KIC 8462852 Hereford Arizona Observatory (HAO) Photometry Observations #15
Bruce Gary, Last updated: 2024.04.20, 02 UT

It's the start of a new observing season.

The last observing season had the fewest dips per unit of time compared with all previous 7 years of ground-based observations.  The 0.4 % features in mid-September and early-October are likely statistical artifacts (noting that a 2-sigma event can be expected whenever ~ 20 measurements are present, and I have 28 measurements so far this season). The only credible depaaaarture from steadiness was the rise in brightness during December (2023).

I expect that this 17-year trend (of shallower dips) will continue until the next big collision. We should consider that the big collision that was recorded by Kepler in 2011 was a rare event. We are currently "stabilizing" at lower levels than a few years ago (e.g., the "clearing" of late 2019 and early 2020). This may mean that the clouds of dust that had been producing dips are now spread out along their orbit into a more opaque but quasi-uniform dust belt. I predict that during this observing season there will be just this currently underway dip structure.
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Links on this web page

    Basic info for KIC846  
    Recent Behavior
    List of observing sessions (for the 2022 observing season)
    Overview of Past 130 and 18 Years
    Finder image (showing my ref stars)     
    References    

Links on other web pages
 
    HAO precision explained (580 ppm) 
    DASCH comment  

    This is the 15th web page devoted to my observations of Tabby's Star for the date interval 2024.04.17 to the present.  

  Go back to 14th web page  (for dates 2023.08.13 to 2023.12.31)
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    Reference Star Quality Assessment  (the 10 best stars out of 25 evaluated)  

Basic Info for KIC846

RA/DE = 20:06:15.44 +44:27:24.9
V-mag = 11.85, g'-mag =12.046, B-V = +0.51 (APASS)
Spectral type: F3V
T_eff = 6750 K
R = 1.58 R_sun (1.10e+6 km)
M = 1.43 M_sun (2.84e+30 Kg)
Observing season centered on Jul 24

Recent Behavior


Figure 1. The 3-week dip in early November is real. The rise in g' OOT is also real. 


Figure 2.  HAO observations during the past two  years.


Figure 3. HAO observations during the past 4 years. Notice the variations of OOT level (dashed lines). OOT at g' band varies more than at longer wavelengths. This is to be expected since small particles affect shorter wavelengths more. Presumably, the OOT variations are due to a more spread-out band (outer orbit, with fewer collisions). The dips would then be due to recently created dust clouds in a different orbit (inner), where collisions are more frequent. Whereas the dust clouds that produce dips last only a few weeks, and don't experience significant Keplerian orbit shear, the dust clouds in the outer orbit last months to years (due to less radiation pressure), and therefore undergo significant Keplerian orbit shear. We don't know if the outer and inner orbits are circular (I envision the inner orbit to be circular and the outer orbit to be highly elliptical, as shown at link).


Figure 4a. This graph includes V band measurements by Barbara Harris (HBB) and my g' band measurements (offset to achieve agreement with V band) for this 2023 observing season.


Figure 4b. During the past 7 years two categories of brightness variations have occurred: a slow variation (associated with a dust donut) and a fast variation in the form of dips (produced by small clumps of dust, or recently-created "dust clouds:). This graph, based on my HAO g' data (observer code GBL) and Barbara Harris's V data  (observer code HBB) shows both components. The slow component is shown by a tan trace. Other observer data (not shown here) was also used to establish the tan trace.


 Figure 5. The "Torus Brightening" underway now reveals that the torus dust cloud consists of only small particles (circumferences < g'-band wavelength). This result is derived from the fact that changes in r'-band are only ~ 40 % of the changes in g'-band, which is what would be expected if all particle sizes were in the Raleigh scattering regime (which for g' and r' would produce a 36 % relationship). For comparison, KIC8446 dips exhibit variations where r' amplitude is 60 % of g' depths, meaning that the dust clouds that produce dips are a blend of small and large particles (both Raleigh and Mie scattering regimes). For the two most-studied white dwarfs with dust clouds orbiting in front of them (WD 1145+017 and J0328+1219) all dust particles scatter in the Mie regime, and are therefore large (based on the observation that dips have the same depth at all wavelengths that have been measured).


