A KIC 8462852 (dipping again in March 2018)

[mfb]

Do you have a reference that dust cannot explain these?

 

[stefan r]

Spitzer measured infrared at 4.5μm . If a black body at 370 degrees C it should radiate 4.5μm radiation. Is there a way to distinguish between a filter that blocks only UV and a filter that blocks some of everything and also emits lower frequencies? The temperature on Mercury's equator rises over 400C.

 

[mfb]

During January and February, the star is too close to the Sun for observations. Measurements resumed two weeks ago, and since March 16 the star shows another dip. Currently 4% below the baseline, the deepest dip seen since the end of Kepler observations.

Image source and more information: tldr: DIPPING!

 

[mfb]

A second dip just a week later. - probably ~5% but with infrequent measurements around the dip time.

 

[rootone]

Could it be that the visible star has two or more very large but non-luminous brown dwarf objects associated in that system?

 

[stefan r]

A second dip just a week later. - probably ~5% but with infrequent measurements around the dip time.

View attachment 222859

How are they calculating the error?
How are they determining normal?

Could it be that the visible star has two or more very large but non-luminous brown dwarf objects associated in that system?

A brown dwarf has close to the same radius as Jupiter. A 4% dip requires more like 7 Jupiter sized objects.

Brown dwarf stars close to KIC8462852 would show some Doppler shift. There could be lots of cold brown dwarfs in many places.

 

[jerromyjon]

Could it be that the visible star has two or more very large but non-luminous brown dwarf objects associated in that system?

It doesn't come in gradually, like a body transiting. It dims suddenly. And randomly.?

 

[mfb]

How are they calculating the error?
How are they determining normal?

I don't know, see the linked web page for details. Kepler just normalized to the flux outside the dips, but the star seems to have a non-constant apparent magnitude outside the dips as well.

It doesn't come in gradually, like a body transiting. It dims suddenly. And randomly.?

Compared to planet transits the dips have quite long slopes. Jupiter moves by 1 diameter in its orbit every 1.5 hours, but the dips start and end over 1-3 days.

 

[JMz]

So the object in orbit is very close, has too little mass to create much of a wobble in the host star, but covers a surface area much larger than Jupiter?

Giant ring huh? Obviously a Halo joke, but it gave me an idea.

If you tipped Saturn on it's side like Uranus and put it close to the sun, would it block enough light? It'd be quite variable since sometimes you'd see the rings head on and it'd block only as much light as the planet disc itself, but sometimes you'd see the rings from "above" and it'd have a shadow of hundreds of thousands of miles.

If the planet is that close to the star, it's moons are probably quite active and could easily create a ring I wo

Saturn's rings have a radius of 120,000 km but are only partially opaque, whereas the Sun has a radius > 400,000 km. So at most, the rings would absorb about 8% if they were opaque and properly oriented wrt the star and properly oriented wrt us.

Note that there is no direction in which a star could see Saturn's rings oriented that way wrt to the Sun.

BTW, if Saturn were so oriented, then every time it passed between the Sun and that star, it would present the same face. That star would not see only the planet sometimes, and planet+rings other times.

 

[Vanadium 50]

BTW, if Saturn were so oriented, then every time it passed between the Sun and that star, it would present the same face.

Why?

 

[stefan r]

Why?

Same reason you see Polaris as the north star.

 

[JMz]

A refinement: The face it presented would change its orientation only very slightly over a few years. (Remember, we have only a few years of observations of this star.)

Because of conservation of angular momentum: the same reason that the Earth's polar axis changes only slightly over a few years, completing a full circuit in 26,000 years ("precession of the equinoxes").

 

[Vanadium 50]

Same reason you see Polaris as the north star.

That didn't clarify anything. Why would a ringed system necessarily show the same face to us every orbit?

 

[stefan r]

That didn't clarify anything. Why would a ringed system necessarily show the same face to us every orbit?

sorry,

If Earth had an ring over the equator then astronomers on Polaris would always see the ring face on. The moon (and earth) would always be near quarter full. The polar ice cap would face Polaris year round but would stop reflecting in the winter when it got dark.

The pole star can be any angle. Uranus has Eta Ophiuchi as a pole star.

 

[Vanadium 50]

Right, but suppose your aliens lived on Regulus rather than Polaris. They would see Earth or Saturn - or better still, Uranus - transit the sun - why is the ring orientation necessarily constant?

 

[JMz]

Because, just like the planet, the rings have angular momentum, and angular momentum is conserved unless acted on by an external torque. What would you propose for the source of that torque?

 

[JMz]

To clarify (I hope): The rings would always appear face-on, whether or not they were between the Sun and that star (though they wouldn't be visible when they weren't occulting the Sun). They don't change orientation relative to the star as they orbit the Sun, just as the Earth's axis doesn't change orientation relative to Polaris or any other star over the course of a year.

