Losing another planet, having back a low-mass star

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Losing another planet, having back a low-mass star

Post by Edasich on 25th September 2009, 4:40 am

A long timespan without any discovery, but with several retractions. How sad

Hipparcos preliminary astrometric masses for the two close-in companions to HD 131664 and HD 43848. A brown dwarf and a low mass star

Context. Several mechanisms for forming brown dwarfs have been proposed, which are today believed not to be mutually exclusive.Among the fundamental characteristics of brown dwarfs which are intrinsically tied to their origin, multiplicity is of particular relevance.Any successful determination of the actual mass for such objects in systems is thus worthwhile as it allows one to improve onthe characterization of the multiplicity properties (e.g, frequency, separation, mass-ratio distribution) of sub-stellar companions.Aims. We attempt to improve on the characterization of the properties (orbital elements, masses) of two Doppler-detected sub-stellarcompanions to the nearby G dwarfs HD 131664 and HD 43848.Methods. We carry out orbital fits to the Hipparcos Intermediate Astrometric Data (IAD) for the two stars, taking advantage of theknowledge of the spectroscopic orbits, and solving for the two orbital elements that can be determined in principle solely by astrometry,the inclination angle i and the longitude of the ascending node. A number of checks are carried out in order to assess thereliability of the orbital solutions thus obtained.Results. The best-fit solution for HD 131664 yields i = 55 33 deg and = 22 28 deg. The resulting inferred true companionmass is then Mc = 23+26−5 Mj . For HD 43848, we find i = 12 7 deg and = 288 22 deg, and a corresponding Mc = 120+167−43 Mj. Based on the statistical evidence from an F-test, the study of the joint confidence intervals of variation of i and, and the comparisonof the derived orbital semi-major axes with a distribution of false astrometric orbits obtained for single stars observed by Hipparcos,the astrometric signal of the two companions to HD 131664 and HD 43848 is then considered detected in the Hipparcos IAD, with alevel of statistical confidence not exceeding 95%.Conclusions. We constrain the true mass of HD 131664b to that of a brown dwarf to within a somewhat statistically significant degreeof confidence (∼ 2 − σ). For HD 43848b, a true mass in the brow
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Re: Losing another planet, having back a low-mass star

Post by Sirius_Alpha on 25th September 2009, 8:47 am

Most of the RV planets are just candidates anyway, with a minimum mass known.There's always the understood possibility of the true mass being much higher.

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Re: Losing another planet, having back a low-mass star

Post by Lazarus on 25th September 2009, 1:26 pm

Well both of these had m sin i exceeding the deuterium fusion limit (though I don't think this is a good dividing line between planets and brown dwarfs). Since there is a brown dwarf desert, it seems likely that more of these are actually stars than would be expected assuming random orbital orientations.
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Re: Losing another planet, having back a low-mass star

Post by Edasich on 7th October 2009, 6:37 am

Now, we've lost HD 150706 b too, shifted between unconfirmed planets.

Here times goes by, no more transiting (TrES-5? or XO-6?) or RV planets but we keep on losing exoplanets...
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Re: Losing another planet, having back a low-mass star

Post by Sirius_Alpha on 7th October 2009, 9:26 am

I'm actually happy about this. I know that sounds odd, but it's true.
The planet candidates either are, or are not, planets. It doesn't matter what minimum masses we assign to them. Objects like HD 131664 b have been shown to be intruders in the list of planet candidates. It's the process of filtering out the imposters and improving the purity of the known planet population.

I say, let's keep filtering. Let's keep kicking out the stars in planet's clothing.

Edit: I love the new "Molecules detected" addition to the EPE.
Edit: I keep hoping that TrES and XO will pull a WASP and release a truck load of planets altogether. But yeah... I keep wondering what happened to those groups.

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