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  • 51.
    Mundy, Lee G.
    et al.
    California Institute of Technology, California, USA.
    Bååth, L.B.
    California Institute of Technology, California, USA.
    Sonic linewidths in warm clouds?1987In: Molecular clouds in the Milky Way and external galaxies: Proceedings of a Symposium Held at the University of Massachusetts in Amherst, November 2-4, 1987 / [ed] Robert L. Dickman, Ronald L. Snell & Judith S. Young, Berlin/Heidelberg: Springer Berlin/Heidelberg, 1987, p. 235-237Conference paper (Refereed)
  • 52.
    Mundy, Lee G.
    et al.
    Owens Valley Radio Observatory, Californa Institute of Technology, Pasadena, CA, USA.
    Cornwell, T. J.
    National Radio Astronomy Observatory, Socorro, NM, USA.
    Masson, Colin R.
    Owens Valley Radio Observatory, Californa Institute of Technology, Pasadena, CA, USA.
    Scoville, Nicholas Z.
    Owens Valley Radio Observatory, Californa Institute of Technology, Pasadena, CA, USA.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Johansson, Lars E. B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    High-resolution images of the Orion molecular ridge in the CS J = 2-1 transition1988In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 325, no 1, p. 382-388Article in journal (Refereed)
    Abstract [en]

    The authors have constructed 7arcsec.5 resolution images of the CS J = 2-1 emission from a 3arcmin.5 section of the Orion molecular ridge using a maximum entropy algorithm to combine Owens Valley Millimeter-Wave Interferometer and Onsala Space Observatory 20 m data. The resulting images include all of the flux and have positional accuracy of 1arcsec-2arcsec on the small-scale features. The observed section of the ridge includes four condensations. The condensations have dimensions from 0.03 to 0.11 pc and virial massses from 30 to 80 M_sun;. Approximately 70% of the total mass within the 3arcmin region is contained in these condensations.

  • 53.
    Mundy, Lee G.
    et al.
    California Institute of Technology, Pasadena, CA, USA.
    Scoville, Nicholas Z.
    California Institute of Technology, Pasadena, CA, USA.
    Bååth, Lars B.
    Onsala Space Observatory, Onsala, Sweden.
    Masson, Colin R.
    California Institute of Technology, Pasadena, CA, USA.
    Woody, David P.
    Owens Valley Radio Observatory, Big Pine, CA, USA.
    Protostellar Condensations within the Orion Ridge1986In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 304, no 2, p. L51-L55Article in journal (Refereed)
    Abstract [en]

    Aperture synthesis observations of the CS J = 2 to 1 line and 95 GHz continuum emission from a 2 arcmin x 3 arcmin region around IRc2 in the OMC-1 molecular cloud have been obtained at 7.5 arcsec resolution with the Owens Valley Radio Observatory millimeter interferometer. These observations reveal four distinct condensations with the OMC-1 molecular ridge. The condensations lie along the edge of the bright central part of the H II region, M 42, suggesting that they may have been formed as a result of shock compression driven by the H II region. Their masses and densities, M about 50 solar masses and n about 10 to the 6th - 10 to the 7th/cu cm, suggest that the condensations will undergo further massive star formation on a short time scale (about 20,000 yr).

