began two weeks
ago, and it's
~ 0.5 % so far).
want to suggest that careful use of AAVSO data can
be used to produce good quality light curves, as I
illustrate below. Congratulations, certain AAVSO
1) This web page is for the 2018 observing season for KIC
8462852 (e.g., "Tabby's Star"), hereafter KIC846.
2) By now everyone knows about two
important papers that appeared at the arXiv preprint web
site on Jan 03: the Tabby Team paper (199 authors)
summarizing Kickstarter observations & others, and a
Deeg et al. paper reporting GTC (10.4-m) observations of
dip depth vs. wavelength. Both confirm that dust with a
small size component (< 0.5 micron radius) produce the
dips. (Long-timescale variations are a completely
different thing.) Links to these two papers are given in
the References section (below).
3) Rafik Bourne and I have published two articles in AAS
Research Notes: 1) "KIC 8462852
Brightness Pattern Repeating Every 1600 Days" at link,
and 2) "KIC 8462852: Potential repeat of the Kepler day
1540 dip in August 2017" at link.
Preprints are available at arXiv:1711.04205
A full-length (9-page) article, covering both AAS
Research Notes topics more fully, has been published
by MNRAS. You can see the final version (after 3
revisions) at link or
4) Finally, since I have probably observed KIC846 more than
anyone, I may have earned the right to comment about the
suggestion of "alien mega-structures" as a possible
explanation for the unexplained dimming behavior before
natural explanations had been exhausted. I'm going to repeat
a complaint by the Dutch astronomer Ignas Snellen of Leiden
Observatory, but first I want to present a brief
justification for my right to complain by describing my
pro-SETI credentials: 1) In the 1950s I demonstrated the
feasibility of an alien civilization in our interstellar
neighborhood to broadcast its location by transmitting a map
of how constellations appeared from their location, and 2)
when I led the JPL Radio Astronomy Group in 1968 I suggested
that SETI should be a group goal with a Deep Space Station
radio telescope, which my successor eventually did, using
DSS-14, until it was killed by a Nevada senator who
complained about this NASA project. (As an aside, I was
hired at JPL in 1964 by Frank Drake who was apparently
impressed by my Jupiter observations with the radio
telescope he used for Project Ozma). OK, here's what Dr.
Snellen wrote (from link):
"...there is no place for alien civilizations in a
scientific discussion on new astrophysical phenomena, in the
same way as there is no place for divine intervention as a
possible solution. One may view it as harmless fun, but I see
parallels in athletes taking banned substances. It may lead to
short-term fame and medals, but in the long run it harms the
sport. Same for astronomy: we should be very careful not to be
ridiculed. I really hope we can stop mentioning SETI for every
unexplained phenomenon.” The article (by Elizabeth Howell) ends with
a quote from Morris Jones, an Australian space observer:
"The media is under pressure to deliver
attention-grabbing news, but it’s hard to expect them to judge
fringe SETI as spurious when it comes from reputable
institutions and qualified researchers. The best way to reduce
these reports is to stop the production of questionable
scientific papers in the first place.” Amen!
on this web page
g', r' & i' Magnitude
and g'-mag vs. date
with AAVSO observations
of observing sessions
image showing new set of reference stars
precision explained (580 ppm)
Go back to 5th of six web
pages (for dates 2017.11.13 to 2018.01.03)
Go back to 4th of six web
pages (for dates 2017.09.21 to 2017.11.13)
Go back to 3rd
of six web pages (for dates 2017.08.29 to
Go back to 2nd
of six web pages (for dates 2017.06.18 to
Go back to 1st
of six web pages (for dates
2014.05.02 to 2017.06.17)
Star Quality Assessment (the 10 best stars out of
This is the 6th web pages devoted to my
observations of Tabby's Star. When a web page has many images
the download times are long, so this is the latest "split."
g', r' and i' Mag's
Figure 1. HAO magnitudes at g'-band for the past 2.5
months. The "OOT only" trace is the second "U-Shaped"
component needed to account for the upper-boundary of
measurements (presumably the out-of-transit, or OOT, level).
V and g'-Mag vs.
Figure 2. HAO magnitudes at g'-band for the
past 7 months. The "OOT only" trace is the second
"U-Shaped" component needed to account for the
upper-boundary of measurements (presumably the
out-of-transit, or OOT, level).
Figure 3. This shows the last 2.5 years of
C-, V- and g'-band HAO measurements (C- and V-mag's adjusted
to match g'-mag's).
Figure 4. Normalized
flux light curve for the past 2 months, based on the OOT
model shown in the previous two graphs.
A one-year plot of "normalized flux"
based on the previously displayed OOT model (with two
U-shaped features). The HAO data for April are too sparse
for showing dip structure well; the graphs in the next
section do a better job of that sine they include AAVSO
of HAO with AAVSO Observations (Demonstration of the value of combining AAVSO
data with other data with emphasis on the biggest ground-based
The following figure shows a selection of AAVSO observer V-band
magnitudes vs. date for a 2.6-year interval.
Figure 6a. Selected AAVSO plus HAO V-band (and
g'-band) magnitudes for a 2.6-year interval. Offsets for each
observer were applied to achieve agreement with HAO data. Two
U-shaped features are included in the OOT Model.
Observers: OAR = Arto Oksanen (Finland), HBB = Barbara
Harris (Florida, USA), HJW = John Hall (Colorado, USA), LDJ =
David Lane (Nova Scotia, Canada).
