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VIII/26     Low-frequency Variable Radio Sources           (Mitchell+ 1994)
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Results of a Five-year Program of Multifrequency Monitoring of Low-frequency
Variable Radio Sources
    Mitchell K.J., Dennison B.K., Condon J.J., Altschuler D.R., Payne H.E.,
    O'Dell S.L., Broderick J.J.
    <Astrophys. Journ. Suppl. 93, 441 (1994)>
    =1994ApJS...93..441M
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ADC_Keywords: Nonstellar objects ; Radio sources ; QSOs ; X-ray sources 

Description:
   The Lowvar dataset is the result of a detailed multi-frequency
   monitoring program of 34 low-frequency variable radio sources.  This
   consists of flux density measurements at five frequencies between 0.3
   GHz and 1.4 GHz over the five year period, 1980.0 - 1985.0.  The sources
   monitored were previously found to be variable or probably variable in
   two- and three-epoch observations at 318 MHz of complete samples of
   extragalactic sources.  Observations were carried out at 318, 430 and
   606 MHz using the National Astronomy and Ionosphere Center Arecibo 305-m
   radio telescope and at 880 and 1400 MHz using the National Radio
   Astronomy Observatory Green Bank 91-m radio telescope. The measured flux
   densities and their errors are given according to source, frequency and
   date.  The measurement error is sufficiently small that variations
   larger than several percent can be identified.  The errors do not
   reflect time-independent uncertainties in absolute scale and therefore
   absolute comparison with other measurements is not possible with high
   accuracy. The Lowvar dataset is expected to be useful for studies of
   radio source variability caused by both extrinsic and intrinsic
   mechanisms, and for studies comparing variations at different wavebands.
   Partial results of these observations on selected sources were reported
   by Payne et al. (1982), Altschuler et al. (1984), Dennison et al.
   (1984a), and Dennison et al. (1984b).  The complete results (tabulated
   in the accompanying data set) and the observations are described in
   detail by Mitchell et al. (1993). 

File Summary:
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 FileName       Lrecl  Records   Explanations
--------------------------------------------------------------------------------
ReadMe             80        .   This file
lowvar.dat         25     3067   Catalog Data
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Byte-by-byte Description of file: lowvar.dat
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   Bytes  Format   Units   Label     Explanations
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   1-  7   A7      ---     ID        Source Name
       8   I1      ---     FreqCode *[1-5] Frequency Code
   9- 10   I2      yr      Obs_yr    Date of Observation - 1900
  11- 12   I2      ---     Obs_m     Date of Observation - Month
  13- 14   I2      d       Obs_d     Date of Observation - Day
  16- 20   F5.2    Jy      Flux      Flux Density
  21- 25   F5.2    Jy      e_Flux    Flux Density Error
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Note on FreqCode:
  Frequency Code - 1 for 318 MHz;  2 for 430 MHz; 3 for 606 MHz
                   4 for 880 MHz;  5 for 1400 MHz.

Remarks and Modifications:
  The source 0723-00 is suspected of having a large scale error at 430
  MHz, owing to the large zenith angle (19.5 deg) used at that frequency,
  which is near the Arecibo telescope limit.  This source is included,
  however, as real and significant variability is clearly present at all
  frequencies, including 430 MHz. 

Acknowledgments
  The original ADC documentation by Brian Dennison (1994) was used to create
  this ReadMe file.
              
References:
  Altschuler, D. R., Broderick, J. J., Condon, J. J., Dennison, B. K.,
    Mitchell, K. J., O'Dell, S. L., and Payne, H. E. 1984, AJ, 89, 1784 
  Condon, J. J., Ledden, J. E., O'Dell, S. L., and Dennison, B. 1979, AJ,
    84, 1 
  Dennison, B., Broderick, J. J., Ledden, J. E., O'Dell, S. L., and
    Condon, J. J. 1981, AJ, 86, 1604 
  Dennison, B., Broderick, J. J., O'Dell, S. L., Mitchell, K. J.,
    Altschuler, D. R., Payne, H. E., and Condon, J. J. 1984a, ApJL, 281, L55
  Dennison, B., Broderick, J. J., O'Dell, S. L., Mitchell, K. J., Altschuler, 
    D. R., Payne, H. E., and Condon, J. J. 1984b, in VLBI and Compact Radio 
    Sources - IAU Symposium No. 110, ed. R. Fanti, K. I. Kellermann, and G. 
    Setti (Dordrecht: Reidel), 309
  Payne, H. E., Altschuler, D. R., Broderick, J. J., Condon, J. J.,
    Dennison, B., and O'Dell, S. L. 1982, in Low-Frequency Variability of
    Extragalactic Radio Sources, ed. W. D. Cotton and S. R. Spangler Green
    Bank: NRAO), 9 
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(End)                        C.-H. Joseph Lyu [Hughes STX/NASA]  08-Apr-1996