KIC 8462852 Observations Options

[Mongo]

Attached is a diagram I made using 2-year bins. I followed the same protocol as the author, with RMS <0.33 mag, AFLAGS <9000, and the measured magnitude more than 0.2 mag above the quoted plate limit. For each bin, I have a large dot indicating the average reading within that bin, plus smaller dots at one sigma standard deviation above and below that value.

The high reading for the 1969-1970 bin is due to a single high outlier, and for the 1989-1990 bin is due to two high outliers (there were a lot more measurements in the latter bin than in the earlier bin). If I remove those three outliers, those two bin magnitudes drop significantly, and become consistent with the other post-1962 bins.

I also added extra lines, indicating the averages plus one sigma standard deviations for all the measurements from 1890-1899, 1900-1952 and 1962-1989. The first time period from 1890 to 1899 definitely shows greater brightness than in the following 1900-1952 plateau. I have it as a plateau, but it visually looks like the brightness is declining over much of that decade.

Visually, the chart seems to show long periods of relatively steady brightness, separated by ~0.1 mag drops in the late 1890s and in the 1950s.

Attached thumbnail(s)

 

[dudley]

KIC 8462852 is reportedly being watched for another instance of dimming. It was proposed to then analyze the light spectroscopically. It was indicated that this could determine if it was dust, or larger objects that were responsible for the dimming.
Dr. Schaefer's findings now seem to show that the star is already being substantially dimmed on a continuing basis. Wouldn't the spectroscopic work already done, which failed to find excess dust, indicate that larger objects cause the dimming? But what sort of larger objects?
Dr. Schaefer's work seems to call the cometary explanation into very serious doubt. Disrupted planets were already doubted, due to the absence of dust. Dimming of 15 and 22 percent suggest objects on the order of 500,000 to 700,000 miles in diameter. Single objects on this scale would appear to be stars, but no other conspicuously shining stars have been found very near KIC 8462852.

[nprev]

In order to keep the Kepler topic open for other observations made specifically by that mission, this topic will be dedicated to this particular star.

Please review the Forum rules before posting. As I'm sure everyone knows there has been a tremendous amount of unconstrained speculation as well as an abnormal amount of anomalism in the popular press concerning this subject, but that will not be permitted here. Posts that do not meet Forum standards will be deleted.

[HSchirmer]

KIC 8462852 is reportedly being watched for another instance of dimming.
It was proposed to then analyze the light spectroscopically. It was indicated that this could determine if it was dust, or larger objects that were responsible for the dimming.
...
Wouldn't the spectroscopic work already done, which failed to find excess dust,
indicate that larger objects cause the dimming? But what sort of larger objects?
...

I believe they thought "inner planet smash" and looked for excess infrared radiation,
didn't see it, and interpreted the lack of signal as the lack of hot dusty debris and concluded no inner planet collisions.
Next, hypothesis for dimming, without infrared, was a comet swarm on an elliptical orbit.
That doesn't seem to fit, it requires a staggering number of comets.
So, it may seem that we are left with a single large object as the 3rd choice.

However, does a lack of IR actually rule out large inner solar system collision?
We consider that additional cold dust further out might blocking starlight, how about blocking IR?
So, what if both #1 and #2 happened? Inner planet collision and comet dust that blocks that IR?

1) What are the chances that there is a planetary system around Tabby's star. Pretty good.
2) What are the chances that planets around Tabby's star could shift orbits? Given the large percentage of hot Jupiters and hot Neptunes that have been observed, pretty good.
3) What are the chances that shifting planets create dust and comet redistribution? Pretty good.
We know/suspect our solar system has been shuffled at some point, comets and asteroids and KBOs all shifted around.

The recent Planet 9 paper's authors did a prior paper about nice model / jumping Jupiter scenario. Their simulations showed that for a sun-sized star, the gas giants generally eject comets or planets from a solar system, while the ice giants generally scatter them around the solar system.

So, here's a mechanism to consider.
Tabby's star is a sun-sized solar system, similar amount of material, similar snow line.
It develops with ice giants but no gas giants, then it experiences planetary migration.
Because it does not have gas giants to scatter comets out to oort distances as long period comets,
Tabby's Star ends up with a massive kuiper belt, and we are seeing either a massive comet shower,
or actual planetary scattering.