Figure 6. KIC846 has the smallest particles of any transiting dust cloud that I know about. The Torus dust is so small that all particles must be within the Rayleigh scattering regime (radii < 0.1 micron). KIC846's dip dust clouds are a mix between Rayleigh and Mie scattering (radii straddling 0.1 micron). Both WDs with well-studied transiting dust clouds are missing small dust particles.


List of Observations

2024.04.18  
2024.04.17  


Daily Observing Session Information (most recent at top)



2024.04.18  



2024.04.17  







































Overview of Past 130 Years

Here's the Harvard DASCH data with group averages, plus my B-band data from 2018. Some time around 1960 the camera optics were changed, and this apparently led to a 0.1 magnitude offset.


Figure P.1. B-band (approximate) measurements, median combined for data groups, during the past 130 years.


Figure P.2. Measurements converted to V-band from many sources.


Figure P.3. The "tops" of measurements (red trace) represent a "slow variation" component (presumably due to an outer orbit dust disk with very few "clearings").


Figure P.4. Removal of measurements shows more clearly the "slow variation" and "dip variation" components.

 
Figure P.6. Zoom last graph to show most recent 7 years.


Figure P.6. Removal of the "slow variation" component allows for display of only the "dip variation" component.

These graphs reveal the following patterns:

  1) There are two types of brightness variations, "slow" and "dip." The "slow" variations have timescales of months to years, and the "dip" variations have timescales of a day.
  2) The "dip" activity began with one big dip in 2011, and every two years later (~ 2.2 years) the dip structure became more numerous, shallower in depth and spread over a longer time interval..
  3) The "dip" fade pattern is superimposed upon the "slow" fade pattern.

Two-Orbit Model
 
These three patterns immediately call to mind a two-orbit system of dust clouds.


Figure P.7. Suggested elliptical orbit of an interloper planetesimal whose present orbit intersects an asteroid belt following a perturbation by some other massive object..

The scenario for this 2-orbit model assumes that the "interloper" was once in a large circular orbit, far away from the asteroid belt (assuming that an asteroid belt existed). Another planetesimal came close to it in way that perturbed it's orbit to become highly elliptical, with periastron within the asteroid belt. After a few passages through the asteroid belt the interloper perturbed orbits of a few asteroids. Two categories of collisions would result: 1) asteroid/asteroid collisions, and 2) interloper/asteroid collisions. The first collision type would populate the asteroid belt with dust clouds having periods close to those of the asteroids (e.g., 2 or 3 years). The second collision type would produce dust clouds having periods close to the interloper's orbital period (e.g., > 15 years). [The lon g period dust clouds assume the interloper is more massive than the asteroids that it collides with; this is an easy assumption to makes since the asteroids have a size distribution that that extends to dust.]

As explained in the next section, dust clouds will spread-out along the orbit - a celestial mechanics process called "Keplerian shear." The longer a dust cloud exists, the greater the spreading along the orbit.

Radiation pressure will push the small orbit dust clouds away, disbursing them to eventual non-existence. The timescale for this could be several months. When these inner orbit dust clouds pass in front of the star we see "dip structure." Young dust clouds in the inner orbit will produce short-duration dips (e.g., days long). Old dust clouds will produce long-duration dips (e.g., weeks long).

The dust clouds in the outer, eccentric orbit will last much longer because they spend most of their time far away, where radiation pressure is less. The timescale for the existence of these dust clouds could be decades to centuries. This allows them to populate the entire eccentric orbit, with densities that vary gradually along the orbit. The reduction of starlight produced by this belt of dust produces what I refer to as the OOT level (out-of-transit). Because this component of dust will have a size distribution that can be small compared with optical wavelngths the OOT variations it produces can be greatest at the shortest wavelength, and decrease with wavelength (this is observed). 

