## APOD: Four Planets Orbiting Star HR 8799 (2017 Feb 01)

Comments and questions about the APOD on the main view screen.
DavidLeodis
Perceptatron
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### Re: APOD: Four Planets Orbiting Star HR 8799 (2017 Feb 01)

I am uncertain as to where the 4 planets are in the video. In information from one of the links in the explanation it states "The forth HR 8799 planet was found after further observations in 2009–2010. That planet orbits inside the first three planets”. I wonder therefore if the very faint object to the upper left of the star is one of the 4 or not, as there are 3 bright objects that I assume to be planets on the right of the star. If that on the left is one of the 4 planets I wonder why it was spotted before the 4th planet as that seems likely to be one of the 3 bright ones. Am I correct in that the faint object on the left is one of the 4 planets?

Chris Peterson
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### Re: APOD: Four Planets Orbiting Star HR 8799 (2017 Feb 01)

DavidLeodis wrote:I am uncertain as to where the 4 planets are in the video. In information from one of the links in the explanation it states "The forth HR 8799 planet was found after further observations in 2009–2010. That planet orbits inside the first three planets”. I wonder therefore if the very faint object to the upper left of the star is one of the 4 or not, as there are 3 bright objects that I assume to be planets on the right of the star. If that on the left is one of the 4 planets I wonder why it was spotted before the 4th planet as that seems likely to be one of the 3 bright ones. Am I correct in that the faint object on the left is one of the 4 planets?
Yes, the body up around 10 o'clock is the fourth (outermost) planet. I would assume that it was found earlier, with the next two inward, and it was the innermost one that was found later. The innermost planet is the one most easily lost in the glare of the star, and therefore easily missed without using very careful occultation masking and other techniques.
Chris

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Chris L Peterson
Cloudbait Observatory
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DavidLeodis
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### Re: APOD: Four Planets Orbiting Star HR 8799 (2017 Feb 01)

Thanks again Chris for your regular help with the queries that I keep posting .

MarkBour
Subtle Signal
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### Re: APOD: Four Planets Orbiting Star HR 8799 (2017 Feb 01)

Whoa. Is this the first-ever movie of a solar system? (Given a few appropriate qualifiers.) How about that, Mr. Kubrick !?
WangMaroisKeck20160505.JPG
Although the four planets are clearly the lead characters in this, I'm also intrigued by the goings-on closer in to the star. There is so much activity there. If our own Sun were imaged similarly, I doubt it would be showing that much activity that far out. Indeed, there are a couple of spots that appear at the end just to the left of HR 8799. I suppose they could even be planets, though that seems pretty unlikely. But then what is all of this stuff? Prominences? Mass ejections? Simply a huge undulating corona? It seems the "inner seething activity" shown here has a radius of about 15-20 AU.
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Mark Goldfain

geckzilla
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### Re: APOD: Four Planets Orbiting Star HR 8799 (2017 Feb 01)

MarkBour wrote:Whoa. Is this the first-ever movie of a solar system? (Given a few appropriate qualifiers.) How about that, Mr. Kubrick !?
WangMaroisKeck20160505.JPG
Although the four planets are clearly the lead characters in this, I'm also intrigued by the goings-on closer in to the star. There is so much activity there. If our own Sun were imaged similarly, I doubt it would be showing that much activity that far out. Indeed, there are a couple of spots that appear at the end just to the left of HR 8799. I suppose they could even be planets, though that seems pretty unlikely. But then what is all of this stuff? Prominences? Mass ejections? Simply a huge undulating corona? It seems the "inner seething activity" shown here has a radius of about 15-20 AU.
Nothing but PSF fluctuations. The star itself is less than a fraction of a pixel.
Just call me "geck" because "zilla" is like a last name.

Chris Peterson
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### Re: APOD: Four Planets Orbiting Star HR 8799 (2017 Feb 01)

MarkBour wrote:Although the four planets are clearly the lead characters in this, I'm also intrigued by the goings-on closer in to the star. There is so much activity there. If our own Sun were imaged similarly, I doubt it would be showing that much activity that far out. Indeed, there are a couple of spots that appear at the end just to the left of HR 8799. I suppose they could even be planets, though that seems pretty unlikely. But then what is all of this stuff? Prominences? Mass ejections? Simply a huge undulating corona? It seems the "inner seething activity" shown here has a radius of about 15-20 AU.
It's just noise. You can't have signal (the light from the star that is visible around the edge of the occulting mask) without having noise, as well. In the best possible case, there is always an uncertainty on the signal equal to the square root of the measured signal. In this video, the situation is further complicated by the fact that there were only seven frames, and all the intermediate frames were synthesized by animation software, which was taking the noise between data frames and trying to create smooth transitions. The only thing statistically meaningful here is the position and mean intensity of the planets.
Chris

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Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

SaraBiga

### Re: APOD: Four Planets Orbiting Star HR 8799 (2017 Feb 01)

Thank you so much Ann and Chris for the exhaustive explanations!