APOD: Kepler's Suns and Planets (2011 Mar 29)

[Jfarabaugh]

Kepler cosmic corn on the cob

[neufer]

You never have two planets with the same period.

While this is technically true, smaller bodies (e.g., moons, asteroids & dwarf planets)
can share the same period with planets (e.g., Trojan objects in the L4 and L5 points of Jupiter & Neptune)
or the same period with each other (e.g., plutinos in a 2:3 resonance with Neptune).

[JohnD]

Thanks, Chris!
I know of Fourier, but in a different application(Transducers) that doesn't help me understand.
Help me think, or write, aloud.
The transit of a single planet will have a duration that depends on its orbit and how fast or slow it crosses the disc. If two planets cross at the same time, there will be two superimposed dimmings with different durations. If the wave form of the dimming is broken down into the fundamental frequency(ies) (by Fourier) that can reveal the two dimmings.

If so, pretty good for one, or rather half a cycle!

John

[Chris Peterson]

You never have two planets with the same period.

While this is technically true, smaller bodies (e.g., moons, asteroids & dwarf planets)
can share the same period with planets (e.g., Trojan objects in the L4 and L5 points of Jupiter & Neptune)
or the same period with each other (e.g., plutinos in a 2:3 resonance with Neptune).

Yes, but those scenarios wouldn't produce synchronous transits on each orbit.

[Chris Peterson]

The transit of a single planet will have a duration that depends on its orbit and how fast or slow it crosses the disc. If two planets cross at the same time, there will be two superimposed dimmings with different durations. If the wave form of the dimming is broken down into the fundamental frequency(ies) (by Fourier) that can reveal the two dimmings.

If so, pretty good for one, or rather half a cycle!

It would be. But Kepler doesn't look for a single transit. A transit isn't confirmed until a dimming is observed at least three times. It takes years to identify planets in Earth-like orbits around their stars. Most of the planets identified so far are much closer to their stars, in fast orbits.

Where you have two planets, they may be in near simultaneous transit in some observations, but certainly not in each orbit. So the two different dimming cycles will be separable by Fourier or wavelet analysis.

[aildoux]

I fear this image is going to generate a lot of confusion. It is easy to come away thinking that these are stellar images produced by Kepler. In reality, Kepler is unable to resolve any stars, and simply produces a curve of intensity versus time for each of its targets. This image was synthesized based on the known stellar characteristics and the measured transit characteristics of each target.

Quite right Chris. But I have a question: has a star EVER been resolved to it's disc shape? Coupling the SolarMax technology to the HST could do the job? Or maybe even the HST does not have enough magnification power to resolve a star point to a disc.

[rstevenson]

The red giant star Betelgeuse can be resolved by large telescopes. I'm not sure there are any others.

Rob

[Chris Peterson]

Quite right Chris. But I have a question: has a star EVER been resolved to it's disc shape? Coupling the SolarMax technology to the HST could do the job? Or maybe even the HST does not have enough magnification power to resolve a star point to a disc.

Yes, a handful of very large nearby stars have been resolved. This is actually better done using ground-based telescopes with much larger apertures than HST.

[StarCuriousAero]

Perhaps somebody can help...

The graphic portrays the smallest stars on the bottom-right to be smaller in diameter than the largest planet orbiting the largest star in the top-left. This seems to contradict the idea that any planet with a mass larger than Jupiter would not show an increase in size, just density. With brown dwarves in the 10-30 Jupiter-mass-range being the same size as (or even slightly smaller than) Jupiter, how should we interpret Kepler's finding of a planet with a diameter several times that of Jupiter? Bottom line: how can a body that large be considered a planet and not a stellar companion?

One could argue that a planet of Jupiter's mass could be heated externally by its local sun to a size much larger than Jupiter.

On the other hand, Wikipedia claims that none of Kepler's planets are more than twice the size of Jupiter (in apparent contradiction with today's APOD).

<<On 2 February 2011, the Kepler team announced ... 1235 planetary candidates circling 997 host stars. (The numbers that follow assume the candidates are really planets, though the official papers call them only candidates. Independent analysis indicates that at least 90% of them are real planets and not false positives.) 68 planets were approximately Earth-size, 288 super-Earth-size, 662 Neptune-size, 165 Jupiter-size, and 19 up to twice the size of Jupiter.>>

The response above was mildly helpful, but I was really hoping for a response to the size/mass vs planet/star question posed by beefcalf. I may have to go do some independent google research though since I'm afraid this discussion quelled a couple weeks ago (I've been behind on my apods).

I too, had the same thought when I saw the relative sizes of the largest planet "candidate" compared to not only Jupiter but the smallest star at the bottom of the chart. I'm no star expert, (so correct me if I'm wrong and please explain) but I had thought that mass determined whether or not it could support fusion, etc., (unless it's a white dwarf or something past that stage), thereby making it a star or stellar companion, and thus not a "planet" by our current definition. So basically I'm pretty confused now, and am wondering if I'm simply misinterpreting the image and how Kepler's data gives size. Is it taken into account that if a red or brown dwarf passes in front of a brighter star that there will be dimming not proportional to actual size of the object, since it may emit some of its own light? Is the dimming measured across multiple or specific wavelengths to prevent this? Or am I way off-base?