Collision Basics

Before comparing this collision model with KIC846 observations I want to treat the generic case of collisions.

Let's consider the case of one object colliding with a larger one, such as a comet hitting a more massive asteroid. Let's assume that the mass of each object is small enough that all fragments have speeds much larger than the "escape velocity" for each object. In other words, all ejected material, ranging in size from the largest (fragments) to the smallest (dust), escape their source object and leave the collision site on trajectories that define new orbits for every bit of debris. It is useful to imagine particles ejected in the three coordinate directions: up/down, fore/aft and in/out. If a particle is ejected "upwards" or "downwards" (i.e., perpendicular to the asteroid's initial orbit plane) it will be in an inclined orbit (and have the same period as the asteroid). If it is ejected "forward" or "backward" (parallel to the asteroid's initial orbital motion), it will be in an eccentric orbit that is either larger or smaller than the original asteroid orbit (and will be in an orbit with a period that differs from the asteroid's). If it is ejected "in" or "out" (toward or away from the star) it will be in an orbit that is eccentric (but will have the same period as the asteroid). All of this is explained in more detail at http://www.brucegary.net/collisions/.

It is commonly assumed that a collision produces ejecta that goes in all directions equally ("isotropic"). This probably is rarely true, but it's a good starting point. We should assume that essentially all particles will be ejected having all three components of velocity. Therefore, the cloud of particles will expand and contract twice per orbit, and due to the slightly different periods for almost all particles the cloud will elongate (along the orbit) in a way that accumulates over time (called "Keplerian shear."). Read the previous sentence again, because it's counter-intuitive, and even some astronomers don't know this.

Because Keplerian shear acts quickly the cloud can be thought of as stretched out along the orbit by an amount that is several star diameters, even when it may have a smaller vertical size (measured perpendicular to the orbit plane). Therefore, Earth viewers can assume that the obscuring dust cloud is a "band" extending along the orbit many star diameters and extending vertically by a fraction of a star diameter (allowing us to estimate the depth of the dip). This assumes the dust cloud is opaque. For example, a dip depth of 20 % could be produced by an opaque dust cloud that had a vertical extent that is ~ 15 % of the star's diameter (because a band 15 % the diameter of a circle, placed on the circle's center, covers ~ 20 % of the circle's area).

A dust cloud reaches its maximum vertical extent 1/4th of an orbit after the collision. It then collapses to a very small vertical extent during the following 1/4th of an orbit (at the 1/2 orbit location). Size maxima occur at the 1/4 and 3/4 locations. Therefore, the greatest possible dip depths will occur for collisions that occur 1/4 and 3/4 of an orbit before the dust cloud orbits in front of the star. Close to zero depth will occur for collisions that occur "in front of" and "behind" the star. Keep in mind that when "the same" dust cloud is observed more than once it will be at the same vertical expansion phase each time it is observed. For other observers, aliens with other views, the same dust cloud would have a different vertical extent and would produce dips with different depths.

Consider the first deep Kepler dip in 2011, labeled "0" in Fig. 5. Depth is 15 %. This means the band of obscuring dust had a vertical thickness of ~ 10 % of the star's diameter (if the band crossed through the star's center and was opaque). Let's assume that a collision occurred 1/4th (or 3/4th) of an orbit earlier (meaning that we were observing the dust cloud when it was at its maximum expansion phase). Since the KIC846 star is thought to have a radius of 1.1e+6 km, the cloud vertical thickness would have been 2.2e+5 km (at least, because this assumes the cloud is optically thick and crosses the middle of the star). If the orbital period is 790 days, then an isotropic expansion speed of 20 m/s would be required. (The handy equation for this is V = vertical thickness / (P / pi). Of course, the cloud could be optically thin and this would require greater vertical thicknesses, which in turn would require higher speeds. For other values of the expansion phase, higher speeds would also be required. Incidentally, if the Kepler first big dip collision occurred 1/4 orbit earlier, our observation of it at JD4 = 5626 means the collision would have occurred on JD4 = 5430.

