All observations for 2017.06.18 and later
can be found at http://www.brucegary.net/ts/
Kepler Star KIC 8462852 Amateur Photometry Monitoring Project
B. L. Gary, last update: 2017.07.11, 03 UT
"A ... prediction is that future dimming events should
occur roughly every 750 days, with one in 2015 April and another
in 2017 May." Boyajian et al, 2016 (Section 5.2) link.
Final result for Jun 17 (7.6 hours of data),
showing recovery of latest dip.
Normalized flux vs. UT during the Jun 17 observing session,
showing a dip recovery in progress.
RA/DE = 20:06:15.5,
+44:27:25
All-sky photometry: B = 12.493 ± 0.025, V = 11.912 ±
0.025 (B-V = +0.581 ± 0.035)
APASS Mag's: B = 12.360, V = 11.852 (B-V = +0.51), g' =
12.046, r' = 11.697, i' = 11.554
There's a 0.11
mag discrepancy between BV mag's in
Boyajian et al (Table 3) and APASS (article is
brighter).
There's a 0.23 & 0.21 mag discrepancy between BV
mag's in Boyajian et al (Table 3) and my all-sky V-mag
(article is brighter). Speculation About
Collisions
In the 2016 discovery paper Boyajian et al describe a "giant
collision" scenario that prompted them to predict a dimming in 2017
May. Their model for what happened to cause KIC846 to undergo
dips (just one of many models that they described as candidates for
consideration) is a collision between a planet and a smaller
planetesimal. For example, if the brown dwarf that's now at least
900 AU away (1.95 "arc to the east) gravitationally disrupted a
Pluto-size object at some time centuries ago, that was originally
located in an analogue of our solar system's Oort cloud or Kuiper
Belt, and if this Pluto-sized object's new trajectory was pointed
inward toward KIC846, it might have collided with a planet before
reaching the star. If this collision happened sometime within a few
months of the start of Kepler data taking, and if the inclination of
the planet was close to "edge-on," the appearance of the first big
dip (16% depth, ~ 9 days long, Dip#5, Kepler Day 792.74) might be
explained (smooth ingress and smooth but longer egress). If the
planet was at ~ 1.6 AU (i.e., period of 750 days), then one orbit
later, on Kepler (Day#1519.60), the debris and associated cloud
would orbit through our line of sight to KIC846 again. This second
passage through our line-of-sight could account for both the greater
depth (21%) and width (~ 2 months), as well as the many smaller dips
preceding and following the main dip (due to debris fragments
spreading out along the orbit during the intervening 750 days). Two
orbits later would be 2017 May! This "model" also provides a ready
explanation for the fading that's occurring, and the acceleration of
that fading. The dust from the collision is spreading out along the
orbit and causing a general blocking of light. If this is the case,
then the fading will cause the star's apparent brightness to arrive
at some minimum level and slowly return to normal. One possible
problem for this model is that the star may have been fading at 0.14
%/year from 1890 to 1989. I don't know how reliable that data is,
but I mention it as a possible problem for this model. If the model
is true, then I would predict that "the show is over," and we won't
see any more dips with dramatic depths (> 2%). Sampling theory
suggests that Tabby's Star is not unique in being the site for such
dramatic events. This is because of the requirement that for any
observer to view these brightness changes the tilt of the star's
planetary system has to be just right, very close to edge-on. This
is analogous to the exoplanet transit situation, where for every
star whose brightness is observed to undergo fades when the
exoplanet orbits in front of the star there are hundreds of stars
producing fades for observers in different parts of the galactic
neighborhood.
Yearly
Timescale Fade Observations
My observations began in 2015 October with a month of clear filter observations.
On 2016 Sep 25 I resumed observations using a
V-filter, and observed for 3 months. A third group of
observations began 2016 May 02, using a V filter. Comparing
"clear filter" magnitudes with "V
filter" requires an empirical offset adjustment
based on near-simultaneous measurements with both
filters (obtained during the 2016 May observations).
The
results of this adjustment are shown in the next
graph. There's "a hint" of a
non-linear fade during the 610-day interval from 2015
October 16 to the present, as first pointed out to me by
Fredric Parker (private comm., 2017.06.09). This fade
has been modeled using a Gaussian function with a long
1/e
half-width in the date dimension (640 days). The
Gaussian is centered on DOY_2016 = 1080, where the depth
is 0.030 mag. The use of a Gaussian function was guided by the
notion that the fade is caused by a dust cloud that is
expanding along an orbit (at ~ 1.6 A.U, in the
HZ, by the way) in response to a "giant collision" (as
described in the Speculation paragraph above, link).
