KIC 8462852 Hereford Arizona Observatory
Photometry Observations #9
Bruce Gary, Last updated: 2020.10.05 23 UT
current dip is
the 7th one
deeper than 0.5
% since Oct 20
(a mere 10 weeks
ago). The "dip
was quite high,
averaging ~ 2.0
% a couple weeks
ago, but appears
to be recovering
(depth now is
< 0.5 %). If
all dips were
moved in time to
the same date
they were all
produced by dust
clouds with low
produce a single
dip (with an
width) having a
depth of 11 %!
In other words,
the dip activity
during the past
10 weeks has
to the dip
years ago, or
even 7 years ago
It's just that
the recent set
of 7 dips are
if they were
years ago at one
and have been
ever since. End
season, so no
a few months.
Observations (for all
earlier observations, before 2018 Feb 25, go to link)
Session Information (most
recent at top)
Good observing conditions, so I "believe" the fade in g'-band.
Very poor observing conditions: windy & cloudy.
Cloudy the entire time, so I observed during "sucker holes." Image
sets for r' and i' probably not worth processing.
Too cloudy for u' band observations.
Observed through "holes in the clouds"!
dip the rate of change of brightness at one wavelength
with respect to another is determined by the dust
cloud's particle size distribution (PSD). Since I'm now
observing at 3 wavelengths I could produce 3 mag/mag
scatter diagrams. Instead, I will consider only r'-mag
vs. g'-mag and i'-mag vs. g'-mag.
Figure 3.1. r'-mag versus g'-mag, showing
smaller dip depths for r' than g'.
discus this more, later.
viewing the shape of
the various dust
along its orbit.
Assume that it is
frozen in shape and
merely passes in
front of the star
during the course of
a couple months.
Imagine further that
the dust clouds are
optically thick out
to a border with
abrupt drop off. The
depth of the
observed dip at each
band (g', r' and i')
can be converted to
a vertical width
(assuming the dust
cloud is broad in
relation to the
star). Here's the
shape I derive from
the 2019 October
u' band Observations
the u' problem later.
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.
Figure 5.2. "Deeper"
version of same FOV (r' band).
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").
6.2. Ground-based HAO g'
measurements during the past 3 years (plus
Figure 6.3. Ground-based HAO g', r'
& i' measurements during the past year.
Ground-based HAO g', r' & i'
measurements during the past 4
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
Figure 6.6. TESS data for 2019
(using passband equivalent to Rc+Ic
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 past 3 years.
for the past 2
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.
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: 2019.10.20. Nothing on this web page is copyrighted.