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The European VLBI network
0273—1177/91 $0.00 + .50 Copyright © 1991 COSPAR
Adi’. Space Res. Vol. 11, No.2, pp. (2)397—(2)401. 1991 Printed in Great Britain. All rights reserved.
THE EUROPEAN VLBI NETWORK R. S. Booth Onsala Space Observatory, Chalmers University of Technology, S-439 00 Onsala, Sweden
ABSTRACT The European VLBI network, EVN, is an informal group of Radio Astronomy observatories in Europe dedicated to operate YLBI experiments in an organized and user-friendly manner. The structure and organization of the network is described and the salient features of the network telescopes and their receivers are listed. 30% of the observing time on the EVN will be available for the forthcoming Space VLBI projects. 1.
Introduction
Much of the pioneering work in long baseline interferomeiry was carried out at Jodrell Bank in the early 1960s by the late Henry Palmer and his group, using the radio link technique. After the first successful VLBI experiments in Canada and the USA in 1967, individual European observatories participated in experiments, but only on an ad-hoc basis. However, the tremendous potential of VLBI was clear and in the autumn of 1975 a group of interested European radio astronomers met at the MaxPlanck-Institut für Radioastronomie in Bonn and agreed to work towards cooperation in VLBI. A series of informal meetings culminated in the formation of the EVN in 1980 when a meeting of observatory directors agreed to support the goals of the network and formed a programme committee to receive and assess proposals for observing time. The EVN has been described previously by Schilizzi (1989) and by Booth (1990). 2.
Organisation
Today, the EVN is managed by the European Consortium for VLBI which is a group consisting of the Directors of the participating observatories, or their representatives. The following observatories are full members of the Consortium: the Nuffield Radio Astronomy Laboratory, Jodrell Bank, U.K., the Netherlands Foundation for Research in Astronomy, Westerbork, the Max-Planck-Institut für Radioastronomie, Bonn, F.R.G., the Instituto di Radioastronomia, Bologna, Italy, and the Onsala Space Observatory, Sweden, and associate members are: Observatoire de Paris, Meudon, France. Torun Radio Astronomy Observatory, Poland, Geodätisches Institut, University of Bonn, F.R.G., and the Space Research Institute, Moscow, U.S.S.R.
(2)397
(2)398
R. S. Booth
Observing proposals are evaluated by the EVN Programme Committee. Membership consists of observatory representatives and senior askrophysicists invited by the consortium. The programme committee chairman is selected by the Board of Directors. The committee meets three times a year.shordy after each of the tri-annual calls for proposals. Scheduling and organisation of experiments is currently carried out by the scheduler of the MPIfR, Dr. R. Schwartz, in collaboration with the PC chairman. The network is also supported by a Technical Working Group whose members come from the individual observatories. Its chairman is appointed by the Board of Directors. In addition, the Board has appointed a Network Scientist to monitor the performance of the network. He works in liason with both the PC and the Technical Working Group. Finally, the network has appointed a Project Manager who is responsible for coordinating specific network projects and liason with appropriate international funding agencies in the search for capital investment. The on-going projects of the network will be discussed below. The EVN works closely with the US VLBI network. Calls for proposals are sent out at the same time for observing sessions that are usually joint, having a Europe-only and a US-only period at the end. Proposals requiring both arrays are assessed independently by the EVN PC and the US assessment panel and the schedulers assess the results. There is rarely a serious disagreement. VLBI in the United States is in a transition period as we have heard from Paul Vanden Bout in this session. We hope and expect that a useful working relationship will be arranged with the VLBA.
C 50
ONSALA
(
JODRELL BANK ~CAMBRIDGE
WESTERBORK
/
•1
~‘
—
\
• TORUN EFFELSBER
,1,.
S
-
iç ~\ \ \
• WETTZEL’~’;~ ~
NANCAY~~i
\
..
~.—‘
.1~•”
BOLOGNA.l-*T1
SIMEIS
40~-..
NOTO 5
0
5
10
15
Figure 1. Locations ofEVN telescopes Eigure_1. Locations of EVN telescopes
20
25
30
35
(2)399
The European VLBI Network
3.
