Mass of HD 38529 c from Hubble

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Mass of HD 38529 c from Hubble

Post by exoplanet on 1st March 2010, 9:27 pm

http://arxiv.org/abs/1003.0421

Note possible 1/2 Saturn mass HD38529d...

The Mass of HD 38529 c from Hubble Space Telescope Astrometry and High-Precision Radial Velocities

G. Fritz Benedict, Barbara E. McArthur, Jacob L. Bean, Rory Barnes, Thomas E. Harrison, Artie Hatzes, Eder Martioli, Edmund P. Nelan

(Abridged) Hubble Space Telescope (HST) Fine Guidance Sensor astrometric observations of the G4 IV star HD 38529 are combined with the results of the analysis of extensive ground-based radial velocity data to determine the mass of the outermost of two previously known companions. Our new radial velocities obtained with the Hobby-Eberly Telescope and velocities from the Carnegie-California group now span over eleven years. With these data we obtain improved RV orbital elements for both the inner companion, HD 38529 b and the outer companion, HD 38529 c. We identify a rotational period of HD 38529 (P_{rot}=31.65 +/- 0.17 d) with FGS photometry. We model the combined astrometric and RV measurements to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size due to HD 38529 c. For HD 38529 c we find P = 2136.1 +/- 0.3 d, perturbation semi-major axis \alpha =1.05 +/-0.06$ mas, and inclination $i$ = 48.3 deg +/- 4 deg. Assuming a primary mass M_* = 1.48 M_{sun}, we obtain a companion mass M_c = 17.6 ^{+1.5}_{-1.2} M_{Jup}, 3-sigma above a 13 M_{Jup} deuterium burning, brown dwarf lower limit. Dynamical simulations incorporating this accurate mass for HD 38529 c indicate that a near-Saturn mass planet could exist between the two known companions. We find weak evidence of an additional low amplitude signal that can be modeled as a planetary-mass (~0.17 M$_{Jup}) companion at P~194 days. Additional observations (radial velocities and/or Gaia astrometry) are required to validate an interpretation of HD 38529 d as a planetary-mass companion. If confirmed, the resulting HD 38529 planetary system may be an example of a "Packed Planetary System".

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Re: Mass of HD 38529 c from Hubble

Post by Edasich on 2nd March 2010, 10:18 am

The 3rd planet's presence is suspected since long time (2005 I think). I hope it may be officially confirmed soon Smile
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Re: Mass of HD 38529 c from Hubble

Post by Lazarus on 2nd March 2010, 12:22 pm

Well if the middle planet does exist, chalk one up to the packed planetary systems hypothesis (talking of which, what's the current status of HD 74156d?)

Also would raise a problem similar to the one found at 55 Cancri: why did the middle planet apparently fail to accrete substantial mass when the inner and outer ones did.
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Re: Mass of HD 38529 c from Hubble

Post by Sirius_Alpha on 2nd March 2010, 12:58 pm

As for the status of HD 74156 d, the existence of the planet is challenged, but apparently it hasn't been ruled out. Probably pending more radial velocity measurements.

Could it be that the inner and outer planets simply formed before the middle? They would grow faster, depriving the middle planet of material from which to build itself. This sounds like the formation of ice giants.

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Re: Mass of HD 38529 c from Hubble

Post by Lazarus on 3rd March 2010, 6:56 pm

Dredging up this paper, it is interesting to see how the plans of 2008 have worked out...

Over the next year we will finish our analysis and determine actual masses for HD 47536 b, HD 136118 b, HD 168443 c, HD 145675 b, and HD 38529 c. But, before those results, we will have finished our analysis of the υ Andromedae system (McArthur et al. 2008).
So far the released results are HD 38529 c, HD 136118 b. McArthur et al. 2008, listed in the bibliography as being in preparation, is apparently still in preparation.

Just goes to show, predicting the future is a dangerous business Smile
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Re: Mass of HD 38529 c from Hubble

Post by Lazarus on 21st March 2013, 3:54 am

Host Star Properties and Transit Exclusion for the HD 38529 Planetary System
http://arxiv.org/abs/1303.4735

No evidence for the third planet.
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