KIC8462852 Hereford Arizona Observatory Photometry Observations #3
Bruce Gary, Last updated: 2017.09.28, 05 UT

I've switched from V-band to g'-band, starting Sep 21. The g'-band observations can be found at

Figure 1.1a. Light curve for "May to now" for HAO V-band observations, with an adjustment for an "Inverse Gaussian" model for the long-term variation/fade of OOT brightness (described below). Starting Sep 18 there's an unknown offset due to a change of configuration.

Notice the different asymmetries for the three major fade events: the May fade begins fast and recovers slower, the June fade begins slower and its recovery is interrupted by a small fade, while the August fade began slowly and recovered fast. None of these shapes resemble exo-comet tail transits (as described by Rappaport et al, 2017 link); so the mystery of what's producing these week-timescale dips continues!

The current dip is "in recovery." even the detailed observations (15-minute averages) show the increasing brightness during the past two nights (see next two figures).

Figure 1.1b.  Detail showing "shape" of the latest dip, and
45-minute averages for last two days. It has a "negative curvature" (of normalized flux) on the ingress; let's see what the curvature is for egress. Note: a comet pass would produce an opposite pattern of curvatures (positive for ingress and negative curvature for egress), so already this doesn't look like a comet tail transit. The Sep 11 45-minute averages exhibit an RMS scatter of 0.00028 (i.e., 0.28 mmag), which is my all-time best performance for me. Don't believe the Spe 18 data.

Figure 1.2. Tabby Team r'-band LC. Last data is for Sep 18. 

Tabby's Star undergoes variations on many timescales. The ASAS and ASAS-SN V-band observations reported by Simon et al. (2017) illustrate the presence of multi-year and multi-month variations, and the Kepler data, plus recent ground-based data, show multi-day variations (dips). If one category of variation is to be studied in isolation of the others some method must be devised for modeling the other variations. For example, for the study of multi-day dips it is necessary to model the multi-month and multi-year variations. This process is inherently subjective, both in the timescale to be represented by the model and the model chosen for that purpose. The next graph shows Tabby Star V-mag the last 4 months, and I used the inverted Gaussian model with parameter values chosen to fit just the past 4 months of OOT data. Identifying OOT data when dips are present is also somewhat subjective. Finally, I have used a subjective process for correcting Tabby Star magnitudes for small linear drifts in reference star brightness (as will be described in another section). 

Figure 1.3. Tabby Star V-magnitudes after removal of small systematics based on behavior of 21 reference stars. The inverse Gaussian model parameter values were chosen for fitting just this 4-month span of data.

Figure 1.4.  V-magnitude measurements after removing small reference star systematics. Reference star trends have been used to adjust TS magnitudes.

Links on this web page

History of why this web page 
List of observing sessions
A prediction  

Go back to 2nd of three web pages   (for dates 2014.05.02 to 2017.08.28)
Go back to 1st of three web pages    (for dates 2017.06.18 to 2017.06.17)
Reference Star Quality Assessment  (the 10 best stars out of 25 evaluated)  

History of this web page

This is the third of three web pages devoted to my observations of Tabby's Star. One reason for splitting the pages is that when a page has a lot of images the download time becomes excessive. But the real reason for this page splitting is to avoid the attention of people who post things on Reddit, "the paparazzi of the internet" (a place meant for Roobs). 

List of Observations (for all earlier observations, before Aug 29, go to link)

2017.09.18 V  
2017.09.17 V  
2017.09.16 V  
2017.09.14 V  
2017.09.13 V  
2017.09.12 V  
2017.09.11 V  
2017.09.10 V  
2017.09.08 V 
2017.09.07 V  
2017.09.06 V  
2017.09.05 V  
2017.09.03 V  
2017.09.01 V  
2017.08.31 V  
2017.08.30 V  
2017.08.29 V  

Daily Observing Session Information (most recent at top)

2017.09.18, V-band, 2.5 hrs 

Configuration change: removed focal reducer. Image scale changed from 1.70 "arc/px (binned 2x2) to 0.83 "arc/px (binned 2x2). Smller FOV, new flat fields.
Because of the new configuration the systematics may have changed, so don't take any differences from the past seriously! It appears that there's a 7 mmag (0.7%) systematic difference in V-mag for the new configuration.