 

[stefan r]

To clarify (I hope): The rings would always appear face-on, whether or not they were between the Sun and that star (though they wouldn't be visible when they weren't occulting the Sun). They don't change orientation relative to the star as they orbit the Sun, just as the Earth's axis doesn't change orientation relative to Polaris or any other star over the course of a year.

When Galileo first looked at Saturn he noticed that Saturn had ears. If the rings had been face on it would have looked like another sphere. Rings viewed off of axis might be better for explaining strange light curves.

 

[mfb]

Right, but suppose your aliens lived on Regulus rather than Polaris. They would see Earth or Saturn - or better still, Uranus - transit the sun - why is the ring orientation necessarily constant?

It is not*, but the stellar occultation always happens at the same point in the orbit. And at the same point of the orbit the orientation of a ring system would be constant over short timescales. If precession would be relevant over tens of orbits then the ring system should be extremely short-living.

*edit: I was wrong. It is, see two posts below, the same point in the orbit is not even necessary.

 

[JMz]

When Galileo first looked at Saturn he noticed that Saturn had ears. If the rings had been face on it would have looked like another sphere. Rings viewed off of axis might be better for explaining strange light curves.

The more tilted the rings are, the less they will occult. This hypothesis is already aiming for substantially more coverage than even Saturn's unusually large and dense rings can provide, even if they were oriented like Uranus's.

 

[DaveC426913]

That didn't clarify anything. Why would a ringed system necessarily show the same face to us every orbit?

Am I missing something here? Or are you? (I question myself because I know you're super smart.)

From a distant viewpoint a planet's axial tilt and ring system will always look the same, no matter where it is in its orbit, and no matter what year you look at it.

Planets are gyroscopes!

Saturn's axis and rings are likewise fixed relative to the stellar background. From outside our solar system, it too will always be seen at the same angle.

Like so: (but with rings)

It is only because we are in the solar system that we see Saturn from different angles, and therefore different orientations of its rings.

 

[mfb]

The more tilted the rings are, the less they will occult. This hypothesis is already aiming for substantially more coverage than even Saturn's unusually large and dense rings can provide, even if they were oriented like Uranus's.

We don't know if Saturn's rings are unusually large. J1407b probably has a ring system with 200 times the diameter of Saturn's rings. Easily large enough to obscure the whole star, leading to a massive (>90%) dip in brightness.
The duration and frequency of the dips in KIC 8462852 rule out a similar explanation there.

 

[Vanadium 50]

I now see what you're saying, and my problem is I wrote what I wrote, not what I meant. What I was imaging was a set of irregular rings, darker/thicker in spots, partially obscured by the planet. This would give you a kind of irregular periodicty.

 

[Birrabenzina]

This star is pretty interesting.
Has someone any link to some paper which analyzes this star in detail? Maybe it's a double system with a type Y or T brown dwarf

 

[JMz]

We don't know if Saturn's rings are unusually large. J1407b probably has a ring system with 200 times the diameter of Saturn's rings. Easily large enough to obscure the whole star, leading to a massive (>90%) dip in brightness.
The duration and frequency of the dips in KIC 8462852 rule out a similar explanation there.

A good point. For rings in the Solar System, big planets have rings -- but they're all insignificant (in blocking sunlight for distant observers) except for Saturn. My unstated hypothesis was that large, dense ring systems are very rare, and that the few we know of are known just because of a very strong observational selection effect.

But of course, even if that's true, this star could be one of those few -- after all, it's obviously a rare beast, one way or another.

 

[JMz]

I now see what you're saying, and my problem is I wrote what I wrote, not what I meant. What I was imaging was a set of irregular rings, darker/thicker in spots, partially obscured by the planet. This would give you a kind of irregular periodicty.

Got it -- sort of like Neptune's. My impression is that such rings would not be both large/dense and incomplete, except for a brief interval soon after formation. (And this star is not newly born.) But whether or not that's typical, we are dealing with an atypical system: All explanations so far are either poor fits to the data or improbable scenarios.

 

[stefan r]

This star is pretty interesting.
Has someone any link to some paper which analyzes this star in detail? Maybe it's a double system with a type Y or T brown dwarf

Here is the "official" web site. It has links to peer reviewed papers and also an ongoing blog with current data. The wikipedia entry is fairly good.

A brown dwarf would not eclipse 20% of a type-F main sequence star. It might block 1% or 2%. The light curve of a planet or brown dwarf transiting a star has a flat bottom. The flat bottom light curve is there if you toss a basketball in front of a movie projector. Moths in front of street lights also have flat bottom light curves. You could get a pointy light curve by throwing a basketball partially in front of a street light. The object has to be big.