  • 54.
    Mundy, L.G.
    et al.
    California Institute of Technology (Caltech), Pasadena, California, United States.
    Scoville, N.Z.
    California Institute of Technology (Caltech), Pasadena, California, United States.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Masson, C.R.
    California Institute of Technology (Caltech), Pasadena, California, United States.
    Woody, D.P.
    California Institute of Technology (Caltech), Pasadena, California, United States.
    Interferometer Maps of the CS J=2-1 Emission Around Orion IRC21985In: Bulletin of the American Astronomical Society, ISSN 0002-7537, E-ISSN 2330-9458, Vol. 17, p. 563-563Article in journal (Refereed)
  • 55.
    Mundy, L.G.
    et al.
    California Institute of Technology (Caltech), Pasadena, CA, USA.
    Scoville, N.Z.
    California Institute of Technology (Caltech), Pasadena, CA, USA.
    Masson, C.R.
    California Institute of Technology (Caltech), Pasadena, CA, USA.
    Cornwell, T.J.
    The National Radio Astronomy Observatory (NRAO), Green Bank, West Virginia, USA.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Velocity and Spatial Structure in the Orion Molecular Ridge1986In: Bulletin of the American Astronomical Society, ISSN 0002-7537, E-ISSN 2330-9458, Vol. 18, p. 931-931Article in journal (Refereed)
  • 56.
    Okopi, J. E.
    et al.
    Onsala Space Observatory, Onsala, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Wide field mapping of 5C121991In: Radio Interferometry: Theory Techniques and Applications / [ed] T. J. Cornwell & R.A. Perley, San Francisco, USA: Astronomical Society of the Pacific , 1991, p. 253-256Conference paper (Refereed)
    Abstract [en]

    A wide-field mapping technique aimed at resolving problems which occur in the radio mapping of very wide fields is described. The technique has been successfully applied to Merlin observations of the 5C12 region covering an area of 1800 arcsec x 180 arcsec.

  • 57.
    Rantakyro, Fredrik T.
    et al.
    Dept. of Astronomy and Astrophysics, Chalmers University of Technology, Gothenburg, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Onsala, Sweden.
    VLBI observations at 18 cm and 3 mm of the quasar 3C3451990In: Nordic-Baltic Astronomy Meeting: Proceedings of a meeting held at the Astronomical Observatory of the Uppsala University, June 17-21, 1990, celebrating the 250th anniversary of the Celsius Observatory / [ed] C.-I. Lagerkvist, D. Kiselman, M. Lindgren, Uppsala: Uppsala universitet, 1990, p. 253-255Conference paper (Refereed)
  • 58. Rantakyrö, F. T.
    et al.
    Bååth, Lars B.
    Halmstad University, School of Business and Engineering (SET).
    Structural Changes in CTA1021996In: Extragalactic radio sources: proceedings of the 175th Symposium of the International Astronomical Union, held in Bologna, Italy, 10-14 October 1995 / [ed] R. D. Ekers; C. Fanti & L. Padrielli, Boston: Kluwer , 1996, p. 39-40Conference paper (Other academic)
  • 59.
    Rantakyrö, F. T.
    et al.
    University of Gothenburg, Gothenburg, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Pauliny-Toth, I. I. K.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Matveyenko, L. I.
    Space Research Institute, Moscow, Russia.
    Unwin, S. C.
    California Institute of Technology, Pasadena, California, United States.
    High dynamic-range VLBI observations of 3C 345 at 18 cm wavelength1992In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 259, no 1, p. 8-16Article in journal (Refereed)
    Abstract [en]

    This paper presents very high dynamic range VLBI observations of the quasar 3C345 at 18 cm wavelength at two epochs, 1981.11 and 1985.27. We find that the direction of the jet changes drastically and the surface brightness decreases with increasing distance from the core. We show that a true three-dimensional curvature of the jet in space is needed to obtain the observed decrease of intensity with distance from the core, both in an adiabatic expansion model as well as in a model where the comoving flux is constant. Our observations confirm the detection of a previously reported low surface brightness component, C0. In addition, there is a large component extended perpendicular to the jet axis which we associate with a stationary shock at a distance consistent with the expected position of the narrow line region. Models for the intensity of the jet fitted to the observed dependence of intensity with distance from the core suggests this shocked region to be the place where the jet is expanding adiabatically after having had a constant width closer to the core. A limit on the allowed viewing angle theta less-than-or-similar-to 40-degrees is derived from the lack of any detectable counterjet.

