[vsnet-alert 790] AB Dra entering a standstill?

[Taichi Kato <tkato>]

     Observations reported to vsnet-obs suggest the Z Cam-type dwarf nova
AB Dra has entered a standstill or a stage of extremely decreased outburst
amplitudes.  Selected observations:

  YYMMDD(UT)   mag  code
  970218.092   126  HSG
  970218.812   130  POY
  970219.126   128  HSG
  970219.214   127  BMM
  970220.533   132  HSG
  970221.544   137: HSG
  970221.780   139  POY
  970224.112  <136  HSG
  970226.785   134  POY
  970227.167   125  JEN
  970228.869   134  POY
  970301.188   129  BMM
  970301.522   131  HSG
  970301.880   131  PIE
  970302.478   132  HSG
  970302.835   138  POY
  970303.473   135  HSG
  970305.025   128  JEN
  970305.501   135  HSG
  970305.953   138  POY
  970306.485   133  HSG
  970306.801  <126  MOE
  970306.828   134  POY
  970307.526   129  HSG
  970307.769   129  PIE
  970308.316   130  HSG
  970309.494   129  HSG
  970309.860   129  PIE
  970310.117   130  HSG
  970310.508   131  HSG
  970310.776  <123  MOE
  970310.780   135  PIE
  970310.819   135  POY
  970311.167   136: HSG
  970312.815   138  POY
  970313.516   134  HSG

     Looking back through the AFOEV and VSOLJ records, the last such events
occurred several times in 1987-1988.  The star, otherwise rather regular
recently, showed a marked brightness drop in 1984 July - August just like
the recent one in RX And.  This finding seems to support such phenomena
(temporary decrease of the mass-transfer rate?) may be rather commonly
associated with Z Cam-stars.

Regards,
Taichi Kato

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