KIC 8462852 Hereford Arizona Observatory
Photometry Observations #10
Bruce Gary, Last updated: 2020.10.27, 03 UT
abrupt dip began
a couple days
ago, and appears
to have ended.
At g' band it was
~ 1.5 % deep (at
r' band depth was
less, at i' band
upon a shallow
dip (~ 0.5 %)
that began 11
days ago. These
two dips were
a 6-month slow
wavelength in a
way that is
(greater fade at
This is just
behavior. So we
now know that
both the short
fade events, or
dips (lasting a
few days), and
months), can be
Observations (for all
earlier observations, before 2020.09.27 go to link)
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
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
Go back to 9th of 10
web pages (for dates 2019.01.20 to
Go back to 8th of 10
web pages (for dates 2018.10.10 to 2019.01.19)
Go back to 7th of 10
web pages (for dates 2018.08.12 to 2018.10.04)
Go back to 6th of 10
web pages (for dates 2018.02.25 to 2018.08.01)
Go back to 5th of 10 web
pages (for dates 2017.11.13 to 2018.01.03)
Go back to 4th of 10 web
pages (for dates 2017.09.21 to 2017.11.13)
Go back to 3rd
of 10 web pages (for dates 2017.08.29 to 2017.09.18)
Go back to 2nd
of 10 web pages (for dates 2017.06.18 to 2017.08.28)
Go back to 1st
of 10 web pages (for dates 2014.05.02 to
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).
Observing Session Information (most recent at top)
Observations still underway.
I have the image sets for i' in case they need to be processed.
I have the image sets for r' & i' in case they need to be
Figure 5.1. Finder
image showing the 17 reference stars that I use. KIC846 is in
the blue square. FOV = 15.6 x 10.5 'arc, NE at upper-left.
The Big Picture
is the overall character of KIC846 brightness variations?
I like to distinguish between short-term and long-term
variations. The short-term variations are referred to as
"dips." The dips last a few days typically. By long-term I
refer to whatever is left over after removing the dip
data. The long-term data can have variations with
timescales of months to years. The next plot covers a 14
year interval and includes both Kepler and ground-based
data, and it shows long-term variations (red model
6.1. 14 years of Kepler and ground-based
measurements. The black dots are Kepler data with dips
removed; these data show the long-term variation during
the 4 years of Kepler observations. Starting in 2017
(with only ground-based data) the dip and long-term data
are shown with different symbols. None of Tabby's LCO
data are shown (because a digital version of this data
is not in the public domain) and none
of the AAVSO data are shown (because most of
it is noisy and adding the less noisy data
would make the plot too "busy").
Figure 6.2. Ground-based HAO
g' measurements during the past 3 years (plus
Figure 6.3. Ground-based HAO g', r'
& i' measurements during previous
(2018/19) observing season.
let's return to the Kepler data that
has long-term variations removed, allowing
us to see just the short-term ("dip")
data for the
data but with
3 months of
the one set of
dips with a
an aside, allow
me to show what
Let's do the same removal of long-term
variations for recent ground-based
Ground-based (HAO) data, plus TESS
data, with long-term variations
removed (showing only dip activity)
for the 3 years preceding this
for the last 2
months of last
ground-based data exists but some of it is
not in the public domain in digital form
(LCO data) and I apologize to the AAVSO
observers with data that is not included
above. I'll try to add some AAVSO data if
I get time for processing and selecting
Note, as Rafik Bourne pointed-out to me,
TESS is sensitive to just long wavelengths
(Rc/Ic/z') which does not include g'-band,
and since dip depth is consistently less
at longer wavelengths TESS dip depths will
always be less than g'-band depths. For
example, in the above figure the TESS dip
showing depth = 1.2 % would probably have
been observed with a g' filter to have a
depth of 2.0 or 2.5 %.
We can now ask the question: Are the
long-term and short-term (dip)
activities for the past 3 years similar
or different from what Kepler observed
during 4 years?
Referring back to an earlier figure,
repeated here, the long term variation
during the past 3 years has been
considerably greater than during Kepler's
4 years of measurements.