  • 60.
    Rantakyrö, Fredrik T.
    et al.
    Department of Astronomy/Astrophysics, Chalmers University of Technology, Gothenburg, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Extreme Superluminal motion in CTA102 ?1993In: Sub-arcsecond Radio Astronomy: Proceedings of the Nuffield Radio Astronomy Laboratories' conference, held in Manchester, July 20–24, 1992 / [ed] R. J. Davis & R. S. Booth, Cambridge: Cambridge University Press, 1993, p. 197-198Chapter in book (Refereed)
    Abstract [en]

    We present observations of proper motion in five epoches of VLBI observations of CTA102. The highest observed proper motion was μ=0.64 mas/year, corresponding to a transverse velocity of v = 18.0 ± 4 c.

  • 61.
    Romney, J.
    et al.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Padrielli, L.
    CNR, Istituto di Radioastronomia, Bologna, Italy.
    Bartel, N.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany & Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA.
    Weiler, K.W.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany & Division of Astronomical Sciences, National Science Foundation, Washington, DC, USA.
    Ficarra, A.
    CNR, Istituto di Radioastronomia, Bologna, Italy.
    Mantovani, F.
    CNR, Istituto di Radioastronomia, Bologna, Italy.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Kogan, L.
    Institute for Space Research, Academy of Sciences, Moscow, USSR.
    Matveenko, L.
    Institute for Space Research, Academy of Sciences, Moscow, USSR.
    Moiseev, I.G.
    Crimea Astrophysical Observatory, Academy of Sciences, Moscow, USSR.
    Nicholson, G.
    National Institute for Telecommunications Research, Johannesburg, South Africa.
    The milliarcsecond scale structure of low frequency variable sources1984In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 135, no 2, p. 289-299Article in journal (Refereed)
    Abstract [en]

    VLBI observations were performed of 21 radio sources which exhibit low frequency variability. The integrated flux densities, variability indices at 0.4 GHz, optical magnitudes, redshifts, spectral indices at 0.4 GHz, and flux intensities with respect to a reference energy flux are provided. The VLBI data were synthesized from observatories located on different continents around the world. All structures were emitted from compact sources with sizes confined to milliarcsc scales. Nearly half displayed core-jet morphologies, while 28 percent had complex structures and 14 percent had either simple structures or were not resolvable. Further observations are proceeding at 400 mHz to confirm the presence of synchrotron electrons and magnetic fields ejected at relativistic speeds along the line of sight, which has the appearance of superluminal velocities.

  • 62.
    Schalinski, C.J.
    et al.
    Institut de Radio Astronomie Millimétrique, Grenoble, France.
    Greve, A.
    Institut de Radio Astronomie Millimétrique, Grenoble, France.
    Grewing, M.
    Institut de Radio Astronomie Millimétrique, Grenoble, France.
    Steppe, H.
    Institut de Radio Astronomie Millimétrique, Grenoble, France.
    Graham, D.A.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Krichbaum, T.P.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Standke, K.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Witzel, A.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Alberdi, A.
    Instituto de Astrofisica de Andalucia, Granada, Spain.
    Booth, R.S.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Colomer, F.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    The 86 GHz VLBI Test with Pico Veleta: First Detection of the Quasar 3C454.3 at 3 mm1993In: Sub-arcsecond Radio Astronomy: Proceedings of the Nuffield Radio Astronomy Laboratories' conference, held in Manchester, July 20–24, 1992 / [ed] R. J. Davis & R. S. Booth, Cambridge: Cambridge University Press, 1993, p. 184-185Chapter in book (Refereed)
  • 63.
    Sizhen, Lan
    et al.
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    Lian, Shen
    Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE).
    Microwave Components Based on Magnetic Wires2010Independent thesis Advanced level (degree of Master (One Year)), 40 credits / 60 HE creditsStudent thesis
    Abstract [en]

