Comments on: 55 Cancri – A tough nut to crack. http://oklo.org/2007/11/13/55-cancri-a-tough-nut-to-crack/ characterizing planetary systems Fri, 18 Nov 2011 22:27:52 +0000 hourly 1 http://wordpress.org/?v=3.2.1 By: Sorting Out Science » Blog Archive » Philosophia Naturalis #15 http://oklo.org/2007/11/13/55-cancri-a-tough-nut-to-crack/comment-page-1/#comment-3905 Sorting Out Science » Blog Archive » Philosophia Naturalis #15 Fri, 30 Nov 2007 18:53:48 +0000 http://oklo.org/?p=257#comment-3905 [...] The news is shared by Tom’s Astronomy Blog and Spaceports. Space Scan points out that 55 Cancri’s Fifth Planet Is Perhaps Not It’s Last One, while systemic discusses the radial velocity data set used to tease out the 5 planets’ informations in two posts. Space Scan also discusses the implications of this discovery on the possibility of life elsewhere in the universe. Universe Today and Bad Astronomy wrap up this topic with some good analysis. [...] [...] The news is shared by Tom’s Astronomy Blog and Spaceports. Space Scan points out that 55 Cancri’s Fifth Planet Is Perhaps Not It’s Last One, while systemic discusses the radial velocity data set used to tease out the 5 planets’ informations in two posts. Space Scan also discusses the implications of this discovery on the possibility of life elsewhere in the universe. Universe Today and Bad Astronomy wrap up this topic with some good analysis. [...]

]]> By: andy http://oklo.org/2007/11/13/55-cancri-a-tough-nut-to-crack/comment-page-1/#comment-3745 andy Sun, 18 Nov 2007 01:55:40 +0000 http://oklo.org/?p=257#comment-3745 55 Cancri is just plain evil: you even get significant interactions between the 14-day planet and the 5000-day planet in a 2-planet fit. Another system that seems quite resistant to the console analysis is HD 82943, though since the baseline is not as long in comparison to the orbital periods it is much less evil. For these systems, synthetic datasets for various system inclinations might be useful, short of allowing the console to handle inclination for integrated fits. 55 Cancri is just plain evil: you even get significant interactions between the 14-day planet and the 5000-day planet in a 2-planet fit.

Another system that seems quite resistant to the console analysis is HD 82943, though since the baseline is not as long in comparison to the orbital periods it is much less evil.

For these systems, synthetic datasets for various system inclinations might be useful, short of allowing the console to handle inclination for integrated fits.

]]> By: Eric F Diaz http://oklo.org/2007/11/13/55-cancri-a-tough-nut-to-crack/comment-page-1/#comment-3743 Eric F Diaz Sun, 18 Nov 2007 01:41:30 +0000 http://oklo.org/?p=257#comment-3743 Hi Darin, You are quite correct that integration is a necessary, but insufficient requirement for the solution of the datasets for 55 Cancri. A paper was written about a system similar in complexity to 55 Cancri, HD37124. I think my systemic colleague, Mike Hall put it best when he said the following in a message to me: "the chi^2 landscape for HD37124 is like a mandelbrot fractal, the deeper you go, the more detail there is. It's like a slowly undulating plain with frequent dips and bumps, with maybe the occasional pit."--the pit of course being a relatively low Chi² value. Well the same holds true for 55 Cancri and all other systems of such a highly dynamic nature. I have worked on Gliese 876, and I can tell you right now that Gl 876 is a walk through the park compared to 55 Cancri. After reading the paper--which by the way can be found under arxiv 0710.5440v1--I was left with the impression that the chances of finding a proper solution to 55 Cancri with the current datasets using the current incarnation of the console on a PC was slim to none, and that basically every time we do a fit for 55 Cancri it's a crap-shoot, except the odds are much worse. 55 Cancri is no Gl 876, and it refuses to give up any of its secrets. Eric Hi Darin,

You are quite correct that integration is a necessary, but insufficient requirement for the solution of the datasets for 55 Cancri. A paper was written about a system similar in complexity to 55 Cancri, HD37124. I think my systemic colleague, Mike Hall put it best when he said the following in a message to me: “the chi^2 landscape for HD37124 is like a mandelbrot fractal, the deeper you go, the more detail there is. It’s like a slowly undulating plain with frequent dips and bumps, with maybe the occasional pit.”–the pit of course being a relatively low Chi² value. Well the same holds true for 55 Cancri and all other systems of such a highly dynamic nature. I have worked on Gliese 876, and I can tell you right now that Gl 876 is a walk through the park compared to 55 Cancri.

After reading the paper–which by the way can be found under arxiv 0710.5440v1–I was left with the impression that the chances of finding a proper solution to 55 Cancri with the current datasets using the current incarnation of the console on a PC was slim to none, and that basically every time we do a fit for 55 Cancri it’s a crap-shoot, except the odds are much worse. 55 Cancri is no Gl 876, and it refuses to give up any of its secrets.

Eric

]]> By: darin http://oklo.org/2007/11/13/55-cancri-a-tough-nut-to-crack/comment-page-1/#comment-3691 darin Thu, 15 Nov 2007 04:41:52 +0000 http://oklo.org/?p=257#comment-3691 If the integration is important, then the actual values of the masses and not the minimum masses should be used. If I recall, the current version of the console doesn't do inclinations, so this is a major shortcoming to dynamical fits. Even ignoring mutual inclinations between planets (which are probably small in this system since the eccentricities are also small), it would be interesting to compute the chi-square of the fully-interacting dynamical models at a range of plane-of-sky inclinations (keeping the other parameters fixed, for now). Like Gl 876, it may be that the dynamics is already starting to hint at an inclination of the system. If the integration is important, then the actual values of the masses and not the minimum masses should be used. If I recall, the current version of the console doesn’t do inclinations, so this is a major shortcoming to dynamical fits. Even ignoring mutual inclinations between planets (which are probably small in this system since the eccentricities are also small), it would be interesting to compute the chi-square of the fully-interacting dynamical models at a range of plane-of-sky inclinations (keeping the other parameters fixed, for now). Like Gl 876, it may be that the dynamics is already starting to hint at an inclination of the system.

]]> By: Eric F Diaz http://oklo.org/2007/11/13/55-cancri-a-tough-nut-to-crack/comment-page-1/#comment-3670 Eric F Diaz Tue, 13 Nov 2007 17:30:15 +0000 http://oklo.org/?p=257#comment-3670 Hi Greg, Very nice summary of the situation. Personally, I think that 55 Cancri should be bumped-up to number 1 on the list of the top 100 target stars of the Terrestial Planet Finder (TPF), that is of course, as Petej pointed out, it ever gets launched. Best, Eric Hi Greg,

Very nice summary of the situation. Personally, I think that 55 Cancri should be bumped-up to number 1 on the list of the top 100 target stars of the Terrestial Planet Finder (TPF), that is of course, as Petej pointed out, it ever gets launched.

Best,
Eric

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