Hypothetical Collision

Let's imagine what a collision could look like. For this demonstration I've assumed P = 776 days (because that's what I adopted last year when I made these graphs). Here's an imaginary long light curve that shows more than three orbits worth of brightness.


Figure P.8. Hypothetical light curve showing a single dip from a dust cloud following a collision after the dust cloud had expanded to cover 20 % of the star's disk.After an orbit fragments from the collision had spread apart ("Keplerian shear"), and were producing their own dust clouds. After another orbit these fragments, and others that had begun producing dust clouds, were responsible for dips that were less deep.all 

Another way to view this light curve is with a "waterfall plot," shown next.


Figure P.9. Waterfall plot of the data in the previous figure. Dotted lines can be used to quantify "Keplerian shear."

The slopes of the dotted lines can be used to establish the ejection speeds of fragments that eventually became sources for dust clouds. If these fragments had persisted in producing dust clouds for longer than an orbit it would be possible to project their "drift lines" backward in time to establish a date for the collision. For the case of KIC846 it will be shown that the fragments were not actively producing dust clouds long enough to perform this backward projection (the next section shows that this could be done for a short period collision case.)

Collision Examples for WD1145

WD 1145+017 was discovered from the Kepler second mission, K2, and announced in a discovery publication by Vanderburg et al (2015).  WD1145, as I will refer to it, is a white dwarf that is orbited by at least 6 large pieces of what was once a planetesimal, possibly the size of the moon before its break-up. The periods for these 6 planetesimal pieces range from 4.49 to 4.86 hours (corresponding to Systems A through F). It is likely that the dust clouds observed orbiting WD1145 are produced by collisions. It will therefore be useful to use WD1145 to illustrate approaches for interpreting KIC846 observations.

WD1145 dust clouds can suddenly appear and their tracks on a waterfall plot can reveal when the collision occurred and where it happened in orbit phase. Collisions can be small, and some are large. Here's a small one:


Figure P.10. WD1145 small collision that occurred at D-system (P=4.55 hrs) phase = 0.5 on 2018 Day-of-Year = 416. Four fragments, each the source of a dust cloud, were ejected in the backward direction (opposite of orbital motion for the parent object), causing them to drift to smaller orbital phase values during the several days that they were active. The several drift lines with steep leftward slopes are dust clouds from active fragments in the A-system, with P =4.49 hrs. (Almost all of the ground-based measurements of WD1145 reported here are from HAO.)

Here's another small collision:


Figure P.11.  A small collision that caused the most active dust-producing fragments to be ejected in the forward direction (adding to orbital speed), which caused those fragments to drift to larger phases over time. The parent fragment was producing dust before the collision. All of these fragments belong to the A-System (P = 4.49126 hrs).

The previous two waterfall plots illustrate what happens when an asteroid  fragment is hit from behind (Fig. P.10) and hit from the front (Fig. P.11). For these cases the debris is produced from the trailing and forawrd sides, with speeds that are less than and greater than the target's orbital speed. 

The next graph is a waterfall plot showing a very large collision in late August, 2015, at System-A orbit phase = 0.5.


Figure P.12. This 5-month waterfall plot for WD1145 shows drift lines that appear to diverge from a date in late August, 2015.

The drift lines in this plot last for several months, indicating that the fragments producing these dust clouds must have been large. The total amount of debris resulting from this collision must have been immense. Indeed, the many fragments that were created from this collision started a cascade of collisions that lasted 6 years, as the next graph shows.


Figure P.13. "Activity level" of WD1145 during the 10 years that it has been observed. The first year of activity was registered by the Kepler spacecraft. The second year of low activity was measured by ground-based telescopes. The current year of observations is similar to what Kepler observed. (Almost all ground-based observations are from HAO.)

This graph shows that a single large collision in 2015 initiated a cascade of collisions that maintained a high level of dust cloud "activity" that lasted 8 years. "Activity" is defined to be the fractional loss of flux during one orbit (the A-system orbit with P = 4.49126 hours).