Figure
2.1.Magnitudes on the V-mag
scale vs. date (2.3-year interval).
C-mag's were adjusted empirically to afford
agreement in 2016 May, when both V- and C-filter
observations were made. Only OOT
(out-of-transit) measurements are shown. A
"Gaussian Fade Model" has been fitted to the
measurements. Fade rate changes throughout this
date region, and is currently ~ 1.4 %/year.
Such
a dust cloud will eventually
disperse and lead to a complete
recovery of KIC846 brightness. The
early phase of this recovery can be
seen in the next figure.
Figure
2.2.Same as above, but showing
a 3.8-year interval. The "Gaussian
fade model" reaches a
maximum fade of 0.030 magnitude at the end of 2018, after
which a slow recovery occurs
(according to the model). Maximum
fade rate, according to this model,
occurs in late 2017.
The
next graph shows all 2016
V-band measurements, including those
identified as occurring during dips.
Figure 2.3.All
2016 V-band measurements
to date, including those
made during dips, with OOT
data fitted by the
Gaussian fade model.
Observing
Sessions (Most Recent at Top) Note: Only data
above elevation 24 degrees (air mass < 2.5) should be considered
for scientific use.
Comment about r'-mags: My attempt to determine an offset conversion
for "r' to V" is being thwarted by an apparent inconstancy of the
offset conversion value. In other wards, r'-mag appears to vary in a
slightly different way than V-mag, on a daily timescale. This is
shown in the following two graphs. The first and last observing
sessions (Jun 05 & 10) share the same r'/V offset value of
+0.124 mag. The in-between observing sessions (Jun 06, 07, 09)
require a different r'/V offset conversion (~ +0.131). This 0.007
mag (i.e., 7 mmag) difference may seem small, but it translates to a
0.7% difference in normalized flux, and I'm trying to achieve a
precision of 0.1%. As usual, we need more data! (where have
I heard that before?)
Note: I'm still working on establishing a r'-mag for OOT condition.
Until that's complete my plots of "r'-band normalized flux" will be
subject to an undetermined offset correction.
Note: I'm still working on establishing a r'-mag for OOT condition.
Until that's complete my plots of "r'-band normalized flux" will be
subject to an undetermined offset correction.
Note: I'm still working on establishing a r'-mag for OOT condition.
Until that's complete my plots of "r'-band normalized flux" will be
subject to an undetermined offset correction.
Note: I'm still working on establishing a r'-mag for OOT condition.
Until that's complete my plots of "r'-band normalized flux" will be
subject to an undetermined offset correction.
This graph replaces an earlier version.
This is a corrected light curve (my 1st version showed a
sinusoidal variation, but I determined that that was due to one of
the reference stars saturating when "atmospheric seeing" was
especially good).
I only spent a short time observing KIC846 (at high air mass)
because of a higher priority target. I think this is enough data for
a useful estimate of brightness (i.e., no fade in progress).
2017.05.28 V-band, 6.7 hrs
Notice that I had to adopt a slightly fainter mag to represent
100% (11.907) because there's a slow fade of 0.8% that has been
present for the past 1.5 years.
2017.05.26 V-band, 5.4 hrs
(observing through holes in clouds)
Lots of clouds.
2017.05.25 Winds and forecast clouds led to an abort of
observations for this night. Fellow-amateur Joao Gregorio (Portugal)
won't be observing either due to rain and lightning.
All-sky session, for V-band. Same V-mag as previous ones: V-mag =
11.895.
2016.10.31
2016.10.30
Using Meade 14" with ST-10XME CCD, V-band. Finally, a reliable
system! Data quality is better due to large FOV with smooth flat
field and V filter (small Star Color Sensitivity slope).
2016.10.27
2016.10.24
Switched back to no filter (bec V filter had bubbled surface,
causing bad flat field).
2016.10.20
I began using a V-band filter with the Lodestar.
The variations are undoubtedly due to flat field imperfections!
2016.10.19
2016.10.18
2016.10.17
The wiggles near the end must be due to flat field imperfections.
2016.10.16
The wiggles near the end must be due to flat field
imperfections.
2016.10.15
2016.10.12
CCD failure occurred at 3:30 UT!
2016.10.11
2016.10.10
2016.10.09
2016.10.08
2016.10.06
Fifth C11 observing session.
2016.10.05
Fourth C11 observing session.
2016.10.04
Third C11 observing session.
2016.10.03
Second C11 observation; a slight increase in brightness.
2016.10.02
First observation with the Celestron 11" telescope (C11).