So, my questions
What is the expected IR signal from an inner solar system disrupted rocky planet?
What level of comet dust would be necessary to absorb that IR signal?

[JRehling]

The use of archival data to study the brightness variations lead me to another thought: How many other stars have shown this (or another) sort of hitherto-unexplained dimming? If we had data like this on KIC 8462852, and Kepler was only observing 1/400th of the sky, it is seemingly almost certain that more stars like this exist… depending on the definition of "like this."

Here are the basic observed facts about KIC 8462852, to summarize:

1) Progressive dimming over several decades, which may be occurring in steps rather than smoothly.
2) Sudden and reversible dimming on rare occasions during the Kepler observations. The baseline during this time was quite constant, and the dips occurred during a tiny fraction of the Kepler observations. The duration of these events was similar to planetary occultation, but the magnitude was anomalously large, the timing between them was irregular, and the shape of them was unlike any planet or star transit.
3) The IR spectra indicates that there is not a large amount of warm dust in the system.

The reason why the comet explanation seems to fit (2) and (3) is because comets spend almost all of their time far from the star, and so could absorb a bit of warmth in a small time and radiate it over a long time; the radiation must be re-radiated, but could happen at a longer wavelength than warm dust would.

To assimilate all of these into one exogenous explanation, all I can come up with is: KIC 8462852 is surrounded by a massive amount of material that is occulting it, to a considerable degree, all the time, but the individual particles are predominantly in highly elliptical orbits. Ongoing catastrophic events are generating progressively more occulting material, so the fraction of the star's light that is being blocked is increasing from an already-high degree to an even higher degree.

Alternately, something internal to the star may be occurring, and therein I have no insight to offer. As with the exogenous explanation, any endogenous cause must certainly be something rare and therefore unusual.

It's a puzzler. It's like astronomy as written by Agatha Christie.

[HSchirmer]

...
To assimilate all of these into one exogenous explanation, all I can come up with is: KIC 8462852 is surrounded by a massive amount of material that is occulting it, to a considerable degree, all the time, but the individual particles are predominantly in highly elliptical orbits. Ongoing catastrophic events are generating progressively more occulting material, so the fraction of the star's light that is being blocked is increasing from an already-high degree to an even higher degree.
...
It's a puzzler. It's like astronomy as written by Agatha Christie.

Well, just because a star is middle aged and main sequence, doesn't mean things with the planets
can't get, er, interesting....

Konstantin Batygin, Gregory Laughlin
(Submitted on 11 Apr 2008)

A long-term numerical integration of the classical Newtonian approximation to the planetary orbital motions
of the full Solar System (sun + 8 planets), spanning 20 Gyr, was performed.
...
The experiments yielded one evolution in which Mercury falls onto the Sun at ~1.261Gyr from now, and another in which Mercury and Venus collide in ~862Myr. In the latter solution, as a result of Mercury's unstable behavior, Mars was ejected from the Solar System at ~822Myr.

http://arxiv.org/abs/0804.1946

Apply that sort of scenario to Tabby's star, two rocky planets collide, a third is ejected (likely scattering comets)
and there ought to be plenty of material around to create long term and periodic dimming of the star.

[dudley]

If I recall correctly, the Kepler Space telescope found no periodicities in the dips in light from this star. We're assuming, it seems, that the plane in which any planets, or their shattered debris would travel, aligns with the star from our point of view.

Even if two planets had collided and destroyed themselves, we might have expected other planets, or even just one, to be found, mightn't we? If there was a complete absence of planets around this star, these collisional scenarios would seem to be unworkable.

[JRehling]

Apply that sort of scenario to Tabby's star, two rocky planets collide, a third is ejected (likely scattering comets)
and there ought to be plenty of material around to create long term and periodic dimming of the star.

If two rocky planets collided to create lots of material, then there should be an IR signal as the material re-emits, at longer wavelengths, the visible light that it absorbs. But observations contradict that possibility.

That is, if planets orbiting relatively close-in did so. I agree that a catastrophe located much farther out might be part of the answer, but then it must have generated a truly tremendous amount of material to be covering much of the star, continuously.

