HD 33636 b is not a planet

[Hungry4info]

It seems that HD 33636 b is at an inclination of ~4 degrees, and has a mass of 142 Jupiter masses. Celestia should be updated to show this. Perhaps removing it from the extrasolar planet catalogue, or re-making it as a binary stellar system.

http://www.arxiv.org/abs/0705.1861

Abstract:
We have determined a dynamical mass for the companion to HD 33636 which indicates it is a low-mass star instead of an exoplanet. Our result is based on an analysis of Hubble Space Telescope (HST) astrometry and ground-based radial velocity data. We have obtained high-cadence radial velocity measurements spanning 1.3 years of HD 33636 with the Hobby-Eberly Telescope at McDonald Observatory. We combined these data with previously published velocities to create a data set that spans nine years. We used this data set to search for, and place mass limits on, the existence of additional companions in the HD 33636 system. Our high-precision astrometric observations of the system with the HST Fine Guidance Sensor 1r span 1.2 years. We simultaneously modeled the radial velocity and astrometry data to determine the parallax, proper motion, and perturbation orbit parameters of HD 33636. Our derived parallax, pi = 35.6 +/- 0.2 mas, agrees within the uncertainties with the Hipparcos value. We find a perturbation period P = 2117.3 +/- 0.8 days, semimajor axis a_A = 14.2 +/- 0.2 mas, and system inclination i = 4.1 +/- 0.1 deg. Assuming the mass of the primary star M_A = 1.02 +/- 0.03 M_sun, we obtain a companion mass M_B = 142 +/- 11 M_jup = 0.14 +/- 0.01 M_sun. The much larger true mass of the companion relative to its minimum mass estimated from the spectroscopic orbit parameters (M sin i = 9.3 M_jup) is due to the near face-on orbit orientation. This result demonstrates the value of follow-up astrometric observations to determine the true masses of exoplanet candidates detected with the radial velocity method.

[ajtribick]

The question now becomes what to do with this system in terms of Celestia implementation - clearly it cannot remain in extrasolar.ssc/.stc, but it doesn't really fit with the other binaries files (visualbins and spectbins are PERL generated from catalogue, and it doesn't fit into nearstars).

[Hungry4info]

Do we need to seperate multiple star systems into visualbins.ssc, spectbins.ssc, or nearstars.ssc? Is it possible that we could just have one .ssc for multiple star systems? If not, why? If so, can we see this implimented in 1.5.0 pre3? Or perhaps 1.5.0 final?

[ajtribick]

It's a question of making it obvious what the source data is. The files visualbins.stc and spectbins.stc are generated from different sources - open up the files in a text editor and take a look. If I recall correctly, the nearstars.stc file is from RECONS data. Merging all these files would make it less clear what is going on and where the data comes from - you'd have to annotate each entry individually.

The revised.stc file is primarily used to de-associate stars listed in the Hipparcos catalogue as doubles, but are actually optical doubles (the code used to generate stars.dat assumes they are all physical binaries).

See also the discussion in the stars.txt thread.