Nançay Radio Observatory
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Telescope Nançay Radio Observatory |
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| The secondary mirror of the large radio telescope in Nançay | |
| Type | Large telescope (radio range) |
| Location | near Nançay , Cher department , France
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| height | 150 m |
| Geographic coordinates | 47 ° 22 '50 " N , 2 ° 11' 42" E |
| wavelength | 9 cm to 27 cm |
| Aperture | 200 m × 35 m
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| construction time | 1960 to 1965 |
| Installation | 1965 |
The Nançay Radio Observatory (French: Station de Radioastronomie de Nançay ), which opened in 1956, is part of the Paris Observatory , and is also connected to the Orléans University . It is located in the department of Cher in the region Sologne in France . The station consists of several instruments. The landmark is the large radio telescope for decimeter waves, which is one of the largest radio telescopes in the world. The radio heliograph, a T-shaped arrangement, and the decameter network, which works at wavelengths between 3 m and 30 m, have also been in operation for a long time.
history
The radio astronomy developed after the Second World War , civilian use could be supplied as the experts and unnecessary equipment. The École Normale Supérieure received three Würzburg giants with a diameter of 7.5 m, which were confiscated from the Germans by British troops during the war. These antennas were initially used in a research facility of the French Navy in Marcoussis .
It was clear that radio astronomy needed a large, flat, and secluded location where antennas could be placed that stretch for 1.5–2 km, or that are very large in themselves. Radio interference, such as that generated by modern technology, would also be avoided there. A piece of forest of 150 hectares near Nançay came on the market and was bought in 1953. First, various small instruments were installed - individual antennas and interferometers . Railroad tracks 6 m wide were laid, one line from east to west and one from north to south. These carried and transported the parallactically mounted , 40 t heavy Würzburg antennas.
A predecessor of today's radio heliograph had 16 antennas 5 m in diameter, which were evenly distributed along a 1500 m long east-west line; in addition there were eight antennas 6 m in diameter on a north-south line. The frequency observed was 169 MHz (1.77 m wavelength ).
After the discovery of the 21 cm line in 1951, there was a prospect of observing interstellar and extragalactic emission and absorption lines . This would require radio telescopes with higher sensitivity ; their greater expansion would also result in a higher resolution . The plan for this "large radio telescope" was based on a design by John D. Kraus from 1956. This design combined a large quilt and high resolution with only a few moving parts. Disadvantages, however, were the restriction to the meridian and the asymmetrical angular resolution, which was much coarser in elevation than in azimuth . The elevation control caused big problems in the beginning.
The great radio telescope
The large radio telescope (French: le Grand Radiotélescope , or lovingly le Grand Miroir ) was constructed between 1960 and 1965. Initially, only 20% of the primary and secondary mirrors were built to explore feasibility. The mirrors were expanded to their current full size in 1964, and the telescope was officially opened by Charles de Gaulle in 1965 . Scientific observations began in 1967.
The large radio telescope is a passage instrument . The primary mirror is located at the north end of the facility. It is a flat mirror 200 m wide and 40 m high. This mirror can be tilted in order to select the elevation to be observed . It consists of five segments 20 m wide, each weighing 40 t. The radio waves are reflected horizontally to the secondary mirror, which is 460 m further south. The shape of the secondary mirror is that of a segment of a sphere, 300 m wide and 35 m high. This mirror reflects the radio waves back north into the focus 280 m away , about 60% of the distance to the primary mirror. A cabin with further mirrors and the receiver is in the focus. During the observation, the focus cabin is driven from west to east for about an hour in order to track the daily movement of the observed object through the meridian .
Primary and secondary mirrors are made of wire mesh with 12.5 mm wide holes. The mirror surface is accurate to 4 mm so that wavelengths of 8 cm or longer can be observed. The telescope is therefore designed for decimeter waves, including the 21 cm spectral line of neutral atomic hydrogen (HI) and the 18 cm spectral line of the hydroxyl radical (OH).
The detector for the radio waves is cooled to 20 K in order to keep the electronic noise of the receiver low, and thus to improve the sensitivity to weak signals from the sky.
The large radio telescope observes at frequencies between 1.1 GHz and 3.5 GHz, continuum radiation as well as spectral lines in emission or absorption. The autocorrelator - spectrometer can observe eight spectra at different wavelengths, each spectral channels 1024 and 0.3 kHz resolution. The instrument is particularly suitable for large, statistical surveys and for monitoring objects with variable brightness.
Observation projects include:
- 21 cm HI emission from galaxies to study their rotation, distance, clustering and movement. This includes galaxies that are obscured by the Milky Way in visible light , blue compact galaxies, galaxies with low surface brightness (in visible light), and active galaxy nuclei .
- Pulsars , including pulse times, the distance of the pulsars, and the interstellar medium between the pulsar and the earth. Nançay is part of the European Pulsar Timing Array.
