Extrasolar Planets (updated catalogue)

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fyr02
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Post #41by fyr02 » 05.11.2019, 05:25

According to Sirius_Alpha there's a paper somewhere that effectively deconfirmed Dagon and characterized it as some dust cloud or smth.
I have my messed up origins; I can't control my mind. Also, did you know that cashews grow on top of apples?

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SevenSpheres
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Post #42by SevenSpheres » 05.11.2019, 22:07

According to Wikipedia, it was disconfirmed then reconfirmed, but is not certain to be a planet. I don't know of a more recent paper that disproves it as an object.
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Sirius_Alpha
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Post #43by Sirius_Alpha » 07.11.2019, 20:36

SevenSpheres wrote:Why isn't Fomalhaut b included? It should at least be in Exoplanets_Unconfirmed.ssc.

Great question! Basically, a third observation of the object showed that its orbit crossed the debris ring around Fomalhaut A. This gives you a dynamical constraint on the mass of the planet to being less than ~3 Earth-masses (any higher and it would have disrupted the disk). A ~3 Earth-mass planet cannot be directly imaged with current instrumentation, which demonstrates that the object that was imaged as "Fomalhaut b" must have a significant contribution from dust.

Janson, et al. (2012) pursued Fomalhaut b looking for an infrared detection, but didn't see anything, and noted
Concerning the visible-light point source, its underlying physics is unclear, but the only hypothesis that can be shown to reasonably fit all existing data is an optically thin dust cloud, which is transient or has a transient component. If this interpretation is valid, the cloud may or may not be physically bound to a central object in the super-Earth mass regime.

So now we're at the situation where we know there's probably a lot of dust at the location of "Fomalhaut b," but otherwise no real strong evidence for a planet.

Lawler, et al. (2014) calculate that asteroid collisions within the Fomalhaut disk should produce large debris clouds that we may be able to detect, and that this might be the nature of "Fomalhaut b." They write
The relatively high collision rate that we calculate here would mean that another Fom b-like object should appear within the next decade, and Fom b itself will fade over the coming years, possibly becoming resolved. In order to test these two predictions, continued follow-up observations capable of detecting objects as faint as Fom b are vital. For now, the only telescope capable of detecting Fom b is Hubble, but the upcoming James Webb Space Telescope will be able to resolve the dust cloud, and provide some additional constraints on the dust composition with near IR measurements.

As it stands now, the current status of Fomalhaut b is that there is no reason to think a planet exists there. As a result it has not been added to this addon.

Also, non tidally locked planets are defined with unrealistically long rotation periods. (This is great work otherwise!)

Thanks! I've been curious as to what to do about this. I assume all planets are in a tidal equilibrium -- pseudosynchronous rotation for eccentric fluid planets, spin-orbit resonances for solid planets. Clearly as you point out this is not the case for the vast majority of systems haven't been around long enough to reach tidal equilibrium. If I can find some rotation rate relations for planet's mass vs age, that's what I'd like to do. I've considered just extrapolating downward from the brown dwarf regime -- something that should be somewhat well characterized, but I haven't managed to find some decent research on it since I haven't kept track of brown dwarf research. For terrestrial planets, the various stochastic processes that lead to their formation give them fairly randomized rotation rates, so the only systematic is the influence of tides. This might be worth pursuing -- i.e., planets that are still reaching tidal equilibrium being represented in some sort of intermediate rotation regime. But since the initial rotation rate is random, how do you calculate this?

Unless there's some alternative -- and I'm open to suggestions, for sure -- I figure the tidal equilibrium rotation rate makes the most sense as a "default," at least until I can get some decent mass-age-rotation relations for giant planets.

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SevenSpheres
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Post #44by SevenSpheres » 07.11.2019, 22:45

Re Fomalhaut b:

So the Wikipedia article is incorrect then? Someone should fix it... And why did the IAU name it without vetting it first? :fie:

Re rotation periods:

The 2013 extrasolar.ssc file uses tidal spin-down formulas from a book called "Solar System Dynamics" by CD Murray & SF Dermott. If you can get that book you could potentially use those formulas, taking the system's age into account where known. For the initial rotation period you could use the three arbitrary values from extrasolar.ssc, or try to determine it from the very small sample, or as you said to extrapolate from brown dwarfs. (Somewhat related: this is the only brown dwarf catalog I know of, but it hasn't been updated since 2015. Doesn't have rotation periods either.)
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Sirius_Alpha
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Post #45by Sirius_Alpha » 07.11.2019, 23:24

SevenSpheres wrote:So the Wikipedia article is incorrect then? Someone should fix it...
And that is why I don't use Wikipedia as a source for this.

Yeah the IAU giving names to ... let's face it, radial velocity curves... seemed premature. The IAU-named Pollux b is somewhat controversial as well (the literature has gone back and forth). I only include the proper names in the addon because I know people value such things, but they appear nowhere in the literature, and don't seem to have any interest to the wider astronomical community. "Fomalhaut b" and "Pollux b" are just fine.

SevenSpheres wrote:The 2013 extrasolar.ssc file uses tidal spin-down formulas from a book called "Solar System Dynamics" by CD Murray & SF Dermott. If you can get that book you could potentially use those formulas, taking the system's age into account where known.
Yeah! I have looked for it but haven't found it. I might be able to recover the relation from the rotation periods given in that .ssc file though.

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Post #46by Fafers_br » 08.11.2019, 03:13

Sirius_Alpha wrote:If I can find some rotation rate relations for planet's mass vs age, that's what I'd like to do. I've considered just extrapolating downward from the brown dwarf regime -- something that should be somewhat well characterized, but I haven't managed to find some decent research on it since I haven't kept track of brown dwarf research. For terrestrial planets, the various stochastic processes that lead to their formation give them fairly randomized rotation rates, so the only systematic is the influence of tides. This might be worth pursuing -- i.e., planets that are still reaching tidal equilibrium being represented in some sort of intermediate rotation regime. But since the initial rotation rate is random, how do you calculate this?

Hi Sirius and all forum members. Hope you are all fine.

I have one suggestion.
I used, in my "educated guesses" for Celestia, the paper A UNIVERSAL SPIN-MASS RELATION FOR BROWN DWARFS AND PLANETS from Scholz et al to estimate rotation periods of planets that are beyond the tidal-locking radius of a star. It gives good insight in the matter. They explore the idea that there is a spin-mass relation for solar system planets and extra-solar planetary-mass objects (the idea itself is not new). Refer to figure 6 of the paper, where a graph is presented. Unfortunatelly they don't provide an exact equation but you can deduce it from the graph itself (I found Veq~12.8*M^0.5 Km/s, where M is in Jupiter masses).
This relation gives the final rotation velocity of the sub-stellar bodies (after their contraction). Then, by angular momentum conservation one can find the rotation velocities for other ages, by using a table that gives mass-radius-age relations. There are works from Baraffe et al in that subject:
https://www.aanda.org/articles/aa/abs/2003/17/aa3343/aa3343.html
https://www.aanda.org/articles/aa/full_html/2015/05/aa25481-14/aa25481-14.html
Unfortunatelly, the tables in these papers cover masses above 0.0005Ms (~0.524Mj). So far, I haven't found a source that covers mass-radius-age relations for masses bellow that limit. So, in my "educated guesses" I had to assume that planets bellow that limit have the same radius and rotational velocity throughout their whole lifetime.

Hope this helps.
Best regards from Brazil.


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