A KIC 8462852 (dipping again in March 2018)

[Murphy625]

Hello,
This is my first post here. I have no idea what thread level to use so I just picked the middle one.
I'm hoping someone can tell me if my theory on Tabby's star ( KIC 8462852) is plausible or not.

Since its discovery, there's been much hoopla over the strange behavior of this star. Just last week, an astronomer (Bradley Schaefer?) inspected old photos of the star dating back to the 1890's and discovered that the star has been dimming for over 100 years. Since that, no new theories have come out.

Alien Megastructure? That would be cool.. but not probable. They've pretty much debunked the comet or gas cloud theories and no one has come up with anything since. So, here goes my 2 cents.. I'm hoping someone here can debunk this for me. We have to explain the periodic and regular 20% drops in luminosity (Flux?) and the 100 year trend of dimming something like 20%.

What if 8462852 was a binary system consisting of one main sequence F star and a dwarf star companion?
If the dwarf star was in a highly elliptical orbit around the main star and at its closest approach, being along our line of sight, was close enough to impart tidal forces on the main star, couldn't that account for what we are seeing?
My theory goes like this: As the dwarf circled around the main star, the gravitational pull of the dwarf would cause the main star to bulge via tidal forces. This in turn would reduce the pressure within the main star and result in decreased nuclear fusion which would cause it to dim on the side facing the dwarf. Could that dimming effect, coupled with the dim dwarf blocking some of the light itself, account for the whopping 20% we are seeing?
Additionally, as the dwarf swung around the main star, wouldn't both stars eject material into space from all that disturbance? That ejected material would build up on each pass of the dwarf and if that material remained in a close orbit around the main star, couldn't that account for the century long dimming trend?

 

[Chronos]

It is doubtful a companion star would affect the fusion rate of a star. Local gravitational effects would overwhelm tidal effects of any companion star unless they were extremely proiximate. A more likely explanation is the primary star is accumulating helium in its outer core. Even this explanation is suspect because helium accumulation typically takes many eons, not centuries, to create noticeable effects.

 

[Murphy625]

It is doubtful a companion star would affect the fusion rate of a star. Local gravitational effects would overwhelm tidal effects of any companion star unless they were extremely proiximate.

Extremely proximate: Like within the orbit of Mercury?? Or are we talking something much closer?
I'm also wondering if it would make any difference that Tabby's star has a rotational period of less than a day.. Wouldn't there already be a bulging equator?

 

[Chronos]

There might be a little bit of centrifugal going on there, but, probably not significant. I would guess any companion would need to be at least as close as mercury to matter much. Ordinarily, you need a contact binary to wreak much havoc on a star.

 

[laner]

I would tend to agree with Chronos. As for the material ejection, I would find it difficult to imagine that you could tidally strip a star without having a controlled mass transfer through a Roche lobe or something, which would more likely be seen between a giant star and a high-mass companion.

Also if your dwarf is passing between the giant and our line-of-sight then you are going to pick up the orbital motions through spectroscopy, and I would assume someone has checked for that.

 

[Murphy625]

Is there anything that would prevent a dwarf star from being within a mercury orbit? Not that I'm aware of.

I looked all over and I can find no information relating to anyone checking to see if this star wobbles. The wobble, or lack of, would most certainly confirm or debunk my idea but I can not find anything on the internet that says the wobble has been measured. And to think of it, why would I? The only time that wobble would be seen is during the 750 day event when the dwarf swings quickly around the main star.

 

[mfb]

Is there anything that would prevent a dwarf star from being within a mercury orbit? Not that I'm aware of.

Nothing, and there are binary stars closer than that.
It leads to massive radial velocity changes within this period. Nothing like that has been observed for the star.
It also cannot explain the slow dimming over the last 100 years, or the light curve of the short dimming events.

 

[newjerseyrunner]

How is interstellar dust observed? Is it possible that the century long dimming is simply because it's moving behind a cloud of dust that's unrelated to the star itself? Would spectral analysis show that? From the wikipedia article, it seems like a swarm of asteroids or comets would account for the short dimming, but not the long ones.

I've read that a massive collision has been ruled out because of the lack of infrared energy, but what about a large object straying close to the Roche limit? Would an object getting torn apart by gravity produce the same infrared energy or no? a 750 day orbit that takes something near or past that limit would be highly elliptical, but I see no reason that it's impossible. I imagine an object close to the limit, but not quite there would slowly break apart and recombine, allowing the dust to slowly build up over a century, as well as produce large cyclical dips.

Most objects that get close to that limit are just torn apart all at once, but I'm curious what would happen if it's in an elliptical orbit and only stays close to that limit for a short time before being flung back out. Especially if it's large enough to put itself back together each pass.

 

[Murphy625]

Nothing, and there are binary stars closer than that.
It leads to massive radial velocity changes within this period. Nothing like that has been observed for the star.
It also cannot explain the slow dimming over the last 100 years, or the light curve of the short dimming events.

Can you point me to a link were they have looked at the radial velocity (the wiggle?) during the periodic dimming events?
Also, while I understand the obvious meaning of the light dimming curves, I am not adapt to reading the finer details of the curves which tell us something about the object(s) that are blocking the light. It would be nice to find some good reading on that.

 

[mfb]

We characterize the object with high-resolution spectroscopy, spectral energy distribution fitting, radial velocity measurements, high-resolution imaging, and Fourier analyses of the Kepler light curve.

Guess where: in the original paper.
Section 2.6 sets explicit limits on close companions. For circular orbits, but the limits would not be that different for eccentric orbits.

 

[Murphy625]

Guess where: in the original paper.
Section 2.6 sets explicit limits on close companions. For circular orbits, but the limits would not be that different for eccentric orbits.

