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(1993 Apr. 11)
subject: SN1993J estimates
Sir Dr. Hurst,
Many of Japanese observers use Pogson's step method for magnitude
estimates. However our report format does not include this information.
I have transmitted your request to individual observers and some may
respond. I will relay them to you.
Another possible cause of discrepancies between V mag and visual
observations is background light of the galaxy. Soon after the discovery
we have no good estimates of nearby comparisons (stars A,B etc.). So
observers were urged to use distant comparisons. Such observation is
not only difficult, but also would be affected by galaxy background,
especially when low magnification was used. After acurate determination
of nearby comparisons were published, visual observations became very
close to photoelectric V magnitudes.
I would like to urge visual observers to estimate star A and B using
distant (TB sequence, of course) comparisons to esitmate this possible
systematic bias. One of our observers notes that star A looks brighter
than the determined V magnitude. This finding might be reasonably
explained by the effect above mentioned.
Regards,
Taichi Kato
Return to the Powerful Daisaku Nogami
vsnet-adm@kusastro.kyoto-u.ac.jp
