55 Cnc e

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55 Cnc e

Post by Borislav on 30th March 2010, 4:52 am

http://exoplanet.eu/planet.php?p1=55+Cnc&p2=e#a_publi

30 Mar 2010: Dawson et al. (2010) claim "We find that the period of 2.817 days reported in the literature for planet e (McArthur et al. 2004, Fischer et al. 2008) is actually a daily alias of its true period of 0.737days. This new period of 0.737 days, with a refined mass of 10 Mearth, produces a significantly improved 5-planet Keplerian fit for 55 Cnc and is the shortest known period for a planet."

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Re: 55 Cnc e

Post by Edasich on 30th March 2010, 5:18 am

A Corot-7 kin? Noteworthy...
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Re: 55 Cnc e

Post by Sirius_Alpha on 30th March 2010, 5:47 am

That's interesting. The page on 55 Cnc e hasn't updated to reflect this new 0.737 day period however.'

Edit: I wonder now what the odds are of detecting 55 Cnc e's phase curve with Spitzer.

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Re: 55 Cnc e

Post by Stalker on 30th March 2010, 5:57 am

17 hours 41 minutes... nice. What mean "daily alias"?

May be a transit?
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Re: 55 Cnc e

Post by Edasich on 30th March 2010, 6:01 am

Plus a gap between 55 Cnc b and e.
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Re: 55 Cnc e

Post by Sirius_Alpha on 30th March 2010, 6:12 am

Stalker wrote:17 hours 41 minutes... nice. What mean "daily alias"?

I am not sure on this, but I suspect it means that the rotation of Earth added residuals to the radial velocity data that mimicked a long period for e.

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Re: 55 Cnc e

Post by Lazarus on 30th March 2010, 10:58 am

Wait wait wait, haven't we heard something similar to this before...

Wisdom (2005) Evidence of a Neptune-sized planet in the ρ Cancri system

claiming that the 2.8-day period is an alias, which in the end was resolved like this.

(on the other hand in that case it was not claimed the 2.8-day period was an alias of the 260-day period, unlike here)

Guess we wait for the publication. I wonder if there is a stable zone between e and b when e is shifted to such a short period.

(Incidentally this makes 55 Cancri even more horrendous to do dynamical fits using systemic - probably need to start leveraging the graphics card...)
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Re: 55 Cnc e

Post by Lazarus on 1st May 2010, 8:17 am

Incidentally it is unfortunate that the systemic console's periodograms do not go below 1 day, or it may have been more likely that one of the console users could have found this solution quite a while back.
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Re: 55 Cnc e

Post by Edasich on 1st May 2010, 1:55 pm

Noticed the same when fitting with Corot-7 RV sets. No periodicity at 0.85 days. On the other hand I find more than one outer planet after "c".
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Re: 55 Cnc e

Post by Lazarus on 1st May 2010, 2:15 pm

I'm pretty sure that one of the periods in the dataset for COROT-7 is a stellar rotation signature, IIRC this is mentioned in at least one of the papers about this system.
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Re: 55 Cnc e

Post by Borislav on 24th May 2010, 2:10 am

http://arxiv.org/pdf/1005.4050

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Re: 55 Cnc e

Post by Borislav on 24th May 2010, 2:18 am

Stalker wrote:May be a transit?


Second, 55 Cnc e itself can now be searched for transits at the new period, with high a priori probability of 25%. Given the period and phase of the radial-velocity signal, we report predicted transit epochs in Tables 7 and 8. The predictions differ because the latter assumes zero eccentricity, and the formally significant value of ee matters. Nevertheless, folding the systematic uncertainty related to eccentricity into the predicted transit time, we still can predict transit times good to T'=1 hour in 2010. This search can be accomplished simply by folding the photometric data reported by Fischer et al. (2008) at the new ephemeris. Gregory Henry (priv. comm.) has made such a search, finds no positive signal, and constrains putative transits in the period range 0.7 − 0.8 days to a depth < 0.7 mmag, or < 2.6 Re. Earth-composition models of super-Earths predict a radius 1.9 Re (Valencia et al. 2006), so a search at higher precision is certainly worthwhile.

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Re: 55 Cnc e

Post by Borislav on 24th May 2010, 2:51 am

It looks like a multi-processor computers make a difference in performance. Theorists on the basis of old published data have found an alternative solution for the 5-planetary system with a fundamentally different parameters! And with a much smaller eccentricities for the 4 outer planets and smaller residual noise rms = 5.91 against rms = 6.45 in the old solution.

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Re: 55 Cnc e

Post by Edasich on 24th May 2010, 4:37 am

Radial velocity planets de-aliased. A new, short period for Super-Earth 55 Cnc e

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.

Not only. HD 75898 b's true period is 400 days, not 200 days*.
HD 156668 b has lower mass (3.1 Me) and period (1.27 days, at 0.021 AUs)
Rho1 Cancri b has minimum mass of 8.3 Me and yields the shortest orbital period and separation amongst the 455 planets so far detected. P=0.74 days and a=0.0154 AUs, much closer than Corot-7 b.
Orbital parameters for the 4 planets left in the system do not change.

(*)= I find indeed with Systemic a 3.2 Mj planet in circular orbit (a=1.19 AUs, e=0).
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