    With  the  continuous  advances  in  microwave  technology,  microwave  components  and  related magnetic materials become more important in industrial environment. In order to further develop the microwave components, it is of interest to find new kinds of technologies and materials. Here, we  introduce  a  new  kind  of  material  --  amorphous  metallic  wires  which  could  be  used  in microwave  components,  and  use  these  wires  to  design  new  kinds  of  attenuators.  Based  on  the fundamental  magnetic  properties  of  amorphous  wires  and  transmission  line  theory,  we  design  a series of experiments focusing on these wires, and analyze all the experimental results.    Experimental  results  show  that  incident  and  reflected  signals  produce  interference  and  generate standing  waves  along  the  wire.  At  given  frequency,  the  insertion  attenuation  S21 [dB]  of  an amorphous wire increases monotonically with dc bias current. The glass cover will influence the  magnetic  domain  structure  in  amorphous  metallic  wires.  Therefore,  it  will  affect  the circumference  permeability  and  change  the  signal  attenuation.  It  is  necessary  to  achieve  the impedance  matching  by  coupling  to  an  inductor  and  a  capacitor  in  the  circuit.  The  impedance matching  makes  the  load  impedance  close  to  the  characteristic  impedance  of  transmission  line. The magnetic wire-based attenuator designed in this thesis work are characterized and compared to conventional pin-diode attenuator.

  • 64.
    Standke, K. J.
    et al.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany & Geodätisches Institut, Bonn, Germany.
    Graham, D. A.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Krichbaum, T. P.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Witzel, A.
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Schalinski, C. J.
    Institut de Radioastronomie Millimétrique, Grenoble, France.
    Rogers, A. E. E.
    Haystack Observatory, Westford, Massachusetts, USA.
    Booth, R. S.
    Onsala Space Observatory, Onsala, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    High Sensitivity VLBI at 86 GHz: First Fringes with the 100 m Radio Telescope at Effelsberg1993In: VLBI Technology: Progress and Future Observational Possibilities: Proceedings of the International Symposium Held at Kyoto International Conference Hall on September 6-10, 1993 / [ed] Tetsuo Sasao, Seiji Manabe, Osamu Kameya & Makoto Inoue, Tokyo: Terra Scientific , 1993, p. 75-85Chapter in book (Refereed)
    Abstract [en]

    Inclusion of large and sensitive antennas is of essential importance to further improve the imaging capabilities of VLBI at 3.5 mm wavelength. The combination of the 100 m radio telescope at Effelsberg (illuminated diameter ~60 m at lambda = 3.5 mm) with the 30 m radio telescope at Pico Veleta presently allows the detection of compact flux down to a level of 0.2 Jy (for τ=360 seconds integration time). Fringes have been found for 23 radio sources many of them not observed previously with VLBI at 86 GHz. On European baselines to Effelsberg the SNR typically was 10 to 30 (and ranged up to 107 for 3C279), facilitating model fitting for the brightest sources. Even in spite of chaning weather conditions during the observations (coherence times ranged between 10 to 100 seconds) and a still non-optimum pointing model for the 100 m antenna for observations at high frequencies, these results demonstrate that the 100 m radio telescope can be successfully incorporated in global VLBI experiments at 3.5 mm wavelength.

  • 65.
    Stannard, D.
    et al.
    University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Cheshire, UK.
    Booth, R.S.
    University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Cheshire, UK.
    Spencer, R.E.
    University of Manchester, Nuffield Radio Astronomy Laboratories, Jodrell Bank, Cheshire, UK.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers Institute of Technology, Gothenburg, Sweden.
    VLBI Observations of 3C345 at 1.67 GHz1980In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 192, no 4, p. 555-560Article in journal (Refereed)
    Abstract [en]

    VLBI observations of the quasar 3C 345 suggest that the milliarcsec subcomponents in the core have approximately equal intensities at 1.67 GHz. A new compact feature is detected in the inner jet structure at a distance of ∼ 12 m.arcsec from the core. © 1980 Royal Astronomical Society. Provided by the NASA Astrophysics Data System