Network facilities
3.1
Telescopes
The distribution of the EVN telescopes is shown in Figure 1. The EVN spans a relatively small geographical area but is very powerful in terms of its overall sensitivity because it contains 3 major large telescopes, the lOOm Effelsberg antenna, the 76m Lovell telescope atJodrell Bank and the Westerbork synthesis array which, when phased as a single dish for VLBI, has an effective diameter of 93m. The full list of network telescopes is given in Table 1. Information on the type of recording system and the available frequency standard is also given. Most of the network observatories have Mk3 wide-band recorders and by the end of summer, 1990, these will have been converted to multipass (Mk3A) machines by replacing the normal recording heads by much narrower heads giving a trackwidth of 40 microns. Table 2 lists the available receivers as of June, 1990.
Table 1: The EVN telescopes. Country
Observatory & telescope
Diameter (m)
Jodrell Bank Lovell MkII Cambridge1 Holland NFRA Westerbork FRG MPI, Bonn Effelsberg FGRS2 Wettzell Italy Bologna Medicina Noto Sweden Onsala 26
Recoider
Clock
U.K
76 25 32
Mk2,Mk3A
H
Mk2,VLBA
H
93*
Mk2,Mk3A
H
100 20
Mk2,Mk3A Mk2,MK3A
H H
32 32 Mk2,Mk3 20
Mk2,Mk3A Mk2,Mk3 H
H H
France Meudon Nancay Poland Torun USSR Simeis *
94* 15
22
Mk2 Mk2 Mk2
Rb Rb H
this is the equivalent diameter
1 The telescopeat Cambridge is an extension of the Jodrell Bank Multi-Element Radio Linked Interferometer, MERLIN, and will be completed during 1990. 2 FGRS = Fundamental Geodetic Reference Station
JASR 11:2-AA
R. S. Booth
(2)400
Table 2. EVN receivers available for VLBI Station/wavelength (cm) 92
50
21
18
13
6
Effelsberg
x
x
x
x
x
x
x
x
x
x
Medicina
x
x
x
x
x
x
Noto
x
x
x
x
x
x
x
x
x
x
x
WSRT
x
JodrellBank
x
x
Onsala Torun
x
x
Crimea
x
x
x
3.2
x
x
x
x
x
x
x
x
x x
x
0.3
x
Wettzell Nancay
3.6 1.35 0.7
x
x
VLBI Correlators
The Max-Planck-Institute für Radioastronomie in Bonn supports both Mk2 and Mk3/3A VLBI playback and correlation facilities and makes them available to the VLBI community. The Mk2 correlator is a 3-station system while the Mk3A correlator is a 5-station machine. With the Mk3A processor, the data processing computer is sufficient to allow correlation of data from 5 telescopes, recorded in mode B (28 MHz bandwidth), in one pass through the correlator, or 4-stations recorded at 56 MHz bandwidth. The EVN has ambitious plans to build a 20-station correlator for the future. This will be based on the VLBA recording system. Such a correlator is very expensive, of course, and we are in the process of seeking financial support. The correlator will be built by engineers of the Netherlands Foundation for Research in Astronomy, in Dwingeloo. We are still optimistic that financial support will be forthcoming, although, in the context of the forthcoming space VLBI missions it is clear that even if we are able to commence building in 1990, we can only hope to complete the first phase of the project, a 10-station machine, by 1995. Nevertheless, such a correlator will be extremely valuable for processing some part of the data recorded in the course of the space VLBI missions. It is imperative that Europe has a large correlator for the future.
The European VLBI Network
4.
(2)40 1
Millimetre VLBI
Europe has, in the past few years, built up a strong base in millimetre astronomy and the observatories at Onsala and Effelsberg have played a major role in the development of YLBI at millimetre wavelengths. Recently, Krichbaum et al. (1990) and BAAth et al. (unpublished, but see BAAth, 1989) have produced relatively high (100:1) dynamic range maps of 3C 273 at 43 GHz and 100 0Hz, respectively, from observations with global millimetre arrays, showing that the technique is maturing. As soon as our receiver reliability improves, we should consider persuading the other European miffimetre telescopes to join the EVN and extend our wavelength range downwards. 5.
