Astrometric determination of exoplanet masses.

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Astrometric determination of exoplanet masses.

Post by Sirius_Alpha on 4th September 2008, 6:12 pm

Exoplanet Masses from HST/FGS Astrometry - Progress Report
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Abstract wrote:We present a progress report on our ongoing efforts to produce actual exoplanet masses (as opposed to M sin i). We obtain masses through astrometry of host star perturbations. The Fine Guidance Sensors aboard Hubble Space Telescope provide millisecond of arc per observation precision. Our five targets include HD 38529, HD 47536, HD 136118, HD 145675, and HD 168443. Specific results presented at this meeting will include masses for components of HD 47536 and HD 136118 (Martioli et al. 2008, in preparation). Published radial velocities and high-cadence velocities from the Hobby-Eberly Telescope permit us to characterize the orbits of companions with periods far longer than our roughly 2 year span of HST data. These velocities also occasionally yield previously unknown companions, which, if not properly taken into account, would have introduced noise into our simultaneous astrometry-radial velocity modeling. This project originally had six host star targets. HST astrometry of the first of these, HD 33636 (Bean et al. 2007, AJ, 134, 749), identified the presumed planetary mass companion HD 33636 b as an M dwarf star, HD 33636 B.

HD 145675 --> 14 Herculis

Most of these systems are two-planet systems. It'll be nice to get some true masses for these systems. Also nice would be some possible additional planets in any of the systems.

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Re: Astrometric determination of exoplanet masses.

Post by Lazarus on 4th September 2008, 6:36 pm

HD 38529c and HD 168443c have mass determinations from Hipparcos of 37 and 34 Jupiter masses respectively. It will be interesting to see whether these are confirmed.

If we assume the inner planets in these systems are coplanar with the brown dwarfs, and that interactions between the planets are negligible, their masses would be 2.3 and 15 Jupiter masses for HD 38529b and HD 168443b respectively, which would make the interpretation of HD 168443 quite interesting (two brown dwarfs/superplanets orbiting a star, or a [star+brown dwarf]+brown dwarf triple system?)
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Re: Astrometric determination of exoplanet masses.

Post by Lazarus on 5th September 2008, 5:13 am

A further point: HD 136118b is quite massive - minimum mass 11.9 Jupiter masses. Assuming random orientation of the orbit, this gives a 60% probability that it exceeds 13 Jupiter masses, and is in the deuterium fusion regime (brown dwarfs/superplanets)
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Re: Astrometric determination of exoplanet masses.

Post by Sirius_Alpha on 11th October 2008, 11:55 am

Lazarus wrote:A further point: HD 136118b is quite massive - minimum mass 11.9
Jupiter masses. Assuming random orientation of the orbit, this gives a
60% probability that it exceeds 13 Jupiter masses, and is in the
deuterium fusion regime (brown dwarfs/superplanets)

From the 40th AAS DPS meeting.

HST astrometry identifies HD 136118 b as a M=45 M_jup brown dwarf.
RV yields a second, shorter-period companion HD 136118 c with Msini=0.35 M_jup (Emphasis mine)
Stability analyses suggest that, if real, HD 136118 c is in a dynamically evolving orbit.
We shall have four additional true masses for other systems wthin a few months, repair mission or not.
We may have several tests of system coplanarity within a few years.
SIM could identify and characterize systems containing Earth-mass companions.

10^6 year integration suggests HD 136118 c is in an unstable orbit.


Much more astrometry to do...
The HST cycle 14 TAC is allowing orbits in Cycles 14 and 15 to determine companion masses for five star systems. The Cycle 16 TAC award allows for use of orbits in Cycles 16 and 17 to do coplanarity studies on four additional systems.

Targets-HST Data in Hand
HD 47536 b
HD 168443 c
HD 145675 b
HD 38529 c

Coplanarity Targets for HST Cycle 16-17
HD 128311 b and c
HD 202206 b and c
Mu Arae b and c
Gamma Cephei Ab and B

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Re: Astrometric determination of exoplanet masses.

Post by Lazarus on 11th October 2008, 6:55 pm

Hmmm I should have put some money on that one being a brown dwarf.

I wonder if the results for HD 47536 and HD 145675 (14 Herculis) will provide useful constraints on the second companions in these systems.

The coplanarity check of HD 202206 has the potential to provide interesting insights into the superplanet/brown dwarf question for HD 202206b.
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Re: Astrometric determination of exoplanet masses.

Post by Sirius_Alpha on 27th October 2008, 6:48 pm

Does anyone know where the paper describing the astrometric detection of 55 Cnc d is? I would like to try and contact the writers and see what they think about how the five-planet model affects the RV data.

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Re: Astrometric determination of exoplanet masses.

Post by Lazarus on 27th October 2008, 8:05 pm

Sirius_Alpha wrote:Does anyone know where the paper describing the astrometric detection of 55 Cnc d is? I would like to try and contact the writers and see what they think about how the five-planet model affects the RV data.

I think it is described in the discovery paper for 55 Cnc e.
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Re: Astrometric determination of exoplanet masses.

Post by Sirius_Alpha on 3rd November 2008, 8:26 pm

Lazarus wrote:I think it is described in the discovery paper for 55 Cnc e.
Ah yes, indeed, that's it. Thank-you.

I've written Paul Brown, a co-author of the paper, on the issue. And shall await a reply now.

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Re: Astrometric determination of exoplanet masses.

Post by Sirius_Alpha on 9th February 2010, 8:42 pm

Looks like they nabbed HD 38529 c's mass.

From the EPE:


BENEDICT F. et al. , 2010 (update : 09 February 2010)
The HD 38529 System and the Mass of HD 38529c
Astron. J. , - , -
submitted

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