Re: Additional Planets at Gliese 581

by Galzi on Mon Sep 24, 2012 1:28 pm

Another study found no traces of planets f and g

http://arxiv.org/abs/1208.0814

Using the HARPS dataset, a stable 4 planets solution is found with an eccentric orbit for planet d. Even in this analysis, when taking into account HIRES data, planet d is rejected for insufficient confidence.

by Lazarus on Mon Sep 24, 2012 1:34 pm

That paper doesn't seem to reference the Forveille et al. (2011) paper which contains the extended HARPS dataset, instead they are using the older Mayor et al. (2009) dataset.

by tommi59 on Wed Oct 10, 2012 2:36 pm

http://iopscience.iop.org/0004-637X/759/1/2/

by Sirius_Alpha on Mon Nov 05, 2012 8:19 pm

A search for transits of GJ 581\lowercase{e} and characterization of the host star variability using MOST space telescope photometry
http://arxiv.org/abs/1211.0577

No transits of b, but a photometric signal at about the same period. No detection of e. If it transits, it has a radius less than 1.62 R_e (I feel we've discussed this before but I'm not sure where)

by tommi59 on Tue Nov 06, 2012 5:20 pm

GJ 581 e probably has radius around 1.3 earth so no wonder they did not detect transit

by Sirius_Alpha on Tue Nov 06, 2012 8:12 pm

Another paper on how many planets are there, the same results.

Counting the number of planets around GJ 581. False positive rate of Bayesian signal detection methods
http://arxiv.org/abs/1211.1280

by tommi59 on Fri Nov 09, 2012 6:06 am

A debris disk around the planet-hosting M-star GJ 581 spatially resolved with Herschel

http://www.aanda.org/index.php?option=com_article&access=doi&doi=10.1051/0004-6361/201220325&Itemid=129

by Lazarus on Fri Nov 09, 2012 5:49 pm

A resolved disc? Sweet... never was particularly comfortable with the uncertainties in the modelling of disc locations from the spectrum of the excess radiation...

by Sirius_Alpha on Wed Nov 21, 2012 8:28 pm

Now on arXiv.
http://arxiv.org/abs/1211.4898

This disk complements our view of this remarkable system known to host at least four low mass, close-in planets. These planets cannot perturb sufficiently the modeled cold disk to trigger destructive collisions between planetesimals over the age of the star, but a hypothetical outer planet, for example a Neptune mass planet with an orbital radius of 5 AU and a moderate eccentricity, could replenish the system with dust. Alternatively, the self-stirring mechanism could operate for this old star causing sufficient dynamical excitation to produce the observed dust.

by Lazarus on Thu Nov 22, 2012 1:51 pm

So maybe getting a handle of the 3D orientation of the system:

First, we note that our determination of the inclination of the disk relative to the plane of the sky is 30° < i < 70° (face on disk is i = 0°). This is mostly constrained by the 160 μm image and is fairly insensitive to the masks used for the background sources. If the disk mid-plane and the orbits of the planets are coplanar, this range of inclination makes the masses of the planets of GJ 581 no more than ∼ 1.6 times their measured minimum masses by radial velocity and, interestingly, ensures the long-term stability of the orbits in this system as shown in dynamical studies by Beust et al. (2008) and Mayor et al. (2009).

And also hints that there should be outer planets, even if "Gliese 581 f" turned out to be a systematic error rather than a true planet.

by efroimsk on Fri Nov 30, 2012 11:26 pm

Planets f and g do not exist: arxiv.org/abs/1208.0814

by Sirius_Alpha on Sat Dec 01, 2012 9:17 am

efroimsk wrote:Planets f and g do not exist: arxiv.org/abs/1208.0814

Indeed, see Galzi's post a couple months ago, and just upthread.

by efroimsk on Sat Dec 01, 2012 11:00 am

Lazarus wrote:That paper doesn't seem to reference the Forveille et al. (2011) paper which contains the extended HARPS dataset, instead they are using the older Mayor et al. (2009) dataset.

That was an early version. In the published version (see also the recent update in arxiv) we did use the data by Forveille (2011).

by Sirius_Alpha on Sat Dec 01, 2012 7:43 pm

efroimsk wrote:In the published version (see also the recent update in arxiv) we did use the data by Forveille (2011).

Ah I see. Sorry about that!

by Galzi on Sun Dec 02, 2012 6:08 am

efroimsk wrote:Planets f and g do not exist: arxiv.org/abs/1208.0814

That's true regarding the solution provided by Vogt et al. (2010); on the other hand the study seems to tentatively support the detection of a 32.1 day planet proposed by Vogt et al. (2012), assuming zero eccentricities for all the planets:

In their most recent update on the GJ 581 system, Vogt et al. (2012) used the yet unpublished, much expanded set of RV data from the HARPS (Forveille et al. 2011). They found that a ﬁfth planet (f) can be detected if the eccentricity of the 66.7 day planet (d) is set to zero. Using the same data set, but not rejecting any data points in it, we were able to conﬁrm this statement with our detection algorithm by forcing the eccentricity of the four planets b–e to zero. A 32.1 day planet with a projected mass of 1.99ME emerges at a conﬁdence level above 99%. It is likely therefore that we are dealing with the second harmonic in the signal of an eccentric planet, which can be confused with a separate nearly commensurate planet.

The eccentricity issue needs to be solved. Maybe HARPS, with the latest improvements, has the potential to do that.

Additional Planets at Gliese 581