Quote:
Originally Posted by Andrew Pearce
Hi Robert
Welcome to the world of variable star observing! As you can see it can be quite a difficult thing to sort through observations (.......)
(......)the CCD observations of the SN by only a handful of observers show less scatter than the visual observers and looking at the light curve, they seem to show a clear peak magnitude of 11.6 (....)
(........)However from a visual perspective, the SN has definitely appeared slightly brighter than 11.6 and this can be relatively easy to judge as there is a nearby comparison star of 11.6 and I personally have seen the SN brighter than this star. My own observations indicate a peak brightness of 11.3.(......)
(.....)I feel the peak was somewhere between 11.3-11.6.
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Andrew,
Pity that I don't have the statistical tools you mention, in my 'mental toolkit', so as to sort out that messy magn. data.
But I do know (from experience) a lot about the errors made in visual observations, by means of the "wishful" thinking of the eye-brain system. Given that a 10 or 20 percent difference in apparent brightness is hard for the eye to spot, an observer's
attitude (bias)(his
preconceptions about object brightness) could well influence whether or not a star seems brighter, or the same brightness, or fainter, than a comparison star;
I think, at the level of 0.1 to 0.3 magnitude, a perceptual bias could easily creep in and distort the observer's visual magnitude estimate for a variable star.
Unfortunately, an error of 0.3 magnitudes in the apparent magnitude of the Supernova is large, when we wish to use it for the purposes of estimating the luminosity (absolute magnitude)(absolute brightness) of this astronomical object. The distance error for an individual galaxy can easily amount to 20 percent , which equates to an
additional error of 0.4 magnitudes in the derived luminosity of the supernova.
Galaxyman's question to Mr "Variable" Pearce:
Do your visual (that is, made using the "eye+brain system") magnitude estimates need to be mathematically transformed into the Johnson V-band Magnitudes for the purpose of making a really accurate comparison with V-band measurements made using photoelectric and CCD photometry??
Some of my textbooks state the following:
(1) The Johnson photometric V-band filter was actually chosen so as to
approximate the visual response (the band-pass) of the eye (the eye's response curve). That is, the filter's transmission curve has a peak filter transmission (maximum brightness) near 550nm and a Transmission Curve width ( Full-Width-at-Half-Maximum) of about 90nm.
(2) The bandpass and sensitivity curve of the eye is, however,
different from that of the standard photometric V filter, being composed of a complex mix of responses from the rods and from three different types of cones.
(e.g. the well-known shift of about 50nm in the peak sensitivity between the rods and the cones)
Therefore, do visually-estimated magnitudes (visual magnitudes) need to be mathematically transformed into V-band Johnson-Cousins magnitudes, if they are to be accurately compared with V-band magnitudes?
cheers,
madbadgalaxyman