a width of 5.6 km/s and an integrated intensity of 16.0 mK km/s. The latter constitutes a 6sigma detection. Regardless of the reality of this tentative detection, model calculations indicate that our sensitive limits on the line strengths preclude efficient desorption of water in the UV illuminated regions of the disk. We hypothesize that more than 95-99% of the water ice is locked up in coagulated grains that have settled to the midplane.

108 citations

Journal ArticleDOI
TL;DR: In this article, the authors performed a sensitive search for the ground-state emission lines of ortho- and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI instrument.
Abstract: We performed a sensitive search for the ground-state emission lines of ortho- and para-water vapor in the DM Tau protoplanetary disk using the Herschel/HIFI instrument. No strong lines are detected down to 3sigma levels in 0.5 km/s channels of 4.2 mK for the 1_{10}--1_{01} line and 12.6 mK for the 1_{11}--0_{00} line. We report a very tentative detection, however, of the 1_{10}--1_{01} line in the Wide Band Spectrometer, with a strength of T_{mb}=2.7 mK, a width of 5.6 km/s and an integrated intensity of 16.0 mK km/s. The latter constitutes a 6sigma detection. Regardless of the reality of this tentative detection, model calculations indicate that our sensitive limits on the line strengths preclude efficient desorption of water in the UV illuminated regions of the disk. We hypothesize that more than 95-99% of the water ice is locked up in coagulated grains that have settled to the midplane.

100 citations


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08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal ArticleDOI
TL;DR: Herschel was launched on 14 May 2009, and is now an operational ESA space observatory o ering unprecedented observational capabilities in the far-infrared and sub-millimetre spectral range 55 671 m.
Abstract: Herschel was launched on 14 May 2009, and is now an operational ESA space observatory o ering unprecedented observational capabilities in the far-infrared and submillimetre spectral range 55 671 m. Herschel carries a 3.5 metre diameter passively cooled Cassegrain telescope, which is the largest of its kind and utilises a novel silicon carbide technology. The science payload comprises three instruments: two direct detection cameras/medium resolution spectrometers, PACS and SPIRE, and a very high-resolution heterodyne spectrometer, HIFI, whose focal plane units are housed inside a superfluid helium cryostat. Herschel is an observatory facility operated in partnership among ESA, the instrument consortia, and NASA. The mission lifetime is determined by the cryostat hold time. Nominally approximately 20,000 hours will be available for astronomy, 32% is guaranteed time and the remainder is open to the worldwide general astronomical community through a standard competitive proposal procedure.

3,359 citations

Journal ArticleDOI
TL;DR: The Photodetector Array Camera and Spectrometer (PACS) as discussed by the authors is one of the three science instruments on ESA's far infrared and sub-mil- limetre observatory.
Abstract: The Photodetector Array Camera and Spectrometer (PACS) is one of the three science instruments on ESA's far infrared and submil- limetre observatory. It employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16 × 25 pixels, each, and two filled silicon bolometer arrays with 16 × 32 and 32 × 64 pixels, respectively, to perform integral-field spectroscopy and imaging photom- etry in the 60−210 μm wavelength regime. In photometry mode, it simultaneously images two bands, 60−85 μ mo r 85−125 μ ma nd 125−210 μm, over a field of view of ∼1.75 � × 3.5 � , with close to Nyquist beam sampling in each band. In spectroscopy mode, it images afi eld of 47 �� × 47 �� , resolved into 5 × 5 pixels, with an instantaneous spectral coverage of ∼ 1500 km s −1 and a spectral resolution of ∼175 km s −1 . We summarise the design of the instrument, describe observing modes, calibration, and data analysis methods, and present our current assessment of the in-orbit performance of the instrument based on the performance verification tests. PACS is fully operational, and the achieved performance is close to or better than the pre-launch predictions.

2,645 citations

Journal ArticleDOI
TL;DR: A review of the outer parts, beyond 1 AU, of protoplanetary disks with a focus on recent IR and (sub)millimeter results can be found in this paper.
Abstract: Flattened, rotating disks of cool dust and gas extending for tens to hundreds of astronomical units are found around almost all low-mass stars shortly after their birth. These disks generally persist for several million years, during which time some material accretes onto the star, some is lost through outflows and photoevaporation, and some condenses into centimeter- and larger-sized bodies or planetesimals. Through observations mainly at IR through millimeter wavelengths, we can determine how common disks are at different ages; measure basic properties including mass, size, structure, and composition; and follow their varied evolutionary pathways. In this way, we see the first steps toward exoplanet formation and learn about the origins of the Solar System. This review addresses observations of the outer parts, beyond 1 AU, of protoplanetary disks with a focus on recent IR and (sub)millimeter results and an eye to the promise of new facilities in the immediate future.

1,366 citations

Journal ArticleDOI
TL;DR: A detailed survey of more than 100 comets has been carried out by as mentioned in this paper, which enabled taxonomic groupings based on free radical species and on crystallinity of rocky grains.
Abstract: Cometary nuclei contain the least modified material from the formative epoch of our planetary system, and their compositions reflect a range of processes experienced by material prior to its incorporation in the cometary nucleus. Dynamical models suggest that icy bodies in the main cometary reservoirs (Kuiper Belt, Oort Cloud) formed in a range of environments in the protoplanetary disk, and (for the Oort Cloud) even in disks surrounding neighboring stars of the Sun's birth cluster. Photometric and spectroscopic surveys of more than 100 comets have enabled taxonomic groupings based on free radical species and on crystallinity of rocky grains. Since 1985, new surveys have provided emerging taxonomies based on the abundance ratios of primary volatiles. More than 20 primary chemical species are now detected in bright comets. Measurements of nuclear spin ratios (in water, ammonia, and methane) and of isotopic ratios (D/H in water and HCN; 14N/15N in CN and HCN) have provided critical insights on factors affec...

849 citations