The EVN and the Space YLBI missions
It is worth reiterating that space VLBI depends heavily on the ground VLBI networks, or sub-sets thereof, and so their support is essential. The EVN has agreed that 30% of network time should be made available for observations with the VLBI telescopes in Earth orbiiWe expect to allocate this time in blocks and so experiments involving a space element would take place during these network blocks. The 30% allocation represents an increase in our present commitment to VLBI and demonstrates our view, not only of the importance of the space missions scientifically, but also of the international cooperation which they represent. The EVN is further committed to RADIOASTRON and will supply a space qualified receiver for the mission to operate at a wavelength of 6 cm. The receiver is being built in collaboration by engineers from the MPIfR in Bonn and the Netherlands Foundation for Research in Astronomy in Dwingeloo. 6.
References
Booth, R.S., 1990. In Frontiers of VLBJ, Eds. H. Hirabayashi, M. Inoue and Kobayashi, Universal Academy Press. Bâãth, L.B., 1989. In Submillimetre Astronomy. Eds. G.D. Watt and A.S. Webster, Kluwer Academic Publishers. Krichbaum, T.P., Booth, R.S., Kus, AJ., Ronnang, B.O., Witzel, A., Graham, D.A., Pauliny-Toth, I.K.K., Quirrenbach, A., Hummel, C.A., Alberdi, A., Zensus, J.A., Johnston, K.J., Spencer, J.H., Rogers, A.E.E., Lawrence, C.R., Readhead, A.C.S., Hirabayashi, H., Inoue, M., Morimoto, M., Dhawan, V., Bartel, N., Shapiro, 1.1., Burke, B.F., and Marcaide, J.M., 1990. MPI Preprint No. 391, to appear in Astron. Astrophys. Schiizzi, R.T., 1989. In Very Long Baseline Interferometry, Techniques and Applications. Eds. M. Felli and R. Spencer, Kiuwer Academic Publishers.
Adi’. Space Res. Vol. 11, No.2, pp. (2)397—(2)401. 1991 Printed in Great Britain. All rights reserved.
THE EUROPEAN VLBI NETWORK R. S. Booth Onsala Space Observatory, Chalmers University of Technology, S-439 00 Onsala, Sweden
ABSTRACT The European VLBI network, EVN, is an informal group of Radio Astronomy observatories in Europe dedicated to operate YLBI experiments in an organized and user-friendly manner. The structure and organization of the network is described and the salient features of the network telescopes and their receivers are listed. 30% of the observing time on the EVN will be available for the forthcoming Space VLBI projects. 1.
Introduction
Much of the pioneering work in long baseline interferomeiry was carried out at Jodrell Bank in the early 1960s by the late Henry Palmer and his group, using the radio link technique. After the first successful VLBI experiments in Canada and the USA in 1967, individual European observatories participated in experiments, but only on an ad-hoc basis. However, the tremendous potential of VLBI was clear and in the autumn of 1975 a group of interested European radio astronomers met at the MaxPlanck-Institut für Radioastronomie in Bonn and agreed to work towards cooperation in VLBI. A series of informal meetings culminated in the formation of the EVN in 1980 when a meeting of observatory directors agreed to support the goals of the network and formed a programme committee to receive and assess proposals for observing time. The EVN has been described previously by Schilizzi (1989) and by Booth (1990). 2.
Organisation
Today, the EVN is managed by the European Consortium for VLBI which is a group consisting of the Directors of the participating observatories, or their representatives. The following observatories are full members of the Consortium: the Nuffield Radio Astronomy Laboratory, Jodrell Bank, U.K., the Netherlands Foundation for Research in Astronomy, Westerbork, the Max-Planck-Institut für Radioastronomie, Bonn, F.R.G., the Instituto di Radioastronomia, Bologna, Italy, and the Onsala Space Observatory, Sweden, and associate members are: Observatoire de Paris, Meudon, France. Torun Radio Astronomy Observatory, Poland, Geodätisches Institut, University of Bonn, F.R.G., and the Space Research Institute, Moscow, U.S.S.R.