Repeat of Figure 6.1. The
Kepler data with dip activity removed
(black dots) exhibit just one large
change (2.2 %) following a slow fade (1
%). The ground-based data, starting in
2017, exhibit several changes, or
variations, each about 1 % but adding up
to ~ 3.5 % during 3 years.
Short-Term (Dip Activity) Differences
Again, there are significant differences
between the Kepler 4-year record of dip
activity and the 3-year record of
ground-based dip activity. Consider the
following figure showing the two
"short-term only data" using the same
scale for normalized flux but with the
ground-based data shifted in time.
Figure 6.9. Comparing dip
activity of Kepler and ground-based
(HAO) data (i.e., long-term
variations removed). The HAO data was
shifted 7.9 years (to earlier dates).
It is apparent in this comparison plot of
dip activity that the past 3 years have
exhibited more short-term ("dip") activity
than a comparable 3-year interval of
Kepler data. Another difference is that
during the Kepler dates when dips were
present they could be much deeper!
Physical Model Speculations
A possible explanation for this dip
activity pattern (in the above figure) is
that the Kepler observations were closer
in time to an event, such as a collision,
that created a well-defined cluster of
dust-producing fragments within an orbit,
and during the course of 8 years the
fragments have dispersed along the orbit.
The total amount of light blocking dust
may have not changed much, but since
fragment-based dust clouds spread apart
over time they produce more dips with
The long-term variations in brightness
that seem to have increased during the
past 8 years (cf. Fig. 6.1 and its repeat)
could be caused by 1) reflection of
starlight when the dust cloud is on the
far side of the star, or 2) forward
scattering when the dust cloud is on the
near side of the star (close to our
line-of-sight). With a more spread-out
configuration of dust clouds there is less
chance of one cloud blocking the
reflection, or forward scattering, of
Keep in mind that these are speculations
by an amateur; actual modeling of these
and other ideas are needed by
At my age of 80 I'm entitled to have fun and avoid work.
Photometric observing and figuring things out are fun. Writing
papers is work. So if anyone wants to use any of my
observations for a publication you're welcome to do so. But
please don't invite me for co-authorship!
My light curve observations are "in the public domain." This
means anyone can and may download my LC observations, and use
(or misuse) any of that data for whatever purpose. If my data
is essential to any publication just mention this in the
Gonzalez, M. J. Martinez and 15 others, 2108,
"High-Resolution Spectroscopy of Boyajian's Star During Optical
Dimming Evetnts," arXiv:1812.06837.
Wright, Jason T., "A Reassessment of Families of
Solutions to the Puzzle of Boyajian's Star," arXiv (a
Schaefer, Bradely E., Rory O. Bentley, Tabetha S.
Boyajian and 19 others, 2018, "The KIC 8462852 Light Curve From
2015.75 to 2018.18 Shows a Variable Secular Decline," submitted to MNRAS,
Bodman, Eva, Jason Wright, Tabetha Boyajian,
Tyler Ellis, 2018, "The Variable Wavelength Dependence of the
Dipping event of KIC 8462852," submitted to AJ, arXiv.
Bodman, Eva, 2018, "The Transiting Dust of
Boyajian's Star," AAS presentation, link
Yin, Yao and Alejandro Wilcox, 2018, "Multiband
Lightcurve of Tabby's Star: Observations & Modeling," AAS
(navigate down, etc)
Sacco, Gary, Linh D. Ngo and Julien Modolo, 2018,
"A 1574-Day Periodicity of Transits Orbiting KIC 8462552," JAAVSO,
Boyajian, Tabetha S. and 198 others, 2018, "The
First Post-Kepler Brightness Dips of KIC 8462852," arXiv
Deeg, H. J., R. Alonso, D. Nespral & Tabetha
Boyajian, 2018, "Non-grey dimming events of KIC 8462852 from GTC
Bourne, R., B. L. Gary and A. Plakhov, 2017,
"Recent Photometric Monitoring of KIC 8462852, the Detection of a
Potential Repeat of the Kepler Day 1540 Dip and a Plausible Model,"
Bourne, Rafik and Bruce Gary, 2017, "KIC 8462852:
Potential repeat of the Kepler day 1540 dip in August 2017,"
submitted to AAS Research Notes, preprint: arXiv:1711.07472
Xu, S., S. Rappaport, R. van Lieshout & 35
others, 2017, "A dearth of small particles in the transiting
material around the white dwarf WD 1145+017," approved for
publication by MNRAS link,
Gary, Bruce and Rafik Bourne, 2017, "KIC 8462852
Brightness Pattern Repeating Every 1600 Days," published by Research
Notes of the AAS at link;
preprint at arXiv:1711.04205.