During the first 2 years a steady fade is present
(confirming last year's interpretation of HAO data). It is
interrupted by a U-shaped fade feature in mid-2017, and is
followed by a second U-shaped fade in early 2018. The "OOT
model" trace is meant to show what would be observed if dips did
not occur, so it can serve as a reference level for determining
dip depth and shape. The deepest dip occurs at ~ JD4 = 8203 and
is ~ 67 mmag (~ 6 %) deep.
Figure 6b. Same data as above, but showing just the
last year of data.
David Lane (AAVSO Observer Code LDJ) has reprocessed his 2.6
year's of KIC846 observations (lot's of work!), and has
re-submitted them to the AAVSO database. The LDJ V-band data for
times of known dips were excluded, and the remaining OOT
(out-of-transit) data was averaged in groups of 7 observing
sessions. An arbitrary offset was applied to achieve maximum
agreement (this is legitimate since every observer has a unique
and unknown absolute calibration uncertainty). The purpose for
performing these adjustments was to allow for an assessment of
the presence of a U-shaped OOT pattern with an approximate
1-year timescale that has been derived using HAO data. The next
figure is a light curve showing how the LDJ V-mag measurements
compare with HAO data.
Figure 7. Six-month light curve for two observers,
LDJ (David Lane) and HAO (Bruce Gary). The LDJ symbols are
averages of 4 observing sessions (~ 25 images per
session) while the HAO symbols are for individual observing
sessions (>200 images per session, typically). Dip data for
both LDJ and HAO have been excluded from this LC. The LDJ and
HAO symbols can therefore be viewedd as OOT only. Both data
sets confirm the U-shaped OOT model (centered on
This figure shows agreement of both LDJ and HAO data
with the main U-shaped OOT Model.
I conclude that the U-shaped OOT model has support
from both data sets. The depth of the U-shape is ~ 1.0 % and the
duration of the U-shape is ~ 1.0 year. So far, the LDJ and HAO
data agree in suggesting that since the time of maximum
brightness at the end of the U-shape (near JD4 = 8050) a steep
fade has been underway. LDJ B-band measurements will be
presented here that show a greater U-shape depth than for
V-band! This will provide a significant constraint on modeling
the physical mechanism for the U-shape (large dust cloud vs.
reflection of starlight by the dip clouds).
The next graph is a comparison of downloaded AAVSO
data for March and April.
Data for 5 observers is
shown with offsets chosen to maximize agreement with HAO and
Figure 8. Comparison of g'-mag
(and V-mag, adjusted) for 5 AAVSO observers and HAO during
March, April and May, 2018. Arbitrary offsets have been
applied to each observer data set to achieve agreement
with HAO data, where overlap exists, and with each other
(i.e., internal consistency). The green trace is the sum
of a slowly varying OOT model plus a short-term dip
modeled using "asymmetric
hyper-secant" (AHS) functions. The 60
mmag dip ( ~ 5.3 %, dip at JD4 = 8203.4) is fitted well by
the AHS function. (The data in this figure was downloaded
from the AAVSO web site: https://www.aavso.org/lcg.)
Figure 9. Comparison of B-mag
for two AAVSO observers during March, April and May,
2018. Arbitrary offsets have been applied to each
observer data set to achieve agreement with HBB
data, where overlap exists, and with each other
(i.e., internal consistency). The green trace is the
sum of a slowly varying OOT model plus a short-term
dip modeled using "asymmetric
hyper-secant" (AHS) functions. The
82 mmag dip (6.6 %, at JD4 = 8203.4) is fitted well
by the AHS function. (The data in this figure was
downloaded from the AAVSO web site: https://www.aavso.org/lcg.)
[Still working with this graph, adding data from
Both V-band and B-band exhibit
a significant brightening from early April to early May. There
appears to be a small but significant difference in the
brightening amount at the two bands. The brightening from 8208 -
8215 to 8237 - 8253 is 13.7 +/- 3.0 mmag at V-band and 20.5 +/-
1.7 mmag at B-band (using a sum of chi squares analysis). The
difference in brightening is 6.8 +/- 3.5 mmag, which is
significant at the 2.0-sigma level. In other words, there's a 95
% probability that the difference in amount of brightening at B-
and V-band is real, with a greater amount of brightening at
B-band. If this finding holds up then we would have to invoke a
dust cloud model to explain the slow variation (i.e., the
U-shaped variations), and that dust cloud would have to include
a significant component of small particles (<0.3 micron
The deep dip in late March is also deeper at B-band than V-band.
Again, this is evidence for the presence of a significant
component of small dust particles in the dust cloud producing
Figure 10. Same as Fig. 7,
but showing only HBB, LDJ and HAO data. The good agreement
between three independent data sets (showing a dramatic 2
% brightening) suggests that the variations shown are
real. A similar graph for B-band shows the same
brightening for different observers, again giving credence
to the reality of the brightening.
Figure 12. Rafik Bourne's
comparison of dip depth for different wavelengths. B-band
has the deepest depth while Ic-band has the smallest depth.
(The LCO data are manually read off graphs at Tabby's blog,
made necessary because these data values are not in the
public domain.) Clearly, the dip at JD4 = 8203.5 is due to a
dust cloud dominated by a component of small particles (<
0.3 micron radius).
Transit Pattern and Speculation about Model for KIC846
Dust Cloud Geometry (not
Physical Mechanism Model)
A thorough description of this matter is given in the 5th web
page of this 6-part series of web pages: link