Note: On 2016.10.01 the Meade 14"failed to
turn on, so I moved the SBIG ST-10XME to my Celestron 11"
telescope (also in a dome), and have continued observations with
this "back-up" telescope system. 2016.09.25
This observing session had 4 goals, or questions to answer: 1) Does
the "star color sensitivity" diagram exhibit the same small MRS
scatter about a slope predicted by the all-sky measurements of the
previous week?, 2) What's the "air mass curvature" coefficient of
the blue target star when calibrated by mostly red stars?, 3) Is
there evidence for smal amplitude, short-period variations during a
long observing session? and 4) How accurately can a 1-hour observing
session measure V_mag?
Supercedes the next graph.
Based on cal using V mags adjusted on 2016.11.15.
Supercedes the next few graphs.
Uses the adjusted V-mags of 2016.11.15 (based on 2016 Nov 10, 12, 14
& 15).
After minor adjustments of 11 stars for persistent departures
from Star Color Sensitivity plots (based on 3 observing sessions,
Sep 25, Oct 02, Oct 03).
Star color sensitivity relationship for all-sky calibrated nearby
stars, with an offset solution used for setting the calibration
for this date's observing session.
The star color sensitivity relationship has a small slope, as
expected (same as before), and the scatter of 13 mmag about a slope
fit is what I expected, based on the all-sky measurements. This
scatter is ~ 1/2 of what was present when APASS mag's were used.
This 6.6-hr LC employs an AMC of only 3.0 mmag/airmass. Even using
zero produces a LC that is almost indistinguishable to the eye. When
airmass < 2 it doesn't matter whether AMC is zero or 3.5.
Averaging mag's from groups of 5-images yields a RMS scatter of 1.3
mmag. The formal sinusoid solution is amplitude = 1.3 +/- 0.4 mmag,
P = 1.0 hr. This is below my empirical threshold for being real, so
I conclude that during this 6.6-hr observing session there were no
detectable variations (above ~ 2 mmag). For future reference, a
1-hour data segment (above EL 30 deg) should be sufficient to
determine V-mag with a precision (and repeatability?) of ~ 3 mmag.
This SE is dominated by the use of 23 cal stars and their "star
color sensitivity" solution. The best AMC' = +0.003 mag/airmass. The
effect of AMC' departing from zero is not apparent in the LC,
visually, until airmass > 2.
To investigate how long a data chunk must be in order for its
stochastic SE to be smaller than estimated systematic error (~ 3
mmag), I divided the data into 1-hour chunks of data. The SE per
hourly median is 0.9 mmag, so hour-long observations provide an
average V-mag with a stochastic SE that is several times smaller
than estimated systematic uncertainty. Here's a plot of the hourly
medians and 5-image averages.
LC for 5-image averages (blue diamonds) and hourly averages (red
circles).
I conclude that 20-minute observations should be adequate for
monitoring KIC846 on a weekly basis in search of a secular fade.
2016.09.15
B-band all-sky observations for calibrating the target star field,
involving 8 Landolt star field (25 stars). The observing sequence
was L1-t-L2-t-L3 ... t-L8, where Ln = Landolt star field #n and t =
target (KIC846).
2016.09.05
V-band all-sky observations for calibrating the target star
field, involving 7 star fields.
Clear filter
observations from 2015 October/November
2015.11.12, B. Gary, C filter LC, V-mag = 11.929, r'-mag =
11.703 ± 0.005
2015.10.24, B. Gary, C filter LC, V-mag =
11.929, r'-mag = 11.689 ± 0.003
2015.10.23, B. Gary, C filter LC, V-mag = 11.932, r'-mag =
??.??? ±
?.??? (dew problem)
2015.10.20, B.
Gary, C filter LC, V-mag = 11.933, r'-mag = 11.691 ± 0.005
2015.10.16, B. Gary, C filter LC, V-mag = 11.930, r'-mag =
11.697 ± 0.005
2015.10.15, B. Gary, C filter LC, V-mag =
??.???, r'-mag = 11.689 ± 0.010 (too short for use)
2015.11.12: Clear filter, 1.3 hrs.
The following two graphs are calibrated using my revised B &
V mags for 18 nearby reference stars, and my processing procedure
yielding approximate V-mags (with later-determined bias of ~ 0.038
mag).
The following graph, calibrated using APASS r'-mags, may be ignored
because the preceding two graphs replace it.
2015.10.24: Clear filter, 5.8 hr.
The following two graphs are calibrated using my revised B & V
mags for 18 nearby reference stars, and my processing procedure
yielding approximate V-mags (with later-determined bias of ~ 0.039
mag).
The following graph, calibrated using APASS r'-mags, may be ignored
because the preceding two graphs replace it.