- Stellar shells, eruptive mutable stars and red giants .
- 18 cm OH emission and absorption in comets to determine their rate of loss for water and gas.
The radio heliograph
The heliograph is a T-shaped interferometer , which consists of parallactically mounted antennas several meters (mainly 5 m) in diameter. 19 antennas are located on an east-west line of 3.2 km in length, 25 antennas are arranged on a north-south line of 2.5 km in length. The instrument observes the sun seven hours a day to produce images of the corona in the frequency range 150 MHz to 450 MHz (wavelengths from 2 m to 0.67 m). The resolving power is then similar to that of the naked eye in visible light. Up to 200 images per second can be recorded. This enables the systematic investigation of the calm corona, solar flares and coronal mass ejections .
The observations from Nançay complement simultaneous observations from space probes in visible and ultraviolet light, and in X-rays .
The Dekameter Network
The Dekameter network was constructed between 1974 and 1977. It consists of 144 spiral antennas , which are formed from conductor wires that are wound around conical support structures in spiral curves. The cones are 5 m in diameter at the base and 9 m high; they are inclined 20 ° to the south. The cones are spread over an area of about one hectare. Half of the cones are wound opposite to the other half, so that left and right circularly polarized radio waves can be distinguished. The collection area is approximately 3500 m² for each polarization, equivalent to a dish antenna 67 m in diameter. The instrument is sensitive to wavelengths between 3 m and 30 m; these are the longest radio waves that can be observed through the ionosphere . The instrument is not an interferometer, but a phased array . A single antenna for these long wavelengths would be an impossible size. In addition, a phased array can be switched over to a different viewing direction at the moment by only changing the signal delays electronically.
The angular resolution is approx. 7 ° times 14 °. The Dekameter network does not generate images, but observes a single spectrum and records its change over time. The two basic objects are the Sun's upper corona and Jupiter's magnetosphere ; both have been observed almost daily since 1977. The changes over time are very rapid, for which very fast receivers were developed in Nançay.
The observations of Jupiter from Nançay complement results from space probes such as Voyager and Galileo .
LOFAR and NenuFAR
LOFAR consists of around 50 antenna systems, so-called stations, which are scattered across Europe. These are connected to a computer in the Netherlands via fast Internet connections. LOFAR is optimized for 110 MHz to 250 MHz (2.7 m to 1.2 m), but still works well between 30 MHz and 80 MHz (10 m to 3.7 m).
NenuFAR ( N ew E xtension in N ançay U pgrading LO FAR ) is a phased array that is optimized for the very low frequencies from 10 MHz to 85 MHz (30 m to 4 m). These are the longest radio waves that are not blocked by the ionosphere . The first scientific observations should begin in 2019. The main objectives are:
- Discovery and investigation of (magnetospheres of) exoplanets with radio waves,
- Recognition of the epoch of the formation of the first stars and galaxies approx. 100 million years after the Big Bang , when the neutral, atomic hydrogen was reionized ,
- the investigation, including spectroscopy, of pulsars across the entire Milky Way , at low radio frequencies.
When construction is complete, the system will contain antennas in 1938. Most are in a core 400 m in diameter, but 114 antennas are scattered up to 3 km.
NenuFAR will fulfill three roles:
- a radio telescope that can observe several positions at the same time,
- an autonomous radio wave camera that delivers images of 1 ° resolution within seconds, even 10 'resolution in hours,
- a LOFAR “superstation”, d. H. an extension of the LOFAR station in Nançay, which by combining NenuFAR and LOFAR can create radio wave images with a resolution of less than an arc second.
Other instruments and projects
In recent years and decades, astronomical observation projects have grown beyond national borders, so that more expertise and finances are concentrated. In some cases, the telescopes are so large that they are spread over several countries. In the 21st century, for example, activities in Nançay tend more towards participation in international projects. On the one hand, the location is z. B. available for LOFAR , on the other hand, the local expertise contributes to international projects such as LOFAR and the Square Kilometer Array (SKA).
EMBRACE
Divided between Nançay and Westerbork , EMBRACE ( E lectronic M ulti b eam R adio A stronomy C onc e pt) is a prototype for the second phase of SKA. It is a phased array of 4608 antennas that work between 900 MHz and 1500 MHz. You are under a 70 m² radome. With several lines of sight, several directions in the sky can be observed at the same time.
ORFEES
ORFEES (Observation Radiospéctrale pour FEDOME et les Etudes des Eruptions Solaires) is a 5 m diameter antenna dedicated to observing space weather and predicting solar flares. It makes daily observations of the solar corona between 130 MHz and 1 GHz, and it can monitor radio waves from the sun in almost real time.