So far we know about only two WD systems like this: WD1145 (more info at http://www.brucegary.net/zombie10/) and J0328-1219 (http://www.brucegary.net/J0328/). A possible third WD system is sometimes viewed as similar, J0139 (ZTF J013906.17+524536.89), but with a period of 107 days it would have to be in the transitional phase of orbit shrinkage (more info at http://www.brucegary.net/J0139/). For all three systems collisions is a viable model to consider. WD1145 is the proto-type for WDs with dust cloud transits.

WD1145 is ideal for studying dust cloud creation and evolution. This is because orbits are short in comparison to an observing session. A specific dust cloud can be observed to transit many times, somtimes twice in one night, as this LC shows:


Figure P.14. One observing session showing a deep and brief dip twice, 4.5 hours apart.

Observations such as this one illustrate how a specific dust cloud (for WD1145) can be monitored on a 4.5-hourly basis. Analyses of specific dust clouds show that their features can persist for many weeks, as the following figure shows:


Figure P.15. A specific WD1145 dust cloud's characteristics, depth and width, persisted for 4 months (640 orbits).

Findings such as this one pose serious constraints on dust production and loss mechanisms. There appears to be a steady-state for both. A one-time dust production event would appear totally different: after about a day the depth would begin an exponential decrease as the width increased.

The challenge posed by the previous graph is to think of mechanisms for continuous dust production and continuous dust loss.

Dust production was first suggested to be due to sublimation and recondensation (Vanderburg et al, 2015). Sublimation is likely because an orbit with a period as short as 4.5 hours means that the WD star would heat a star-facing surface to ~ 1400 K. Many minerals sublimate at this temperature. Dust production would then entail the sublimation of molecules of mierals and their condensation to particles above the fragment's surface (before it has drifted far away).

Another dust production mechanism is "sputtering" - a phenomenon in which microscopic particles of a solid material are ejected from its surface by high-speed impacts by small particles. This is a "collision model." After the initial impact (think 2015 August) there will be a cloud of fast moving particles in orbits that come together at the opposite orbit location and at the collision orbit location (the latter orbit location has a much higher density of particles). Every time a newly-created fragment orbits through the initial collision site it will be barraged by fast-moving dust from all directions. These will "sputter" new particles from the fragment's surface.

These two dust production mechanisms are both viable, still. They satisfy the need for a steady-state of dust production. What about dust removal, which is also needed in order to explain a specific dip's unchanging depth and width? A clue comes from the fact that so far all of WD1145 dip depths are the same versus wavelength! This means that all dust particles are larger than ~ 0.5 micron. (Another possible explanation could be that all dust clouds are optically thick, all the way to their edges - which is unlikely.) The lack of smaller than 0.5 micron radius particles can be neatly explained by their inability to shed heat because of their small size in relation to the wavelength of the photons corresponding to their temperature (low emissivity at ~ 10 micron wavelength) in spite of their ability to absorb heat from WD photons (normal Bond albedo). This means it will over-heat, and sublimate away!

What about the particles with radii > ~ 0.5 micron? Radiation pressure will blow away the smallest of these larger particles. Keep in mind that radiation pressure for WD1145 at the distance of the A-System of planetesimals, fragments and dust is 86 times greater than exists for the sun at 1 A.U. I haven't quantified particle loss due to radiation pressure, but I assume it's adequate for removing the particles left alone by the over-heating effect (radii > 0.5 micron) and which are relevant for blocking WD starlight (probably < 5 micron).

Transporting Lessons Learned from WD1145 to KIC846

I want to apply some of the analyses that were done for WD1145 to KIC846, but first we should keep in mind two big differences between the two systems:

1) WD1145 dust clouds are produced by fragments that broke away from a planetesimal orbiting so close to the WD star that the gradient of stellar gravity across the planetesimal, front to back surfaces, was at the critical level referred to as "tidal disruption." This means that any object on the planetesimal that was loose would with the merest nudge simply drift away and be in orbit about the WD star.