Faint gray trace is a predicted variation based on previous
observing sessions (which doesn't allow for air mass curvature).
2015.10.23: Clear filter observations, 3.0 hr. Dew on
corrector plate created a growing systematic error.
The following two graphs are calibrated using my revised B & V
mags for 18 nearby reference stars, and my processing procedure
yielding approximate V-mags (with later-determined bias of ~ 0.039
mag). The last 40 minutes was ruined by the autoguider not
keeping the star field fixed to the pixel field (that data was
ignored in the analysis).
Worsening dew on corrector plate means later data can be ignored.
The following LC was calibrated using APASS r'-mags to yield
r'-mags. You may disregard this graph, which is superseded by the
previous two.
2015.10.20: Clear filter, 0.7 hr.
The following two graphs are calibrated using my revised B & V
mags for 18 nearby reference stars, and my processing procedure
yielding approximate V-mags (with later-determined bias of ~ 0.039
mag).
The following LC was calibrated using APASS r'-mags to yield
r'-mags. You may disregard this graph, which is superseded by the
previous two.
The small-amplitude sinusoidal variation, with P = 0.8 hr,
appears to be statistically significant (same P as in previous
LC).
2015.10.16: Clear filter, 4.2 hrs.
The following two graphs are calibrated using my revised B & V
mags for 18 nearby reference stars, and my processing procedure
yielding approximate V-mags (with later-determined bias of ~ 0.039
mag).
The above graphs replace the following two (calibrated using APASS
r'-mags).
Best 5 ref stars chosen for color similarity to target &
other behavior. The small-amplitude sinusoidal variation, with P =
0.8 hr, appears to be statistically significant.
Square root of "Power Spectrum" showing weird shape.
Observing Project Goals & Plan
This web page records my observations of KIC
8462852 (hereafter KIC846) in an attempt to measure small
amplitude variations on timescales of hours, days, weeks and
years. In support of both goals 25 nearby stars have been
calibrated using all-sky photometry.
My original goal was
to detect the suggested fade rate of 0.34%/year during the 2016 observing
season. The suggested fade rate corresponds to 3.4
mmag/year, or 1.0 mmag every 3.5 months, which is the length of my
observing season (due to the summer monsoon ending in
mid-September). However, I have determined that
systematic errors are present at the level of ~ 3 mmag per
observing session,
and I do not know what systematic errors may exist during
monthly timescales, so it is unreasonable to expect success
in measuring a 1.0 mmag fade during a 3.5-month interval. Instead,
I will attempt to measure the slow secular fade by comparing
results during two observing seasons.
My original secondary goal was to search for short timescale
variability, and this has become a primary goal for the
current observing season. A few observing sessions will be
long enough to search for hourly variations, but most observing sessions
will be limited to an hour. This should allow for a search of day-to-day
changes, as well as weekly timescale changes. If none are found then
the observations will be viewed as providing an observational
upper-limit to such variability.
The observational strategy is to
improve the calibration of nearby stars so that each observing
session produces a better-calibrated V-mag for that date. The
tighter the star color sensitivity scatter plot, which I use
for establishing an observing session's calibration, the
smaller are the systematic errors for that session's target
V-mag. The APASS magnitudes for this star field appear to be
flawed, in both average value and internal consistency
(star-to-star ratios). I will use all-sky photometry,
involving many Landolt stars, to accomplish this calibration.
In order to know how long each weekly observing session will
have to be for the average target V-mag to have a stochastic
SE smaller than the estimated systematic SE I will conduct a
couple long observing sessions (> 6 hrs) and simulate
having just limited time chunks of the data, with a sampling
chunk lengths. KIC846 is bluer than all but one nearby star to
be used for calibration. This means I have to worry about air
mass effects that differ between the target (KIC846) and the
set of nearby calibrator stars. In order to assess the
usability of high air mass data I will determine a best value
for my "air mass curvature correction," AMC', and demonstrate
the stability of this parameter, and use simulations of long
observing sessions to determine how safe it is to use only
high air mass observations (made late in the observing season)
for monitoring secular fade rate.
I will sue the same hardware configuration for all
observations: Made 14" LX200 GPS telescope, in a dome, with a
x2 focal reducer (designed for this Meade model, A CFW-10 with
an Astrodon V-band filter and an SBIG ST-10XME CCD. All
hardware control is performed using MaxIm DL, via 100-foot
buried conduit cabling between my residence office and the
dome observatory. The unbinned image scale for this system is
0.725 "arc/pixel, and the FOV is 28 x 18 'arc. I will use 2x2
binning for all observations, placing the target at the center
of the image, and autoguiding with the 2nd chip of the
ST-10XME CCD. This will remove drift of the star field with
respect to the pixel field during an observing session, and if
I place the target accurately at the same center location for
each observing session this should reduce the effects of
imperfect flat field calibration. Finder Image and
Calibrated Star B-mag and V-mag Table This is a finder chart.