[Ann]

A fact that not a lot of people may be interested in, but that I want to point out, is that I think that there is a shortage of blue stars among the Kepler stars, or to put it differently: The number of blue stars here is not representative of the number of blue stars versus yellow stars in our galaxy. The Kepler stars are placed in rows from the smallest to the largest, but among stars that are in the top two rows, most should be blue or bluish. This is the typical size of main sequence stars of class A and F, or so I believe anyway.

We have no reason to think that class A stars don't usually form planets, since several bright and well-known class A stars have indeed been shown to have planets. That includes Fomalhaut and Beta Pictoris, which have even had their planets directly imaged.

I think I have read someplace that class A stars are more "turbulent" (or something) than some "mild" red giants, so that it is more difficult to detect stars transiting main sequence A stars than it is to detect planets transiting "post class A stars" that have evolved into a certain stage of their red gianthood. If so, the reason for the scarcity of blue stars among the Kepler stars might be that Kepler just hasn't detected all the planets transiting the blue stars.

Or maybe I'm underestimating Kepler here, so maybe there is another reason for the scarcity of blue stars among the Kepler stars.

Ann

[Jyrki]

Joining the chorus of people thanking Chris for that extra bit of information.

But that leads to my question. The biggest black blob of a planet is quite massive. I may have read too much sci-fi, but is it not so that a gas giant a couple orders of magnitude bigger than our own Jove is in danger of igniting as a star?

In other words: can Kepler tell, if the transiting body is actually a brown dwarf, and the star in question is just the more massive and luminous component of a binary star?

Cheers,

Jyrki

Edit: Oh dear, I was ninja'd by several other posters. Should have read page 2.

[neufer]

I too, had the same thought when I saw the relative sizes of the largest planet "candidate" compared to not only Jupiter but the smallest star at the bottom of the chart. I'm no star expert, (so correct me if I'm wrong and please explain) but I had thought that mass determined whether or not it could support fusion, etc., (unless it's a white dwarf or something past that stage), thereby making it a star or stellar companion, and thus not a "planet" by our current definition. So basically I'm pretty confused now, and am wondering if I'm simply misinterpreting the image and how Kepler's data gives size.

I think that we are all somewhat confused now.

On the scale of the Sun/Jupiter figure an earth sized planet would amount to less than one pixel so I am thinking that some funny sort of (nonlinear?) scaling is taking place in this cartoon to allow all the exoplanets to be seen.

Is it taken into account that if a red or brown dwarf passes in front of a brighter star that there will be dimming not proportional to actual size of the object, since it may emit some of its own light? Is the dimming measured across multiple or specific wavelengths to prevent this? Or am I way off-base?

Remember that whatever transits will also be eclipsed so it should be possible to detect red (if not brown) dwarfs.

[StarCuriousAero]

I like the graphic, I'm actually amazed you found something illustrating that. An earlier post called into question Kepler's intensity resolution, and pointed out that it's capable of detecting an earth-sized planet's dimming against a star, is this comparable to the eclipsed red dwarf? On the brown dwarf note though, I have almost entirely lost confidence in our ability to detect those at all (since we can't even seem to find them all within 30 light years of us), much less next to an overwhelmingly brighter star, although maybe that would help us, I'm not sure.

[Chris Peterson]

On the brown dwarf note though, I have almost entirely lost confidence in our ability to detect those at all (since we can't even seem to find them all within 30 light years of us), much less next to an overwhelmingly brighter star, although maybe that would help us, I'm not sure.

A brown dwarf is easy to detect if it is a member of an eclipsing binary. Indeed, it is probably the easiest of all objects to detect. They are challenging to detect in isolation- although that will change as we soon start producing IR sky surveys.

[neufer]

I like the graphic, I'm actually amazed you found something illustrating that. An earlier post called into question Kepler's intensity resolution, and pointed out that it's capable of detecting an earth-sized planet's dimming against a star, is this comparable to the eclipsed red dwarf?

Probably.

The eclipsed red dwarf has a definite advantage in that the period is already well defined by the red dwarf transits.
Therefore if the period is short enough many orbits can be superimposed to obtain a high signal to noise.

On the brown dwarf note though, I have almost entirely lost confidence in our ability to detect those at all (since we can't even seem to find them all within 30 light years of us), much less next to an overwhelmingly brighter star, although maybe that would help us, I'm not sure.

Many of Kepler's Jupiter sized 'planets' are probably brown dwarfs.
All one needs is Doppler analysis to determine the masses.

[NoelC]

A fact that not a lot of people may be interested in, but that I want to point out, is that I think that there is a shortage of blue stars among the Kepler stars

I picked up on that right away, and I find it a fascinating tidbit.

-Noel