(2)397
(2)398
R. S. Booth
Observing proposals are evaluated by the EVN Programme Committee. Membership consists of observatory representatives and senior askrophysicists invited by the consortium. The programme committee chairman is selected by the Board of Directors. The committee meets three times a year.shordy after each of the tri-annual calls for proposals. Scheduling and organisation of experiments is currently carried out by the scheduler of the MPIfR, Dr. R. Schwartz, in collaboration with the PC chairman. The network is also supported by a Technical Working Group whose members come from the individual observatories. Its chairman is appointed by the Board of Directors. In addition, the Board has appointed a Network Scientist to monitor the performance of the network. He works in liason with both the PC and the Technical Working Group. Finally, the network has appointed a Project Manager who is responsible for coordinating specific network projects and liason with appropriate international funding agencies in the search for capital investment. The on-going projects of the network will be discussed below. The EVN works closely with the US VLBI network. Calls for proposals are sent out at the same time for observing sessions that are usually joint, having a Europe-only and a US-only period at the end. Proposals requiring both arrays are assessed independently by the EVN PC and the US assessment panel and the schedulers assess the results. There is rarely a serious disagreement. VLBI in the United States is in a transition period as we have heard from Paul Vanden Bout in this session. We hope and expect that a useful working relationship will be arranged with the VLBA.
C 50
ONSALA
(
JODRELL BANK ~CAMBRIDGE
WESTERBORK
/
•1
~‘
—
\
• TORUN EFFELSBER
,1,.
S
-
iç ~\ \ \
• WETTZEL’~’;~ ~
NANCAY~~i
\
..
~.—‘
.1~•”
BOLOGNA.l-*T1
SIMEIS
40~-..
NOTO 5
0
5
10
15
Figure 1. Locations ofEVN telescopes Eigure_1. Locations of EVN telescopes
20
25
30
35
(2)399
The European VLBI Network
3.
Network facilities
3.1
Telescopes
The distribution of the EVN telescopes is shown in Figure 1. The EVN spans a relatively small geographical area but is very powerful in terms of its overall sensitivity because it contains 3 major large telescopes, the lOOm Effelsberg antenna, the 76m Lovell telescope atJodrell Bank and the Westerbork synthesis array which, when phased as a single dish for VLBI, has an effective diameter of 93m. The full list of network telescopes is given in Table 1. Information on the type of recording system and the available frequency standard is also given. Most of the network observatories have Mk3 wide-band recorders and by the end of summer, 1990, these will have been converted to multipass (Mk3A) machines by replacing the normal recording heads by much narrower heads giving a trackwidth of 40 microns. Table 2 lists the available receivers as of June, 1990.
Table 1: The EVN telescopes. Country
Observatory & telescope
Diameter (m)
Jodrell Bank Lovell MkII Cambridge1 Holland NFRA Westerbork FRG MPI, Bonn Effelsberg FGRS2 Wettzell Italy Bologna Medicina Noto Sweden Onsala 26
Recoider
Clock
U.K
76 25 32
Mk2,Mk3A
H
Mk2,VLBA
H
93*
Mk2,Mk3A
H
100 20
Mk2,Mk3A Mk2,MK3A
H H
32 32 Mk2,Mk3 20
Mk2,Mk3A Mk2,Mk3 H
H H
France Meudon Nancay Poland Torun USSR Simeis *
94* 15
22
Mk2 Mk2 Mk2
Rb Rb H
this is the equivalent diameter
1 The telescopeat Cambridge is an extension of the Jodrell Bank Multi-Element Radio Linked Interferometer, MERLIN, and will be completed during 1990. 2 FGRS = Fundamental Geodetic Reference Station
JASR 11:2-AA
R. S. Booth
(2)400
Table 2. EVN receivers available for VLBI Station/wavelength (cm) 92
50
21
18
13
6
Effelsberg
x
x
x
x
x
x
x
x
x
x
Medicina
x
x
x
x
x
x
Noto
x
x
x
x
x
x
x
x
x
x
x
WSRT
x
JodrellBank
x
x
Onsala Torun
x
x
Crimea
x
x
x
3.2
x
x
x
x
x
x
x
x
x x
x
0.3
x
Wettzell Nancay
