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[vsnet-obs 2966] Re: Fading of V705 Cas

R.J. Bouma wrote:

> We have been puzzled by some recent observations published in
> the VSNET-observations, that have V705 Cas still as bright as
> magnitude 12.3, while our last observations of June 15.0 were
> near magnitude 13.4. We suspect that the recent magnitude
> 12.3-12.5 observations are NOT of V705 Cas, but of nearby GSC
> 4008.1363, listed as magnitude 13.05 (+/- 0.40), but that one
> of us (BMU) estimated at about 12.5 on June 15.0. This star is
> easily identified as the brightest of a small triangle SSW of
> V705, if the field is viewed under sufficient magnification.
> Therefore, we suggest that observers take extra care when
> making future observations. We welcome your comments on this
> issue.

   I agree in that observers should take special care in identifying the
nova, but I am tempted to present another explanation.  Novae during this
stage usually show forbidden emission lines of [OIII] 495.9 and 500.7 nm.
Sometimes the contribution of these lines to visual magnitudes may be so
large that the sensitivity of the individual eye to these emission lines
may determine the visual magnitude.  Since these lines are located in
relatively blue region, sensitivity of the eye to these lines changes
dramatically depending on the degree of dark adaptation.  Dark-adapted
eyes are more sensitive to these lines.  Such effect was very clearly
demonstrated in previous novae like QU Vul etc.  During the "nebular" phases
of these novae, there were discrepancies up to 1 magnitude.  Even the
same observer gave different magnitudes through eye-peices of different
magnification, which probably affected the dark-adaptation through the
surface brightness of the background sky.  Does anyone have a similar
experience?  I also welcome further comments.

Regards,
Taichi Kato