2017.09.17, V-band, 4.5 hrs  DataExchangeFile  

2017.09.16, V-band, 5.1 hrs  DataExchangeFile  

2017.09.14, V-band, 3.1hrs  DataExchangeFile  

2017.09.13, V-band, 5.7 hrs  DataExchangeFile  

2017.09.12, V-band, 6.2 hrs  DataExchangeFile 

A slight increase, suggesting that egress (recovery) is slowing.

2017.09.11, V-band, 5.8 hrs   DataExchangeFile  

This was the first night without "monsoon clouds"! It was clear the entire night, which I haven't seen since June. Data quality is therefore expected to be better than for the past 2.5 months.

Notice the increase in brightness (normalized flux) during this 5.8-hour observing session.

2017.09.10, V-band, 5.5 hrs  DataExchangeFile  

Looks like a recovery is underway.

Darned clouds kept coming and going, which kept me awake much of the night.

Good calibration!

2017.09.08, V-band, 1.9 hrs  DataExchangeFile 

Lot's of clouds, so I observed through holes.


2017.09.07, V-band, 4.2 hrs  DataExchangeFile   

I wonder if the downward trend is real.

2017.09.06, V-band, 5.3 hrs  DataExchangeFile 

2017.09.05, V-band, 3.5 hrs   DataExchangeFile  

Note: This graph adopts the old nverse Gaussion model, which doesn't account for the recent rise in OOT brightness.

2017.09.03, V-band, 0.8 hr, DataExchangeFile  

2017.09.01, V-band, 5.7 hrs   DataExchangeFile  

2017.08.31, V-band, 5.8 hrs DataExchangeFile  

This is interesting: Tabby is seeing a fade (at r'-band) while I'm seeing a brightening (V-band).

2017.08.30, V-band, 4.9 hrs, DataExchangeFile  

2017.08.29, V-band, 2.7 hrs   DataExchangeFile  

A Prediction

I predict that in a matter of months t
he brightness of KIC846 will NOT plummet to zero, but the level of interest in KIC846 by the general public will! This will happen when the professional astronomers present evidence that the fading events are produced by dust clouds, not alien mega-structures. The hit rate for my KIC846 web pages, which is currently about once a minute, will return to the once a month level, just as they were for the 1.5 years before May 19 of this year.

I have experience with the fickleness of such things based on my 2013 observations of Comet ISON - that so-called "Comet of the Century." NASA bought into that terminology, possibly because it garnered public interest in a project that NASA had funded. I was the first to dampen enthusiasm when I made the first "recovery" observation after a 2.5-month hiatus of imaging (due to the sun being close to the line of sight) as the comet was making its approach, and I stated that the comet was about a magnitude fainter than models were predicting, and it might disappoint during the rest of it's approach to perihelion. NASA continued to hype the comet, and I attracted a fan club of cynics who trusted my assessments and almost daily updates more than those by the professionals. Some unscrupulous web hucksters took pictures from my web site for posting on theirs with hyper-hysteric interpretations; one posted a picture I had enhanced to show a forward jet and on his web site he claimed to show a UFO flying in formation ahead of the comet. As perihelion grew closer, and the comet's brightness fluctuated at below expectations, and as my web page hits grew to ever higher levels, and as experts were quoting my kill-joy assessments, Discovery Channel scheduled an interview with me at my observatory to coincide with perihelion passage. But as the sun's heat sublimated the comet to nothing during closest approach; public interest immediately plummeted to zero and the the Discovery Channel interview was canceled. My web page hits went to nothing, and my life returned to normal. But I was wiser, for I finally understood the fickleness of public interest in things scientific.

I predict that by the end September, when the evidence for dust clouds and prosaic decadal variations are accepted, KIC846 will join the "Hype of the Century Club" for being "the alien mega-structure that wasn't."


    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," arXiv: 1708.07556  
    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: 1708.06069 
    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 (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) 
    wikipedia description of HAO  
    My web pages master list, resume

    B L G a r y at u m i c h dot e d u    Hereford Arizona Observatory    resume 
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