FOV = 26 x 18'arc, north up, east left. KIC846 is in the square.
Here's a smaller FOV finder chart showing 25 stars that have been
calibrated using all-sky photometry.
FOV 14.0 x 9.4 'arc showing KIC846 (red square) and 25 calibrated
reference stars. North up, east left.
The table below is a listing of my all-sky photometry B- and V-
magnitudes.
All-sky photometry of KIC846 and 25 nearby stars. Left panel is
based solely on all-sky calibrations; right panel includes small
adjustments to V-mag based on 5 observing sessions and persistent
departures from a Star Color Sensitivity fit. I recommend use of
the right panel magnitudes.
Two stars are "dangerously" red for use with a slightly blue
target.
Observing Start/Stop Local
Times
If an observation of at least 1/2 hour is needed for a usable
measurement, and if measurements should be made when elevation (EL)
is above 20 or 30 degrees, then the following graphs can serve as a
guide for the season that KIC 846 can be monitored from the ground
under dark sky conditions (for my HAO observing site).
Local time for observing start and end, for the HAO observing
site (Latitude +31 deg, Longitude 110 E) for the requirement that
EL > 30 deg. Times for sunset + 1 hour and sunrise - 1 hour are
shown as dashed traces. Local midnight is 12:21 AM due to the
observing site's longitude being -110 deg (vs the standard -105
deg for the HAO time zone).
The number of hours that are potentially available for observing
is plotted in the next graph.
Number of hours when KIC846 is above specified elevation (EL),
and when the sky is dark (more than 1 hour past sunset and 1 hour
before sunrise) versus month number, for an observing site at
latitude +31 deg (Hereford Arizona Observatory). From this graph it can be seen that January is the only month
when KIC846 can't be observed from ground observing sites for
monitoring purposes. December is marginal, since KIC846 is above EL
= 30 deg during darkness for only 0.6 hour (Dec 15). For observing
sites at more northerly latitudes the observing times will be
longer.
References
Boyajian et al, 2015, MNRAS, "Planet
Hunters X. KIC 8462852 - Where's the flux?"
Landolt, A., 2009, Astron. J., 137,
#5
Montet, Benjamin T. and Joshua D. Simon, 2016,
"KIC 8462852 Faded Throughout the Kepler Mission," arXiv
1608.01316
Smith et al, 2002, Astron. J., 123,
2121-2144.
Related Links
https://www.youtube.com/watch?v=XI5GDa9r4No
Fredric Parker dimming rate analysis (Jun 09) https://www.youtube.com/watch?v=risNfZxz6DQ
Metzger & Stone (Columbia Univ.) YouTube discussion of the
state of modeling fluxvariations
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
AAVSO Campaign
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)
My web pages master list, resume
| When Roobs invade and
overwhelm a discipline, and present their opinions as
having the same legitimacy as an academic's, it's time for the
academics to retreat somewhere and abandon public discussion of
the subject, leaving it to the Roobs for eventual ruin. This
matter was first described by Joe Ortega y Gassett (Revolt of
the Masses, 1930), later by Roger Price (The Great Roob
Revolution, 1970), and updated in a chapter by Bruce Gary
(Genetic Enslavement, 2014). Every academic discipline is
subjected to the corrupting influence of the hoi poloi,
and during my 78-year lifetime I've seen two of my favorite
disciplines (sociobiology and neuropsychology) lose vitality
because of the influx of "know-nothing/know-it-all" Roobs. When
this web page suddenly went from about one hit per month to a
hit every 3 minutes (recently, once per minute), I braced myself
for what might happen. For more information about Roobs, go to link.
By the way, the person who cultivates his garden
is on a path to liberation from enslavement by "group think."
"Generally speaking, it is quite
right if great things – things of much sense for men of rare
sense ‑ are expressed but briefly and (hence) darkly, so
that barren minds will declare it to be nonsense, rather
than translate it into a nonsense that they can comprehend.
For mean, vulgar minds have an ugly facility for seeing in
the profoundest and most pregnant utterance only their own
everyday opinion." Jean Paul, as quoted by Friedrich
Nietzsche, Philosophy
in the Tragic Age of the Greeks, 1872.
B L G a r y at u
m i c h dot e d u
WebMaster: B. Gary. Nothing on this web page is copyrighted. This
site opened: 2015.10.15, Ended: 2017.06.17
B L G a r y at u
m i c h dot e d u