[JRehling]

Kepler found no planets around this star, but that doesn't mean that there are no planets. Kepler can miss a planet larger than Earth even if it transits a star, because the signal-to-noise ratio can be sub-threshold. It can certainly miss a bunch of Mars-sized planets. And it could even miss a whole host of planets that almost transit a star while the debris from a collision, slightly off that plane, does transit the star.

[HSchirmer]

If I recall correctly, the Kepler Space telescope found no periodicities in the dips in light from this star. We're assuming, it seems, that the plane in which any planets, or their shattered debris would travel, aligns with the star from our point of view.

The did see something with a 750 day period.
For reference, mars' orbit is 687 days, so assuming the "something big" is in orbit,
that would be, eh, roughly around the inner edge of our asteroid belt.

Even if two planets had collided and destroyed themselves, we might have expected other planets, or even just one, to be found, mightn't we? If there was a complete absence of planets around this star, these collisional scenarios would seem to be unworkable.

Brilliant question!
Complex answer.

Rephrased-
"If Kepler was looking at our own solar system from Tabby's planet, how many of our planets would it see transit?"

If all the planets around a sun have the same angle, and the same 'phase' (argument of perihelion?) then yes.
In practice, no.

Here are our planet's orbital tilts relative to earth.

Mercury 7.01°
Venus 3.39°
Earth 0
Mars 1.85°
Jupiter 1.31°
Saturn 2.49°
Uranus 0.77°
Neptune 1.77°
https://en.wikipedia.org/wiki/Orbital_inclination

It's a difference of a few degrees, but at several million KM away from the sun, a small angle leads to
a big distance above or below the orbital plane.

And, each tilt is going to be oriented in a different direction-
imagine looking down at the solar system as if it were a compass.
So, Mercury's tilt is above the plane towards North and below towards South,
but Venus' might be above at East and below at West.

Another way to think about it- why are solar eclipses special?
Even though we have a (relatively) large moon, that is close to the same plane as the sun,
it's actually quite rare for the orbit of the moon to line up with the orbit of the sun.

[dudley]

If two rocky planets collided to create lots of material, then there should be an IR signal as the material re-emits, at longer wavelengths, the visible light that it absorbs. But observations contradict that possibility.

That is, if planets orbiting relatively close-in did so. I agree that a catastrophe located much farther out might be part of the answer, but then it must have generated a truly tremendous amount of material to be covering much of the star, continuously.

So, suppose two super-Earth sized rocky planets were ejected to the outer part of that star system, and then happened to collide very recently. Could that be a reasonable scenario? Could this create a distant debris cloud sufficient to account for the observed century-long dimming trend, yet not produce a conspicuous infra red signature from the dust? Could localized denser patches in that debris cloud maintain themselves long enough to also account for the instances of short term dimming?

[JRehling]

So, suppose two super-Earth sized rocky planets were ejected to the outer part of that star system, and then happened to collide very recently. Could that be a reasonable scenario? Could this create a distant debris cloud sufficient to account for the observed century-long dimming trend, yet not produce a conspicuous infra red signature from the dust? Could localized denser patches in that debris cloud maintain themselves long enough to also account for the instances of short term dimming?

Inner planets are not ejected into orbits with periapses much farther out than the body that ejected them. They are either sent into elliptical orbits that return to the inner system or they are ejected from the system entirely. The answers to the other questions you ask are less clear to me, anyway.

[JRehling]

The did see something with a 750 day period.

No. The first dip, which by itself resembled one planetary transit, was seen at mission day ~792 and then a very strange series of several dips took place roughly from days 1510 to 1570. Nothing in the later series of dips is obviously a repeat of the first observed dimming event. The paper has a section discussing the possibility of the second event being related to the first, with a ~750 day period; in the discussion, that possibility is called "problematic." Follow-up observations showing a lack of IR excess further discredit that possibility.

Without a third observation, the inference that two light curve dips indicate one specific "something" is doubtful even in a less strange case. An observer elsewhere could see Venus and Earth both transit the Sun, but wouldn't know whether those two transits were caused by one planet or two planets until a third transit was seen.