2) The planetesimal, and all fragments in a similar orbit, are so close to the WD star that they will be heated to temperatures that cause many minerals to sublimate (go from a solid to vapor without being liquid during the transition). Any such vapor would consist of molecules of the mineral, and some of those molecules could condense onto each other to form a small dust grain. If enough condensation occurs the dust grain could grow in size to become effective at scattering or absorbing starlight. This is the mechanism proposed to produce the (low depth) dust cloud fades reported in the discovery paper (Vanderburg et al., 2015). At the time the discovery paper was written WD1145's fade activity had not exploded by a factor of 100 (c.f., Fig. P.13), as happened while the paper was under review and when WD1145 could not be observed due to its proximity to the sun. Given the 100-fold increase in dust cloud activity questions arise about how well this mechanism can account for the higher level of observed fading (how much condensation is likely). Collisions is another model that has gained credibility and is a contender for the sublimation model.

Only some of what happens at WD1145 can also happen at KIC846. Among the things that won't happen is the drifting away of loose material on the surface of planetesimals orbiting KIC846. Another thing that won't happen is sublimation as a source for dust production. Also, small dust particles (<0.5 micron) won't be removed due to over-heating.

Here's a graph showing showing orbit size versus period for KIC846:


Figure P.16. Orbit size versus period for KIC846. For objects to transit the star KIC846 they would have to be inclined from "orbit plane inclination to Earth viewing line" less that the green line value.

Adopting P = 790 days for consideration, fragments with that period would orbit at a distance of 1.8 A.U.. For them to transit an Earthly view their orbit would have to be inclined < 0.2 degrees.  (No wonder only one Tabby-like star has been discovered!)

And here's a graph of predicted surface temperature for a fragment in a circular orbit with a known period.


Figure P.17. Surface temperature for an object (without an atmosphere) in a circular orbit of KIC846 versus orbit period.

Again, if we adopt P = 790 days, for example, T_surface = 300 K (assuming the fragment rotates). I hesitate to mention this because that's 81 F, which is close to "room temperature." That's an equatorial temperature, so it will be cooler at latitudes closer to the poles!







Finder Image  
 

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.

Recently, star #3 has been changing brightness erratically so it is now rarely used!

Data Exchange Files

    more to come ...


My Collaboration Policy

At my age of 84 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 acknowledgement section.
 
References

    Gonzalez, M. J. Martinez and 15 others, 2018, "High-Resolution Spectroscopy of Boyajian's Star During Optical Dimming Events," arXiv:1812.06837. 
    Wright, Jason T., "A Reassessment of Families of Solutions to the Puzzle of Boyajian's Star," arXiv  (a 1.1-page paper)
    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, arXiv 
    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 presentation, link (navigate down, etc)
    Sacco, Gary, Linh D. Ngo and Julien Modolo, 2018, "A 1574-Day Periodicity of Transits Orbiting KIC 8462552," JAAVSO, #3327, link
    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 spectrophotometry" arXiv 
    Bourne, R., B. L. Gary and A. Plakhov, 2018, "Recent Photometric Monitoring of KIC 8462852, the Detection of a Potential Repeat of the Kepler Day 1540 Dip and a Plausible Model," MNAS;  arXiv:1711.10612     
    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, preprint arXiv: 1711.06960 
    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, 3267-3280; arXiv
    Neslusan, L. and J. & Budaj, 2016, "Mysterious Eclipses in the Light Curve of KIC8462852: a Possible Explanation, arXiv: 1612.06121v2  (a "tour de force"; I highly recommend this publication)
    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," 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 
    Neslusan, L. and J. Budaj, 2017, "Mysterious Eclipses in the Light Curve of KIC8462852: A Possible Explanation," A & A, link
    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
    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) 
    wikipedia 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    Hereford Arizona Observatory    resume 
 
This site opened:  2023.08.16.  Nothing on this web page is copyrighted.