on this web page
g', r' & i' magnitudes vs. date (for last 2 months & last year)
List of observing
sessions (starting 2019 Oct 04)
(showing my ref stars)
The Big Picture
My collaboration policy
about physical model
Links on another web page
precision explained (580 ppm)
the 10th web page devoted to my observations of
Tabby's Star for the date interval 2020.09.27 to
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web pages (for dates 2019.01.20 to
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web pages (for dates 2018.10.10 to 2019.01.19)
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web pages (for dates 2018.08.12 to 2018.10.04)
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Star Quality Assessment (the 10 best stars out of
r' and i' Mag's vs. Date
Figure 1. HAO g', r' and i'-magnitudes
for the past month. The horizontal dashed lines
are suggestions for OOT levels, set to the brightest
magnitudes observed during the past two years (when I began
observing in three bands).
Figure 2. HAO g', r' and
i'-magnitudes for the past year. The g' trace from JD4 9000
to 9120 are from Sjoed Dufoer's AAVSO-submitted V
band magnitudes (shift adjusted to match my g'-mags, and
smoothed). The r' and i' traces are departures from the
respective OOT levels multiplied by the g'-mag departures
from the g' OOT level. The multipliers for r' band and i'
band are 0.56 and 0.40. In other words, the r' and
i' fade amounts are 56 and 40 % of the g' fade amounts.
Here's my suggestion for
understanding the previous two figures:
1) During the past two years there was a 10-day interval
(early November, 2019) when all bands were at their maximum
brightness. I interpret these to be OOT levels (no dust
clouds, just an unobstructed view of the star).
2) There are two components of dust cloud: broad, producing
slow fades of brightness (month timescale) and small,
producing brief fades (a few days timescale).
3) Both dust cloud components have similar "particle size
distributions" (PSDs) that are dominated by small particles
(< 0.5 micron radius), so they produce greater fades at
4) The fade ratios for r' to g' and i' to g' would be the same
for all dust clouds if they had the same PSDs. Since specific
dust cloud PSDs may differ the observed ratios may vary over
5) On the assumption that all dust clouds have the same PSD it
should be possible to predict r' and i' fade amounts by
multiplying the g' fade amount by fixed ratios.
6) So far it appears that the fixed ratios are 0.54 and 0.40.
These values should provide a constraint on PSD functions. (I
need help with that.)
The overall conclusion from these
observations is that both the short-timescale dipping and
long-timescale variations are caused by dust clouds
dominated by small particles!
Figure 3. Comparison of Sjoed Dufoer's
AAVSO-submitted V band magnitudes and my g' band
magnitudes (shifted for approximate "agreement").
ASASS SN B
band measurements support the above fade variation (as Rafik
Bourne has determined).