Whatever was seen between days ~1510-1570 was seen only once, and what was seen at day ~792 was not obviously seen even one more time, much less two more times.

[HSchirmer]

No. The first dip, which by itself resembled one planetary transit, was seen at mission day ~792 and then a very strange series of several dips took place roughly from days 1510 to 1570. Nothing in the later series of dips is obviously a repeat of the first observed dimming event. The paper has a section discussing the possibility of the second event being related to the first, with a ~750 day period; in the discussion, that possibility is called "problematic."
...

Yep, I should have said "they're looking" at a 750 day period, but more data is needed.

The dip at D1500 is then interpreted as the same material seen one orbit later,
with the 750 day period implying an orbit at 1.6 AU.
...
A more robust prediction is that future dimming events should occur roughly every 750 days,
with one in 2015 April and another in 2017 May.
..,.
Thus, while this scenario is attractive because it is predictive, the periodicity argument may be inconsistent, and the probability of witnessing such an event may be very low
...

Likewise, if the two deep dipping events at D800 and D1500 are from the same orbiting body (or bodies), a
period of 700 – 800 days remains a possibility.
...

http://arxiv.org/pdf/1509.03622.pdf

So, suppose two super-Earth sized rocky planets were ejected to the outer part of that star system, and then happened to collide very recently. Could that be a reasonable scenario?

Eh, I think that would be overkill.
The paper mentions that you don't need a really huge impactor to create a suitable dust cloud-

A broad range of scenarios for the dipping behavior that involve occultation by circumstellar dust clumps was considered. Among these, we find that the break-up of one or more massive exocomets (or planetesimals on comet-like orbits) provides the most compelling explanation consistent with the data in hand.
The required mass of the original body may have been in excess of 3×10^21 grams (only 0.3% the mass of Ceres, and perhaps 100 km in diameter).

It's not that hard to conceptualize an area where several 100 km objects orbit, we call it the asteroid belt. The problem seems to be that there is no known mechanism for comets or asteroids to break up in a coordinated manner to generate the 100 year dimming, or the series of Kepler dips. The papers about KIC 8462852 follow current ideas about comets and assume that extra-solar comet clouds have stable circular orbits which require passing stars to trigger comet showers.

That's why I though the comet-ejected-by-gas-giant versus comet-scattered-by-ice-giant issue was interesting.
It's a tangent about the circularization of hyperbolic comet orbits to create the Oort cloud. The rule stated above

Inner planets are not ejected into orbits with periapses much farther out than the body that ejected them. They are either sent into elliptical orbits that return to the inner system or they are ejected from the system entirely.

doesn't seem to apply to Oort cloud comets. Comets that were ejected from the solar system are though to somehow have circular orbits which require another perturbation to return them to the inner solar system.

Computer simulations of our solar system suggest that 1) planets like to form near the "snow line" where ices first condense, 2) planets can shift because of orbital resonances, and 3) when planets shift they toss lots of small stuff like comets around. Gas giants like Jupiter and Saturn have enough gravity to scatter comets so far out (50k - 100k au) that the comets stay out there in the Oort cloud, and the Oort cloud is estimated to have about 5 earth masses worth of comets, divided into trillions of bodies, with several billion 20km or larger. In contrast, when ice giants like Uranus and Neptune scatter comets, they don't go as far and are assumed to return along the elliptical orbits they started on.

Point is: current theories about Sol like systems indicate that when planets shift with gas giant(s) to eject comets you end up with 5 earth masses of comets into trillions of distant, stable, circular orbits. Then you need a passing star to disturb those circular orbits and create killer comet showers. However, it seems that ice giants only scatter comets, so you should end up with 5 earth masses of comets into trillions of nearby, unstable, elliptical orbits. Then you don't need any second event to get killer comet showers.
So, could KIC 8462852 be the model for a "Kessler catastrophe" solar system?

[dudley]

I wonder if trillions of comets, especially after colliding and reducing themselves to bits, wouldn't make for a uniform debris field around a star, rather than one comprised of distinct clumps of material. The latter is what seems to be present at KIC 8462852.
I also wonder if perturbations of comets by Neptune-mass planets would be great enough over a single century, so as to account for a fairly steady dimming of the star's light by about one fifth.