Thank you so much for the link.

 

[mfb]

A new arXiv submission questions the reliability of the old magnitude measurements, they find similar trends for 18 of 28 similar stars.
KIC 8462852 did likely not fade during the last 100 years

Here the original dimming paper as reference
They also checked reference stars, obviously, but maybe not enough?

 

[Bernie G]

Same group too.

Sounds reasonable ... maybe a rocky volcanic planet in an elliptical orbit is being shredded by this star.

 

[Murphy625]

A new arXiv submission questions the reliability of the old magnitude measurements, they find similar trends for 18 of 28 similar stars.
KIC 8462852 did likely not fade during the last 100 years

Here the original dimming paper as reference
They also checked reference stars, obviously, but maybe not enough?

I read that this morning! Looks like I'm just going to have to hold my breath until they figure out if the 100 year trend is valid or not. Thank you.

 

[Chronos]

The photometry artefact explanation is entirely reasonable. It is certainly a challenge to mine much useful data from old photometric plates and the fact that nearly 2/3 of similar stars examined for complarison displayed similar patterns of variability is the stuff of legends. This is a prime example why most scientists are reticent, if not terrified, to announce such odd findings. Nobody wants to make a splash at a conference and be tagged as 'old 8462852'.

 

[Murphy625]

Mr. Schaefer's analysis of plates dating from 1890 to 1989 does not include data after 1989. So where is the data from 1989 to present? That's 26 years of information that no one seems to mention, unless I missed it somewhere.
Shouldn't the last two and a half decades of a century long dimming trend be detectable in the modern data?

 

[Borg]

Mr. Schaefer's analysis of plates dating from 1890 to 1989 does not include data after 1989. So where is the data from 1989 to present? That's 26 years of information that no one seems to mention, unless I missed it somewhere.
Shouldn't the last two and a half decades of a century long dimming trend be detectable in the modern data?

From the second sentence in mfb's link, the analysis was performed against archival photographic plates. I would presume that the data was stored electronically after that.

 

[Murphy625]

From the second sentence in mfb's link, the analysis was performed against archival photographic plates. I would presume that the data was stored electronically after that.

Thank you. I have since learned that the data for the time after 1989 to present showed no gradual long term dimming trend. If Schaefer's analysis was correct, wouldn't we expect to see a continuation of that dimming for the 26 years after his last data point?

 

[Borg]

A newly submitted paper on arxiv - KIC 8462852 Faded Throughout the Kepler Mission.

 

[member 342489]

This seems relevant...

https://carnegiescience.edu/node/2102

 

[newjerseyrunner]

Finally https://www.google.com/amp/s/phys.org/news/2017-01-explanation-alien-megastructure.amp

A new hypothesis is that about 100 years ago a planet took a dive into the star, which caused it to get brighter. Since then, it's been dimming back to its natural state. It also theorizes that the rapid periodic dimming is caused by remnants left after gravity ripped he planet apart.

 

[mfb]

or a large number of smaller objects – such as moon-mass bodies that were about 1 km in diameter. This latter possibility seems more inviting

Edit: Ah, many 1km objects with a total mass similar to the Moon.

Unless KIC 8462852 is an extremely obscure case, TESS in 2018+ and later PLATO (2024+) will find more of them (3 and 6 times the number of observed stars, respectively).

 

[mfb]

It is dimming again!
News article
Blog article

~2% at the time the articles were written. This time, it will get a lot of telescope time to study the transit in as much detail as possible.

 

[Borg]

I can't remember if this has been discussed in this thread but has any consideration been given to the dimming being due to a debris field from two planet-sized bodies that have collided?

 

[mfb]

That is similar to the comet approach, one of the most plausible options. It cannot be in a circular orbit, however, as that would lead to notable infrared emissions and a more periodic transit structure.

 

[nikkkom]

I can't remember if this has been discussed in this thread but has any consideration been given to the dimming being due to a debris field from two planet-sized bodies that have collided?

Just like other many theories, this one has problems.

Why this debris field is not elongating along its orbit, like fragmenting comets do in our system? Why it stays in a "cloud"?
Debris should have lots of dust, why no IR excess is seen?

 

[stefan r]

A new arXiv submission questions the reliability of the old magnitude measurements, they find similar trends for 18 of 28 similar stars.
KIC 8462852 did likely not fade during the last 100 years

Here the original dimming paper as reference
They also checked reference stars, obviously, but maybe not enough?

Dyson spheres growing on 18 out of 28 F type stars.

 

[mfb]

Here is a recent light curve from Tabetha Boyajian‏:

The current Julian Day (at the time of this post) is 2457895.41, or 17.41 on the scale of this plot. 17 on the plot was 10 hours ago.The first dip was seen 3*750 days ago, then three more dips 2*750 days ago, then we don't have much data from 750 days ago so we might have missed events, and now a pattern again. All numbers +- 20 days. Whatever is going on there, it seems to have a 750 day pattern. The next 750 day window is around June 2019.

 

[craigi]

The first dip was seen 3*750 days ago, then three more dips 2*750 days ago, then we don't have much data from 750 days ago so we might have missed events, and now a pattern again. All numbers +- 20 days. Whatever is going on there, it seems to have a 750 day pattern. The next 750 day window is around June 2019.

The nice smooth curve 3x750 days ago looks so dubious now.

 

[newjerseyrunner]

Hasn't it been determined that the most likely scenario is that the star ate a planet? That causes an increase in brightness, which will then, of course, dims back to its original brightness over time. The planet gets ripped apart before being swallowed creating a massive dust cloud.