Gary, B. L., S. Rappaport, T. G. Kaye, R. Alonso,
J.-F. Hambsch, 2017, "WD 1145+017 Photometric Observations During
Eight Months of High Activity", MNRAS, 2017, 465,
Neslusan, L. and J. & Budaj, 2016,
"Mysterious Eclipses in the Light Curve of KIC8462852: a Possible
1612.06121v2 (a "tour de force"; I highly recommend this
Neslusan & Budaj web site with animation of
their way of explaining Kepler D1540 dip: http://www.astro.sk/~budaj/kic8462.html
Wyatt, W. C., R. van Lieshout, G. M. Kennedy, T.
S. Boyajian, 2017, "Modeling the KIC8462852 light curves:
compatibility of the dips and secular dimming with an exocomet
interpretation," submitted to MNRAS, arXiv
Grindlay interview about Schaefer's assertion
that KIC846 exhibited a century long fade using DASCH data: link
Hippke, Michael and Daniel Angerhausen, 2017,
"The year-long flux variations in Boyajian's star are asymmetric or
aperiodic," submitted to ApJL, arXiv
Sacco, G., L. Ngo and J. Modolo, 2017, "A
1574-day Periodicity of Transits Orbiting KIC 8462852," arXiv
Rappaport, S., B. L. Gary, A. Vanerdurg, S. Xu,
D. Pooley and K. Mukai, 2017, "WD 1145+017: Optical Activity During
2016-2017 and Limits on the X-Ray Flux," arXiv, Mon. Not.
Royal Astron. Soc.
Steele, I. A. & 4 others, 2017, "Optical
Polarimetry of KIC 8462852 in May-August 2017,"MNRAS (accepted), arXiv.
Simon, Joshua D., Benjamen J. Shappee and 6
others, "Where is the Flux Going? The Long-Term Photometric
Variability of Boyajian's Star," arXiv:1708.07822
Meng, Huan Y. A., G. Rieke and 12 others
(including Boyajian), "Extinction and the Dimming of KIC 8462852,"
Sucerquita, M., Alvarado-Montes, J.A. and two
others, "Anomalous Lightcurves of Young Tilted Exorings," arXiv: 1708.04600
Also: New Scientist link
and Universe Today link.
Rappaport, S., A. Vanderburg and 9 others,
"Likely Transiting Exocomets Detected by Kepler," arXiv:
Montet, Benjamin T. and Joshua D. Simon, 2016, arXiv
Boyajian et al, 2015, MNRAS, "Planet Hunters
X. KIC 8462852 - Where's the flux?" link
Ballesteros, F. J., P. Arnalte-Mur, A.
Fernandez-Soto and V. J. Martinez, 2017, "KIC8462852: Will the
Trojans Return in 2011?", arXiv
Washington Post article, 2015.10.15: link
Notice requesting KIC646 observations
AAVSO LC Generator https://www.aavso.org/data/lcg
(enter KIC 8462852)
Web page tutorial: Tips for amateurs observating faint asteroids
(useful for any photometry observing)
Book: Exoplanet Observing for Amateurs,
Gary (2014): link
(useful for any photometry observing)
description of Tabby's Star
My web pages master list, resume
B L G a r y at u m i c h dot e d u
Arizona Observatory resume
This site opened: 2020.10.05. Nothing on this web page is copyrighted.