RV Aliases: Revised periods for 55 Cnc e, HD 156668 b, others?

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RV Aliases: Revised periods for 55 Cnc e, HD 156668 b, others?

Post by Sirius_Alpha on 23rd May 2010, 8:41 pm

I know this has been discussed elsewhere, but the paper is now available and looks worth of its own thread.

Radial velocity planets de-aliased. A new, short period for Super-Earth 55 Cnc e
http://arxiv.org/abs/1005.4050

Abstract wrote:Radial velocity measurements of stellar reflex motion have revealed many extra-solar planets, but gaps in the observations produce aliases, spurious frequencies that are frequently confused with the planets' orbital frequencies. In the case of Gl 581d, the distinction between an alias and the true frequency was the distinction between a dead, frozen planet and a planet likely hospitable to life (Udry et al. 2007; Mayor et al. 2009). To improve the characterization of planetary systems, we describe how aliases originate and present a new approach for distinguishing between orbital frequencies and their aliases. Our approach harnesses features in the spectral window function to compare the amplitude and phase of predicted aliases with peaks present in the data. We apply it to confirm prior alias distinctions for the planets GJ 876d and HD 75898b. We find that the true periods of Gl 581c and HD 73526b/c remain ambiguous. We revise the periods of HD 156668b and 55 Cnc e, which were afflicted by daily aliases. For HD 156668b, the correct period is 1.2699 days and minimum mass is (3.1 +/- 0.4) Earth masses. For 55 Cnc e, the correct period is 0.7365 days - the shortest of any known planet - and minimum mass is (8.3 +/- 0.3) Earth masses. This revision produces a significantly improved 5-planet Keplerian fit for 55 Cnc, and a self-consistent dynamical fit describes the data just as well. As radial velocity techniques push to ever-smaller planets, often found in systems of multiple planets, distinguishing true periods from aliases will become increasingly important.

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Re: RV Aliases: Revised periods for 55 Cnc e, HD 156668 b, others?

Post by Lazarus on 31st May 2010, 5:07 pm

Greg Laughlin has a post up at the systemic blog about this issue (and a nice graphical explanation of how aliasing works) here

If Gliese 581d does turn out to have a 1-day period, I guess the habitability discussion goes out of the window...
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Re: RV Aliases: Revised periods for 55 Cnc e, HD 156668 b, others?

Post by Lazarus on 29th March 2012, 3:06 am

Distinguishing between a true period and its alias, and other tasks of model discrimination

Confirms the results for 55 Cnc e, HD 75898 b and Gliese 876 d, but HD 156668 b remains ambiguous.
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Re: RV Aliases: Revised periods for 55 Cnc e, HD 156668 b, others?

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