  • 66.
    Tang, G.
    et al.
    Harvard–Smithsonian Center for Astrophysics, Cambridge, Massachusetts, United States & Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Bartel, N.
    Harvard–Smithsonian Center for Astrophysics, Cambridge, Massachusetts, United States.
    Ratner, M. I.
    Harvard–Smithsonian Center for Astrophysics, Cambridge, Massachusetts, United States.
    Shapiro, I. I.
    Harvard–Smithsonian Center for Astrophysics, Cambridge, Massachusetts, United States.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Rönnäng, B. O.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Recent Evolution of Jet Components in 3C345 at 3.6 cm1990In: Parsec-Scale radio jets: proceedings of a Workshop held at the National Radio Astronomy Observatory, Socorro, New Mexico, October 17-18, 1989 / [ed] Zensus, J. Anton & Pearson, Timothy J., Cambridge: Cambridge University Press, 1990, p. 32-37Chapter in book (Refereed)
    Abstract [en]

    A series of 3.6 cm VLBI maps of 3C345 (1980.79 to 1988.38) is presented. The evolution of the jet components in this quasar is briefly discussed. Recent behavior of component C5 is described and the presence of a new component, tentatively labeled C6, is suggested.

  • 67.
    Tang, G.
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Rönnäng, B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Radio source structure from geodetic VLBI observations: evolution of the quasar 3C 345 at 8 GHz1989In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 216, no 1-2, p. 31-38Article in journal (Refereed)
    Abstract [en]

    Eight VLBI maps of 3C 345 were obtained at 8.3 GHz between 1980 and 1986. During this period, the two jet components C4 and C5 were shown to emerge from the core in succession and to move superluminally toward the west with angular velocities of 0.17 + or - 0.5 and 0.11 + or - 0.02 mas/yr, respectively. An emission detected between D and C5 after 1985.46 suggests that a new component emerged from the core, moving at an angular velocity of 0.2 mas/yr. The C3 component retained a velocity of about 0.44 mas/yr, and its proper motion was found to accelerate in the y-direction and decelerate in the x-direction.

  • 68.
    Tang, Guoquiang
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Rönnäng, B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Radio source structure from geodetic VLBI observations: 8 GHz multi-epoch maps of the quasar 4C 39.251987In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 185, no 1-2, p. 87-93Article in journal (Refereed)
    Abstract [en]

    Techniques for estimating and/or eliminating the effects of structure variations in the extragalactic radio sources used as fiducial points in 8.3-GHz geodetic VLBI observations are described and demonstrated. Particular attention is given to the data base statistics, the calibration of visibility data, the production of hybrid maps with AIPS, and the implementation of these steps in a software package. A set of X-band maps of 4C 39.25, obtained with the receivers of the Mark III dual-frequency VLBI network at six epochs during 1980-1985, is presented. Such maps are shown to be of value (1) for maintaining submarcsec accuracy in the extragalactic reference frame and (2) for qualitative astronomical monitoring of the sources. In 4C 39.25, for example, apparent superluminal motions, complex internal kinematics, and a double western component are observed.

  • 69.
    Tateyama, Claudio E.
    et al.
    Nobeyama Radio Observatory, NAO, Minamisaku, Nagano, Japan & Centro de Rádio-Astronomia e Aplicações Espaciais/CRAAE, Escola Politécnica da Universidade de São Paulo, Brazil.
    Inuoe, Makoto
    Nobeyama Radio Observatory, NAO, Minamisaku, Nagano, Japan.
    Krichbaum, Thomas P.
    Max-Planck Institut für Radioastronomie, Auf dem Hügel, Bonn, Germany.
    Bååth, Lars B.
    Onsala Space Observatory, Onsala, Sweden.
    Kameno, Seiji
    Nobeyama Radio Observatory, NAO, Minamisaku, Nagano, Japan.
    Rogers, Alan E. E.
    Northeast Radio Observatory Corp., Haystack Observatory, Westford, MA, USA.
    Alberdi, Antonio
    Instituto de Astrofisica de Andalucia, Granada, Spain.
    Backer, Don C.
    University of California, Berkeley, CA, USA.
    Bartel, Norbert
    Harvard Smithsonian Center of Astrophysics, Cambridge, MA, USA.
    Booth, Roy S.
    Onsala Space Observatory, Onsala, Sweden.
    Burke, Bernard F.
    Massachusetts Institute of Technology, Cambridge, MA, USA.
    Carlstrom, John E.
    University of California, Berkeley, CA, USA.
    Dhawan, Vivek
    Harvard Smithsonian Center of Astrophysics, Cambridge, MA, USA & Raman Research Institut, Bangalore, India.
    Global 3- and 7-mm VLBI Observations of OJ 2871996In: Nippon Tenmon Gakkai obun kenkyu hokoku, ISSN 0004-6264, Vol. 48, no 1, p. 37-44Article in journal (Refereed)
    Abstract [en]