CODALEMA
CODALEMA ( Co smic ray D etection A rray with L ogarithmic E lectro M agentic A ntennas) is an instrument for finding ultra-high energy cosmic rays that create cascades of particles in the atmosphere. These air showers generate very short electromagnetic signals in a wide frequency band from 20 MHz to 200 MHz. The network of around 50 antennas is widely spread across the site.
Surveillance antenna
An antenna on a 22 m high mast above the treetops has been monitoring the radioelectric quality of the station near Nançay for 20 years. With this, interference can be detected, which can disturb the observations of the radio heliograph and the decameter network. The frequency bands from 100 MHz to 4000 MHz are monitored in their entirety and in several directions.
Pôle des Étoiles
The large radio telescope, a series of display boards, and one or two of the antennas of the radio heliograph can be seen from the parking lot of the Pôle des Étoiles visitor center . During the opening hours, the visitor center has a permanent exhibition on astronomy and the work of the observatory. Once a day there is also a demonstration in the planetarium and a guided tour of the large radio telescope and radio heliograph.
Individual evidence
- ↑ a b c d Jean-Louis Steinberg: La création de la station de Nançay . In: l'Astronomie . tape 118 , 2004, ISSN 0004-6302 , p. 626-631 .
- ^ Jean-Louis Steinberg: Radio astronomy interférométrie . In: l'Astronomie . tape 118 , 2004, ISSN 0004-6302 , p. 622-625 .
- ↑ a b c Gilles Theureau, Ismaël Cognard: Le grand miroir . In: l'Astronomie . tape 118 , 2004, ISSN 0004-6302 , p. 10-16 .
- ↑ a b c d e Jean-Louis Steinberg: Les cinquante ans de Nançay . In: l'Astronomie . tape 118 , 2004, ISSN 0004-6302 , p. 5-9 .
- ^ A b Karl-Ludwig Klein: Le soleil en ondes radioélectriques - Le radiohéliographe de Nançay . In: l'Astronomie . tape 118 , 2004, ISSN 0004-6302 , p. 21-25 .
- ↑ a b c Philippe Zarka: Le réseau décamétrique de Nançay et l'interaction électrodynamique Io-Jupiter . In: l'Astronomie . tape 118 , 2004, ISSN 0004-6302 , p. 17-20 .
- ↑ a b c d e f Station de Radioastronomie de Nançay . ( obs-nancay.fr [accessed November 15, 2019]).
- ↑ a b c NenuFAR - New Extension in Nançay Upgrading LOFAR . ( obs-nancay.fr [accessed November 15, 2019]).
- ↑ Inauguration de NenuFAR, un radiotélescope unique au monde . October 3, 2019 ( obspm.fr [accessed November 15, 2019]).
- ↑ a b Nicolas Dubouloz, Wim van Driel, Alain Kerdraon, Philippe Zarka: La station de Nançay et les projets internationaux de 'radiotélescopes du futur' . In: l'Astronomie . tape 118 , 2004, ISSN 0004-6302 , p. 26-29 .
- ↑ Pôle des Étoiles de Nançay . ( poledesetoiles.fr [accessed November 7, 2019]).
literature
- Wayne Orchiston, James Lequeux, Jean-Louis Steinberg, Jean Delannoy: Highlighting the history of French radio astronomy - 3: The Würzburg antennas at Marcoussis, Meudon and Nançay . In: Journal of Astronomical History and Heritage . tape 10 , no. 3 , 2007, ISSN 1440-2807 , p. 221–245 , bibcode : 2007JAHH ... 10..221O (English).
- Wayne Orchiston, Jean-Louis Steinberg, Mukui Kundu, Jacques Arsac, Émile-Jacques Blum, André Boischot: Highlighting the history of French radio astronomy - 4: Early solar research at the École Normale Supérieure, Marcoussis and Nançay . In: Journal of Astronomical History and Heritage . tape 12 , no. 3 , 2009, ISSN 1440-2807 , p. 175–188 , bibcode : 2009JAHH ... 12..175O (English).
- James Lequeux, Jean-Louis Steinberg, Wayne Orchiston: Highlighting the history of French radio astronomy - 5: The Nançay Large Radio Telescope . In: Journal of Astronomical History and Heritage . tape 13 , no. 1 , 2010, ISSN 1440-2807 , p. 29–42 , bibcode : 2010JAHH ... 13 ... 29L (English).
- Monique Pick, Jean-Louis Steinberg, Wayne Orchiston, André Boischot: Highlighting the history of French radio astronomy - 6: The multi-element grating arrays at Nançay . In: Journal of Astronomical History and Heritage . tape 14 , no. 1 , 2011, ISSN 1440-2807 , p. 57–77 , bibcode : 2011JAHH ... 14 ... 57P (English).
Web links
- Nançay Radio Observatory (Official website, French)
- Pôle des Étoiles (Official website of the visitor center, French)