3.6 1.35 0.7
x
x
VLBI Correlators
The Max-Planck-Institute für Radioastronomie in Bonn supports both Mk2 and Mk3/3A VLBI playback and correlation facilities and makes them available to the VLBI community. The Mk2 correlator is a 3-station system while the Mk3A correlator is a 5-station machine. With the Mk3A processor, the data processing computer is sufficient to allow correlation of data from 5 telescopes, recorded in mode B (28 MHz bandwidth), in one pass through the correlator, or 4-stations recorded at 56 MHz bandwidth. The EVN has ambitious plans to build a 20-station correlator for the future. This will be based on the VLBA recording system. Such a correlator is very expensive, of course, and we are in the process of seeking financial support. The correlator will be built by engineers of the Netherlands Foundation for Research in Astronomy, in Dwingeloo. We are still optimistic that financial support will be forthcoming, although, in the context of the forthcoming space VLBI missions it is clear that even if we are able to commence building in 1990, we can only hope to complete the first phase of the project, a 10-station machine, by 1995. Nevertheless, such a correlator will be extremely valuable for processing some part of the data recorded in the course of the space VLBI missions. It is imperative that Europe has a large correlator for the future.
The European VLBI Network
4.
(2)40 1
Millimetre VLBI
Europe has, in the past few years, built up a strong base in millimetre astronomy and the observatories at Onsala and Effelsberg have played a major role in the development of YLBI at millimetre wavelengths. Recently, Krichbaum et al. (1990) and BAAth et al. (unpublished, but see BAAth, 1989) have produced relatively high (100:1) dynamic range maps of 3C 273 at 43 GHz and 100 0Hz, respectively, from observations with global millimetre arrays, showing that the technique is maturing. As soon as our receiver reliability improves, we should consider persuading the other European miffimetre telescopes to join the EVN and extend our wavelength range downwards. 5.
The EVN and the Space YLBI missions
It is worth reiterating that space VLBI depends heavily on the ground VLBI networks, or sub-sets thereof, and so their support is essential. The EVN has agreed that 30% of network time should be made available for observations with the VLBI telescopes in Earth orbiiWe expect to allocate this time in blocks and so experiments involving a space element would take place during these network blocks. The 30% allocation represents an increase in our present commitment to VLBI and demonstrates our view, not only of the importance of the space missions scientifically, but also of the international cooperation which they represent. The EVN is further committed to RADIOASTRON and will supply a space qualified receiver for the mission to operate at a wavelength of 6 cm. The receiver is being built in collaboration by engineers from the MPIfR in Bonn and the Netherlands Foundation for Research in Astronomy in Dwingeloo. 6.
References
Booth, R.S., 1990. In Frontiers of VLBJ, Eds. H. Hirabayashi, M. Inoue and Kobayashi, Universal Academy Press. Bâãth, L.B., 1989. In Submillimetre Astronomy. Eds. G.D. Watt and A.S. Webster, Kluwer Academic Publishers. Krichbaum, T.P., Booth, R.S., Kus, AJ., Ronnang, B.O., Witzel, A., Graham, D.A., Pauliny-Toth, I.K.K., Quirrenbach, A., Hummel, C.A., Alberdi, A., Zensus, J.A., Johnston, K.J., Spencer, J.H., Rogers, A.E.E., Lawrence, C.R., Readhead, A.C.S., Hirabayashi, H., Inoue, M., Morimoto, M., Dhawan, V., Bartel, N., Shapiro, 1.1., Burke, B.F., and Marcaide, J.M., 1990. MPI Preprint No. 391, to appear in Astron. Astrophys. Schiizzi, R.T., 1989. In Very Long Baseline Interferometry, Techniques and Applications. Eds. M. Felli and R. Spencer, Kiuwer Academic Publishers.