    We present new results from global VLBI observations of the highly active blazar OJ287 at 7 and 3 mm wavelengths. We show the first map of the mas to sub-mas structure of OJ287 at 43 GHz and discuss this image in the context with models of the source structure seen at 100 GHz.

  • 70.
    Zensus, J. A.
    et al.
    Owens Valley Radio Observatory, California Institute of Technology, Pasadena, California, USA.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden & Owens Valley Radio Observatory, California Institute of Technology, Pasadena, California, USA.
    Cohen, M. H.
    Owens Valley Radio Observatory, California Institute of Technology, Pasadena, California, USA.
    Nicolson, G. D.
    Hartebeesthoek Radio Observatory, Johannesburg, South Africa.
    The inner radio jet of 3C2731988In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 334, no 6181, p. 410-412Article in journal (Refereed)
    Abstract [en]

    Radio maps of 3C273 obtained with very long baseline interferometry (VLBI) have been limited by low dynamic range and poor north-south resolution resulting from the low declination (2°) of this quasar1. Dramatic improvement can now be achieved using larger arrays and antennas in the Southern Hemisphere2,3. A new VLBI map, made at 5 GHz with angular resolution and dynamic range unsurpassed at this frequency for this source, shows a narrow jet extending to a projected distance lproj∼125 h-;1 parsecs from the core. Superluminal motion exists out to at least lproj≈46h-1 parsecs. Successive superluminal components emerge from the core and appear to move on a fixed curved path with similar speeds of about 1 milliarcseconds per year. © 1988 Nature Publishing Group.

  • 71.
    Zhang, F. J.
    et al.
    University of Manchester, Nuffield Radio Astronomy Laboratories, Macclesfield, UK.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology.
    THE SUBMILLIARCSECOND RADIO STRUCTURES OF THE 2 BL LAC OBJECTS MKN421 AND 0735 + 1781991In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 248, no 3, p. 566-571Article in journal (Refereed)
    Abstract [en]

    Very high-resolution (approximately 0.15 mas) VLBI hybrid maps of the two BL Lac objects Mkn421 and 0735 + 178 have been produced at lambda-1.35 cm. The structures of both sources are simple. Only an unresolved core is found in Mkn421. It is magnetic field dominated, and the motion of relativistic electrons is strongly restrained by the magnetic field. Relativistic electrons with relatively low energy are responsible for the synchrotron radiation. The maps of 0735 + 178 show that the radio structure at lambda-1.35 cm is dominated by a strong core, and there is a weak component outside. We can put a lower limit to the angular velocity of the outer component (0.32 +/- 0.03) mas yr-1, corresponding to an apparent transverse speed of (5.4 +/- 0.6)c which tallies with previous results. The outer component has an extension towards the south-east, a tendency also seen in the 6-cm VLBI maps. With our 1.35-cm VLBI observations, we demonstrate that it is possible to study a new component emerging from its core during an outburst and to study its behaviour on its way out.

  • 72.
    Zhang, F. J.
    et al.
    Nuffield Radio Astronomy Laboratories, Jodrell Bank, Cheshire, U.K..
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Chu, H.S.
    Purple Mountain Observatory, Academia Sinica, Nanking, China.
    What is responsible for the new outburst of 0735+178?1992In: Variability of Blazars: Proceedings of a conference in honour of the 100th anniversary of the birth of academician Yrjö Väisälä, held at Tuorla Observatory, University of Turku, Finland, January 6-10, 1991 / [ed] E. Valtaoja & M. Valtonen, Cambridge: Cambridge University Press, 1992, p. 234-237Conference paper (Refereed)
  • 73.
    Zhang, F. J.
    et al.
    Nuffield Radio Astronomy Laboratories, University of Manchester, Cheshire, UK.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Spencer, R. E.
    Nuffield Radio Astronomy Laboratories, University of Manchester, Cheshire, UK.
    1404+286: A non-ideal calibrator for VLBI observations1994In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 281, no 3, p. 649-652Article in journal (Refereed)
    Abstract [en]

    The radio source 1404+286 was observed with global VLBI arrays at 5 and 1.67 GHz in 1990.88 and 1991.45 respectively. High quality maps are presented in this paper, and show the source to be resolved at both frequencies with a core-jet like structure extending approximately 6 mas in position angle approximately -145-degrees. The jet direction is similar in both maps. 1404+286 has often been used in the past as a flux density calibrator or a phase referencing source. Our results show that this source is not an ideal calibrator on VLBI scales.

  • 74.
    Zhang, F.J.
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    The radio fine structure of the BL Lacertae object Mk 4211990In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 236, no 1, p. 47-52Article in journal (Refereed)
    Abstract [en]

    The BL Lac object Markarian 421 (Mk 421) has been mapped using VLBI arrays at a wavelength of 6 cm on four epochs from 1980.41 to 1983.43. It has a core-jet like structure with the jet pointing to the direction of NW with a stable position angle of about -45 deg. Almost all of the flux variation is accounted for by the change of the peak flux density of a compact component in the core. The results show that Mk 421 may exhibit apparent superluminal motion with apparent transverse speeds of components of (1.92 + or - 0.03)c (from 1981.25 to 1981.94) and (1.79 + or - 0.23)c (from 1981.94 to 1983.43) for C1; and (1.36 + or - 0.22)c for C2. The position angles of both the components C1 and C2 are nearly the same as the position angle of the jet, and there is no significant change of position angle as they move away from the core.

  • 75.
    Zhang, F.J.
    et al.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Spencer, R.E.
    Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield, Cheshire, United Kingdom.
    Schilizzi, R.T.
    Netherlands Foundation for Research in Astronomy, Dwingeloo, The Netherlands.
    Fanti, C.
    Dipartimento di Astronomia dell'Universita & Instituto di Radioastronomia CNR, Bologna, Italy.
    Bååth, L.B.
    Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden.
    Su, B.M.
    Yunnan Observatory, Chinese Academy of Sciences, Kunming, China.
    Are there two engines at the center of 3C 286?1994In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 287, no 1, p. 32-37Article in journal (Refereed)
    Abstract [en]

    This paper presents images of the compact steep-spectrum quasar 3C 286 obtained with global VLBI arrays at 4.99 and 1.66 GHz. The morphology appears to be intermediate between the core-jet types and grossly distorted objects. The central portion is resolved into two components of almost equal peak brightnesses and spectral indices. On the 1.66 GHz map, the jet extends in position angle approximately -136-degrees, up to a knot (W1) (approximately 75 mas from the component C2) from which it curves rapidly towards the west to form another knot (W2). It is possible that the VLBI jet bends further towards the secondary component separated from the core by approximately 2.6'' in p.a. -115-degrees seen in high dynamic range VLA or Merlin maps. The jet has a sinuous feature shown clearly on the 5 GHz map. There is a low brightness extension at the North (designated N1) shown on both the 1.66 and 5 GHz maps, which is connected to the component C1 and bends towards the east.

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